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NUTRITION OF ARTHROPOD NATURAL ENEMIES
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Overview The
nutrition of entomophagous arthropods was originally discussed in detail by
Doutt (1964) and Hagen (1964). Slansky (1982, 1986) and Thompson & Hagen
(1999) illustrate the complex interactions of behavioral, physiological and
nutritional factors in arthropod nutrition. Nutrition is thus the action or
processes of transforming substances found in foods into body materials and
energy to do all the things attributed to life. Nutritional requirements are
dependent on the synthetic abilities of the organism, which is controlled
genetically. House (1977) stated that "... through nutrition we have a
direct and essential connection between an environmental factor, foodstuff
and the vital processes of the insect organism." Most nutrition research
with insects has been aimed at improving rearing and not developing a basic
understanding of their nutrition. Research has emphasized feeding and the
development of artificial diets, which are concerned with dietetics (Beck
1972). Although critical to insect rearing, such research has given only a
little understanding of insect nutrition per se. Qualitative
nutritional requirements of all insects are very similar in spite of a great
diversity of feeding habits (Beck 1972, Dadd 1973, Hagen 1986b). Although a
knowledge of dietetics and nutrition has advanced, practical application of
principles to insect rearing to support biological control is lacking.
Rearing each insect species is a unique challenge as there is meager
knowledge of nutrition principals that might provide a broad and sound basis
for approaching insect husbandry (house 1977). With entomophaga, foodstuff is
in a continuous state of qualitative and quantitative change, and very little
is known of the quantitative nutritional requirements for various life stages
and physiological functions of these insects. The requirements for many
nutrients are often dependent on the presence and concentration of others and
correct nutrient balance may be critical for successful nutrition. Those
parasitoids and predators for which artificial diets have been developed may
serve as models for in vitro investigation on
quantitative requirements for specific nutrients. Thompson
(1976a, 1982) used a defined artificial medium to examine the quantitative
requirements for supporting larval growth of Exeristes roborator.
Parasitoid development is intimately associated with host physiology. Changes
in the host's physiology following parasitism are adaptive for the
parasitoid, which insures successful development (Vinson & Iwantsch 1980,
Thompson 1986). Parasitoids overcome potential nutrient constraints by
altering their host's behavior and physiology (Slansky 1986). Changes in
composition of the host's internal milieu may have significant nutritional
consequences for a parasitoid (Grenier 1986, Thompson 1989). Endocrine
interactions seem critical to successful parasitoid development. Synchrony in
development between many larval endoparasitoids and their hosts occurs
(Beckage 1985), and this suggests that the host's hormones and endocrine
physiology influence parasitoid development (Lawrence 1986a.). The
physiological basis of developmental synchrony is not well understood and
knowledge is restricted to investigation of the relationship of Biosteres longicaudatus with its host Anastrepha suspensa
(Lawrence 1982, 1986b). Some studies have tested the effects of hormones on
the development of parasitoids in
vitro with little success.
The potential of using insect hormone supplements in artificial media to
achieve successful growth and development of parasitoids in vitro
deserves research emphasis. The
importance of ecological considerations in the nutrition of insects was
discussed by Slansky (1982). It was emphasized that behavior and regulatory
physiology of insects are in a state of continuous flux in response to food
supply, and that nutrition can be fully understood only by considering the
insects "nutritional ecology." With entomophaga both the ecology of
the entomophage as well as that of the host or prey needs to be known. Dietary
and nutritional requirements are genetically based and genetic manipulation
holds promise as a way to modify the nutrition of entomophages. Chabora
(1970) suggested that nutritional content varies between strains of insects
when he demonstrated that the yields of two parasitoids, Nasonia vitripennis
(Walker) and M. raptor Girault & Sanders
were significantly increased when they were reared on a hybrid of two strains
of the host, Musca domestica L. The selection of
desired traits for insect rearing was discussed by Collins (1984). The
potential for genetic improvement of entomophages was outlined by Rousch
(1979) and Hoy (1979, 1986). Most genetic selection has been directed to
increase field effectiveness of entomophages, such as improving sex ratio,
host finding ability, host preference, pesticide resistance and improved climatic
tolerance. However, genetic improvement must also guarantee the preservation
of vigor and vitality of the entomophage. Because these are intimately
associated with nutrition, genetic programs may involve selection for
nutritionally related traits. Advances
in recombinant DNA technology indicates a possibility for genetic
manipulation of the nutrition of entomophages (Thompson 1989). The
incorporation of foreign or in
vitro altered genes for the
expression of desirable traits by an organism, is rapidly advancing
(Beckendorf & Hoy 1985), but is still not suited for practical
application as of 1991. History of
Parasitoid Nutrition.--Salt (1941) probably was the first to emphasize the
complexity of parasitoid nutrition in studies that demonstrated that the host
influences growth and survival of the developing parasitoid as well as sex
ratio, fecundity, longevity and vigor of the adult wasp (Clausen 1939, Salt
1941). Such complexities were demonstrated in work by Arthur & Wylie
(1959), Wylie (1967), Nozato (1969) Sandlan (1979a) and others (Vinson &
Iwantsch 1980). It has long been known that there is a relationship between
host biomass and size of solitary parasitoids, larger parasitoids developing
from larger hosts. This relationship exists for parasitoids which attack
every host developmental stage, but applies more generally to parasitoids of
host eggs and pupae where host size is fixed (Sandlan 1982). The relationship
applies when a parasitoid is reared on different host species of variable
size as well as when reared on different sized individuals of a single host
species (Salt 1940, Jowyk & Smilowitz 1978, Mellini & Campadelli
1981, Sandlan 1982, Mellini & Beccari 1984). It does not seem to hold
with ectophagous parasitoids, however (Legner 1969 ). The size of
adult Trichogramma pretiosum Riley reared on the
eggs of five hosts showed a direct correlation between parasitoid size and
the volume of the host egg from which it emerged (Bai et al. 1989). A
correlation also exists between total parasitoid biomass and/or numbers with
host size in the case of gregarious larval parasitoids (Wylie 1965,
Bouletreau 1971, Thurston & Fox 1972). The means by which gregarious
organisms moderate their development relative to host size has been shown
(Beckage & Riddiford 1983). The
relationship between size of host and parasitoid is closely associated with
food quality and quantity (Arthur & Wylie 1959, Sandlan 1982). Salt
(1940) found that adult Trichogramma
evanescens Westwood display
behavioral dimorphism related to host size. Large females obtained from large
hosts failed to oviposit on small hosts, whereas small females accepted hosts
of all sizes. Male wing development was influence by host size, and this was
also found in Gelis corruptor (Foerster) by Salt
(1952). Adult female Coccygomimus
(= Pimpla) turionellae (L.) did not show
morphological and behavioral polymorphism, but larger females found it
difficult to oviposit in small hosts. On the other hand small females were
more efficient in attacking small hosts. Fecundity was influenced by
longevity with the greatest longevity reported for larger individuals reared
from large hosts (Sandlan 1982). The
success of parasitoids in parasitization activity is directly related to
nutritional factors. Smith (1957) found differences in larval mortality and
adult size, sex ratio and reproductive rate of several species when reared on
Aonidiella aurantii (Maskell) and Comperiella bifasciata Howard maintained on
different food plants. Habrolepis
rouxi Compere displayed
limited mortality on A. aurantii when feeding on
citrus, but 100% mortality when feeding on sago palm. Pimentel (1966) and
Altahtawy et al. (1976) showed differences in parasitoid fecundity and
longevity depending on host food source. Thurston & Fox (1972) reported
that nicotine influenced the emergence of Cotesia
(= Apanteles) congregata (Say) when reared on
Manduca sexta (L.) feeding on tobacco. Hyposoter exiguae
(Viereck) was harmed by tomatine in Heliothis
zea (Boddie) feeding on
tomato (Campbell & Duffey 1979). Aphelinus asychis
Walker required a longer larval developmental time and showed a decreased
adult longevity when reared on Myzus
persicae (Sulzer) fed on
defined diets deficient in sucrose or iron (Zohdy 1976). The effects seemed
related to decreased host size rather than a difference in nutritional
quality of the host, however. The survival of Aphaereta pallipes
(Say) was affected by the balance of amino acids and glucose in the
artificial diet used for rearing its host, Agria housei
(= affinis) Shewell (House
& Barlow 1961). Differences in larval development and adult size,
fecundity and sex ratio were observed in Tetrastichus
israeli (Mani & Kurian)
when reared on several host species, which was correlated to the total level
of essential amino acids in host tissues (Nadarajan & Jayaraj 1975). Even
though parasitoids reared from some host species with high levels of
essential amino acids were larger and longer lived, the results were
variable, as were the specific amino acid compositions of the different
hosts. In general it may be assumed that parasitoid fecundity, reproductive
size, sex ratio and longevity are correlated with host size and nutritional
factors (Charnov et al. 1981, Charnov 1982, Luck et al. 1982, Mackauer 1986,
Strand 1986). The importance of rearing Chelonus
sp. nr. curvimaculatus on
the natural host for vigor retention was demonstrated by Legner &
Thompson (1977), as discussed in previous sections. In
contrast to parasitoids, few studies have been done on the effects of various
natural foods on the biological character of predators. Smith (1965) reported
that 10 coccinellid species fed dried, powdered aphids, grew larger and
faster when feeding on Acyrthosiphon
pisum (Harris) and Rhopalosiphum maidis (Fitch) than on Aphis fabae Scopoli. Coccinella
septempunctata L. gained
more weight when feeding on Lipaphis
erysimi (Kaltenbach) than on
two other aphid species, and it was demonstrated that L. erysimi
had higher protein levels (Atwal & Sethi 1963). Parasitoids
have been thought to show high efficiencies in food utilization. Larvae
consume food of high nutritional content and are mostly inactive within the
host which offers a limited food supply, which points to selection for high
food efficiency (Fisher 1971, 1981; Slansky & Scriber 1985, Wiegert &
Petersen 1983). Parasitoids examined for food utilization include Coccygomimum (= Pimpla) instigator (F.), Pteromalus
puparum (L.) (Chlodny 1968),
Gelis macrurus (Thompson), Hidryta
frater (Cresson) (= sordidus) (Edgar 1971), Brachymeria intermedia (Nees) and C. turionellae (Greenblatt et al. 1982), Diadromus pulchellus
Wesmael (Rojas-Rousse & Kalmes 1978) and Trypatgilum (= Trypoxylon)
politum (Say) (Cross et al.
1978), Phanerotoma flavitestacea Fischer
(Hawlitzky & Mainguet 1976), Venturia
(= Nemeritis) canescens (Gravenhorst) (Fisher
1968), Cidaphus alarius Gravenhorst and Phygadeuon dumetorum Gravenhorst (Varley 1961), and Cotesia glomerata (L.) (Slansky 1978). In these species, the mean
net conversion efficiency (= proportion of assimilated food converted to body
mass (Petrusewicz 1967, Calow 1977, Hagen et al. 1984) varied broadly
(11-62%), with a mean of 37% that was <
than for many groups of insect herbivores and detritivores. Cameron &
Redfern (1974) of two studied parasitoids, Eurytoma tibialis
Boheman and Habrocytus elevatus (Walker), were at the
high end of this range. Net conversion efficiencies may not be very high
because selection might have been for rapid rather than efficient growth
(Slansky 1986). Possibly the well known inverse relationship between growth
efficiency and assimilation (Welch 1968) may also be important. In contrast
to net conversion efficiency, the above parasitoids had relatively high
percentages of assimilation (= percentage of ingested food that is
assimilated) ranging from 55-94%, with mean of 67%, compared with means of
40-50% for most herbivores and detritivores. Howell
& Fisher (1977) reported the highest nutritional efficiencies for a
parasitoid in the ichneumonid V.
canescens. Larvae had a 65%
net conversion efficiency and 95% assimilation when maintained on the host Anagasta (= Ephestia) kuehniella (Zeller); net conversion efficiency to the
adult was 20%. The
proportion of food/host available that is consumed by the parasitoid and
converted to parasitoid biomass was calculated by Slansky (1986) and Howell
& Fisher (1977). Calculated exploitation indices varied among species
from 3-80%, and V. canescens larvae consumed 90%
of its host's biomass and converted 55%, but there was no clear correlation
between host size and parasitoid size nor biomass conversion. Food
utilization by predators has also been thought to be highly efficient, for
reasons similar to that for parasitoids. This is especially true when
predators spend much time waiting for their food (Lawton 1971), thus avoiding
metabolic expenditure. Studies on food utilization of 11 predators was
reviewed by Slansky & Scriber (1985). All had similar net conversion
efficiencies (4-64%, mean = 34%), but higher assimilation efficiencies
(37-98%, mean = 86%) than those of parasitoids. Cohen (1984, 1989) in studies
of food utilization by Geocoris
punctipes (Say) when reared
from 1st instar nymphs to adults on eggs of Heliothis virescens
(F.), found an assimilation efficiency of ca. 95%, gross conversion
efficiency of 53% and net conversion efficiency of 55%. Nutritional Requirements in Development Qualitative
nutritional requirements of insects, determined by use of defined and
deficient artificial diets, were presented by several authors (Dadd 1973,
1977, 1985; Friend & Dadd 1982, Hagen et al. 1984). All insects have
similar requirements for ca. 30 chemicals that include protein and/or 10
essential amino acids (arginine, histidine, isoleucine, leucine, lysine,
methionine, phenylalanine, threonine, tryptophan and valine), the B-vitamin
complex (biotin, folic acid, nicotinic acid, panthothenic acid, pyridoxine,
riboflavin and thiamin), as well as other water soluble growth factors,
including choline and inositol, some fat soluble vitamins, cholesterol or a
structurally similar phytosterol, a polyunsaturated fatty acid, minerals and
an energy source usually provided by simple or complex carbohydrates and/or
lipids. Nutritional
requirements of entomophagous insects are similar, and similar to those of
nonentomophagous species. House (1977) referred to this common characteristic
of insect nutrition as the "rule of sameness" (House 1966a, 1974).
The rule has been confirmed by recent studies with parasitic and predaceous
insects. In assessing the need for nutrients, it is important to consider
that most studies were done by rearing a single generation on a synthetic or
semi-synthetic diet. Some investigations overlooked the potential
contribution of nutrients stored within the egg. Stored nutrients may support
limited development and, in the case of trace nutrients, supply a sufficient
quantity to ensure development of at least one generation. Studies with Itoplectis conquisitor (Say) (Yazgan 1972) and Exeristes roborator
(F.) (Thompson 1981a) demonstrated partial larval development on diets
lacking various essential amino acids and B-complex vitamins. Other studies
have demonstrated that entomophagous insects have no unusual qualitative
nutritional requirements. A requirement for asparagine by Eucelatoria bryani Sabrosky (Nettles 1986a)
and the absence of a requirement for a polyunsaturated fatty acid by A. housei (House & Barlow 1960) were consistent with
findings for nonparasitic Diptera (Dadd 1977). The
quantitative balance of different nutrients is a critical and dominating
factor determining dietary acceptability and suitability (House 1969, 1974).
The predominant foods of both parasitic and predaceous insects are of animal
origin and, thus, are generally high in protein content and low in
carbohydrate and fat (House 1977). Thompson (1986a) found a high requirement
for protein and/or amino acids in parasitoids. Exeristes roborator
at the 6% amino acid level completed larval development without glucose
and/or fatty acids (Thompson 1976a). However, glucose markedly improved
survival when the amino acid level was reduced to 3% and at 1% amino acid, no
development occurred with the carbohydrate. Similar effects of amino acid
level on larval development were reported by Yazgan (1972) for I. conquisitor. Adult eclosion was reduced by dietary amino
acid levels of <6% and by deletion of glucose. Fatty acids were only
marginally beneficial in enhancing growth and development rates of both
species. A polyunsaturated fatty acid, however, was required in small
amounts. Adult I. conquisitor (Yazgan 1972) and E. roborator (Thompson 1981a) displayed crumpled wings and/or
bent ovipositors without a polyunsaturated fatty acid in the larval diet.
Linolenic acid alleviated these deformities in I. conquisitor,
and linoleic and linolenic acids were provided together in the case of E. roborator . Thompson
(1983a) described the effect of nutritional balance on larval growth of Brachymeria lasus (Walker). Media
containing 0-10% glucose with 2% amino acids, and 1-8% amino acids with or
without 2% glucose were tested. All media contained 15% albumin and 2.5%
lipids. Weight gain increased on diets containing 2% glucose when the amino
acid level was increased from 1-4%, but was reduced at the higher amino acid
levels. Similar effects of varying the amino acid level were obtained with
diets lacking glucose, but the overall weight gain was less than observed
with the diets containing glucose. On diets containing 2% amino acids, weight
gain increased dramatically when glucose was increased from 0.5-4%, but
decreased at higher glucose levels. Growth rates on the above diets were
generally in the range of 15-200 mg/g/day. The maximal rate, 260 mg/g/day, was
obtained on a medium containing 2% glucose and 2% amino acids. The effects of
nutrient balance were closely related to the osmolality of the artificial
medium (Thompson 1983b). House
(1966b) demonstrated similar quantitative requirements to those of hymenopterous
parasitoids in the dipteran Agria
housei Shewell. Maximal
growth and survival were achieved when all nutrients were increased
proportionately over the levels in a basal diet that contained 2.25% amino
acids, 0.05% salts, 1.16% lipids and 2.25% other ingredients, including
glucose, ribonucleic acid, vitamins and agar. When amino acid level alone was
increased, survival was reduced. On a diet containing nutrient levels
equivalent to pork liver (= 20% amino acids, 4% glucose, 3.5% lipids, 2%
salts and 0.75% ribonucleic acid), survival was >80%. House (1967, 1970)
showed that the relative balance of amino acids and glucose was critical in
determining growth or development and that A. housei
larvae selected diets for feeding on the basis of nutrient balance. Quantitative
nutritional studies with parasitoids have generally evaluated the effects of
nutritional balance by univariate or monofactorial analysis. Grenier et al.
(1986) thought that such an approach had severe limitations because it
ignored potential interactions between nutrients, including
"...additivity, competitivity, antagonism or synergy." Thus,
interpretation of effects of nutrient variation aimed at medium optimization
was difficult, and it was suggested that nutritional studies be designed and
analyzed in a multidimensional manner that accounted for interactions between
all nutrients and biological criteria. Canonical
correlation analysis, which constructs maximum correlations between all
linear combinations of variables within sets, such as between growth and
development, and dietary parameters, were reported with Lixophaga diatraeae
(Townsend) by Bonnot (1986, 1988). Because biologically meaningless
correlations may be generated, accurate interpretation requires knowledge of
biological correspondence between variables. Bonnot varied the concentrations
of 30 medium components and determined the effects on 9 developmental
criteria. Nine linear correlations were obtained and three had correlation
coefficients of >0.95. There
is little information about the effects of developmental nutrition on the
behavior of parasitoid larvae apart from measurements related to growth and
development rate. However, Veerman et al (1985) reported that a photoperiodic
response by C. glomerata was influenced by the
carotenoid content of its host's diet. Vitamin A was essential for
photoperiodic induction of diapause and it was suggested that this vitamin or
a derivative may function as a photoreceptor pigment. Optimal
nutritional balance can be influenced by environmental factors, as was shown
by House (1966b) with A. housei that the effects of
dietary glucose level on larval survival and development could be modulated
by temperature. The nutritive value of a basal medium (House 1966a) was
increased by increasing the temperature from 20 to 25 and 30°C at glucose
levels between 0-1.5%. At higher glucose levels larval survival and
development were reduced with increasing temperature. Two media of different
composition were formulated whose superiority for larval growth and
development of A. housei was reversed at two
different temperatures (15 & 30°C) (House (1972). Such nutritional
effects might have ecological significance in affecting insect host range
(House 1966b). It was thought that in establishing host range, an insect
might be affected differently if the nutrient composition of its food were
uniform but the temperature varied within the range rather than if the
temperature were uniform but the composition of food was variable. On the
other hand, the insect might not be affected if variation in food composition
was accompanied by compensatory changes in temperature. Therefore, an insect
species that attacks a particular foodstuff in a region with a specific
temperature might, if introduced into another area with a different
temperature, adapt to a different food source whose nutrient composition is
favored at the new temperature . Non-nutritional
factors are intimately and intrinsically involved in food acceptance and
ingestion. These include physical properties such as form, texture, etc., but
also non-nutritive chemicals that elicit specific behavioral and/or
physiological responses essential for finding and accepting foodstuff and in
some cases for initiating behaviors associated with the feeding process
itself (Bernays & Simpson 1982, Bernays 1985). Although such factors have
been best shown in phytophagous insects, they also play a role in the biology
of entomophaga and will likely be of importance in the development of
continuous in vitro culture. The
artificial rearing of predators has stressed maintenance of the adult stage
for maximizing egg production rather than complete in vitro
culture. Predator larvae are the preferred biological control agent, and eggs
and larvae produced by adults are placed directly in the field. However, some
effort has been aimed at complete artificial culture of predators.. Among the
first reared artificially from egg to adult was the coccinellid Coleomegilla maculata maculata (DeGeer) by Szumkowski (1952). Adults fed on raw
liver or meat being kept for months on these food in the absence of prey.
However, survival of larvae was poor on meat products alone and only 38%
reached the adult stage. Supplementing vitamins resulted in ca. 86% of the
larvae reaching adults. Oviposition and egg viability were increased by
addition of vitamin E to the adult diet. The culture methods were refined and
a diet of fresh yeast and glucose supported larval development (Szumkowski
1961a,b). Smith (1965, 1966) reared several coccinellid species including C maculata lengi
on dried aphids supplemented with pollen. Success also was achieved on a diet
of 40% brewer's yeast, 55% sucrose, inorganic salts, cholesterol, RNA, wheat
germ oil and vitamins. Adults were fed the same diet supplemented with
powdered liver. Attallah & Newsom (1966) reared 8 generations of this
coccinellid on a defined diet of casein, sucrose, wheat germ, soybean
hydrolysate, glycogen, butter fat, corn oil, a liver factor, dextrose, cotton
leaf extract (with carotenoids and steroids), brewer's yeast, ascorbate,
inorganic salts, vitamins and agar. Adults reared in vitro
were fecund and mating was stimulated by addition of vitamin E to the diet.
The medium failed to support growth of Coccinella
novemnotata Herbst, Cycloneda spp., Hippodamia convergens Guérin and Olla
v-nigrum (= abdominalis) (Mulsant). The
last species was successfully cultured in
vitro by Bashir (1973).
Optimum egg production required inclusion of vitamin E in the larval diet,
which was in contrast to the results of Szumkowski (1952) where
supplementation of the adult diet alone was insufficient for maximum egg
production. Several
coccinellid species were reported to be successfully cultured in vitro by Smirnoff (1958). These included Psyllobora (= Thea) virgintiduopunctata (L.), C. septempunctata,
Oenopia (= Harmonia) doublieri (Mulsant), O.
(= Harmonia) conglobata (L.), Rhizobius lophantae (Blaisdell), R.
litura (F.), Rodolia cardinalis (Mulsant), Exochomus
anchorifer Allard, E. quadripustulatus (L.), E.
nigromaculatus Erhorn, Scymnus suturalis Thunberg, S.
pallidivestis Mulsant, S. kiesenwetteri Mulsant, Stethorus
punctillum Weise, Chilocorus bipustulatus (L.), Clitostethus
arcuatus Rossi, Pharoscymnus numidicus Pie, P. ovoideus Sicard and Mycetaea
tafilaletica Smirnoff
(Endomychidae). The diet contained sucrose, honey, alfalfa flour, yeast,
royal jelly and agar supplemented with dried pulverized prey. Larval rearing
in a few species was improved by adding beef jelly. All species developed
more rapidly and lived longer on the artificial diet compared with insects
reared under natural conditions, and the adults were very healthy. Harmonia axyridis (Pallas), C.
septempunctata and Chilocorus kuwanae Silvestri were reared on Smirnoff's (1958) diet
and other artificial media by Tanaka & Maeta (1965). Successful culture
of all species was obtained but adults failed to lay eggs. Chumakova (1962)
reared Crytolaemus montrouzieri Mulsant on similar
crude diets supplemented with dried prey. Okada
et al (1971a, 1972) and Matsuka et al. (1972) successfully reared H. axyridis on diets containing powdered larvae and pupae of
drone honeybees (Apis mellifera L.). Sixteen
generations of H. axyridis and three generations
of Menochilus sexmaculatus (F.) were cultured
in vitro. Okada & Matsuka (1973) and Matsuka et al.
(1982) later improved the rearing method for maintaining adult Rodolia cardinalis. Chilocorus
rubidus Hope, Scymnus hilaris Motschulsky, S.
otohime Kamiya, Vibidia duodecimguttata Poda and S. hilaris
adults were maintained on the diet but did not lay eggs (Matsuka et al.
1972). Niijima et al. (1986) described the use of drone honeybee powder for
rearing several coccinellids including A.
bipunctata, Anatis halonis Lewis, Coccinella
explanata Miyatake, C. septempunctata, Coccinula
crotchi (Lewis), Eocaria muiri, H.
axyridis, Harmonia yedoensis Takizawa, H.
convergens, Hippodamia tredecimpunctata L., Lemnia
beplagiata (Swartz), M. sexmaculatus, Propylea
japonica, S. hilaris and S.
otohime. Variable results
were obtained, but 11, 16 and 25 successive generations of E. muiri, H.
axyridis and M. sexmaculatus respectively were cultured from the egg to
adult stage. Larval development, adult longevity and fecundity were
satisfactory. The
fractionation of honeybee powder was described by Matsuka & Okada (1975)
who found that the active factor stimulating predator growth was unstable but
nonproteinaceous. Expanded attempts to analyze bee powder was described by
Niijima et al. (1977). Niijimi et al. (1986) then formulated several
chemically defined diets for rearing H.
axyridis. Larvae developed
from the 1-3rd instar on a diet containing 18 amino acids, sucrose,
cholesterol, 10 vitamins and 6 minerals. Kariluoto
et al. (1976) described rearing of A.
bipunctata. About 60
variations of seven artificial diets were tested. These contained varying
amounts of wheat germ, brewer's yeast, casein, cotton-leaf extract, egg yolk,
sucrose, liver fractions, honey, glycogen, soybean hydrolysate, butter fat,
corn oil, amino acids, dextrose, ascorbate, choline, inorganic salts, vitamin
E and antibiotics. The best diets yielded 60-80% of larvae that became
adults, but development time was slowed and adult weight lowered. Kariluoto
(1978) modified the medium, and Kariluoto (1980) obtained fecund adults of A. bipunctata, C. septempunctata
and others reared in vitro. In vitro
culture attempts with Chrysopa
species did not succeed until Hagen & Tassan (1965) got a complete
culture of Chrysoperla carnea (Stephens) on an
encapsulated liquid medium (in paraffin droplets). The diet consisted of
enzymatic yeast, protein hydrolysate, ascorbate, fructose, choline and casein
hydrolysate. Adults were fecund but development time from the egg stage was
ca. 2X that of insects reared on aphids. Vanderzant (1969) then successful
cultured C. carnea for 7 generations on
pieces of cellulose sponge soaked in enzymatic casein and soy hydrolysates,
fructose, inorganic salts, lecithin, cholesterol, choline, ascorbate,
vitamins and inositol. Development on this diet was slow, but 50-65% of
larvae reached the adult stage compared with 85% when reared on natural
insect eggs. Hassan & Hagen (1978) reported obtaining three generations
of C. carnea on an artificial diet of honey, yeast flakes,
sucrose, casein, yeast enzymatic hydrolysates and egg yolk. Developmental
time and pupal weights were similar to those of insects on eggs of Sitotroga cerealella (Olivier). Chrysoperla
sinica (Tjeder) was cultured
for 10 generations on a diet of egg, brewer's yeast, sucrose, honey and
ascorbate (Ye et al. 1979). Adults were fed powdered liver, honey and
brewer's yeast. Cai et al. (1983) reared this species on an encapsulated
medium of soybean and beef hydrolysates, egg yolk, sucrose, honey, brewer's
yeast, ascorbate and linoleic acid, with similar success reported by Zhou
& Zhang (1983). The
hemipteran predator, Geocoris
punctipes may be reared on
several diets (Dunbar & Bacon 1972). Media were nevertheless supplemented
with insects. Cohen (1981) reported in
vitro culture of G. punctipes from 1st stage nymph to adult on encapsulated
semidefined diets. Six media containing casein hydrolysates, yeast, sucrose,
cholesterol, corn oil, lecithin, agar, inorganic salts, phenylalanine and a
vitamin mixture were formulated and encapsulated in different forms. The
latter included mixtures of polybutene 32, dental impression wax, Vaseline,
epoline C-16, candelilla wax, Sunoco, and Paraplast. Best results were with
vitamin enriched medium encapsulated in a mixture of 5% polybutene 32 and 95%
dental impression wax. Development of G.
punctipes in vitro was better than when reared on Spodoptera exigua
(Hübner). The percent of nymphs that reached adults and survival of the in vitro reared predators were significantly greater on the
artificial diet. Cohen (1983) then described modifications of media content,
preparation and encapsulation and could rear two generations of G. punctipes. Geocoris
pallens Stal, H. convergens, H.
axyridis and Nabis spp. also successfully
fed on the encapsulated medium. In all cases superior results were obtained
on medium encapsulated with 30% polybutene 32 and 70% dental wax. A diet
composed of equal parts of fresh ground beef and beef liver supplemented with
sucrose for continuous rearing of G.
punctipes was produced
(Cohen 1985). The ingredients were blended into a paste and small aliquots
wrapped in stretched Parafilm presented to developing nymphs for feeding.
Twelve generations were successfully cultured, and artificially reared
predators displayed greater fecundity and adult weight than individuals
reared on insect eggs and coddled larvae (Cohen & Urias 1986).
Nevertheless, development was slower on the artificial diet. In vitro culture
offers a simple alternative for mass culture (Mellini 1978, Greany et al.
1984), and also enables dietary and nutritional manipulations for fundamental
studies of nutrition and biochemistry. Some benefits of in vitro
culture were given by Greany et al. (1984). However, the physiological and
metabolic adaptations exhibited by insect parasitoids in relation to their
parasitic way of life are of critical importance for successful in vitro culture (Mellini 1975a, Thompson 1981a, Grenier et
al. 1986, Campadelli & Dindo 1987). Parasitoid/host relationships are
often incorrectly thought to lack the complex physiological interactions
typical of the host associations of other Metazoa (Thompson 1985, 1986a,
Dindo 1987). The immature stages of many parasitoids are truly parasitic and
such parasitoid/host relationships are characterized by extensive
physiological and biochemical interaction (Beckage 1985, Thompson 1985,
1986a; Lawrence 1986a). Such interactions are often intimately associated
with nutrition and successful development of the parasitoid in the host
(Beckage & Riddiford 1983, Thompson 1983a, 1986a). The potential
importance of the host endocrine system and of hormonal interaction in in vitro culture was discussed by Mellini (1975b, 1978, 1983)
and Grenier et al. 1986). Greany (1986) discussed physiological interaction
with reference to the culture of hymenopterous larval endoparasitoids. The
extent that parasitoid/host physiological interactions need to be considered
in the successful development of in
vitro culture must still be
determined but will undoubtedly vary with the parasitoid species. Diptera.--A variety of natural foodstuffs, including fish and
liver products, were utilized in early rearing attempts with parasitoids.
House & Traer (1948) reared the sarcophagid A. housei
for many generations on a diet of salmon and liver. Contrasted to 38%
pupation among larvae reared on the host, Choritoneura
fumiferana (Clemens), 88%
pupated when reared on the artificial medium. A related species, Sarcophaga aldrici Parker was reared on the same medium and on liver
alone (Arthur & Coppel 1953) and subsequently Coppel et al. (1959)
maintained A. housei in the laboratory on
fresh pork liver. About 1,000 A.
housei larvae were reared on
1/2 lb. of sliced liver and were not affected by putrefaction of the tissue.
Smith (1958) maintained Kellymyia
kellyi (Aldrich) for 40
generations on pork liver and was also able to rear larvae on a mixture of
powdered milk, powdered egg and brewer's yeast moistened with water to form a
thick paste. House
(1954) developed the first chemically defined medium for rearing a
parasitoid, using A. housei. The diet contained 19
amino acids, ribonucleic acid, dextrose, inorganic salts (U.S.P. XII), B
vitamins, choline and inositol. It was prepared aseptically and gelled with
agar. About 84% of the larvae reached the 3rd instar, 60% of those pupated
and 32% of the pupae emerged as adults. The medium was later refined and many
of the developmental nutritional requirements of A. housei
were determined (House 1977). Vitamin E was necessary for reproduction (House
1966c). Other
dipterous parasitoids have been more difficult to culture outside the host.
Many of these species have specialized physiological adaptations associated
with parasitism that are lacking in sarcophagids. Tachinids, for example,
have relatively high respiratory rates (Ziser & Nettles 1979, Bonnot et
al. 1984) and during or immediately following the first stadium form a direct
connection to the host's tracheal system (Kellen 1944, Fisher 1971). First
instar larvae of the parasitoid E.
bryani attach to the host's
tracheal system 12 hrs after hatching, and respiratory considerations were
critical for the development of in
vitro cultures (Nettles et
al. 1980). During initial studies, first instar larvae dissected from the
host were placed directly in a liquid artificial diet. They were then
transferred to diets gelled with agar, thereby exposing larvae directly to
atmospheric oxygen. Improvements in the methods allowed development without
transfer. Powdered artificial diet containing 1.5% agar was preconditioned by
maintaining it at 5% RH for 24 hrs. The diet was then poured into petri
dishes and held at 90% RH. Young larvae dissected from the host 18-24 hrs
after larviposition fed on the liquid diet covering the surface of the gelled
medium, and this was consistent with the normal feeding habit of first instar
larvae that feed on and develop in the host's hemolymph. As the liquid was
slowly absorbed by the agar gel, the surface of the gelled medium dried and
larvae were exposed to the atmosphere. The artificial medium for rearing E. bryani was composed of mixtures of organic acids, amino
acids, nucleic acid bases, B and fat soluble vitamins, phospholipids and
derivatives as well as ATP, lactalbumin hydrolysate, bactopeptone,
yeastolate, albumin, cholesterol, triolein, glucose and trehalose. When thus
reared, larvae developed at an equivalent rate as when reared on the host, H. virescens, and 13% developed into adults with a sex ratio
of ca. 66% females. Adults were fecund but produced fewer progeny than host
reared insects. The medium was later refined and simplified and some of the
basic developmental nutritional requirements of E. bryani
were determined (Nettles 1986a). The nutritive values of adding albumin or
soy flower to the medium was tested, which greatly increased adult yields and
fecundity (Nettles 1986b). Other
tachinid parasitoids have been successfully reared on artificial media.
Larval development of Phryxe
caudata Rondani to the 3rd
instar was obtained with a liquid artificial diet (Grenier et al. 1974).
However, in contrast to the results of Nettles et al. (1980) with E. bryani, development of P.
caudata was not improved by
rearing larvae on gelled diets (Grenier et al. 1975). It was suggested that
this may have resulted from the slower development rate and respiratory
requirements of the latter when reared in
vitro (Nettles et al. 1980).
Bonnot (1986) discussed the importance of respiratory requirements in the in vitro culture of P.
caudata. The first tachinid
that was successfully cultured in
vitro on artificial media
from the first instar larvae to the adult was Lixophaga diatraeae
(Townsend) (Grenier et al. 1978). This medium contained organic acids, amino
acids, B and fat soluble vitamins, gelatin, enzymatic hydrolysates of casein,
soy protein, lactalbumin, ovalbumin, ATP, cholesterol, lecithin and gelled
with agarose. Adults were fecund and their progeny developed normally on Galleria mellonella. One critical factor for successful development
of both P. caudata and L. diatraeae was osmolality, which could not exceed 450
mOs/Kg (Grenier et al. 1986). Grenier
(1979) investigated the embryonic development of P. caudata
and L. diatraeae on artificial media. Newly fertilized eggs were
removed from adult females and placed on an agarose-gelled medium similar to
that for the larvae. Larval yield was equal to that observed in vivo and was much greater than when reared on a liquid diet.
Again, respiratory requirements seemed critical for success. Hymenoptera.--Simmonds (1944) made the first attempt to rear
hymenopterous parasitoids in
vitro. Three species of
ichneumonid ectoparasitoids were maintained as larvae for extended periods on
raw beef and gelatin. Although some growth was observed, none could complete
their development. Bronskill & House (1957) did succeed in rearing C. turionellae on a slurry of pork liver in 0.8% saline. An
autoclaved homogenate of the liver was dispensed into sterile test tubes and
surface sterilized eggs were dissected from host pupae and transferred to
this medium. Mature larvae were placed in gelatin capsules for pupation and
7% of the eggs developed to adults. When reared naturally on G. mellonella, 50% parasitoid adults were obtained. Culture
of the ichneumonid I. conquisitor on a diet similar
to that developed by House (1977) for A.
housei was obtained by
Yazgan & House (1970). The first holidic diet for rearing a hymenopterous
parasitoid in vitro was reported by Yazgan
(1972) for I. conquisitor. The diet was a
mixture of amino acids, fatty acids, fat soluble vitamins, B vitamins and
lipogenic growth factors, and glucose, RNA and gelled with agar. It was
ground into a viscous slurry. Parasitoid eggs dissected from the host were
placed directly on this medium, and development from egg to fecund adult was
obtained with a development time twice that observed on the natural host, G. mellonella. Exeristes
roborator was reared on a
diet with a similar nutrient composition (Thompson 1975), but unlike I. conquisitor, larvae of this parasitoid would not tolerate
direct contact with gelled media. Direct exposure to atmospheric oxygen was
important for successful in vitro culture of E. roborator and success was achieved by retaining
suspensions of the liquid diet in lipipholic Sephadex LH-20 gel filtration
medium. Mortality, size and development time of the parasitoid reared in vitro were similar to those of individuals reared on Pectinophora gossypiella (Saunders). Many of
the developmental nutritional requirements of I. conquisitor
and E. roborator were determined by Yazgan (1972) and Thompson
(1976a,b). Thompson
(1980, 1981d) described the various chemically defined diets for rearing
various chalcids of the genus Brachymeria.
Complete development of B. lasus from egg to adult at
rates approximating those observed in G.
mellonella were obtained on
diets containing heat-denatured albumin, amino acids, glucose, B vitamins,
inorganic salts, lipogenic growth factors and Intralipid. The latter, a
phospholipid emulsion of soybean oil, was necessary for complete development.
Larvae were reared from eggs dissected from host pupae immediately following
oviposition and parasitoids were cultured individually in the wells of micro
tissue culture plates. Development of larvae was ca. 2X as long on the
synthetic medium compared to the insect host, and ca. 80% reached the active
adult stage. Interestingly, the yellow coloration of the femur did not develop
if vitamin A was lacking. A
critical factor in formulating the artificial media for B. lasus
was osmotic pressure (Thompson 1983b). The effect of both carbohydrate and
amino acid levels was similar and appeared closely related to osmolality.
Optimum osmotic pressure in the artificial diets ranged from 550-700 mOs/Kg
which was much greater than the 350-450 mOs/Kg of host hemolymph and tissues.
Complete
development of the pteromalid Pachycrepoideus
vindemiae (Rondani) was not
obtained on an artificial medium similar to that used successfully for in vitro culture of Brachymeria
(Thompson 1981c). When the amino acid component was replaced with a mixture
of the corresponding polymerized amino acids and the osmolality was reduced
to ca. 390 mOs/Kg, development from egg to adult was obtained (Thompson et
al. 1983c). These
studies demonstrate that the importance of osmotic pressure varies with the
parasitoid species. Parasitoids such as I.
conquisitor and E. roborator are very tolerant of osmotic pressures. Artificial
diets that supported in vitro culture of these species
had osmolalities of ca. 2,000 mOs/Kg. On the other hand, the tachinids, P. caudata and L.
diatraeae (Grenier et al.
1986), and the pteromalid P.
vindemiae did not develop at
osmolalities of >450 mOs/Kg. Pteromalus puparum
was cultured in vitro by Bouletreau (1968,
1972). Complete development on host hemolymph in hanging drop slide mounts
was obtained. Similar results were reported by Hoffman et al. (1973). Hoffman
& Ignoffo (1974) had limited success with an artificial medium containing
yeast hydrolysate, fetal bovine serum and Grace's tissue culture medium.. Tetrastichus schoenobii Ferriere was reared
on modified Gardiner's tissue culture medium supplemented with egg yolk, milk
and hemolymph from Anteraea pernyi Guérin (Ding et al.
1980a). About 60% of the parasitoids completed development to the adult stage
with no deformities nor abnormal fecundities. Greany (1980, 1981) described
studies on the in vitro embryonic development of
the braconid Cotesia (= Apanteles) marginiventris (Cresson), maintained in Grace's tissue
culture medium supplemented with fetal bovine serum, bovine serum albumin and
whole egg ultrafiltrate. Insects were reared from the embryonic germ band stage
to mature first instar larvae on this diet cocultured with host fat body
tissue. Greany (1986) obtained similar results with Microplitis croceipes.
Emphasis was placed on the importance of protein nutrition for success and
protein secretion by the fat body was considered a factor to explain the need
for this tissue for successful embryonic development. Vinson
& Iwantsch (1980) found that teratocytes (cells derived from the
embryonic membrane of the parasitoid egg) are released into the host hemocoel
at the time of egg hatching. It was suggested that the teratocytes may play a
role in parasitoid nutrition. Sluss (1968) demonstrated that the teratocytes
of Perilitus coccinellae (Shrank) increased
in volume several times in the coccinellid host and where then subsequently
eaten by the developing parasitoid larvae. Greany (1980) found that
teratocytes present in artificial culture medium for C. marginiventris
caused dissociation of cocultured fat body and suggested that the teratocytes
might facilitate larval growth. Rotundo et al (1988) obtained complete larval
development of the braconid Lysiphelebus
fabarum (Marshall) on a
similar artificial diet that was lacking in fat body and teratocytes. Strand
et al. (1988) demonstrated a role for teratocytes in the successful in vitro culture of the egg parasitoid Telenomus heliothidis
Ashmead. Embryonic development of T.
heliothidis was obtained in
Hinks TNH-FH medium containing 30% w/v M.
sexta hemolymph. Mature
embryos were transferred to a medium containing 40% M. sexta
hemolymph, chicken egg yolk, trehalose and milk. Development to the adult
stage required one day more than on the host H. virescens
and 42% of the larvae became adults. The sex ratio was ca. 50% females. The
presence of teratocytes had no effect on larval development to the third
instar. However, when teratocytes were removed from the medium during larval
development, pupation was greatly reduced and the development time of
parasitoids that completed development increased. The authors concluded that
the teratocytes aided larval feeding by dispersing the particulate material
in the medium and solubilizing nutrients. It was suggested by Strand et al.
(1986) that teratocytes of T.
heliothidis aided in
decomposition and necrosis of host tissue partially due to release of lytic
enzymes. Therefore their function in
vitro might be the same that
occurs during the normal development of the parasitoid in the host, Heliothis virescens. Culture
of Trichogramma pretiosum in vitro
was first attained by Hoffman et al. (1975) following unsuccessful attempts
by Rajendram (1978) with T. californicum Nagaraja &
Nagarkatti. Trichogramma pretiosum completed development
on filter paper discs soaked in sterile H.
zea hemolymph. In vitro culture to the adult stage required ca. 25% more
time than observed on the host, Trichoplusia
ni (Hübner). Even though
most adults did not fully expand their wings, they mated and laid eggs
without difficulty. Progeny from eggs of in
vitro cultured parasitoids
had a sex ratio of 1.2:1 males/females when reared on host eggs. Hoffman et
al. (1975) reported development to the prepupal stage on a semisynthetic
artificial diet similar to that described by Hoffman & Ignoffo (1974) for
P puparum, but supplemented with wheat germ oil. Strand
& Vinson (1985) obtained complete in
vitro culture of T. pretiosum on an artificial medium similar to that used by
Thompson (1981d) for B. lasus but supplemented with ca.
40% M. sexta hemolymph, the latter being required to induce
pupation. Survival to the adult stage was 70s% and the sex ratio ca. 1:2
males/females. Xie et al. (1986a) also reported that host hemolymphs was
required for pupation of T. pretiosum and that factors in
the host egg influenced adult emergence. Irie et al. (1987) reported that the
requirement of host hemolymph for the complete in vitro
development was due to the presence of specific factors that could be
extracted in 76% ethanol. Purification of the pupation factor by
chromatographic methods showed the presence of two active carbohydrate
containing factors. Trichogramma dendrolimi
Matsumura was cultured in vitro in hanging drop mounts of
hemolymph from A. pernyi Guan et al (1978). Liu
et al (1979) reported success in hanging drop mounts containing media with A. pernyi or Attacus
cynthia (Drury) hemolymph
and chicken egg yolk, bovine milk, organic acids and procine serum. The
extent of development of Trichogramma
japonicum Ashmead, T. australicum Girault and T. evanescens
was not reported, however. Wu et al. (1980, 1982) and Wu & Qin (1982a)
obtained successful culture of T.
dendrolimi to the adult
stage on media without host hemolymph but containing chicken egg yolk,
chicken embryo fluid, bovine milk, and amino acid mixture and peptone.
However, only 16% of the eggs completed development, and most adults were
females of poor vitality. The results did suggest that in contrast to T. pretiosum, the in
vitro culture of T. dendrolimi does not require host factors (Xie et al.
1986a, Irie et al. 1987). Liu & Wu (1982) reported on in vitro culture of T.
dendrolimi, Trichogramma confusum Viggiani and T. pretiosum on a medium of yeast hydrolysate, fetal calf
serum, Grace's tissue culture medium, chicken embryo extract, bovine milk and
chicken egg yolk. However, adults were less viable than normal and displayed
abnormal wing development. The cooperative Research Group of Hubei Province,
China (CRGHP 1979) has carried out extensive studies on the complete in vitro culture of T.
dendrolimi in artificial
media encapsulated in artificial eggs into which the adult females
oviposited. Gao et al (1982) reported rearing 35 continuous generations of
this species in hanging drop mounts of the artificial medium. Some
studies have tried to determine the effects of hormone supplementation on
parasitoid development in vitro, with generally negative
results. The tachinid Gonia cinerascens Rondani depends on
its host's endocrine system for growth and development, but was not induced
to mold from the 1-2nd instar by addition of 20-hydroxy (b) ecdysone to an
artificial medium of host tissue homogenate and Grace's tissue culture
medium. Development from the 2nd instar to adult was reported on artificial
medium in the absence of hormones, indicating that some hormones may be
necessary for the 1-2nd instar molt in
vitro. The 20-Hydroxy
ecdysone failed to stimulate development of B. intermedia
in vitro (Thompson 1980); however, Greany (1980, 1981)
reported that this hormone inhibited egg hatching in C. marginiventris
and ecdysone, 20-hydroxy ecdysone and the juvenile hormone analog hydroprene
had no effect on larval growth or development. The deleterious effect of this
hormone could be overcome by simultaneous application of hydroprene. Nenon
(1972a,b) demonstrated that hormones greatly increased in vitro
survival of developing embryos and larvae of the encyrtid Ageniaspis fuscicollis (Dalman). The parasitoid was maintained on a
diet of chicken embryo extract, beef peptone and equine serum. Ecdysteroid or
juvenile hormone added in the medium had little effect, but when included
together, resulted in nearly 100% survival to the 2nd instar. Further study
of the effects of host hormones in
vitro culture systems must
require careful and detailed experimental design. Hormones act in a complex
and often synergistic way, and the timing of their application as well as the
method of exposure may prove critical to assessing their potential. There is
no doubt as to the importance of hormonal interaction to the successful development
of parasitoids in vivo, particularly with regard
to synchronizing parasitoid development to the host's life cycle. Adults
of many entomophaga must feed, and although adult parasitoids and predators
are usually fed in the laboratory, the significance of such feeding in nature
had been largely ignored by early workers. Bierne (1962) considered that many
biological control attempts failed as a result. Leius (1967a) gave one of the
first field demonstrations of the importance of adult feeding when he
reported a relationship between the natural abundance and variety of wild
flowers in apple orchards and the incidence of parasitism of Malacosoma americanum (F.) and Laspeyresia
(= Carpocapsa) pomonella (L.) by the
parasitoids, I. conquisitor, Apophua (= Glypta) simplicipes
(Cresson), Scambus hispae Harris, Telonomus sp., Ooencyrtus clisiocampae (Ashmead), and Eupelmus spongipartus
Foerster. Eighteen times as many M.
americanum pupae, four times
as many M. americanum eggs and five times
as many L. pomonella eggs were parasitized
in orchards with an undergrowth of wild flowers when compared with other
orchards lacking such flora. The
early literature describing how adult parasitoids feed from flowers and other
plant parts was reviewed by Leius (1960). Generally insects fed on floral and
extrafloral nectars as well as pollens. Although knowledge of the specific
nutritional requirements of adult entomophagous insects is limited, much data
are available on the chemical and nutritional requirements of adult
entomophaga is limited, much is available on the chemical and nutritional
composition of these plant products. Floral nectars contain up to 75% by weight
of simple sugars, mainly sucrose, fructose and glucose (Baker & Baker
1983), but considerable qualitative and quantitative differences exist
between plant species. Free amino acids are also abundant in nectars although
most nectars do not contain all 10 essential amino acids. Small amounts of
proteins, lipids, dextrins and vitamins that are nutritionally beneficial are
also found. The composition of extrafloral nectars is also complex (Baker et
al. 1978). Pollens have a complex composition of small molecular nutrients
and many pollens have high levels of free amino acids (Barbier 1970, Stanley
& Linskens 1974). By comparison, pollens generally have higher levels of
protein, lipid and polysaccharides. Pollens and nectars together can provide
a complete diet for successful growth, development and reproduction. The
predator Coleomegilla maculata lengi Timberlake can complete larval development on pollen
alone (Smith 1961); therefore, when prey are scarce, plant products may play
a critical role in maintaining predators (Hodek 1973). Hagen (1986a)
discussed the complex ecological and evolutionary interactions between plant
flowers, nectars and pollens and several insect groups. Leius
(1960) examined the plant feeding habits of I. conquisitor,
Scambus buolianae (Hartig) and Orgilus
obscurator (Nees). The
attractiveness of the flowers of wild mustard, white sweetclover, wild
parsnip, silky milkweed and annual sowthistle were tested. Except for annual
sowthistle, I. conquisitor was attracted to
and fed from all flowers tested, but was most attracted to wild parsnip.
Similar results were shown with S.
buolianae. Orgilus obscurator was attracted to and fed on wild parsnip only,
but further tests revealed that this parasitoid also fed on other
umbelliferous plant flowers, including those of wild carrot and water
hemlock. The nutritive value of various pollens for fecundity and longevity
of S. buolianae was reported by Leius (1963). Itoplectis conquisitor and S.
buolianae accepted various
semi-natural foods also, including honey, sucrose solution with or without
plant pollens and raisins. Plant feeding behavior of O. obscurator
examined by Syme (1975) showed a broad range of food plants, including
species from five families. Adult parasitoids may emerge prior to the availability
of the insect host, and Syme (1977) suggested that a variety of plant species
be provided as food to ensure sufficient longevity of the adult female. Lingren
& Lukefar (1977) demonstrated that adult Campoletis sonorensis
(Cameron), a parasitoid feeding on the extrafloral nectar of cotton, lives
longer when exposed to extrafloral nectaried cotton than nectariless cotton.
Parasitism of hosts was higher on the nectaried form. Adejei-Maafo &
Wilson (1983) showed that 15 categories of entomophaga, including the
predators Deraeocoris signatus (Distant), Geocoris lubra (Kirkaldy), Nabis
capsiformis Germar, Chrysopa spp., Laius bellalus Guérin, Coccinella
repanda (Thunberg) and Verania frenata Erichson, were present at densities of 2-3 times higher
on nectaried versus nonnectaried cotton. Although semiochemicals
contribute to attraction for plants in these insects, the nutrition provided
by nectars and pollens seems to be important. Hemptinne & Desprets (1986)
reported that following hibernation Adalia
bipunctata (L.) fed on
pollens as an alternate food which allows the predators to lay eggs as soon
as prey become available. As
was discussed in an earlier section, in addition to feeding plants and plant
products many parasitoids are host-feeders. Adult female Hymenoptera puncture
or damage host larvae or pupae and feed on the hemolymph and/or internal
tissues. Kidd & Jervis (1989) estimated that as much as 1/3rd of the
world's parasitoid fauna (>100,000 species) host feed. Some parasitoids
may kill more host individuals by host feeding including ovipositor probing
followed by host rejection, than by parasitization (Johnston 1915, DeBach
1943, 1954). Legner (1979) emphasized that consideration of a parasitoid's host
destructive capacity was important to correctly evaluate the impact of
periodic inundative field releases on pest populations, and Greathead (1986)
and Yamamura & Yano (1988) suggested that host feeding behavior was
important for assessing the potential of a biological control agent. Kidd
& Jervis (1989) recently discussed the significance of host-feeding on
parasitoid-host population dynamics. Bartlett
(1964) in examining host-feeding in the encyrtid, Microterys flavus
Howard, was among the first to correlated host-feeding behavior with
nutrition. He hypothesized that host feeding developed coincidentally with
depletion of eggs and suggested that host mutilation was a reflection of
"frustrated" host feeding when the host failed to bleed readily. Host
feeding by M. flavus was usually displayed
following egg-laying, and oviposition resumed after host feeding. Reviewing
this predatory habit for adults from 20 families of Hymenoptera, Bartlett
concluded that the behavior was indicative of the necessity for dietary
supplementation of some ubiquitous substances required by many diverse
species. He reported that a food supplement of enzymatic yeast and soy
hydrolysate with honey satisfied the nutrient requirements for sustaining
reproductive activity in M. flavus, and suggested that a
protein nutrient source may be necessary. The
difference between proovigenic and synovigenic Hymenoptera was discussed
earlier, categories proposed by S. E. Flanders (1950). Females of proovigenic
parasitoids complete oogenesis prior to or shortly after emergence and lay
eggs over a relatively short period of time principally on larval stages of
their host. Host feeding is important for ensuring that the female lives long
enough to deposit all eggs. In contrast, females of synovigenic species
eclose with a minor fraction of their total egg complement as mature eggs.
Synovigenic parasitoids attack primarily host eggs and pupae, are longer
lived than proovigenic species and produce eggs throughout their adult lives.
To sustain oogenesis the females of many synovigenic species require
additional nutrients. Based on the egg type, Dowell (1978) described two
types of synovigenic parasitoids: (1) those producing large anhydropic or
yolk-rich eggs that contain sufficient nutrient for completion of embryonic
development prior to oviposition. Parasitoids that produce anhydropic eggs
obtain nutrition for sustaining egg production by host-feeding; (2) those
producing hydropic or yolk-deficient eggs. Embryonic development in hydropic
eggs occurs in the host following oviposition, in which case the adult does
not require additional nutrient to support egg development and has no
requirement to host feed. Legner & Gerling (1967) showed the
importance of early host feeding and oviposition to pteromalids of the first
type, as was previously discussed. Leius (1962, 1967b) demonstrated the
importance of feeding habits to fecundity of S. buolianae.
Egg production was reduced to 1/3rd and longevity to 2/3rds, when females
were permitted to host-feed intermittently or were deprived after 15 days of
age. No eggs were laid if females were deprived for 20 days. The effects of
feeding host body fluids, in conjunction with honey, pollen and raisins on
fecundity and longevity of S.
buolianae and I. conquisitor were examined by Leius (1961a,b). Maximum
fecundity and longevity of both species were obtained when host fluids and
seminatural foods were provided together. Host feeding was nevertheless
essential, and S. buolianae did not lay eggs when
deprived of host hemolymph or tissues. The
feeding behavior of 140 hymenopterous parasitoids was also reviewed by Jervis
& Kidd (1986), who concluded that host feeding was important for egg
fecundity or egg production, while non-host foods were important for
maintenance and longevity. Four types of host feeding distinguished were (1)
concurrent feeding where the female used the same host individual for feeding
and oviposition, (2) nonconcurrent if the female used different host individuals
for feeding and oviposition, (3) the feeding habit may be nondestructive or
destructive (the host may survive or may die), and (4) destructive feeding
which generally resulted in a host that was unsuitable for oviposition.
Parasitoids were found to differ in their lifetime and diurnal patterns of
feeding, and it was concluded by Jervis & Kidd (1986) that
concurrent/nondestructive feeding was most likely when hosts were readily
available and that destructive feeding was advantageous when host density was
low. Jervis
& Kidd (1986) also gave several models to assess how the energetic
demands and constraints on a parasitoid affect its host-feeding strategy. One
model predicted the feeding strategy for maximizing egg production of a
single synovigenic female (see Thompson & Hagen 1999, for formulae). Host
feeding also occurs among dipterous parasitoids but is not as common as in
Hymenoptera (Clausen 1940). Host feeding by tachinid parasitoids may affect
longevity and fecundity (Shahjahan 1968)(. Nettles (1987b) demonstrated that
fecundity was prolonged by feeding E.
bryani host hemolymph
compared with feeding a sucrose solution. The effect of host feeding on
fecundity could not be simulated by substituting a solution of free amino
acids or bovine serum albumin. The excretion of various Homoptera, such as honeydew, may serve as a food for many adult entomophaga. Neuropterans of the genus Chrysoperla and other genera with nonpredaceous adults feed actively on honeydew as well as on nectar and pollen (Principi & Canard 1984). Although honeydew does not contain all the essential amino acids, yeast symbiotes residing in the gut can provide the missing amino acids in some nonpredaceous species (Hagen & Tassan 1972). Neuropteran predatory adults also feed on honeydew, but reproductive activity ensues only after prey are eaten (Hagen 1986a). Hagen (1962) found that honeydew alone will not stimulate egg production in coccinellid predators. Dipterous and hymenopterous parasitoids also have been found to feed on honeydew (Clausen 1940, Zoebelein 1956). The importance of honeydew as a supplementary food was suggested by Clausen et al. (1933) in work with Tiphia |