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NEUROPTERA, Chrysopidae (Hagen 1866). -- <Images>
& <Juveniles> Description &
Statistics
Chrysopids are considered wholly beneficial and have been used in
augmentation release programs against homopterous pests throughout the
world. A number of species of Chrysopa were introduced to New
Zealand for use in the control of aphid and mealybug pests and also against
Chermidae attacking pines (Clausen 1940/62). Chrysopidae feed on a variety of soft-bodied insects, but mostly
on aphids and mealybugs. Leafhoppers,
thrips, lecaniine Coccidae, mites, etc., may also be attacked. Extensive feeding occurs at intervals on
eggs of Lepidoptera. Larvae of Chrysopa rufilabris Burm. have been found to pierce leaf tissue with the
mandibles in order to feed on larvae of Agromyza
jucunda v.d.W. in their mines. This species is a valuable predator of red
mites on cotton, the larvae consuming an average of 80 per day during the
entire developmental period (Clausen 1940/62). Generally, adults feed on the same insects that serve as prey
for larvae, although their activities in this respect are less. Extended early accounts of the biology and
behavior of Chrysopidae are by Wildermuth (1916), Smith (1921, 1922b) and
Withycombe (1923). Adults usually live 4-6 weeks.
Oviposition occurs the day following emergence from the cocoon and
mating, but occasional species pass the winter as adults and oviposit the
following spring and summer.
Killington (1935) referred to a spermatophore being produced at mating
by Nathanica fulviceps Steph., although Withycombe (1923) did not find
one. The number of eggs laid by the
different species varies, the maximum being recorded by Smith of 617 by a
female of Chrysopa occulata Fitch in 42 days. The general average is thought to be
100-200. Killington (1936) cited
oviposition records, among which are those by Okamoto of 550 eggs from C. nipponensis
Okam. and by Withycombe of 480 eggs from a female of C. phyllochroma Wesm. The eggs of all species are similar in form, being oblong in
outline, with a small micropylar structure at the anterior end. They are usually borne at the ends of
filamentous but rigid stalks. There
is a lot of variation in the form of the stalk itself and the position in
which it is placed. The length of the
stalk varies directly with the length of the female's abdomen (Smith 1921,
1922b). In the larger species the
maximum length is ca. 15 mm. Some
species lay their eggs singly or in small groups on the underside of leaves,
but C. albolineata Kill. places them at the edge, with the stalks in the
same plane as the leaf. Chrysopa flava Scop. and C. flavifrons Brauer lay the cluster of
eggs, numbering up to 40, on a common stalk, from the tip of which they
radiate like a brush (Withycombe (1923).
The stalk really represents a number of individual stalks which have
fused. In Notochrysa capitata F.
the eggs are placed radially on pine needles, and the stalks are knotted at
regular intervals, or moniliform. The
provision of a stalk on which the eggs are borne is thought to be for
protection. However, this is not
entirely successful, for newly hatched larvae often feed on the still
unhatched eggs, and they may be parasitized by several species of
Scelionidae. Williams (1931) found
that the numerous species of Anomalochrysa,
native to Hawaii, have elongated oval eggs which are laid on the foliage and
lack the stalk entirely (see Clausen, 1940 for diagrams). Eggs are white or pale yellowish-green
when freshly laid, but change to bluish-green and finally to gray before they
hatch. The newly hatched larvae of C
jacobsoni v.d.W. return to the egg
cluster during the first two nights after hatching and remain head downward
on the stalks (Jacobson 1912). The three larval instars do not differ very much. Each has a rather elongated body, with 9
abdominal segments, and is clothed with hairs that, in trash-carrying
species, are hooked at the apex. The
head is flat, and the gigantic sickle-like jaws and the maxillae extend
directly forward. The mandible and
maxilla on each side are held together by a flange which fits into a groove,
which forms a sucking tube through which the body fluids of the host are
removed. The true mouth seems to be
completely closed. Carrying a packet of trash dorsally over the body serves as a
means of distinguishing the larvae of certain species of the family from
those of Hemerobiidae. These larvae
have the abdomen arched and shortened.
The packet is rebuilt after each molt. Various materials such as host remains and debris, are used in
its construction. In C. lineaticollis
Fitch the larva first thrusts its head beneath the bit of debris and then
utilizes the jaws in working it backward to the thorax. The numerous fragments are a bit woven
together and are forced backward as new additions are made at the front. The anterior half of the packet is free
but rests on the thoracic tubercles (Smith 1921, 1922b). In other species the fragments are thrown
backward over the dorsum and are not fastened together. Species carrying trash packets live almost
entirely in the open, and the adaptation is thus considered to be for protection. When mature, the larvae of some species
seek protected places for pupation, while others spin the cocoon on the flat
leaf surface (Clausen 1940/62). The oval, parchment-like cocoon is formed from silken strands
produced by modified Malpighian tubules and released through the anal
opening. The pupa pushes off the
hinged lid at the time of emergence rather than being cut with the
mandibles. Jacobson (1912) found that
the larva forms this lid at the time of cocoon formation, but other
researchers are uncertain regarding the way it is formed. The pupa lies curled within the cocoon and
becomes active only a short time before adult eclosion. It is able to inflate its body to several
times the original volume, thus facilitating the opening of the cocoon lid,
after which it crawls out, wanders about for 1-2 hrs. and then transforms to
the adult. Some individuals pass
through the pupal stage without forming a cocoon. In multibrooded species, overwintering adults are somewhat
brownish as contrasted with the green of the summer broods. This seasonal color change is comparable
to that found in Hemerobiidae. Life cycles of Chrysopidae are influenced by climate, and marked
differences occur for the same species under summer conditions in various
sections and countries. Generally,
the development from egg to adult takes ca. one month. Wildermuth (1916) recorded the duration of
the egg, larval and cocoon stages of C.
californica Coq. as 6-12, 11-22 and
14-23 days, respectively. Eggs of C. rufilabris
hatch in 3-5 days, and the larval and cocoon stages require 18 and 6 days,
respectively. Hibernation may be in
any stage except the egg, although most pass the winter in the larval or
prepupal stage within a cocoon. Chrysopa californica, C. carnea Steph., and C. ploribunda
Fitch hibernate as adults in protected spots. The generations per year vary, ranging from only one for C. albolineata
in England to at least 6 for C. californica in Arizona. Chrysopidae is a moderately large, worldwide family with more than
802 species known by 2000. There are
about. 87 species in North America.
Diagnostic characters of these
include a long antennae, slender and tapering at the apex, a forewing with 12 or more cross-veins
between R-1 and R-2, costal cross-veins not formed, and S-c and R-1 not fused
at apex of wing. Chrysopids are
usually green with golden or copper-colored eyes. Species of Eremochrysa
in western North America are often tan, resembling hemerobiids. Some species produce a disagreeable odor. The larvae and adults of all chrysopids are predators that
usually feed on aphids, whiteflies, mealybugs and other soft-bodied insects
and mites. Some adults feed on pollen
(Meleoma) and others on honeydew (Eremochrysa). The eggs are stalked and the size, shape
and surface features of the egg are diagnostic. The larvae of some species transport a packet of debris, which
is renewed after the molt. They
pupate in silken cocoons that usually are attached beneath leaves Further Behavior & Description Green lacewings are
insects in the large family Chrysopidae of the order Neuroptera. There about
87 genera and (differing between sources) 1,300–2,025 species in this
widespread group. Members of the genera Chrysopa and Chrysoperla
are very common in North America and Europe; they are very similar[1] and many of their species have been moved
from one genus to the other times and again, and in the non-scientific
literature assignment to Chrysopa and Chrysoperla can rarely be
relied upon. Since they are the most familiar neuropterids to many people,
they are often simply called "lacewings". But actually most
of the diversity of Neuroptera are properly referred to as some sort of
"lacewing", so common lacewings is preferable. Green
lacewings are fragile insects with a wingspan of 6 to over 65 mm, though the
largest forms are tropical. They are characterized by a wide costal field in
their wing venation, which includes the cross-veins. The bodies are usually
bright green to greenish-brown, and the compound eyes are conspicuously
golden in many species. The wings are usually translucent with a slight
iridescence; some have green wing veins or a cloudy brownish wing pattern.
The vernacular name "stinkflies", used chiefly for Chrysopa
species but also for others (e.g. Cunctochrysa) refers to their
ability to release a vile smell from paired prothoracal glands when handled. The adults have tympanal
organs at the forewings' base, enabling them to hear well. Some Chrysopa
show evasive behavior when they hear a bat's ultrasound calls: when in
flight, they close their wings (making their echolocational signature
smaller) and drop down to the ground. Green lacewings also use substrate or
body vibrations as a form of communication between themselves, especially
during courtship. Species which are nearly identical morphologically may
sometimes be separated more easily based on their mating signals. For example
the southern European Chrysoperla mediterranea looks almost identical
to its northern relative Chrysoperla carnea, but their courtship
"songs" are very different; individuals of one species will not
react to the other's vibrations. Adults also are
crepuscular or nocturnal. They feed on pollen, nectar and honeydew
supplemented with mites, aphids and other small arthropods, and some, namely Chrysopa,
are mainly predatory. Others feed almost exclusively on nectar and similar
substances, and have symbiotic yeasts in their digestive tract to help break
down the food into nutrients. Larvae have either a more slender "humpbacked"
shape with a prominent bulge on the ., or are plumper, with long bristles
jutting out from the sides. These bristles will collect debris and food
remains – the empty integuments of aphids, most notably – that provide
camouflage from birds. The eggs are deposited
at night, singly or in small groups; one female produces some 100–200 eggs.
Eggs are placed on plants, usually where aphids are present nearby in
numbers. Each egg is hung on a slender stalk about 1 cm long, usually on the
underside of a leaf. Immediately after hatching, the larvae moult, then
ascend the egg stalk to feed. They are voracious predators, attacking most
insects of suitable size, especially soft-bodied ones (aphids, caterpillars
and other insect larvae, insect eggs, and at high population densities also
each other). Therefore, the larvae are colloquially known as “aphid lions”
(also spelled "aphidlions") or “aphid wolves,” similar to the
related antlions. Their senses are weakly developed, except that they are
very sensitive to touch. Walking around in a haphazard fashion, the larvae
sway their heads from one side to the other, and when they strike a potential
prey object, the larva grasps it. Their maxillae are hollow, allowing a
digestive secretion to be injected in the prey; the organs of an aphid can
for example be dissolved by this in 90 seconds. Depending on environmental
conditions, larvae need about 1–3 weeks to pupation which takes place in a
cocoon; species from temperate regions usually overwinter as a prepupa,
though Chrysoperla carnea overwinters as newly-hatched adults. Some green lacewings
will feed on only about 150 prey items in their entire life, in other cases
100 aphids will be eaten in a single week. Thus, in several countries,
millions of such voracious Chrysopidae are reared for sale as biological
control agents of insect and mite pests in agriculture and gardens. They are
distributed as eggs, since as noted above they are highly aggressive and cannibalistic
in confined quarters; the eggs hatch in the field. Their performance is
variable; thus, there is a lot of interest in further research to improve the
use of green lacewings as biological pest control. Lacewings and their
their larvae may be attracted to gardens by using companion plants. They are
attracted by angelica, dill, coreopsis, cosmos, sunflowers, and the
beneficial weed, dandelion. For long, green
lacewings were considered close relatives of the pleasing lacewings (Dilaridae)
and brown lacewings (Hemerobiidae) and placed in the superfamily
Hemerobioidea. But this grouping does not appear to be natural and misled
most significantly by the supposed hemerobioideans' plesiomorphic larvae.
Today, the Hemerobioidea are usually considered monotypic, containing only
the brown lacewings; the green lacewings seem to be very closely related to
the osmylids (Osmylidae), which have much more advanced larvae superficially
resembling those of the spongillaflies (Sisyridae) with which the
spongillaflies were thus formerly allied. Thus, though the superfamily
Osmyloidea is often considered monotypic these days too following the
spongillaflies' removal from there, it is arguably better to include the
osmylids as well as the green lacewings there. References: Please refer to <biology.ref.htm>, [Additional references
may be found at: MELVYL
Library] Banks, N.
1903. A revision of nearctic
Chrysopidae. Trans. Ent. Soc. Amer.
29: 137-62. Smith, R. C.
1922. The Biology of the
Chrysopidae. NY. Agr. Expt. Sta. Mem.
58: 1232-1372. Withycomb, C. L. 1923. Notes on the
biology of some British Neuroptera (Planipennia). Trans. Ent. Soc. London (1922): 501-94. |