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An
Introduction to Insect Pollination & Bee Keeping (Contact) Insects especially are of enormous
importance in the pollinations of many agriculturally important crops. Although gravity, wind, water, mollusks, birds,
bats and humans are agents of pollination, it is often possible to manipulate
insects in their performance on high value cropping systems. This section discusses the processes
involved in plant reproduction and pollination with emphasis on agriculture. The kinds and numbers of insects of
importance in these processes are detailed.
Links (blue & underlined) are posted that refer to subject matter
within this database; photos and illustrations of the insects involved may be
viewed by clicking on underlined insect groups in the text and by referring
to <Beneficials> or <Families>. Appreciation is extended to George E. Bohart, Donald L. Davis,
Department of Entomology, Utah State University and the U. S. Dept. of
Agriculture, Logan, Utah (see USDA)
for inspiring the creation of this section. Citations CONTENTS Background and Overview
Pollination of plants may involve two basic
procedures: Self-pollination and
Cross-pollination. In Self-pollination
the transfer of pollen is from the anther to stigma of the same plant or to
another plant having the same genetic composition. With an identical genome the two would either belong to a
single clone or to members of an entirely Homozygous variety. Clones or clonal varieties are composed of
a series of plants that have been propagated vegetatively from a single
plant. This type of reproduction does
not cause any change in the genetic makeup of the offspring. A completely homozygous plant possesses
sex cells where the two parental sets of chromosomes are identical. Thus when they undergo reduction division,
the products of the division are identical.
When such plants are self-fertilized, the offspring will be equal
genetically and pollen transfer between them does not introduce any new
characteristics. Two types of Self-pollination are Auto Self-Pollination
and Indirect Self-Pollination. In the
Auto-type there is no external agent of transfer. Pollen is transferred within one flower or between adjacent
flowers. In the Indirect-type the
pollen transfer involves an external agent.
When such pollination occurs within one flower, insects are usually involved. When it is between flowers on the same
plant, both insects and gravity are involved. When it is between plants that are completely homozygous or
from a single clone, both insects and wind are the main agents of
transfer. For example, in some varieties
of flax that are nearly homozygous, seed from fields of such varieties is
especially uniform even where much pollen interchange has occurred from plant
to plant. Another example is the
pollination between plants in a vineyard of a single variety of European
grapes that were propagated by stem cuttings. Three type of Cross-pollination are Intra-varietal,
Inter-varietal and Interspecific or Intergeneric. In the Intra-varietal type pollen transfer is between two
plants of a single variety. An
example is the pollination between plants of cauliflower (Brassica
oleracea var.). For the
Inter-varietal type, pollen is transferred between two varieties that differ
widely in their genetic makeup. An
example is the pollination between cauliflower and cabbage (two varieties of Brassica
oleracea). In the Interspecific
or Intergeneric type, pollen transfer is between separate species or
genera. An example is the pollination
between cauliflower and turnip (two distinct species of Brassica). Pollination and Plant Breeding. Pollen is basically a spore that has been produced
asexually. It germinates on contact
with the stigma of a flower and grows as a pollen tube through the style to
the embryo sac where it discharges two nuclei. One nucleus unites with the egg cell of an ovule and results in
fertilization. The fertilized egg
develops into a mature plant. The
other nucleus from the pollen tube unites with the polar bodies to form the
endosperm nucleus in the same ovule.
The seed endosperm, or nutritive tissue like yolk in an animal egg,
develops from this union. It then
dies early in the development of the young seed or seedling which drains it
of nutriment. Sperm cells and egg
cells mature by dividing the number of their chromosomes in half. Then when egg and sperm unite, the
original number of chromosomes characteristic of the cells in the plant is
restored. Inheritable traits of the
parents of both the egg and the sperm cells are now combined in the
developing embryo. If these parents should be one and the same (i.e., as a
result of self-pollination) no new genetic traits will be introduced. However, because the original ones were
independently segregated during reduction division, they can recombine in
different patterns so that the plants that result from self-fertilization may
differ somewhat from their parents.
Long sustained self-fertilization combined with artificial selection
of one type will eliminate these variations so that in time the plants can be
considered “homozygous” and will breed true when self-fertilized. That is, unless an entirely new
inheritable variation or “mutation” occurs in the sex cells. Sometimes the attribute of “breeding true” for a desirable type is desirable for plant
breeders, but most of the time the close inbreeding that is necessary to
bring it about results in a loss of vigor or partial sterility or both. Many plants that are self-sterile still
produce few or no offspring when self-fertilized. An example is alfalfa that produces few seeds when self-pollinated. Although relatively self-fertile varieties
of alfalfa exist, they are poor in growth and reproductivity. When plants are cross-fertilized, the traits of both
parents are present in different combinations among the offspring. Plants from such unions remain variable
and certain individuals with undesirable characteristics may appear. Nevertheless, vigor and reproductivity
remain high. In plant breeding there is an effort to achieve both
uniformity of desirable traits and continued vigor. Several methods may be employed as follows: Sometimes a desirable type of plant shows up that will
self-fertilize without losing much vigor or reproductivity. If it can also be easily self-pollinated
it can become a standard variety. Examples are in most varieties of wheat. Close inbreeding can segregate at times desirable
traits in two stocks. These two
stocks, weak though they may be, might then be crossed so that their
offspring will again be vigorous and retain the desirable characteristics of
the inbred parents. Following several
generations the crossed stock may again become variable and the desirable
characteristics lost. But this in turn
can be prevented by asexual propagation (stem cuttings, root pieces, bulbs, etc.). Here the genetics do not change and the
desirable traits are maintained. Some
hybrid varieties of grape are good examples.
Also some plants cannot be propagated vegetatively in
practicality. Preserving the inbred
lines for breeding purposes may also prevent it and producing crossed seed
from them for use in one planting only.
Examples are the production of hybrid maize. Uniformity may also be attained by vegetative
propagation of cross-fertilized plants that have been selected but not inbred
for desirable characteristics.
Apples, for example, are vegetatively propagated from seedlings that
were observed to have certain useful traits.
But the seeds of these seedlings will usually be worthless because of
their mixed “heterozygous” inheritance. Controlled crossing may also be deployed to create
uniformity. Here undesirable plants
re rejected. Many undesirable traits
can be eliminated or reduced in this way and at the same time vigor is
retained. Fields used for seed
production of varieties produced in this way must be isolated from wind or
insect transported pollen of foreign varieties that could reintroduce
undesirable traits. An example is
Ranger alfalfa.
CLICK to enlarge
General Botanical Terminology Asexual
reproduction = New plants formed without the union of sperm and egg cells
(as in rhizomes, tubers, grafts, stolens, etc.)
Also known as vegetative propagation. Dioecious plants = These produce only pollen or only embryo sacs (the sexes
occur on separate plants). Fertilization = The union of sperm cells from pollen grains with egg cells
in the embryo sac. Flowers = Structures on the plant the maintain pollen for the
production of sperm cells and embryo sacs for the production of egg cells. Imperfect
flowers = Flowers that
produce only pollen or only embryo sacs.
The sexes occur in separate flowers.
Occasionally a “perfect” flower will also have one sex
sterile or aborted (pseudoperfect). Monecious plants = These possess imperfect flowers of both sexes on the same
individual plant. Perfect flowers = Flowers that produce both pollen and embryo sacs. Both sexes occur in the same flower. Pollination = The transfer of pollen from the pollen-bearing organ, or
“anther”, to the receptive surface of the female organ or “stigma.” Reproduction = The formation of new plants Sexual
reproduction = The formation of
new plants from fertilized egg cells.
This is equal to the typical flower- seed-new plant sequence. ---------------------------------------------------------------- Fruit Formation
Pollination and subsequent fertilization are usually necessary for the
formation of a plant embryo, its adjoining nutritive matter and the
protective coats that together compose the seed. Fertilization is also usually required to provide a stimulus
for the development of fruit around the seed or seeds. The nature of the stimulus probably involves
hormones as shown in tomato hormones that have been successfully used to
provide a substitute stimulus and have resulted in the development of
seedless fruit without pollination (= parthenocarpic fruit formation). Fertilization of each ovule in the ovary has been shown to
stimulate fruit development in the area adjacent to it so that each ovule
must be fertilized for maximum fruit development. Incomplete pollination in plants with more than one ovule
usually results in the formation of stunted or deformed fruit. Apples and strawberries may be stunted and
malformed for this reason. Pollinating Agents
Both surface and subsurface water may disseminate
pollen. Gravity and wind, sometimes
aided by insects, may play a role.
Various animals such as bats, birds, mollusks, insects and humans are
frequent pollinators. Humans may be
involved by hand pollination, in breeding efforts, where the natural sources
of pollen are inadequate as in apple orchards, and where natural agents of pollination
are scarce. An example is vanilla
which must be hand pollinated because no pollinators exist in most of the
areas where it is commercially grown. Floral characters that favor pollination by insects are
a conspicuousness of flowers and inflorescences, a distinct odor, the
presence of nectar and a sticky or large pollen grain. Those characters favoring pollination by wind are an
abundant, dry, lightweight pollen, mechanisms for rapid dehiscence of pollen,
anthers exposed to the wind and a feathery stigma. Cross pollination is favored in imperfect flowers
(including psuedoperfect), dioecious plants, dichogamy (anthers and stigma
maturing at different times), where the stigma is in such a position that the
anther or its pollen cannot touch it, and by the prepotency of foreign
pollen. Characteristics favoring Self-pollination are perfect
flowers, flowers that do not open (cleistogamous), homogamy (anthers and
stigma mature at the same time), flowers in which the receptive portion of
the stigma is easily touched by anthers or pollen that is shed there
from. In the latter case the parts
may be on the same plane and close together or the stigma is below the
anthers, the stigma may grow up through a ring of dehiscing anthers, the
flower may close at night, bringing the parts close together, or the lobes of
the stigma may recoil and contact pollen shed from the anthers. Self-pollination may also be favored by
self-fertility and a lack of pre-potency of foreign pollen. Floral characters that favor cross-pollination at one
time and self-pollination at another include incomplete dichogamy
(cross-pollination favored at first but self-pollination possible later as
the parts coincide in maturity), flowers that mature upon opening at which
time cross-pollination is favored, then close at which time self-pollination
is favored. Also flowers assuming
upright positions at day or early in the cycle (the stigma is above the
anthers) and pendant position later (the anthers are above the stigma). Flowers in which the lobes of the stigma
recoil at the end of the day and contact anthers or pollen caught in special
hairs on the pistil beneath the stigma tend to alternate cross and
self-pollination. Finally, plants that
bear imperfect flowers in the early part of the flowering cycle, and later
they bear perfect flowers. Floral characters that favor particular types of
insects or other animal pollinators are those with a light or dark color,
which are dull or bright, greenish, white or yellow, red or blue or
variegated. They are also favored if
they bear quantities of nectar, a scent, abundant available pollen and
peculiar shapes. Attractive shapes
include size, regular or irregular, depth and breadth of the corolla tube,
special explosive or retractable mechanisms that can be triggered by the
pollinator, special landing structures, the position of the flower, the
structures to exclude certain insects, and special trapping mechanisms to
hold insects. Certain types of
inflorescences, such as heads, racemes, catkins and panicles, are also
attractive. Insect-Pollinated Flowers
Classified According to Insect Adaptation
Flowers such as rose, poppy,
elderberry and potato, have no nectar but may be scented, they are generally
conspicuous, simple, regular, with pollen freely exposed and usually
abundant. A great variety of color
types are included. Insects involved
are usually Syrphidae flies, soldier flies and pollen feeding beetles. Many pollen gathering bees, including honeybees, usually frequent these flowers. They are generally unattractive to Colletiidae bees, male bees, bee flies, moths,
butterflies and hummingbirds. Flowers With Exposed Nectar (Group II).
Maple, carrot, some elderberries, Euphorbia, poison oak, grapes and
saxifrage flowers are included here.
Their sparce nectar is freely exposed as droplets, the flowers are
simple, open and regular, and the inflorescence is usually inconspicuous and
greenish-white. They attract many
kinds of wasps and short-tongued flies and bees. They are not very attractive to long-tongued
bees or flies and Lepidoptera, but
some are attractive to honeybees. Flowers With Partly Concealed Nectar
(Group III).
Examples are strawberry, cactus, raspberry, stone fruits, many
cruciferous species and buttercups.
Here the nectar is partly concealed by numerous stamens or hairs or
overlapping petals. The flowers are
usually completely open only in sunshine and may be moderately to quite
conspicuous. White and yellow colors
predominate, but pink can be common.
Attracted insects are Syrphidae flies and short-tonged bees. Some Rosaceae are also attractive to long-tonged bees and honeybees. Sawflies are
common on many species, and some beetles and butterflies may also be
attracted. Flowers With Concealed
Nectar (but not sexual organs or deep narrow corollas) (Group IV).
Currant, onion, orange, mallow and blueberry are included here. The nectar is completely hidden in pouches
or by hair tufts. The flowers usually
have corolla tubes and may be somewhat irregular. They are generally conspicuous flowers with blue, red or violet
predominating. Long-tongued bees and honeybees
are attracted. Also some short-tonged bees, bee flies, long-tongued wasps, Lepidoptera. Rarely attracted are most wasps and short-tongued flies and
beetles. Social Flowers With Completely
Concealed Nectar (Group V). The Compositae such as dandelion, aster, sunflower and Scabiosa
are included. The nectar is hidden in
narrow but not deep corolla tubes, but access to nectar is blocked by the
stigma and the cone of stamens.
Pollen is very abundant. The
inflorescence is conspicuous because of the grouping of flowers into
heads. The color groups white and
yellow, and red and blue, are attractive.
This group is very attractive to short and long-tongued bees, many butterflies and polleniferous
beetles and Syrphidae flies. Insects
that visit white and yellow flowers in this group are akin to those visiting
flowers with partly concealed nectar, while those visiting red, blue and
purple flowers are akin to those visiting flowers with concealed nectar. Hymenoptera Flowers (Group VI). Violets, legumes, sages, mints, monkshood, Delphinium,
iris and some lilies are included here.
The nectar is concealed in bilaterally symmetrical flowers with slightly
long corolla tubes closed at the throat.
The sexual organs are usually partially concealed by modified petals
that require operation of a special mechanism to expose them. They are usually positioned horizontally,
with special landing structures for the pollinator. These flowers are visited primarily by medium to long-tongued bees that can operate the
mechanisms to get at the pollen and nectar.
Lepidoptera that visit these
flowers generally do not operate the mechanism exposing pollen so they do not
accomplish pollination. They are
visited in the same manner by long-tongued Conopidae flies and bee
flies. Many have such deep nectarines
as to be accessible only to bumble bees and a few other insects. Others have tough tripping mechanisms that
require large, powerful bees for pollination. Other bees may bite holes in the corollas to rob the nectar
without pollinating. One group of
Hymenoptera flower might be called “wasp flower.” It has a ventral pouch filled with nectar and a dull red color. Lepidoptera Flowers (Group VII). This group includes such species as tobacco, trumpet
flowers, honeysuckle, croc gentian, many orchids and some lilies. The flowers bear nectar at the base of
long, narrow corolla tubes and spurs.
They are rather large and conspicuous with a strong scent. Mainly Lepidoptera pollinate these, but long-tongued Hymenoptera may frequent
some species. In tropical areas
stingless bees are able to crawl into the slender corollas and spurs. Long-tongued bee flies may also use
them. Hummingbirds and honey birds
are also important pollinators in tropical regions. Within the Lepidoptera butterfly and moth flowers differ. Butterfly flowers have variable colors and
they usually open and are fragrant during daytime. On the other hand, moth flowers usually open and are fragrant
only at night. They are generally
white or pale colored. Special Types of Flowers (Group VIII). Nauseous flowers that are attractive to flies include
some umbellifera, calla lilies, skunk cabbage and many types of saxifrage. They may give off odors of feces, carrion
or ammonia. They are especially
attractive to filth flies, dung beetles and others. Pitfall flowers are also often nauseous. Included are Jack-in-the-pulpit, pitcher
plants and Dutchman’s pipe. They
capture flies, holding them until they become covered with pollen, after
which they are released before the stigma is receptive. Pinch-trap flowers include the milkweeds and some
orchids. The pollen born on
“pollenia” fastens onto visitors and are later pulled off in stigmatic
grooves of the pistil. These are
attractive to flies, bees and wasps. Syrphid fly flowers
include Veratrum and Veronica.
The flowers bear radiating streaks that lead to small, definite
centers. Two long stamens are able to
dehisce on the back of the syrphid fly when grasped at the base. Only syrphids are able to accomplish this. Small insect flowers include some aquatic species and
euphorbias and figs. There is an
array of minute flowers that are attractive to tiny insects. The flowers may be clustered in a hollow
receptacle (as in the fig) with an opening to the inflorescence that is just
large enough to accommodate the tiny insect. Importance of Pollination to Agriculture
Insects in their pollination activities have a direct
impact on the evolution of flora and fauna.
It is believed that angiosperm plants and the more highly evolved insects
evolved together. Primitive flowering
plants are all insect pollinated.
Therefore, grasses and all other angiosperms arose from plants
dependent upon insects. Some beetles,
most Hymenoptera, many Diptera and almost all Lepidoptera are dependent upon
materials provided by flowers.
Without angiosperms the evolution of mammals would certainly have been
different. Rodents, herbivores and
primates are especially dependent upon the products of flowering plants. Thus, angiosperms were a required
forerunner to the stocks, which gave rise to humans, and insect pollination
was necessary to the development of angiosperms. There would be grave consequences for the flora and
fauna were pollinating insects to disappear or cease pollinating. Many types of plants would most likely
perish eventually because in time they would be dependent on insect
pollination for competitive reproduction.
These would embrace by far most of the angiosperms. Certain elements of flora would rapidly
perish. Plants that are usually
propagated by seed are dependent upon insects for adequate pollination. Included here would probably be over half
of the existing species. Plants that
usually propagate asexually could probably survive for many seasons or
generations. But asexual propagants
are very limited in powers of dissemination and those species would have a
fixed genetics incapable of adjusting to changes, which would be expected to
be rapid under such conditions.
Self-fertile plants that are capable of auto-self pollination might be
able to persist longer. However, most
of these are dependent upon occasional crossing in order to retain
vigor. All would require some
crossing in order to retain the genetic plasticity necessary to adjust to
changing environmental conditions. Some plants might survive indefinitely without insect
pollinators and some might increase in the absence of normal
competition. These include many
nut-bearing trees, grasses, all conifers, and various other wind pollinated
plants such as poplars, birches, elms, alders, etc. Even so, many grasses and other plants most certainly depend
upon the surrounding flora for their survival. Those plants that are produced as crops by humans and
propagated by asexual means might also be unaffected. Breeding for disease resistance, for
example, could be done with hand pollination. Nevertheless, there are many consequences of a drastic
reduction and elimination of most floras.
These include the loss of plants with nitrifying bacteria, soil erosion,
a drastic curtailment of the human diet, loss in forage values for livestock,
loss of many kinds of animals, loss of most kinds of wild flowers, and a
general upset in the balance of nature, with unpredictable results. Advanced agriculture manages the production of products
that require pollination, which are primarily fruits and seeds. Seeds are used for general plant
propagation and for bedded plants.
Some plants like papaya require occasional seeding; alfalfa is seeded
every few years and spinach is seeded annually. Alfalfa and forage grasses often require a large amount of
seed, while tomatoes and melons need little seeding. Plant breeding by crossing, selfing and
selecting is done with pollination and planting with seeds. Plant products that are consumed directly
include cereals, beans, nuts, oils, fruits, preserves and many
vegetables. Seeds such as grains,
oilcake and peanuts are also used for livestock feed. Many seeds are used as medicines, spices
and flavorings. Seeds, fruit oils and
seed fibers are deployed in industry for soaps, paints, plastics, explosives,
alcohol and textiles. Common Agricultural Crops Requiring
or Benefiting From Insect Pollination (Medicinals and
Ornamentals Excluded)
Insect Pollinators Other Than Hymenoptera There are more insect species than all other animals
and plants combined, the total number estimated to be over two million as of
2010. Joined appendages and an
external skeleton characterize insects as part of the Arthropoda. Included are spiders, crustaceans,
centipedes and scorpions. Insects are classified into 28
major orders, but seven comprise most of the species. These are, in order of increasing
specialization and importance as pollinators, the Orthoptera (cockroaches, grasshoppers,
crickets, walking sticks, praying mantis), Hemiptera
(true bugs, cicadas, leafhoppers, scale insects, aphids), Thysanoptera (thrips), Coleoptera (beetles), Diptera (flies, gnats, mosquitoes), Lepidoptera (moths and butterflies), and Hymenoptera (ants, wasps, bees, sawflies,
Ichneumon flies and chalcid flies).
For the most part the Orthoptera of no importance as pollinators. Only a few Hemiptera of value are Anthocoridae (minute pirate bugs), Phymatidae (ambush bugs) and Reduviidae (kissing bugs). The Anthocoride prey on thrips in flowers;
a few Reduviidae prey on bees in flowers and most Phymatidae prey on bees and
flies in flowers. Anthocoridae are
found in almost any flowers that are visited by thrips. Phymartids and reduvids are found
primarily on Compositae and flowers that are grouped into tight heads. Except for a few flower-inhabiting forms, the Coleoptera
are not as important pollinators as the Diptera, Lepidoptera and
Hymenoptera. There are nine families
of Coleoptera that are at times involved in the pollination of flowers. Most species of Cantharidae,
the leather-winged beetles, that are predaceous as larvae occasionally
pollinate.. Polleniferous species are
also predaceous as adults. The
majority of Meloidae, or blister beetles,
occasionally are involved in pollination.
The larvae of some species are parasitic in bee nests; others are
parasitic on grasshopper egg masses.
All adult Meloidae feed on pollen or on both nectar and pollen. The larvae of some species of Cleridae are flower inhabiting. They are mainly parasites in the nests of
wasps and bees. The adults are
predaceous, but they also feed on pollen.
Most Melyridae are predaceous as larvae
and both predaceous and polleniferous as adults. One genus of Buprestidae, Acmaeodera)
(flat-headed borer) is polleniferous.
The larvae bore into wood and the adults feed on pollen. Many genera of Cerambycidae, or long-horned beetles and
round-headed borers, can be involved as pollinators. The larvae bore into wood but the adults
feed on pollen. Several genera of Scarabaeidae, or white grubs, visit flowers. They are primarily root-feeders as larvae,
but they also feed on pollen as adults.
Elateridae, or click beetles, are mostly
root-feeders as larvae, but adults will feed on nectar and pollen. In the Dermestidae,
the genus Anthrenus feed on decaying animal matter as larvae, but
adults may also utilize pollen (especially Anthrenus). There are also other small families of
Coleoptera, such as the Mordellidae, Oedemeridae, Lycidae
and Rhipiphoridae, whose members have been observed to
act as pollinators. Most groups of flowers do not escape visits by beetles
feeding on their petals as well as nectar and pollen. Some blister beetles will feed on legume
petals in order to expose the pollen and nectar. Some very tiny flower-visiting beetles may crawl into the
narrowest corollas or tightest keels.
Nevertheless, only a few groups of flowers are visited regularly by a
variety of beetles. Examples are
flowers with abundant pollen, social flowers with concealed nectar, flowers
with exposed nectar and flowers with partially concealed nectar. The adults of several large families of Diptera
feed frequently on nectar or pollen or both, but the larvae are usually
harmful to plants. Examples are found
in the Anthomyidae (hovering house flies), Bombyliidae (bee flies), Calliphoridae (blow flies & bottle flies), Ceratopogonidae (biting midges) Conopidae (thick-headed flies), Cyrtidae (small-headed flies), Empididae
(dance flies), Muscidae (house flies), Sarcophagidae (flesh flies), Stratiomyidae (soldier flies), Syrphidae (flower flies, syrphid flies, hover
flies), Tabanidae males (horse flies), Tachinidae (tachinid flies), Tephritidae (fruit flies). These families might be considered in the
following order of decreasing importance:
Syrphidae, Muscidae, Calliphoridae, Sarcophagidae, Bombyliidae,
Conopidae, Tachinidae, Empididae, Stratiomyiidae, Tabanidae, Tephritidae,
Ceratopogonidae and Cyrtidae.
However, this order may differ for any one-plant species. A few of the
more important pollinating Diptera are discussed in the following. Syrphidae have larvae with a wide variety of
habit. They occur under bark, manure
and liquid and are predatory on small insects such as aphids. The adults re almost all flower visitors. Most species feed on nectar and pollen or
only nectar. Nectar-feeding species
have a long, slender proboscis and generally visit the same group of flowers
as the long-tongued bees. Those
syrphids with short or moderate tongue length visit predominantly flowers of Groups I, Group II and Group III. Some also consume pollen on flowers of Group V. Bombyliidae have larvae that either feed on
grasshopper egg masses or those that feed on the larvae of wasps and wild
bees. Adults of the latter group have
a long, slender proboscis and visit flowers of Group III to Group VIII, but mostly Group III and Group IV. Although a few genera are intermediate,
most have very a short proboscis and visit primarily flowers of Group II. Muscidae have larvae with various habits. Some are internal parasites of other
insects, while some feed on plant roots, and a great many feed on decaying
animal and plant material. The adults
of most species visit flowers and eat pollen and nectar. Flowers of Group II are favored, but
a few others like onion in Group IV are also
visited. Species in other families of Diptera will on rare
occasions pollinate plants either directly or accidentally. Adults of most Lepidoptera feed mainly on nectar
from flowers, while their larvae feed on herbage, some roots or stored food
products and wool and are therefore pestiferous. Their preferred flowers are in Groups IV to VII. Encounters with Hymenopterid flowers (Group VI) often do not
expose the pollen and therefore do not result in pollination. The tongue lengths of Lepidoptera vary from 1 to 250
mm. Those with 4-10 mm. Tongues are
most often seen on flower Groups IV
& V, while those with longer tongues are most apt to be seen
on Groups VI & VII. Butterflies tend to frequent day-blooming flowers and
moths visit constantly open or evening and night-blooming flowers. The entire suborder, Rhopalocera and 5
families of Heterocera that are numerous or specially adapted as pollinators
are Arctiidae (tiger moths & wooly
bears), Geometridae (loopers), Noctuidae (nun moths, cut worms), Pyralidae (snout moths), Rhopaloceridae
(butterflies) and Sphingidae (hawk moths
& horn worms). Because investigations of visits to flowers have been
made primarily in daylight, the value of moths as pollinators is probably
underestimated. Butterflies often spend
a lot of time on the same flowers and they are regularly less effective than
bees in pollination. Haw moths that
fly in the evening or at night are assiduous flower visitors by darting
rapidly from plant to plant. Their very
long proboscis seems to be especially suited for the most highly developed Lepidoptera
flowers that have musky odors, long and narrow corolla tubes or long spurs
that contain nectar. Butterflies tend
to prefer red flowers while moths prefer white flowers. Nun moths are similar to haw moths in
rapid flight and long tongues. They
are usually more abundant also. Many
flowers are sometimes referred to as haw moth flowers, and where the corolla
tube exceeds 25 mm. the term is deserved.
But, hummingbirds and honeybirds contribute more effectively to the
pollination of such flowers in some areas. A small order, Thysanoptera are tiny but
individual species occur in large numbers.
Adults and larvae feed either mostly on honey and pollen or are
predators of other thrips in flowers.
It has been suggested that few indigenous flowers in Europe escape
from occasional or frequent visits by thrips. Even though individual thrips may only convey pollen
accidentally, their great abundance enhances their value for pollination. Nevertheless, they are generally thought
to be ineffective in the pollination of many flower species and consequently
they are rarely credited with much influence. They rarely migrate from plant to plant so that their role
would be primarily self-pollination. Generalizations On The Use of Non-Hymenoptera Pollinators Among the Coleoptera, larvae of most species are
destructive and not advisable for propagation. One genus of Cantharidae (Chauliognathus) are predators
as larvae on aphids and as adults they feed on nectar and pollen. It is able to trip alfalfa and might be
adaptable to mass production in insectaries and mass release in field crops. The larvae of many genera of Diptera are
destructive. Adults may pose a health hazard and are thus unsuitable for
purposeful deployment. Muscidae may
be useful in confinement for breeding work and small-scale increase of
desirable plant stocks. There are may
good pollinators among the Syrphidae,
however. They could be increased
rapidly and used as predaceous forms in insectaries. Although species may
resemble bees and wasps, they are non-biting. Semi-aquatic species could be
increased in field crops. The drone
fly, e.g., is an efficient fruit pollinator and might be propagated in
shallow tanks infused with organic material. Most larvae of Lepidoptera are also destructive
and thus the group is mostly unsuitable for deployment. There may be some exceptions, but any
species considered would need to be carefully studied for any possible
destructive tendency. Vanessa cardin
& V. atalanta (L.) feed on thistles as larvae and might be
considered for the pollination of some ornamentals. Sphinx moths are more destructive to weeds than crops
(excluding grapes) and could be deployed to pollinate ornamental plants. Vanilla is usually hand-pollinated, and
the search for a nondestructive Lepidoptera might be made. The possibilities for deploying
Lepidoptera as pollinators are probably greatest for agriculture in tropical
regions. |
