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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 & Overview

 

Botanical Terminology

 

Fruit Formation

 

Pollinating Insects

 

Flowers Classified According to Insect Adaptation

 

Importance of Pollination to Agriculture

 

Insect Pollinators Other Than Hymenoptera

 

Generalizations On The Use of Non-Hymenoptera Pollinators

 

Hymenoptera Pollinators

 

Apoidea Classified According to Biological Type

 

Pollination by Honeybees

Flower Selection by Honeybees

 

Communication in Honeybees

 

Agricultural Chemicals & Pollination

 

Wild Bees Utilized For Pollination

 

Alkali Bee Nesting Sites

 

Pollination of Legumes

 

Insect Pollination of Rosaceous Fruit Crops

 

Insect Pollinators for Fruit Crops

 

Collected and Stored Pollen

 

Pollination of Nonrosaceous Fruit Varieties

 

Some Special Considerations for Pollination

 

Bibliography

Examinations & Exercises

 

 

Background and Overview

 

Types of Pollination.

 

          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.

 

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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

 

 Pollen Flowers (Group I).

 

          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)

         

Fruit Crops

 

Almond

Apple

Apricot

Avocado

Blackberry

Cherry

Citron

Cranberry

Cucumber

Currant

Dewberry

Eggplant

Goosberry

Grape

Guava

Loquat

Mango

Muskmelons

Nectarine

Okra

Papaya

Peach

Pear

Pepper

Persimmon (American)

Plum

Pumkin

Quince

Squash

Strawberry

Watermelon

Food Oil & Fiber

 

Buckwheat

Celery

Cotton

Flax

Horse beans

Lima beans

Mustard

Rape

Sunflower

Tung

 

Seed Crops For Propagation

 

Alfalfa

Asparagus

Broccoli

Brussel sprouts

Buckwheat

Cabbage

Carrot

Cauliflower

Celery

Citron

Clovers (many kinds)

Colloids

Cotton

Cucumber

Eggplant

Flax

 

 

 

Horse beans

Kaer

Kali

Kohlrabi

Kudzu

Lima beans

Muskmelon

Mustard

Onion

Okra

Parsnip

Pepper

Pumpkin

Radish

Rape

Rutabaga

Squash

Sunflower

Sweet clover

Trifoil

Turnip

Vetches

Watermelon

 

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. 

 

Hemiptera

 

          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.

 

Coleoptera

 

          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.

 

Diptera

 

          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. 

 

Lepidoptera

 

          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.

 

Thysanoptera (Thrips)

 

          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.

 

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