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For educational purposes

A Public Service for Information on  the basics of Insect Pollinators & Bee Keeping

 

 

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INSECT POLLINATION (cont’d.)

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Hymenoptera Pollinators

 

          The order Hymenoptera is one of the four largest insect orders containing over 300,000 identified species.  However, estimates of the total number of species in existence have exceeded one million.  The order is characterized by having two pairs of membranous wings with net-like veins consisting of 20 or fewer cells.  The labium and maxilla are combined into a sucking and lapping structure.  The mandibles are well developed for chewing and seizing prey.  The swift and agile body is strongly armored.  Females have their egg-laying structure (the ovipositor) developed for piercing.  There are distinct larval and pupal stages (= holometabolous).  Larvae are terrestrial and may be either active or degenerate.  Adults supply food to their young by laying their eggs in a food source or by storing provisions.  The adults of most species feed at least partially on pollen and nectar.  There are three main groups in this order:  Plant-feeding, Parasitic and Stinging.

 

Plant-feeding Group (Symphyta).

 

          The sawflies, horntails and pear slug are examples.  The ovipositor is saw-like, and the abdomen and thorax are broadly joined.  Larvae have 13 segments, well-developed thoracic legs and usually several pairs of abdominal prolegs.  They feed on living plant tissue.  Very few species are parasitic.  Adults of one family, Tenthredinidae (sawflies) are often found on flowers, especially those of Groups II and III.  They are prevalent on buttercups in high canyons of the Rocky Mountains of North America.  The larvae of some species of sawflies construct galls on willows.  A few species have been observed in large numbers pollinating strawberry blossoms.  However, the caterpillar larvae ore very destructive.

 

Parasitic Group.

 

          Examples of this group include Ichneumonoidea, Chalcidoidea and Cynipoidea (gall wasps).  The ovipositor is generally long and developed for piercing.  Eggs pass down the entire length of the ovipositor.  The trochanters in most genera are divided into two apparent segments.  The larvae do not have thoracic legs and are internal parasites (some are also internal parasites) of other insects and spiders.  However, gall wasp larvae construct galls in plant tissue and a few chalcids infest seeds.  The adults of less than 10 percent of species feed somewhat regularly on flowers, especially those in Groups II & III.  But some specially modified members of Group VI may be used.  Most visitors to flowers are in the family Ichneumonidae.  Adults may be found on deer brush, elderberry, Umbellifera, buttercups and serviceberry.  They are of importance as pollinators to a small number of “ichneumon flowers” in Group VI.  They probably rank with bees as beneficial insects because of their parasitic habits on harmful insects.

 

Stinging Group (Aculeata).

 

          Ants, bees, hornets and wasps are members of this group of insects.  The ovipositor is usually developed as a stinging structure that is provided with a poison receptacle.  The eggs do not traverse the ovipositor.  The abdomen and thorax are divided by a definite constriction and the trochanters are not divided.  Larvae do not have legs and possess variable diets.  Most feed on paralyzed insects or on pollen and honey.  Several groups are external parasites of insects and two groups, the ants and paper wasps) are omnivorous.  The adults of most genera spend much time on flowers and feed on pollen and nectar.  One large group, the bees, and a few others also collect pollen and honey for their offspring.  The females of most species are able to sting in self-defense.  This is by far the most valuable of the three main groups.

 

          In the Formicidae (ants) the base of the abdomen has a double constriction, the center of which bears a swelling or node.  Females may occur in several casts including wingless workers and usually also wingless soldiers, both with a greatly reduced thoracic region.  The first segment of the antenna is almost as long as all other segments combined.  The body is polished and naked or very sparsely hairy.  The larvae are almost all omnivorous, but some species may have specialized diets such as fungus, seeds or honeydew.  All ant species are colonial and most of them develop very large colonies with many specialized castes.  Only a few species will visit flowers.  Those that do travel primarily by walking so that they would usually not contact the stigma in a flower.  If they did make it to a flower only self-pollination would be accomplished.  Sometimes they will stand guard on a flower, warding off more efficient pollinators and thereby being detrimental.

 

          Vespoid Wasps include the velvet ants, hornets, scoliid wasps and cuckoo wasps.  The posterior lobe of the prothorax lies alongside the tegula or cap at the base of the forewing.  The largest family, Vespidae, folds the forewings lengthwise.  Several families have wingless females but among the social Vespidae all of the castes have wings.  The diets of the larvae are variable and all consume food that is provided by adult females.  Most genera have larvae that feed on paralyzed insect prey that is provided by the mother wasp, but some are external or internal parasites.  A few species feed on pollen and honey and the social Vespidae are usually omnivorous.  Several genera in the Vespidae are social and construct small or large paper nests.  Adults of two of the families, Scoliidae and Vespidae, are frequently found on flowers where they feed on nectar.  The flowers that are used the most are in Group II and in some short-corolla members of Group VI.  One family (Masaridae) supplies its brood cells with pollen and nectar in the manner of bees.  Its host range is very restricted, however.  These may be found on Phacellia above 6,000 feet in western mountain canyons.  They appear as large yellow jackets with clubbed antennae.  Some of the larger Scoliidae (Campsomeris) can trip and pollinate alfalfa in warm areas.  Because they paralyze scarab beetle larvae for their offspring, they are very beneficial.  Their large hairy body is well adapted for pollination and they are commonly found on in cotton and sweet clover fields.

 

          Pompilidae (Spider wasps) are blue-black or green-black on color, with close-cropped silky hair.  Most species are slender, laterally compressed with long spiny and smooth legs that give the appearance of “streamlined” bodies.  The posterior lobe of the prothorax barely touches the tegula.  Both sexes have wings.  Almost all species provide their offspring with paralyzed spiders.  They are all completely solitary insects.  The adults of most species feed on honeydew that is excreted by aphids and scale insects and on exposed nectar in flowers.  They frequent flowers of tamarix, willow, milkweed, wild buckwheat and Umbellifera.  Their value as pollinators is really not vital because the flowers they visit are also attractive to many bees and wasps.

 

          Sphecidae (Digger wasps) include cicada hawks, mud daubers, sand wasps and thread-waisted wasps.  The posterior lobes of the prothorax do not extend as far back as the tegulae, and there are no branched body hairs.  Females of most species have a long fringe or “rake” on the fore tarsus that is used to scoop soil.  Most species have a silver-colored face and many have a long constriction at the base of the abdomen.  Sphecids almost always provide their offspring with a specialized diet of paralyzed insects or spiders.  There are no colonial species but some are very gregarious.  Adults of most species feed on nectar or both pollen and nectar from flowers.  These flowers are usually those in Group II, a few of Group VI such as sweet clover, and some social flowers like rabbit bush and yarrow that have short corolla tubes.  A few have developed long tongues and can obtain food from many kinds of social flowers and hymenopterid flowers.  One group (Philanthus) provisions their nests with bees.  Sphecidae are more valuable than the preceding groups of Hymenoptera as pollinators, but not nearly as valuable as bees.  Some sand wasps visit alfalfa and trip it accidentally with their legs, but it is doubtful that this often results in cross-pollination.  They are among the most frequent visitors to celery, carrot, cotton, sweet clovers, sunflower, avocado and wild plants such as rabbit bush, goldenrod, matchweek and croton.  To increase their number would be difficult because it requires provisioning insect prey.  Sandy areas are the most favorable for a wide variety of spechids.

 

          Apoidea (Bees) consists of over 12,000 species.  Included are honeybees, sweat bees, bumble bees, stingless bees, carpenter bees and nomad bees.  All species have the first tarsal segment of the hind leg at least two-thirds as long as the tibia and in most species it is not over three times as long as broad.  All Apoidea have some branched hairs on their bodies.  Females of all except Hylaeus and parasitic groups have distinct pollen-collecting structures on the abdomen or hind legs.  Most species are very hairy or furry and many have long retractable tongues.  A salient habit in the biology of all bees is that the young are provided with nectar and pollen collected from flowers.  Only a few genera are colonial, but these include some of the most abundant one such as honeybees, bumble bees and some sweat bees.  Many genera have gregarious species.  Most are entirely solitary, however.  Many genera deposit their eggs on the pollen stores of other bees, but most of these are not very abundant.  Included are the genera Nomada, Psithyrus, Sphecodes and Coelioxys.  Adults of all species feed on nectar and pollen in addition to their collecting activities.  With the exception of male honeybees, male bees visit flowers for feeding purposes just like their females.  However, the females because they also collect for their young, are more industrious and constant in their attentions to one species of flower than are the males.  Female bees also construct nests and brood cells, store the food materials, lay the eggs and tend the young.  Bees have characteristic nesting places, which cover a wide range of habitats such as soil, wood and cavities in hollow logs, snail shells, mouse nests, etc.).

 

          The Apoidea are definitely the most important agents of pollination.  Honeybees are the most important in agricultural areas.  However, in some areas and for some crops this is not the case.  In wild or sparsely cultivated areas there are species of native bees that can be the principal pollinators of crops and wild plants alike.  Some plants such as Phlox and Delphinium, monkshood, irises, orchids, etc., must depend on wild pollinators because honeybees cannot utilize them properly.  Honeybees because of their wide host range, long season, large size and the fact that they are controlled by humans in large quantities for the products of their hives, have the greatest possibilities for specific utilization as pollinators.  Some of the native species are nevertheless more suited to the pollination of some crops and to certain climates and in some cases compare favorably in numbers with honeybees.  There is also considerable evidence that some of them are more suited to controlled pollination work in confinement such as in glasshouses, cages, etc.  The possibility for exploiting any special advantages of native bees or of merely using them supplemental to honeybees is good for some situations.

 

Apoidea Classified According to Biological Type

 

Cuckoo Bees (Anthophoridae).

 

          These bees lay their eggs in the nests of other bees.  Their larvae then consume the pollen and honey that had been stored for the host larvae.  In the genus Psithyrus (Guest bumble bees), the adult female occupies the nest of the host bumblebee and feeds on the honey stored by the host.  She then lays eggs on cells constructed and provisioned by her hosts.  These eggs are brooded by the hosts and, when hatched, the larvae are reared like a member of the family!  In the genera Nomada, Stelis, Melecta and Sphecodes, the adult female enters the nest while it is being provisioned and lays an egg next to that of the host before the cell is sealed.  The first instar larva consumes the host egg or young larvae and then feeds on the honey and pollen stored there.

 

          Female cuckoo bees are distinguished by absence of any pollen-collecting structure, by their sparse or very short pubescence, their heavy armor, and well developed stinging apparatus.  The colors of many species are bright and contrasting.  In some cases they may be closely related to their hosts.

 

Solitary Bees (Andrenidae).

 

          The females provision individual cells in her own nest and lays one egg on the surface of the stores before sealing the cell.  The larva develops without assistance by feeding on the stored food.  These bees are completely solitary.  The nests are not aggregated but they tend to be scattered sparsely over available nesting sites.  They are gregarious and the nests are grouped into large or small, dense or loose aggregates.  There is no cooperation among the females.

 

Social Bees (Halictidae).

 

          The cooperative relationship between parents and offspring is a basic step toward a true insect society.  In the Halictus type, a female is fertilized in the late summer; she overwinters, and begins construction of her nest in the spring just like a solitary bee.  But she lays only female eggs.  Instead of dying when the nest is finished, she remains in it until the brood emerges.  The young new females are slightly smaller than their mother and have no males with which to mate.  Although they lay some male eggs, most of the new cells they construct in the old nest have eggs in them that were laid by their mother.  The mother does not continue to forage but she does serve as an egg-layer and protector of the nest.  The next generation contains males, which mate with the females of the same generation.  These females then carry the species through the succeeding winter.  There is no progressive feeding of the young in this society and there is no cooperation between sisters:  only between mothers and daughters.

 

          In the Bumblebee type of social bee, behavior is similar to the Halictus type.  However, the young are fed progressively by the overwintered queen and later by the successive broods of workers.  In this case progressive feeding the egg is laid in an empty cell or is not initially provided with sufficient food to carry the hatched larvae through to maturity.  The first bees reared by the queen are stunted because of scarce food, but they assume provisioning duties for succeeding generations, which are all produced from eggs laid by the queen.  The workers cooperate in the foraging, feeding, food storing, cleaning and guarding the nest.  Subsequent generations are better fed and the males and the new queens are produced in the final generation.  Again, as in the Halictus type, the new fertilized queen must carry the species through the winter.

 

Stingless Bees—Apidae Meliponini  (Melipona & Trigona).

 

          This is an important tropical group that differs from the bumblebee type mainly in that the queen is perennial and the colony is reproduced by a group of workers that swarm with a newly produced queen.  The colonies grow to a large size, rivaling those of the honeybee, and honey storage may be nearly as great.  The queen does not need to forage or work in the nest except to lay eggs.  This type does not seem to be as advanced as the bumblebee type.  The young are not fed progressively, but each cell is furnished with a full complement of food and sealed.  Many individuals take part cooperatively in the process.  This type is specialized inn that the male is a true drone and must be fed in the nest by the workers.

 

Honeybee Type--Apidae. (Domestic honeybees).

 

          Included here are several species of Apis, of which Apis mellifera is a member.  This society combines the advancements of the bumblebee and stingless bees, but there are also a few additional advancements.  Colony reproduction is by swarming, but the workers swarm with the old queen instead of the new one.  In this system a colony never has to die out as long as eggs exist for the workers to develop into new queens by specialized feeding.  Stingless bees, living in the tropics, do not have to overwinter.  Honeybees survive winter not by hibernating but by clust4ring for warmth and consuming honey.  Bumblebees and stingless bees either destroy old cells or use them only for storing honey.  Honeybees are able to use the cells repeatedly for food storage and rearing of the broods.

 

Pollination by Honeybees

 

          For commercial crops in temperate climates the honeybee is the most valuable insect pollinator.  Honeybees have a number of the common characteristics of a good pollinator.  They are completely dependent on flowers for food and they frequent only the parts of plants that bear pollen or nectar.  They are clothed in feathery hairs that retain pollen.  They are not injurious to plants and do not pose a public nuisance.  Because they are so diligent in providing and storing nectar and pollen for their offspring, they are more reliable flower visitors than insects that only have to feed themselves.

 

          Honeybees also have several traits that especially qualify them as pollinators.  Some of these are common to other bees as well, but no other species has as many of such attributes.  The foraging season of honeybees begins with the first flowers in springtime and ends with the last flowers in autumn.  Honeybee colonies can be manipulated to a great extent, and they can be moved to different cropping areas as required.  Their body size and length of the proboscis are intermediate and enable them to work many small as well as large flowers.  However, some flowers may only be pollinated efficiently by larger or smaller species.  Due to their need for storing large food surpluses in order to survive winter in an active state it is necessary for them to visit more flowers than other species that remain dormant for part of the year.  The constancy of an individual honeybee to a plant species increases its pollinating efficiency.  This trait is less pronounced in many wild bee species.  The ability of scouting and foraging honeybees to communicate the location of attractive blooms allows the colony to quickly locate a food source.  The host range of the honeybee is very wide for a single species.  Thus, it is able to serve as a pollinator for a wide variety of plants.

 

          Of course honeybees have some limitations as pollinators as well.  They do not fly very much in wet or cloudy weather or at temperatures below 60 degrees Fahrenheit.  Flight is reduced by winds of 10 mph and almost ceases by winds over 15 mph.  Thus, some of the wild bees, e.g., bumblebees, can fly under more adverse conditions.  Honeybees tend to restrict their foraging to one area and this can result in a greater tendency for self-pollination for trees or clonal plantings.  They are able to obtain nectar from certain flower species, e.g., alfalfa, without pollinating.  Also, they may collect their pollen from plants that are normally pollinated by wind and gravity, such as sorghum, cattail, maize, box elder and Bermuda grass.

 

Flower Selection by Honeybees

 

          Even though honeybees forage over a wide range of flower species, they will tend to concentrate on blooms that are more attractive to them.  The sugar concentration and volume of nectar are important attractants.  These attributes vary among flower species and variety.  Sugar concentrations range from 5-80 percent, but those below 40 percent are less attractive to honeybees.  When plants are grown for a high seed production it is possible for breeders to increase the nectar sugar concentration through selection.  Atmospheric humidity and time of day also affect the frequency of visits to flowers by honeybees.

 

          When pollen is very abundant in a flower species honeybees will be more attracted.  They may also prefer different kinds of pollen.  The bees quickly learn when certain flowers will dehisce their pollen.  The bees are able to organize their field activities by sending out scouts.  These are usually individuals that had been performing other duties in the colony.  Scouts will search for new sources of pollen and nectar and are not influenced by communication from other bees.  When a new source is discovered they take a sample to the hive and communicate its location to foragers in the hive.

 

          Forager honeybees are usually individuals that have had previous experience as scouts.  They visit food sources that have been communicated in the hive by scouts and other foragers.  In some species of flowers the nectar cannot be collected separately from the pollen, but in nearly all cases pollen can be collected separately from nectar.  But most pollen collectors take small amounts of nectar as well.  Some overlapping of this habit may occur there is a definite distinction.  It has been observed that nectar collectors are usually older bees than pollen collectors.

 

          Bees that return from the field communicate several kinds of information to other bees in the hive.  The kind of flower is communicated by the odor of the cargo.  The distance and direction to the source is communicated by the signal dance.  This information is rapidly spread as the informed bees locate the source themselves and return to become more informants.

 

          The flight range to a food source may range up to about 10 miles, but they prefer to forage within 1.5 miles of the food sources are plentiful.  Within one mile the desirability to the food source is most important.  Young field bees are usually restricted to foraging close to the hive for around two days.  The preferred range of pollen collectors is usually shorter than that of nectar collectors.  For commercial honey production beekeepers usually do not expect the flower source to exceed two miles from the hive.  With pollination the closer the flower source the more bees will locate it and the more visits can be made.

 

          The number of flowers that honeybees will visit varies with the abundance of pollen or nectar in a flower.  This may be up to 1,000 flowers visited for a cargo of nectar in maple blossoms, or as low as one from tulip poplar.  It may require as many as 400 visits for a pollen cargo from yellow sweet clover or as few as 25 visits from dandelion.  Honeybees will rarely obtain a full cargo from scarce sources.  Flowers with a maximum amount of nectar are optimum for honey production but they do not seem to make the most effective use of pollinators.

 

Communication in Honeybees

 

          Honeybees communicate with other members of the hive by performing a “Round Dance” and a “Waggling Dance.”    The round dance is done usually within 50 ft of a hive and is of variable duration.  In the waggling dance bees make a semi-circle and then run in the direction of the food source.  This is all done in accordance with the position of the sun.  The number of waggles in the straight run communicates distance.  The closer the food source the more waggles per second.  The kind of food is communicated by samples brought back to the hive.  This behavior is confined to the genus Apis.  Some primitive bees use a platform outside the hive and point directly toward the food source.  When a bee colony is moved from the Northern to the Southern Hemisphere, it will confuse their communication abilities. 

 

Agricultural Chemicals & Pollination

 

          The agricultural chemicals of principal concern with the pollination activities of insects are fungicides, herbicides, fertilizers, fruit-setting hormones, blossom-thinning compounds and insecticides and miticides.

 

          Fruit-setting Hormones patterned after natural compounds present in pollen provide a stimulus for the setting fruit, either with our without previous pollination.  When these hormones are applied before pollination, parthenogenetic development of seedless fruits may result.  If they are applied after pollination the set of fruit with seeds may be more prolific through less blossom abscission or the fruits may become larger than normal.  For some fruits, hormones applied after fruit formation reduces preharvest fruit drop.  In breeding work with self-sterile plants some hormones may temporarily overcome self-sterility.  For commercial production tomatoes have been very successfully treated with hormones through the production of seedless and seeded tomatoes in glasshouses.

 

          Plants that receive good nutrition are usually best able to obtain good pollination, and thus the application of commercial fertilizer is advantageous.  Some crops may have a tendency toward vegetative rather than reproductive growth if the nitrogen-phosphorus-potassium ratio is not adjusted to their requirements.  There are also various additives to fertilizers, e.g., minerals that can increase a plant’s attractiveness to pollinators.

 

          Blossom thinning chemicals, such as dinitros and hormones, have been used especially in apple orchards.  An overabundance of fruit set can result in apples of smaller size.  It is best to do chemical thinning only when flowering and pollination events are near optimum.  With the dinitros application should be made when tapping the branch causes petals to fall from the tree.  Dinitros and hormones do not seems to have an adverse effect on bees even when applied during daytime. 

 

          Herbicides applied as defoliators or as hormones do not have significant harmful effects on bees if they are not applied directly to them.  The primary adverse effect such chemicals can have on bees is to destroy their forage.  Many pollen and honey plants are important for honeybees and wild bees.  However, selective herbicides can increase the abundance of valuable bee forage plants if their usage results in the reduction of competitive weed species.

 

          Fungicides have very little known adverse effects on honeybees and wild bee species.

 

          Insecticides and Miticides are essential for the control of harmful insects and mites in the commercial production of many crops.  The chemical control of insects can increase forage for honeybees and allows plants to take advantage of the pollination they have received.  However, almost all insecticides are toxic to bees, so that insect control has to avoid application in the bloom stage, which is the most attractive to bees.  It is important to prevent chemicals from drifting onto undercover plants (as in orchards) or drifting to roadside and ditch flowers or to adjacent fields in bloom.  Poor application practices can result in the death of foraging bees, and although this may not result in the death of the colony it may prevent a honey crop and ruin the colonies for effective pollination.  Overwintering a colony may be a subsequent problem.  Nurse bees may die that received poisoned materials from the field bees.  The widespread use or arsenic-based compounds during the early 20th Century was disastrous to honeybees.  The contamination of honey by field chemicals has not been a significant concern to consumers, however.

 

          Whenever the application of insecticides to flowering plants is required, it is best to remove all hives from the immediate vicinity.  Of course, applications are best made when bees are not in a field or orchard.  Also, insecticides with the least toxicity to bees should be chosen whenever possible.

 

          Commonly used insecticides can be rated as to their effects on bees.  Some materials have no appreciable effect on bees if they are applied while bees are not in the field.  These are the botanicals rhotenone, pyrethrum and nicotine, and sulfur, oils, fumigants and dinitros.  In modern advanced agriculture more reasonably priced insecticides may take precedence, however.  By the 21st Century many compounds that were toxic to bees have been removed from the market, including the chlorinated hydrocarbons.  Nevertheless, the usage of some banned materials may still be widespread in third-world countries.

 

Utilization of Wild Bees For Pollination

 

          Wild bees have great potential for commercial pollination, but their abundance is greatly hindered ty the growth of towns, the destruction of natural host plants and by land use involving drainage, tillage, irrigation, clearing and clean cultivation.  Erosion, floods, the use of insecticides and herbicides on blooming plants also disfavors wild bee populations. 

 

          Nevertheless, there are ways in which wild bees may be favored.  These include the introduction of new honey and pollen plant species, drainage and irrigation that favors bee populations, fence rails, and shingled buildings, nail holes, barns, etc.  The introduction of some hollow, pithy-stemmed plants such as milk thistle, Ailanthus, etc. also favor wild bees.  These alterations are all to frequently unstable and may not favor wild bee populations over the long run.  Their establishment in an area can require several years.

 

          Several conservation practices can result in the establishment of wild bee populations.  The maintenance of hedgerows with pithy, hollow-stemmed plants that have been stomped down provides wild bee habitat.  Natural vegetation should be maintained for some distance on either side of water courses.  Good pollen and nectar plants should be favored along roadsides and in unused fields.  Broad-leafed plants should not be removed.  Known nesting sites of wild bees can be fenced off as a protection from ploughing and flooding, but they should not be allowed to become choked with vegetation.  All use of insecticides should be eliminated in these areas.

 

Alkali Bee Nesting Sites (Photo)

 

          Studies by Dr. George E. Bohart of the U. S. Dept. of Agriculture have uncovered many attributes of wild alkali bees for pollination in the Western North America especially.  Recommendations for their establishment indicate a climate with low rainfall and a mineral type soil that is structureless (sandy or clay).  Favorable terrains are hammocks, low ridges and gentle slopes where water will never remain on the ground surface.  Subsurface features are a hard pan or one where there is natural artesian pressure.  In some cases one can locate an area that receives sub irrigation from the surface water given to irrigated crops at a higher level.  But these may be difficult to maintain in a stable condition.  The site should be close to the fields where crops occur unless there is no interference with other fields nearby.  In large fields there should be several nesting sites located around it.  Alkali bees forage the closest flowers first and then gradually spread away.

 

          Removing vegetation or at least thinning it out to a scattered pattern should begin preparation of nesting sites.  Surface drainage can be controlled in low-lying areas by grading the surface into a series of low ridges.  It must be protected from flood irrigation and natural high water from streams.  Soil moisture needs to be sub irrigated in order to maintain the soil in a moist condition up to the surface beginning in early summer and extending into autumn.  Moisture needs to be present at a depth of 5-10 inches. If a hard pan is already present, one needs to put in a series of parallel ditches to grade, spaced so that areas between will be completely seeped after a few days of funning a light stream through the ditches.  If a hard pan is lacking one can be created by scraping off 16-18 inches of soil and packing subsoil with heavy equipment.  A clay layer will give a better result.  Vegetation should be kept at a minimum because it uses up moisture.

 

          The maintenance of sites is very important.  Dense weed growth should be prevented.  Sub-irrigation is often required to maintain the proper moisture conditions.  Efforts should be made to have sufficient moisture at the surface during the nesting season to prevent the formation of a hard alkaline crust or a dry, powdery layer under a thin crust of black alkali.  It may be necessary to scrape off the alkali at the surface from early to late summer.  The site should never be allowed to hold standing water.  Livestock may roam the site, but avoid excessive trampling especially if the surface tends to become dry:  fence the area if necessary.  Skunks and badgers dig up the larvae at all times of the year and may even catch adults.  They are easily trapped or poisoned.  Bee flies that hover over the burrows with outstretched wings throw eggs into the nest entrances and the maggots destroy many alkali bee larvae.  Efforts to control them are essential.

 

          The more nesting sites there are the better.  Alkali bees migrate and it is best to try to keep them near desired fields.  Two or three unoccupied sites nearby will aid in their remaining in the area.

 

          Alkali bees may be established by natural migration if the fields are within 1-2 miles of existing sites.  Bees may also be moved to a site.  Alkali bee larvae can be used for short-range moves.  Blocks of soil from existing sites may be transplanted.  Steel cylinders can be driven into the ground and the contained soil moved.  Adults can be captured with a sweep net as they emerge from an existing site.  From the net the bees can be emptied into paper sacks and placed in a cool, damp container.  They can be released in the late afternoon on the proposed nesting sites.

 

Examinations & Exercises

 

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