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INSECT POLLINATION (cont’d.)
(Contact) 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. 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. 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. 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. |
