Report on the Agricultural Experiment Stations, 1952 Page: 60
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60 REPORT ON EXPERIMENT STATIONS, 1952
were excluded only 3 seeds per 50 heads were formed. When the
blossoms were in a cage with honey bees 90 seeds per 50 heads were set.
Open-pollinated Ladino blossoms-produced outside of a cageyielded
73 seeds per 50 heads. The pollinizers visiting the open-pollinated
blossoms consisted of approximately 10 honey bees to one other
kind of bee. The other bees visiting the Ladino clover blossoms were
mainly small bumblebees. A few were small solitary bees.
An experiment was conducted by the Alabama station to determine
the value of honey bees in the pollination of crimson clover. Honey
bees were placed in or near the clover fields at rates of 2/3, 2, and 51/3
colonies per acre. Screened cages were used to exclude the bees from
small areas. Clover exposed to bees yielded 384 to 535 more pounds
of clean seed per acre than clover from which bees were excluded.
The Oklahoma station found that in 1 year two hives of honey bees
per acre increased vetch seed yields 2.3 times as compared to areas from
which bees were excluded by screens. The increase of 304 pounds per
acre was worth around $50 to the grower and also provided an increased
seed supply needed for the grasslands program.
Mite-killing Chemicals and Insects Work Together
The California station has developed a method under which the new
acaricides can be used in combination with the predatory dusty wings
to control mites in citrus groves. The dusty wings are delicate,
whitish insects barely one-eighth inch long. Both larval and adult
stages destroy mites. The larvae, with piercing mouth parts, suck
the body juices from their prey. The adults consume whole individuals
of the prey, legs and all. But dusty wings must also have a
source of plant nectar or of honeydew, the fluid secreted by insects
such as scales, mealybugs, or aphids. For this reason dusty wings do
not thrive in groves treated with insecticides which destroy the honeydew-secreting
insects. Careful choice of insecticides is, therefore,
necessary if the dusty wings are to serve as mite killers.
Field experiments of the California station have shown that when
the new acaricides are used on citrus trees, exisiting dusty wings live
on the low populations of mites and insects that remain alive in the
grove despite chemical treatment. The predaceous activity of the
dusty wings is thus maintained and serves to prolong the period of
effective mite control brought about by the acaricide. However, dusty
wings themselves are extremely sensitive to insecticides, a factor in
the increase of citrus mites following the use of DDT.
Insect Carriers of Two Plant Diseases Identified
The California station has discovered that the melon aphid is a carrier
of the citrus quick-decline disease. This virus disease was first
noted in California in 1939 and has been spreading. It is particularly
destructive to trees of sweet orange growing on sour orange rootstocks.
Although under experimental conditions the melon aphid is
a rather ineffective carrier of the disease, studies of dispersal flights
have indicated that enough individuals fly in a citrus orchard to account
for the observed spread of the disease. Surveys have shown
high populations of melon aphid breeding on citrus in certain areas
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United States. Office of Experiment Stations. Report on the Agricultural Experiment Stations, 1952, book, January 1953; Washington D.C.. (digital.library.unt.edu/ark:/67531/metadc5990/m1/62/: accessed April 23, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.