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High-Performance
Insect Diets
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Lygus lineolaris nymph feeds on broccoli
during a feeding test. The insect, raised
on an artificial diet, is tested to make
sure it will feed on natural food sources
before it's released.
(K9249-1)
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Relying on insects that prey on crop
pests can have a serious drawback: By the time predator numbers become large
enough to do a top-rate control job, the pests have already started taking an
economic toll on the crop. But it's been prohibitively expensive to rear
massive numbers of predators in captivity for release into fields at the most
opportune time. Rearing enough host insects to satisfy the predators' voracious
appetites, after all, doesn't come cheap.
That's why ARS scientists are searching
for artificial diets that will satisfy the palates of beneficial insects, such
as the spined soldier bug, the two-spotted stink bug, the big-eyed bug, and the
minute pirate bug.
Simply providing a cheap diet that will keep the beneficial insects alive is
not the final answer, says Thomas A. Coudron, a chemist at the ARS Biological
Control of Insects Laboratory, in Columbia, Missouri. The diets must also help
the insects thrive and produce multitudes of offspring fit for the field.
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Insect weight and egg production
are two of the main measures of
diet performance. Research aide
Parvaneh Khosravi prepares to
weigh insects reared on one of
several diets being tested.
(K9248-1)
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Coudron and his colleagues have been
combining their expertise in insect biochemistry and physiology to improve the
prospects for using beneficial insects. Currently sold mostly to organic
gardens and greenhouses, these helpful bugs already make up a
$750-million-per-year business. But releasing them in large numbers to help
protect field crops—not just organic gardens and greenhouses—will
only make sense if the cost of rearing the insects can be significantly
decreased, says Coudron.
ARS has already made progress toward this goal. Captive-reared lacewings,
Chrysoperla carnea, once required an insect-egg diet costing more than
$300 per pound. By 1997, ARS had developed a lacewing diet that could be
produced for $2.50 per pound. The artificial diet, invented by entomologist
Allen C. Cohen, now at the ARS Biological Control and Mass Rearing Research
Unit, Mississippi State, Mississippi, also works for the big-eyed bug,
Geocoris punctipes. This predator and the lacewing have voracious
appetites for a wide range of plant-feeding insects, such as whiteflies,
aphids, scale insects, moth eggs and larvae, and mealybugs.
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Technician Patrick Crittenden
(seated) and entomologist Allen
Cohen, discuss PAGE gel of
hemolymph (blood) proteins from
Lygus bugs. The protein banding
in the gel Crittenden is pointing
to (enlargement at far right) tells
them the physiological age of
the insect.
(K9245-1)
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Cohen and his colleagues at
Mississippi State also developed biochemical and biological tests that
commercial insectaries can use to quickly and accurately determine whether or
not insects reared on artificial diets are able to devour large quantities of
pest insects.
Artificial diets are also being developed to feed captive host pests. These
insects are used in mass-rearing of beneficial predators and parasites. Cohen
is trying various combinations of a basic recipe, which consists mainly of
cooked chicken eggs, lima bean meal, wheat germ, soy flour, yeast, vitamins,
and preservatives.
"The diets differ from one another in their nutritional quality,"
says Cohen. To determine which recipe gets the blue ribbon, the researchers
measure differences in the pests' weight, longevity, biomass accumulation, and
fecundity.
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The scientists have proven that there
is a correlation between a better diet and an increase in egg production. They
used tests such as colorimetry, electrophoresis, and enzyme-linked
immunosorbent assay (ELISA) to measure protein in the insect eggs. ELISA is
based on the ability of an antibody to recognize and bind to a specific
antigen, thereby identifying yolk proteins in the adult females and the eggs.
Test results were clear. One example is a diet for Lygus hesperus, a
destructive bug that devours cotton plants. L. hesperus bugs reared on a
diet of chicken egg and a plant product, rather than chicken egg and a meat
paste, had more yolk proteins in their hemolymph and eggs. This measurement is
predictive of a healthier insect and an adult with higher egg-producing
capacity.
"This means that a simple immunological/biochemical test can be used early
in the rearing process to predict that a diet or other rearing condition is
good for or harmful to the insects," says Cohen. This translates into
fewer insect losses and significant cost savings for producers. |
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Carrageenan gel pack containing
several thousand Lygus lineolaris
eggs from adults reared on
the new diet developed by
Allen Cohen.
(K9247-9)
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By linking research in the areas of physiology, biochemistry, genetics,
nutrition, and digestion, Cohen hopes to further improve the formulation and
long-term storage of artificial diets—with the ultimate goal of making
mass-rearing efficient and economical.
Coudron is also working on part of an immunological/biochemical test that would
link to a method developed by ARS entomologist Terrance S. Adams to score the
reproductive potential of spined soldier bugs and two-spotted stink bugs. The
spined soldier bug feeds on more than 50 species of insects, and both predators
feed on the Colorado potato beetle, a major pest of potatoes and related
plants. Adams is at the Red River Valley Agricultural Research Center, Fargo,
North Dakota. By tracing the biochemistry and physiology of egg production, he
and Coudron are looking for ways to alter the diet, perhaps for different
production stages, to tune up the bugs' nutritional, endocrine, and
reproductive systems.
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Special insect diets are contained
in the larger white packets being
inspected by entomologist Gay
McCain. The smaller packets
contain eggs from insects reared
on the diets.
(K9247-1)
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The fine-tuning may result in an increase in fertile egg production in
insectaries that will far exceed the reproductive capacity of beneficial
insects in nature, says Coudron. That's because of a tradeoff: Faced with
fluctuating food supplies in the wild, adults may be programmed to enhance
their chances for survival by producing fewer eggs.
The study of dietary effects on reproduction could help lead to year-round
production of beneficial insects and their eggs. This would allow more
efficient use of insectaries and encourage commercial investment in
them.—Ben
Hardin, and Jesús
García, Agricultural Research Service Information Staff.
This research is part of Crop Protection and Quarantine, an ARS National
Program (#304) described on the World Wide Web at
http://www.nps.ars.usda.gov.
Thomas A. Coudron is with the
USDA-ARS Biological Control of
Insects Research Laboratory, 1503 South Providence Rd., Research Park,
Columbia, MO 65203; phone (573) 875-5361, fax (573) 875-4261.
Allen C. Cohen is in the
USDA-ARS Biological
Control and Mass Rearing Research Unit, P.O. Box 5367, Mississippi State,
MS 39762; phone (662) 320-7560, fax (662) 320-7571.
Terrance S. Adams is with
the USDA-ARS Red River Valley
Agricultural Research Center, P.O. Box 5674, University Station, Fargo, ND
58105; phone (701) 239-1277, fax (701) 239-1202. |
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"High-Performance Insect Diets" was
published in the February 2001
issue of Agricultural Research magazine.
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