...From the pages of Agricultural Research magazine
A Fertility Test for Beneficial Insects
Entomologists Jeffrey Shapiro
(left) and Stephen Ferkovich
examine ELISA plates scanned
in a microplate reader. The
intensity of color in each
sample is proportionate to yolk
protein content in a predatory bug.
Insect predators are used in biological control to suppress
pests in fields and greenhouses. These beneficial insects are mass reared
commercially, and producers need to be able to assess the quality of
their insects. One way to do this is to look at reproductive rates.
But it's obviously difficult and time consuming to measure rates of
egg production in a very small insect.
Instead, entomologists Jeffrey P. Shapiro and Stephen
M. Ferkovich developed enzyme-linked immunosorbent assays (ELISAs) that
measure yolk proteins in insects' blood (hemolymph) or whole bodies.
Yolk protein levels predict reproductive response to artificial and
natural diets and the resulting variations in fertility. Shapiro and
Ferkovich are with ARS' Behavior
and Biocontrol Research Unit at the Center for Medical, Agricultural,
and Veterinary Entomology in Gainesville, Florida.
ELISAs are sensitive laboratory tests that use antibodies
to detect and measure antigens in samples. In this case, Shapiro and
Ferkovich used monoclonal antibodies to measure very small quantities
of the yolk proteins. Other scientists have used ELISAs to measure yolk
protein levels in insects, but this is the first time one has been used
to predict reproductive fitness of mass-reared predators or parasitoids.
Beneficial insects are fed a range of artificial diets.
Shapiro says short-term changes in yolk proteins occur after adult females
feed. Bugs produce large amounts of yolk proteins on nutritious diets
and less on less-nutritious diets. The ELISAs gauge the amount of yolk
protein in female insects and reveal how many offspring they are capable
Artificial diets have advantages over natural-prey diets,
especially if costs can be reduced and the quality of the resulting
insects can be maintained. Artificial dietstypically containing
ground beef, beef liver, and chicken eggsmay cost less than natural-prey
diets and are more efficient and easier to control. But the proper nutrients
must be included to stimulate the normal life cycle of the insect.
"Our approach is to try to isolate critical chemicals
present in the insects' natural hosts and replicate them in nutritious
diets with artificial ingredients," Shapiro says.
The monoclonal antibodies used to develop the ELISAs came
from the yolk proteins vitellin and vitellogenin of the spined soldier
bug, Podisus maculiventris, and the minute pirate bug, Orius
insidiosus. Both of these bugs are used as biocontrols against a
wide variety of crop pests.
"Our ELISAs determine the reproductive fitness of
female insects," Shapiro says. "It's a quality-control practicelike
the ones used in other industries to produce a superior product. Growers
will see the results in the field and develop more confidence in using
beneficial insects or arthropods."
ARS is licensing the antibodies, but they will not be
patented. ARS is negotiating with a company to develop a commercial
test, which should be available this year, to analyze insectaries' samples
and tell them if the beneficial insects meet set standards.By
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 www.nps.ars.usda.gov.
Shapiro and Stephen
Ferkovich are in the USDA-ARS Behavior and Biocontrol Research Unit,
Center for Medical, Agricultural,
and Veterinary Entomology, 1700 S.W. 23rd Dr., Gainesville, FL 32604;
phone (352) 374-5988 [Shapiro], (352) 374-5767 [Ferkovich], fax (352)
"A Fertility Test for Beneficial Insects" was published in the June 2003 issue of Agricultural Research magazine.