Tactics Simplify Wasp-Rearing
Biosteres arisanus wasps inject their eggs into oriental fruit fly
Helpful wasps that kill crop-destroying fruit flies should be easier to
breed indoors, thanks to ongoing work by scientists with the Agricultural
Research Service in Hawaii.
Massive numbers of lab-reared beneficial wasps can be deployed outdoors to
attack Mediterranean fruit flies and other tropical and subtropical fruit fly
pests. The wasps, harmless to humans, "may reduce reliance on chemical
insecticides," says ARS entomologist Ernest J. Harris in Honolulu.
Harris is the first to establish a thriving indoor colony of Biosteres
arisanus wasps. He says the insect, less than a quarter inch long, "is
one of the most important wasp enemies of medfly and oriental fruit fly, in
part because it outcompetes other parasitic wasp species."
Medflies attack more than 400 crops worldwide; oriental fruit flies pester
more than 230.
Female wasps can easily reach and parasitize the fruit fly eggs that ARS
entomologist John Spencer places on agar in laboratory petri dishes.
ARS colleagues at Honolulu have used the "Harris strain" of B.
arisanus, along with other species of beneficial wasps, in experiments to
streamline mass-rearing. A key discovery was that female B. arisanus
wasps readily lay their eggs in fruit fly eggs that are placed atop a
gelatinous substance called agar.
A wasp egg is about 8 times smaller than a fruit fly egg, notes Renato C.
Bautista, a researcher with the University of Hawaii who works with Harris.
"Agar keeps the fruit fly eggs from drying out," says entomologist
John P. Spencer of the Honolulu laboratory. "We put about 5,000 fruit fly
eggs on agar in a 3-3/4-inch-square petri dish and give caged female wasps
about 22 hours to insert their eggs into the fruit fly eggs. After that, it's
easy to move the parasitized eggs from the agar block to large trays that we
use for the next steps of production. Using agar has probably boosted our
production at least fivefold compared to our previous method."
The lab procedures are the work of a team led by Spencer. The techniques
have attracted interest from scientists in other countries trying to combat
non-native fruit flies.
When a wasp egg hatches, the insect grows inside the developing fruit fly,
eventually killing it. Wasps that emerge from pupal cases--the capsulelike
chambers that housed the immature flies--can then be put to work outdoors.
Entomologists Ernest J. Harris (left), who is with the Agricultural Research
Service, and Renato C. Bautista, with the University of Hawaii, examine a
papaya fruit trap with oriental fruit fly eggs parasitized by Biosteres
Related experiments have shown that a pneumatic air separator--a device
normally used for cleaning seeds--simplifies sorting of parasitized from
unparasitized fruit flies. The chore is best handled when the fruit fly is a
pupa; that is, just before it becomes an adult.
These studies were led by ARS food technologist Harvey T. Chan at Hilo,
The separator swiftly and accurately sorts fruit fly pupae parasitized by
any of three wasps--Diachasmimorpha longicaudata, D. tryoni, and
Psyttalia fletcheri. "Unparasitized pupae," explains Chan,
"are heavier than their parasitized counterparts. That creates a natural
division of floaters versus sinkers."
The approach, Chan says, should be easy to automate.--By
Marcia Wood, Agricultural
Research Service Information Staff.
Honolulu and Hilo researchers mentioned in this article can be contacted
through the USDA-ARS Tropical
Fruit, Vegetable, and Ornamental Crop Research Laboratory, P.O. Box 4459,
Hilo, HI 96720; phone (808) 959-4300, fax (808) 959-4323.
"Tactics Simplify Wasp-Rearing" was published in the July
1998 issue of Agricultural Research magazine. Click here to see this
issue's table of contents.