Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/9/2004
Publication Date: 7/10/2004
Citation: Panizzi, A.R., Berhow, M.A., Bartelt, R.J. 2004. Artificial substrate bioassay for testing oviposition of the southern green stink bug conditioned by soybean plant chemical extracts. Environmental Entomology. 33(5):1217-1222. Interpretive Summary: The southern green stinkbug is a major worldwide pest. One of the methods of biocontrol of this pest is the use of parasites that feed on eggs. In order to mass-produce these parasites, large quantities of eggs are required. The stinkbug generally does not produce large quantities of eggs in laboratory colonies, so methods are needed to enhance this production. We are investigating components found in the pest plant hosts, which induce the stinkbugs to lay more eggs in captivity. We have developed a bioassay for assessing the attraction of captive stinkbugs for laying eggs on an artificial 'leaf' made from cheesecloth coated with extracts prepared from soybeans. Using this bioassay system, we will isolate and identify compounds from soy, which the stinkbugs recognize for egg laying. Once completed, this research may lead to improved stinkbug egg mass production techniques and other biocontrol methods in the field.
Technical Abstract: The southern green stink bug, Nezara viridula (L.) (Heteroptera: Pentatomidae), a major pest worldwide, is effectively controlled with egg parasitoids and egg production is an important component of this strategy. Therefore, a laboratory bioassay was developed for testing its oviposition preference toward chemicals extracted from soybean pods and leaves. In this bioassay, an artificial substrate (cheesecloth) was stretched over a wooden ring (embroidery hoops), treated with plant extracts or chromatographic fractions, and then exposed to adult stink bugs to assess oviposition preference. To obtain samples of chemicals for bioassay testing, freeze-dried soybean leaves and pods were extracted, first with hexane, then with methanol, and finally with water. The organic solvent extracts were then fractionated by liquid chromatography, first on a C18 reverse phase column, then on a normal phase silica column, and finally by thin layer chromatography (TLC) on silica gel. The methanol extract of pods showed the greatest bioassay activity. The most active reverse phase fraction derived from this extract was that eluted with 20% methanol in water. After subjecting this fraction to chromatography on silica, the greatest activity occurred in the fraction eluted with 60% methanol in methylene chloride. Further fractionation of this material by TLC gave no single fraction with demonstrated activity, but the recombined fractions were again active, indicating that multiple components may be involved in eliciting oviposition. Hairs (long and short trichoidea) present in the female genitalia might be involved in chemical and/or mechanical recognition of oviposition stimulants.