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Research underway in the laboratory investigates the complex chemical ecology of the wheat stem sawfly. Pheromones that involve the sawflies’ mating system have been identified (Cosse et. al 2002). Host location and selection by both sawflies and parasitoids may also be guided by chemical signals.
There are several levels of analysis involved in the evaluation of wheat stem sawfly chemical ecology:
1. Collection of volatile compounds: Chemicals emitted by plants and/or insects are collected using a volatile collection system (VCS). A stream of purified air flows over the plants or insects in a glass collection tube. A vacuum system pulls the air and volatile components from the tube at the same rate. Compounds collected by the vacuum system are trapped in a glass tube that contains 30 mg SuperQ adsorbent (Alltech Associates).
2. Analysis of volatile compounds: Samples collected using the VCS are analyzed using a coupled Gas Chromatograph/Mass Spectrometer (GC/MS), which allows for identification and quantification of volatile components.
3. Physiological response to volatile compounds: A gas chromatograph- electroantennogram (GC/EAD) detector is used to identify which components of the sample stimulate a response by the insect.
4. Behavioral assays: Insect attraction or repellence to behaviorally active compounds can be measured in a wind tunnel or y-tube olfactometer in the lab. Oviposition preference by the sawfly for compounds emitted by different wheat varieties is tested in both greenhouse and field trials.
Preliminary data identify several compounds produced by wheat plants that elicit a response by the wheat stem sawfly. Wheat varieties differ in the amounts of these chemicals produced. Behavioral trials show a correlation between the amount of attractive compound produced and oviposition preference (see graphs below).
Plants damaged by wheat stem sawfly may emit chemical cues that attract parasitoids. The volatile compounds produced by sawfly infested plants are being evaluated and tested for a behavioral response by parasitoids.
The wheat stem sawfly laboratory utilizes a diverse array of tools to investigate the complex biology of the sawfly. Data collected from these studies can be used to guide selection of crops that are more resistant to sawfly attack, while maximizing the potential for parasitoids to locate hosts.
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