Responses ton-dipropyl disulfide by ovipositing onion flies: Effects of concentration and site of release.

Onion fly females,Delia antiqua (Diptera: Anthomyiidae) laid the most eggs on ovipositional dishes havingn-dipropyl disulfide (Pr2S2) release rates of 1-6 ng/sec from polyethylene capsules placed beneath a sand substrate. When dipropyl disulfide was released from the wax coating of surrogate foliage rather than from the substrate, ovipositing females again responded differentially to various concentrations, laying more eggs around stems containing 0.075 and 0.089 mg/stem. Factorial combinations of several concentrations released from surrogate foliage and substrate showed that releases from surrogate foliage stimulated four times more egg-laying than releases from the substrate. Females tended to lay more eggs around surrogate stems having Pr2S2 at the base rather than on the upper half of foliage. Observations of individual females performing preovipositional examining behaviors on Pr2S2-treated surrogate stems indicated that females tended to land on the upper portions of the foliage, but after landing, spent most of their time examining areas of soil and surrogate within 1 cm of the soil-surrogate foliage interface. Surrogate stems provide a realistic context for investigating effects of plant chemicals on host-acceptance behaviors.