Search

Temporal changes in the pre- and post-alighting responses of mated female diamondback moth, Plutella xylostella L. ( Lepidoptera: Plutellidae), to two species of Brassica ( Brassicaceae) host plants induced by larval feeding were studied using olfactometer and oviposition assays. Females displayed strong olfactory and oviposition preferences for herbivore-induced common cabbage ( Brassica oleracea var. capitata L. cv. sugarloaf) plants over intact plants; these preferences decreased with time and disappeared by the 7th day after induction. In herbivore-induced common cabbage plants, eggs were clustered near feeding damage on the younger leaves (leaves 5-7), whereas in intact plants, eggs were clustered on the stem and lower leaves (leaves 1-4) . However, as the time interval between larval feeding and oviposition increased, more eggs were laid on the lower leaves of induced plants. This demonstrates a change in egg distribution from the pattern associated with induced plants to that associated with intact plants. In contrast, females displayed strong olfactory and oviposition preferences for intact Chinese cabbage [ Brassica rapa ssp. pekinensis (Lour.) Hanelt cv. Wombok] plants over induced plants; these preferences decreased with time and disappeared by the 5th day after induction. More eggs were laid on the upper leaves (leaves 4-6) than on the lower leaves (leaves 1-3) of intact Chinese cabbage plants at first, but the distribution changed over time until there were no significant differences in the egg count between upper and lower leaves by the 4th day post induction. For both host plant species, pre-alighting responses of moths were reliable indicators of post-alighting responses on the first 2 days post induction. The results suggest that temporal changes in a plant's profile (chemical or otherwise) following herbivory may influence attractiveness to an insect herbivore and be accompanied by changes in olfactory and oviposition preferences. [ABSTRACT FROM AUTHOR]

Parasitoids use herbivore-induced plant volatiles ( HIPVs) to locate their hosts. However, there are few studies in soybean showing the mechanisms involved in the attraction of natural enemies to their hosts and prey. The objective of this study was to evaluate the influence of volatile organic compounds ( VOCs) of soybean, Glycine max ( L.) Merr. ( Fabaceae) (cv. Dowling), that were induced after injury caused by Euschistus heros ( Fabricius) ( Hemiptera: Pentatomidae), on the searching behavior of the egg parasitoid Telenomus podisi Ashmead ( Hymenoptera: Scelionidae). Four HIPVs from soybean, ( E, E)-α-farnesene, methyl salicylate, ( Z)-3-hexenyl acetate, and ( E)-2-octen-1-ol, were selected, prepared from standards at various concentrations (10−6 to 10−1 m), and tested individually and in combinations using a two-choice olfactometer (type Y). Telenomus podisi displayed a preference only for ( E, E)-α-farnesene at 10−5 m when tested individually and compared to hexane, but they did not respond to the other compounds tested individually at any concentration or when combinations of these compounds were tested. However, the parasitoids stayed longer in the olfactometer arm with the mixture of ( E, E)-α-farnesene + methyl salicylate at 10−5 m than in the arm containing hexane. The results suggest that ( E, E)-α-farnesene and methyl salicylate might help T. podisi to determine the presence of stink bugs on a plant. In addition, bioassays were conducted to compare ( E, E)-α-farnesene vs. the volatiles emitted by undamaged and E. heros-damaged plants, to evaluate whether ( E, E)-α-farnesene was the main cue used by T. podisi or whether other minor compounds from the plants and/or the background might also be used to locate its host. The results suggest that minor volatile compounds from soybean plants or from its surroundings are involved in the host-searching behavior of T. podisi. [ABSTRACT FROM AUTHOR]

As studies demonstrating attraction of natural enemies to synthetic herbivore-induced plant volatiles ( HIPVs) accumulate, it is becoming increasingly important to investigate how deployment of these compounds influences arthropod behavior and distribution in the field. There is currently an unexplained dichotomy in the literature regarding the distance over which HIPVs are thought to be effective. It is assumed that these compounds increase recruitment of natural enemies into fields, whereas experiments have found the effects of attraction to dissipate as little as 1.5 m from lures. Through the use of the common HIPV phenylethyl alcohol in soybean [ Glycine max ( L.) Merr ( Fabaceae)] fields, we used replicated mini plots to test the spatial scale and consequences of attraction by analyzing the response of a complex arthropod community to HIPVs along a distance gradient from the HIPV source. Although repellent effects were more common than attractive ones, we found that insect responses to HIPVs are generally consistent out to a range of 8 m, corroborating the idea that volatiles can influence a wide area and are capable of increasing arthropod recruitment at a field scale. Evidence of redistribution (i.e., depletion of patches surrounding HIPV-augmented plots) was found for a single taxon, braconid wasps, for which augmentation occurred around the lure, but with a reciprocal decline in abundance at greater distances from the emission site. These results are both encouraging and cautionary. Although broad-scale diffusion of HIPVs appears to be common, redistribution of key predators and/or parasitoids may complicate natural enemy management on a landscape scale by aggravating pest outbreaks in areas robbed of their normal carnivore assemblage. [ABSTRACT FROM AUTHOR]