Less is more: treatment with BTH and laminarin reduces herbivore-induced volatile emissions in maize but increases parasitoid attraction.

Chemical plant strengtheners find increasing use in agriculture to enhance resistance against pathogens. In an earlier study, it was found that treatment with one such resistance elicitor, BTH (benzo-(1, 2, 3)-thiadiazole-7-carbothioic acid S-methyl ester), increases the attractiveness of maize plants to a parasitic wasp. This surprising additional benefit of treating plants with BTH prompted us to conduct a series of olfactometer tests to find out if BTH and another commercially available plant strengthener, Laminarin, increase the attractiveness of maize to three important parasitic wasps, Cotesia marginventris, Campoletis sonorensis, and Microplitis rufiventris. In each case, plants that were sprayed with the plant strengtheners and subsequently induced to release volatiles by real or mimicked attack by Spodoptera littoralis caterpillars became more attractive to the parasitoids than water treated plants. The elicitors alone or in combination with plants that were not induced by herbivory were not attractive to the wasps. Interestingly, plants treated with the plant strengtheners did not show any consistent increase in volatile emissions. On the contrary, treated plants released less herbivore-induced volatiles, most notably indole, which has been reported to interfere with parasitoid attraction. The emission of the sesquiterpenes (E)-ß-caryophyllene, ß-bergamotene, and (E)-ß-farnesene was similarly reduced by the treatment. Expression profiles of marker genes showed that BTH and Laminarin induced several pathogenesis related (PR) genes. The results support the notion that, as yet undetectable and unidentified compounds, are of major importance for parasitoid attraction, and that these attractants may be masked by some of the major compounds in the volatile blends. This study confirms that elicitors of pathogen resistance are compatible with the biological control of insect pests and may even help to improve it.

Prevalence of Wolbachia supergroups A and B in Bemisia tabaci (Hemiptera: Aleyrodidae) and some of its natural enemies.

Wolbachia, a bacterial symbiont, is maternally transmitted in arthropods and nematodes. We report a systematic survey of Wolbachia taxonomy in the sweetpotato whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), and in some of its natural enemies. For the first time, Wolbachia infections in B. tabaci are correlated with various whitefly genetic groups, host plants, and natural enemies as well as with geographical regions. Polymerase chain reaction using 16S rDNA and fisZ genes revealed two Wolbachia supergroups, A and B, exist as single or double infections in B. tabaci as well as in some of its aphelinid parasitoids and predatory beetles. Approximately 89% of B. tabaci sampled were infected by Wolbachia, among which 34% were infected by A, 51% were infected by B, and 5% were infected by both A and B supergroups. These infection frequencies differed among B. tabaci genetic groups and locations. The invasive B. tabaci genetic group from the Middle East Asia Minor 1 (also referred as B biotype) and Mediterranean (also referred as Q biotype) was more likely to harbor A than B, whereas native genetic groups in AsiaI and AsiaII were more likely to harbor B than A. Although 60% of aphelinid parasitoids and 72% of coccinellid beetles also were infected by Wolbachia, they were more likely to host B than A. Furthermore, for the first time we report Wolbachia in B biotype from specimens collected outside of China. Construction of a phylogenetic tree clearly indicated that the Wolbachia sequences from different genetic groups of B. tabaci were not only similar to each other but also to sequences from beetles and parasitoids, which may provide evidence of coevolution and horizontal transmission of Wolbachia populations.