Volatiles released by Oryza sativa L. and its implications for the chemotaxic behavior of Tibraca limbativentris Stal. (Hem., Pentatomidae) and egg parasitoids

The rice stem bug, Tibraca limbativentris, is one of the most important pests of rice in Brazil. Plant defense strategies against these bugs may involve the emission of chemical compounds which are released following herbivore attacks and directly or indirectly compromise pest performance. The egg parasitoids are important natural enemies for this stink bug, but little is known about the chemical communication involved in this tritrophic interaction. The aim of this study was to identify the substances present in extracts of rice plants (Oryza sativa L.) that suffered herbivory by rice stem bugs, as well as the behavioral responses of T. limbativentris adults and the egg parasitoids Trissolcus basalis and Telenomus podisi when exposed to these odors. Plant volatiles were collected from undamaged plants of the rice cultivar IRGA 424 and from plants subjected to herbivory damage by five males or five females of T. limbativentris. Extracts were analyzed by GC-FID and GCMS, and insect responses evaluated in a "Y" olfactometer. T. limbativentris herbivory induced the release of secondary compounds by rice plants, including alcohols, aldehydes, and terpenoids. Female bugs were significantly more attracted to volatiles from undamaged plants, while males showed no such preference. T. podisi females were significantly more attracted to the extracts of plants damaged by females, while T. basalis responded equally to volatiles from plants damaged by males and females. These results suggest that rice plants may be emitting defense compounds which induced antixenosis in T. limbativentris females and also acted indirectly by attracting natural enemies.