Chemical and visual stimuli for conservation biological control of stink bugs in soybean: potential use and flaws on egg parasitoid recruitment

Stink bug egg parasitoids (Scelionidae) use several host and non-host chemical and physical cues to find suitable hosts. These cues can interact in the field producing multimodal stimuli, which can be manipulated to increase parasitoid attraction and biological control of stink bugs in conservation biological control strategies. We aimed to investigate how multimodal chemical and physical stimuli affect stink bug egg parasitoid recruitment and parasitism in soybean crops. We performed a field experiment where semiochemicals and visual stimuli were presented alone or in combination during three soybean growing seasons. We evaluated the occurrence of stink bug parasitoids and parasitism rates using sentinel eggs, and stink bug species abundance. Long-distance semiochemicals (herbivore-induced plant volatiles and sex pheromone) did not interfere on Scelionidae parasitoid recruitment. Visual stimuli and stimuli combinations negatively interfered on parasitoid recruitment or had no effect. The parasitism of sentinel eggs varied among seasons, and long-distance semiochemicals increased parasitism on one season. In the other seasons there was a significant effect of predation on the sentinel stink bugs eggs. Predation, mostly by ants, was the main egg mortality factor, which could have masked parasitism effects. The stink bug Euschistus heros (Hemiptera: Pentatomidae) was always the most abundant species occurring with other seven species. Our results indicate the relevance of different biological control agents on stink bug egg mortality. We discuss the applications and major flaws for conservation biological control of stink bugs and its compatibility with augmentative releases of egg parasitoids, especially for Telenomus podisi.