TRI-TROPHIC INTERACTIONS IN SOYBEAN AGRO-ECOSYSTEMS: MECHANISMS, ECOLOGICAL RELEVANCE, AND APPLICATION POTENTIAL OF NATURAL ENEMIES OF KUDZU BUGS

Abstract

A series of studies were conducted to evaluate herbivore-herbivore and herbivore-parasitoid interactions that may impact the kudzu bug, Megacopta cribraria F. (Hemiptera: Plataspidae) population in soybean. Experiments on herbivore-herbivore interactions using kudzu bugs and either southern green stink bug, Nezara viridula L. or brown marmorated stink bug, Halyomorpha halys Stål aimed to examine the potential competition or facilitation among these herbivorous pests. Parasitoid-herbivore interactions were conducted using kudzu bug egg parasitoids, Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae) and Paratelenomus saccharalis Dodd (Hymenoptera: Platygastridae) to better understand the factors influencing parasitoid effectiveness and improve biological control strategies for kudzu bug management. To understand kudzu bug-stink bug interactions, the direct and indirect impacts of kudzu bug infestation on the behavior of two stink bug species were investigated. The brown marmorated stink bug preferred healthy soybean plants in the presence of kudzu bugs but shifted towards infested plants when kudzu bug adults were removed, while the southern green stink bug consistently preferred infested plants. Kudzu bug density had a more significant effect on brown marmorated stink bug landing preference than on southern green stink bug. Kudzu bug infestation altered responses in soybean, reducing interspecific interaction for brown marmorated stink bug but enhancing it for southern green stink bug. To further understand kudzu bug-parasitoid interactions, the effects of different adult parasitoid food sources, host eggs: adult parasitoid ratios, and host exposure times on the proportion and sex ratio of the parasitoid offspring were evaluated. The study found that honey as a food source, a 21:7 host: parasitoid ratio, and three-five days of exposure time resulted in the highest proportion of female-biased offspring for O. nezarae, while the same food source and host to parasitoid ratio at a one-day host exposure were optimal for P. saccharalis to maximize female offspring production. These findings provide new insights into the biology of these egg parasitoids. Building on this knowledge, the study also investigated parasitoids' olfactory responses influenced by their physiological state and learning status during host-foraging strategies. It was found that both parasitoid species innately responded to host-associated stimuli, regardless of their hunger or host experience. Female parasitoids used volatile cues from infested soybean plants with kudzu bug eggs and footprint trails left by adult kudzu bugs to locate their host. In a final study, interspecific interactions between O. nezarae and P. saccharalis were investigated. It was found that simultaneous release of both parasitoids led to higher host egg parasitism than sequential release. Ooencyrtus nezarae produced more total offspring but mostly male offspring. In aggressive behavior, P. saccharalis used head butting to fight O. nezarae. Ooencyrtus nezarae was able to develop in host eggs parasitized by P. saccharalis, acting as a superior larval competitor. The findings of this project provide valuable insights for enhancing biological control strategies against kudzu bugs by understanding kudzu bug-stink bug interactions, kudzu bug egg parasitoids’ requirements, behaviors, and their interspecific interactions.

Keywords: Kudzu bug, Parasitoids, Biological control programs, Olfactory behavior, Plasticity, Chemical footprints