Semiochemicals Used by Insect Parasitoids and Hyperparasitoids in Complex Chemical Environments and Their Application in Insect Pest Management

Insect parasitoids are key biological agents within terrestrial ecosystems, offering a promising avenue for controlling insect pests. Hyperparasitoids are a group of insects that lay their eggs in or on the body of parasitoid hosts, which can greatly hamper the effectiveness of parasitoids. To optimize their reproductive success, adult parasitoids/hyperparasitoids must find sufficient food sources and mate partners (when they do not reproduce parthenogenetically) and locate suitable hosts for their offspring. To complete these tasks, parasitoids largely rely on their ability to detect relevant chemical cues (semiochemicals or infochemicals). In the last three decades, the identities of semiochemicals and their ethological significance have been widely characterized, and the possibility of using these chemical cues in insect pest management has received a lot of attention. Insects have evolved a highly sensitive and sophisticated chemosensory system adept at navigating complex and dynamic chemical environments. In this review, we first summarize the semiochemicals used by insect parasitoids, primarily including semiochemicals involved in food location, host foraging, and mate finding, while also addressing semiochemicals employed by hyperparasitoids. Next, we discuss recent progress in elucidating the chemosensory mechanisms underlying parasitoid responses to semiochemicals, with a focus on olfactory and gustatory pathways. Finally, we evaluate the potential applications of semiochemicals in pest management, highlighting the roles of parasitoids and hyperparasitoids. This paper aims to establish a theoretical framework for the effective employment of parasitoids in biological control of insect pests.