Behavioral defenses against parasitoids: Genetic and neuronal mechanisms

Abstract

Abstract The main biotic threats organisms face in nature are competition, predation, and parasitism. Behavioral responses are an evident way that organisms can outcompete rivals and avoid predation, but it can be hard to imagine how behaviors limit parasitism given that parasites are usually small and live inside their hosts. However, many new discoveries have shown that hosts use behavioral defenses to prevent themselves or their offspring from becoming parasitized, or to cure themselves once infected. These include many examples of host behaviors deployed against parasitoids, which are ubiquitous and important threats to insects. This chapter reviewed the diversity of host behaviors that protect against parasitoid infection. Then, focusing on the fruit fly genetic model Drosophila melanogaster, it covers parasite cues and the sensory systems hosts use to perceive parasitoids, and examines the neuronal processing events that occur deeper in the host central brain, including the roles of learning and memory. Finally, it discusses how the brain controls behavioral output leading to successful defense against parasitoid infection. Understanding how hosts recognize and respond to parasitoids can inform future studies into the ecological parameters responsible for host–parasitoid community structure. As is true of other kinds of behaviors, large gaps still exist in our mechanistic understanding of defense behaviors.