Locust Bacterial Symbionts: An Update

SIMPLE SUMMARY: Locust plagues have been devastating vegetation and agriculture since ancient times. The tendency of locusts to form huge swarms and migrate long distances is a hallmark of the locust phenomenon. The ecological and economic importance of locust plagues has attracted much research into different aspects of the natural history of these insects. One of the many investigated aspects of the locust phenomenon is that of their interaction with the bacteria they harbor in and on their body. These locust-associated bacteria have been shown to affect certain physiological traits (such as immunity and swarm cohesion), as well as possibly affecting and being affected by different factors in the locust biology. Here, we review the current understanding of the locust–bacteria interaction. We focus on identifying the bacterial strains and their locations within the insects; the role of the bacteria and their importance to their host’s life; the mechanism of transmitting important bacteria across locust generations; and more. Finally, we offer some new perspectives and research directions that could broaden our understanding of the locust-associated bacteria and their role in locust outbreaks. ABSTRACT: As one of the world’s most infamous agricultural pests, locusts have been subjected to many in-depth studies. Their ability at one end of their behavioral spectrum to live as solitary individuals under specific conditions, and at the other end of the spectrum to form swarms of biblical scale, has placed them at the focus of vast research efforts. One important aspect of locust ecology is that of their interactions with the bacteria that reside in and on them. Although this aspect of locust ecology has been little studied relative to the mainstream locust research, these bacteria have been shown both to affect locust immunity and to participate in maintaining swarm integrity through the secretion of attractant volatiles. The interaction between locusts and their bacteria seems, however, to be bi-directional, with the bacteria themselves, as recently shown, being influenced by their host’s swarming tendencies. This seems to be a consequence of the bacterial composition in the locust’s gut, reproductive organs, and integument undergoing change with the change in their host’s behavior. In this review we describe the current state of knowledge of the locust–bacteria interactions (data exists mainly for the desert and the migratory locusts), as well as highlighting some newly-gained understanding; and offer perspectives for future research.