The maternal foam plug constitutes a reservoir for the desert locust's bacterial symbionts

Abstract

Summary A hallmark of the desert locust's ancient and deserved reputation as a devastating agricultural pest is that of the long‐distance, multi‐generational migration of locust swarms to new habitats. The bacterial symbionts that reside within the locust gut comprise a key aspect of its biology, augmenting its immunity and having also been reported to be involved in the swarming phenomenon through the emission of attractant volatiles. However, it is still unclear whether and how these beneficial symbionts are transmitted vertically from parent to offspring. Using comparative 16S rRNA amplicon sequencing and direct experiments with engineered bacteria, we provide evidence for vertical transmission of locust gut bacteria. The females may perform this activity by way of inoculation of the egg‐pod's foam plug, through which the larvae pass upon hatching. Furthermore, analysis of the composition of the foam revealed chitin to be its major component, along with immunity‐related proteins such as lysozyme, which could be responsible for the inhibition of some bacteria in the foam while allowing other, more beneficial, strains to proliferate. Our findings reveal a potential vector for the transgenerational transmission of symbionts in locusts, which contributes to the locust swarm's ability to invade and survive in new territories.

Obstacle Negotiation in Female Locust Oviposition Digging

“…Subsequently, while concomitantly withdrawing her abdomen, she fills the burrow to the top with this specialized foam, which is intended (in addition to its other roles, e.g. Lavy et al, 2021) to provide the future hatchlings with a quick and safe route to the surface (Symmons and Cressman, 2001; Uvarov, 1977; Hägele et al, 2000). The female locust abdomen at rest is no longer than 2.5-3 cm.…”

Genomic and Transcriptomic Insights into the Genetic Basis of Foam Secretion in Rice Spittlebug Callitettix versicolor

“…Similarly, many locusts (Orthoptera) lay their egg pods deeply in the soil and then envelop the eggs in foamy secretions to prevent them from desiccation. These foams allow beneficial, symbiont bacteria to proliferate [4]. The poplar sawfly, Stauronematus compressicornis, uses its salivary gland to excrete foam that can inhibit the feeding of other insects and occupy the food niche [5].…”