Spiroplasma dominates the microbiome of khapra beetle: comparison with a congener, effects of life stage and temperature

Abstract

Khapra beetle, Trogoderma granarium (Coleoptera: Dermestidae), is among the world’s most invasive and destructive pests of stored agricultural products. Its pest status is enhanced by the ability of the larvae to undergo diapause, which increases their tolerance to adverse conditions including insecticides and extreme temperatures. The ability of insects to tolerate extreme conditions can be influenced by their associated bacterial community (the microbiome). Understanding this relationship may lead to improved methods of pest control, but the microbiome of T. granarium is unknown. Here we use next-generation sequencing to address three main questions: 1) How similar are the microbiomes of the closely-related species T. granarium and T. variabile? 2) How does the microbiome change across life stage and physiological state? 3) How is the microbiome of adult T. granarium affected by extreme temperatures? Our results show that the core microbiomes of T. granarium and T. variabile are similar in composition. However, adults of former species have a microbiome dominated by Spiroplasma bacteria (99% of amplified sequences), whereas Spiroplasma in the latter species is almost absent (< 2%). The microbiome of T. granarium differs across life stage (feeding vs non-feeding life stages); its presence in eggs confirms the vertical transmission of Spiroplasma. High temperatures significantly reduced the relative abundance of Spiroplasma, but an effect of low temperatures on the microbiome of T. granarium was not detected. Given its dominance in a key pest species, further study of the interaction between Spiroplasma and its T. granarium host is warranted.