Abstract
Dendroctonus valens LeConte, an invasive bark beetle, has caused severe damage in pine forests and has the potential to disperse into new geographic ranges in China. Although the gut microbiota of D. valens and its fundamental role in host fitness have been investigated widely, little is known about the relationship between the seasonal shifts of both cold tolerance and the gut microbiome of D. valens during overwintering, which occurs at the larval stage. In this study, to examine seasonal variations in the composition of the microbiome, we collected D. valens larvae in September (autumn), January (winter), and May (spring), and then analyzed the bacterial and fungal communities of the gut via sequencing of partial 16S rRNA and ITS genes. In addition, changes in the supercooling capacity and antioxidant enzyme activities of D. valens larvae collected in the different seasons were evaluated. Overwintering resulted in changes to microbial communities. In particular, the abundances of Enterobacter, Serratia, Erwinia, and Klebsiella decreased during overwintering. Concurrent with these changes, the cold tolerance of D. valens larvae was enhanced during overwintering, and the activities of the antioxidant enzymes catalase and peroxidase were reduced. We hypothesize that seasonal shifts in the gut microbiome may be connected to changes in cold tolerance and antioxidant enzyme activity in D. valens. It will be worthwhile to confirm whether seasonal changes in the microbiome contribute to the success of host overwintering.
Highlights
Insects are chronically infected by microorganisms, most of which are beneficial or even obligatory to their insect hosts [1,2]
Our findings presented here reveal that overwintering affects the compositions of the bacterial and fungal communities in the gut of D. valens larvae
We propose that tissue metabolism in D. valens larvae is reduced in January; the production of Reactive oxygen species (ROS) in the tissues decreases
Summary
Insects are chronically infected by microorganisms, most of which are beneficial or even obligatory to their insect hosts [1,2]. The large majority of these infecting microbes are colonized in the gut of their host, where they aid the digestion of unpalatable food components, improve undernourished diets, help their hosts defend against predators, parasites, and pathogens, and even affect host physiological action by neuroendocrine signaling [1,2,3,4]. Changes in the microbial community can affect a number of host phenotypes [2]. Overwintering insects undergo deep seasonal changes in feeding [6], intestinal contents [7], immune system [8], and physiological function [9]. These seasonal changes in host physiology have the potential to affect the composition of the gut microbiome [10]. Wang et al [11] revealed that gut bacterial communities from Chinese white pine beetle
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