Survey of bacteria associated with western corn rootworm life stages reveals no difference between insects reared in different soils

Abstract

Western corn rootworm (Diabrotica virgifera virgifera LeConte) is a serious pest of maize (Zea mays L.) in North America and parts of Europe. With most of its life cycle spent in the soil feeding on maize root tissues, this insect is likely to encounter and interact with a wide range of soil and rhizosphere microbes. Our knowledge of the role of microbes in pest management and plant health remains woefully incomplete, yet that knowledge could play an important role in effective pest management strategies. For this study, insects were reared on maize in soils from different locations. Insects from two different laboratory colonies (a diapausing and a non-diapausing colony) were sampled at each life stage to determine the possible core bacteriome. Additionally, soil was sampled at each life stage and resulting bacteria were identified to determine the possible contribution of soil to the rootworm bacteriome, if any. We analyzed the V4 hypervariable region of bacterial 16S rRNA genes with Illumina MiSeq to survey the different species of bacteria associated with the insects and the soils. The bacterial community associated with insects was significantly different from that in the soil. Some differences appear to exist between insects from non-diapausing and diapausing colonies while no significant differences in community composition existed between the insects reared on different soils. Despite differences in the bacteria present in immature stages and in male and female adults, there is a possible core bacteriome of approximately 16 operational taxonomic units (i.e., present across all life stages). This research may provide insights into Bt resistance development, improved nutrition in artificial rearing systems, and new management strategies.

Host resistance to Bacillus thuringiensis is linked to altered bacterial community within a specialist insect herbivore

“…Selection for Bt resistance could potentially favour bacteria known to degrade Cry proteins or alter the gut environment (i.e., biofilms, antimicrobials) to reduce binding or competitively exclude harmful bacteria (Patil et al, 2013;Shan et al, 2014;Vásquez et al, 2012). In addition, the harbouring of nutrient-providing or plantdigesting bacteria could increase tolerance to Bt as nutritional differences in diet correlate to alterations in Bt susceptibility (Deans et al, 2017;Ludwick et al, 2018). Previous experiments involving combinations of bacterial spray formulations, spores and purified crystals, following antibiotic treatment on artificial diet have yielded conflicting results Raymond et al, 2009).…”

Western Corn Rootworm, Plant and Microbe Interactions: A Review and Prospects for New Management Tools

“…Douglas [170] theorized the exploitation of insect microbiomes could provide new pest management techniques. Studies have shown the western corn rootworm actively selects for microorganisms it harbors [171,172]. Larvae reared in two different soils harbor similar bacterial communities even though the soil samples vary widely in community composition [172].…”

“…Studies have shown the western corn rootworm actively selects for microorganisms it harbors [171,172]. Larvae reared in two different soils harbor similar bacterial communities even though the soil samples vary widely in community composition [172]. The WCR bacterial community commonly consists of species of Serratia, Pseudomonas, Klebsiella, Acinetobactor, Streptomyces, and Tsukamurella, with other species appearing in high abundance but sporadically [171][172][173][174].…”

“…Larvae reared in two different soils harbor similar bacterial communities even though the soil samples vary widely in community composition [172]. The WCR bacterial community commonly consists of species of Serratia, Pseudomonas, Klebsiella, Acinetobactor, Streptomyces, and Tsukamurella, with other species appearing in high abundance but sporadically [171][172][173][174]. Studies have focused on surveying the bacterial community of WCR but have done little to try to characterize func-tionality of that community.…”

“…Antibiotics were given to adults, and only the presence of Wolbachia was analyzed using PCR, so it is unclear what other bacteria remained after antibiotic treatment, or what bacteria were acquired from the soil during larval feeding. A majority of WCR populations also carry a high proportion of the maternally transmitted endosymbiont, Wolbachia [171,172,176]. Wolbachia can play an influential role in insect reproduction by inducing cytoplasmic incompatibility, parthenogenesis, feminization, and male killing [177].…”