Maternal and dietary source influence bacteria associated with gypsy moth (Lymantria dispar)

Microbial symbioses with insect herbivores are receiving increased attention because of their ability to influence insect performance and mediate ecosystem processes. For example, gypsy moth (Lymantria dispar) contains a diverse community of gut bacteria, some of which may affect larval development, susceptibility to biological control agents, and other life history processes. However, our understanding of the sources of these facultative bacteria, and of the relative stability of gut communities, is limited. There is substantial evidence of horizontal transmission of microbial midgut symbionts in a number of arthropods, but this is not well understood in gypsy moth. Even less is known about potential vertical transmission. Moreover, it is unknown whether and how midgut bacterial communities change through the gypsy moth ‘s development. We evaluated the sources of bacteria in gypsy moth, and the relative contribution of each source, using 16s-rRNA amplicon pyrosequencing. We obtained egg masses from laboratory and field sources, reared the larvae on white birch, and maintained test insects through adult eclosion, and analyzed various life stages and products. We examined post-hatch egg mass, 1^st instar larvae, 3^rd and 5^th instar larval midguts and frass, eggs dissected from gravid females, and birch foliage. We detected bacteria from several ecologically important families, including Bacillales, Burkholderiales, and Actinobacteriales. Bacterial diversity of the egg mass was much higher from wild populations than laboratory maintained colonies. Additionally, our results indicate that there is a high likelihood of maternal transmission in addition to the contribution of diet.