Changes in the gut microbial community of larvae of the harlequin lady beetle in response to cannibalism and intraguild predation

Abstract

Diet affects the gut microbial community in most organisms, but the potential effects of cannibalism and intraguild predation (IGP) on the gut microbiota of predatory arthropods remain unexplored. Here, a series of feeding experiments examined changes in the gut microbial community of larvae of the predatory lady beetle Harmonia axyridis resulting from egg and larval cannibalism and IGP. We found that gut microbial abundance increased in fourth instar H. axyridis larva when conspecific eggs plus aphids were consumed as neonates, but did not change when their consumption was sustained across larval stages. In contrast, the consumption of Coccinella septempunctata eggs plus aphids over all larval stages decreased gut microbial abundance, whereas neonate consumption of the same had no such effect. Gut microbial composition differed following consumption of either conspecific or heterospecific eggs. Consumption of a C. septempunctata larva by molting H. axyridis third instar larvae decreased gut microbial abundance and diversity, whereas consumption of a conspecific larva increased them. Larval cannibalism and IGP appear to have variable effects on microbial composition due to differences in relative abundance of prevailing bacterial groups associated with these prey items. Our results indicate that cannibalism and IGP can have both quantitative and qualitative consequences for the gut microbial community in aphidophagous lady beetles.