Alterations in the Gut Microbiome of Loxostege sticticalis in Response to Temperature and Photoperiod Changes

Loxostege sticticalis is a destructive pest that survives winter by entering diapause. Photoperiod and temperature trigger this dormancy, but their effects on gut bacteria are unclear. We hypothesized that photoperiod and temperature interact to alter the gut bacterial community structure and function and that these microbial changes may be involved in diapause preparation. To test this hypothesis, this study investigated how different photoperiod (L10:D14 and L16:D8) and temperature (18, 22, 26 and 30 °C) combinations shape the gut bacterial communities and their predicted functions in L. sticticalis larvae using 16S rRNA sequencing. The larval gut contained 29 phyla, 52 classes, 128 orders, 205 families, 407 genera, and 281 ASVs at species-level taxonomic annotation. Under a short-day photoperiod (L10:D14), the 26 °C treatment caused a dramatic loss of α-diversity and an almost complete dominance of Enterococcus (99.96%). β-diversity clearly separated this group from all others. LEfSe identified Enterococcus as its exclusive biomarker. Functionally, this group showed significantly elevated carbohydrate metabolism but reduced amino acid metabolism, energy metabolism, and metabolism of cofactors and vitamins. No such simplification occurred under long-day photoperiod (L16:D8) or at other temperatures under short-day conditions. These findings raise the hypothesis that gut microbiota may participate in metabolic reprogramming during diapause preparation and that environmental factors such as photoperiod and temperature could mediate host life history strategies via the microbiota. However, because diapause status was not directly measured, this connection remains an inference. If validated, these microbial changes could provide a basis for developing novel pest management strategies by targeting the processes associated with diapause induction.