The Parasitoid Wasp <i>Glyptapanteles porthetriae</i> Induces a Photoperiod‐Dependent Diapause‐Like State in Its Potential Overwintering Host <i>Lasiocampa quercus</i>

ABSTRACT We evaluated Lasiocampa quercus (Lepidoptera: Lasiocampidae) as an overwintering host for the koinobiont larval endoparasitoids Glyptapanteles porthetriae and Glyptapanteles liparidis (Hymenoptera: Braconidae) under three environmental conditions: 20°C with long‐day (16:8 L:D; hereafter LD20) or short‐day (12:12 L:D; hereafter SD20) conditions, and autumn‐like 20/10°C with short‐days (hereafter SD20/10). Developmental progress was assessed based on host molting and parasitoid emergence. Metabolic adaptations were analyzed through quantification of selected metabolites in hemolymph and body tissues. Parasitization by G. porthetriae was highly successful and photoperiod‐dependent: under LD20, endoparasitic development was dramatically prolonged (116 ± 31 vs. 19 ± 6 days under SD20), coinciding with strong suppression of host development. By contrast, G. liparidis showed limited success (6% emergence in LD20; no egression in SD20) and caused high premature mortality in late host instars. Unparasitized L. quercus displayed minimal photoperiodic responses in larval development. Consistent with cold acclimation, low night temperatures (20/10°C day/night) elevated sugar and glycogen levels in body tissues, along with reduced hemolymph protein contents. Glucose was largely absent in the hemolymph of G. porthetriae ‐parasitized larvae. Photoperiodic effects on metabolic profiles were modest relative to developmental effects. Given the photoperiodic control of developmental arrest under favourable conditions, we interpret the response at LD20 as a diapause‐like state. We hypothesize involvement of photoperiodic clock gene pathways that reduce PTTH/ecdysteroid signalling, interacting with modulated neuropeptide secretion in parasitized larvae. This hypothesis warrants experimental testing.