The supercooling and high temperature stupor points of the adult lesser mealworm Alphitobius diaperinus(Coleoptera: Tenebrionidae)

Abstract

Potential thermobiological limits in adult lesser mealworms Alphitobius diaperinus were assessed during winter by measuring individual supercooling points (SCP) and thermostupor points (TSP). Two experimental conditions were tested: (i) SCP and TSP measured at 100% r.h.; (ii) SCP with specimens which survive to the TSP at 0% r.h.. The absolute temperature range compatible with life between the two limits SCP and TSP, termed thermobiological span (TBS), was calculated in both conditions. The potential adaptive capacity to withstand cooling and overheating is: (i) at 100% r.h., mean TSP=46.7°C (SD±0.67); mean SCP=−9.4°C (SD±1.81); absolute TBS 56.1°C; (ii) at 0% r.h., mean TSP=47.4°C (SD±0.61); mean SCP=−12.3°C (SD±2.5); mean TBS 59.7°C (SD±2.43). The TSP at 0% r.h. is reached with a loss of 3.84% in fresh weight vs 1.15% at 100% r.h.. The difference in the SCP (females=2.1°C; males=5.4°C) obtained in dry or moist conditions could also be explained by the influence of the heat shock preceding the SCP measured at 0% r.h. A decrease of water content may increase the osmolarity of the body fluid and thus the supercooling capacity and could be an adaptation to avoid freezing. Supercooling capacity allows adults to survive in areas where freezing temperatures may occur in poultry houses and more specially during the winter litter removals when adult beetles migrate and overwinter in the soil floor or in insulation materials of the building walls. The heat tolerance capacity is mainly ruled by the physiological and behavioural adaptations of this species. Our results suggest that the adult population of A. diaperinus could be controlled by increasing the temperature above 48°C.