Impact of short- and long-duration thermal stress on antioxidant enzyme activity in Parthenium beetles

Insects encounter variable temperature conditions in their natural habitats. Under non-optimal temperatures, they experience thermal stress and oxidative damage, which are mitigated by antioxidant enzymes like superoxide dismutase (SOD), catalase (CAT) and lipid peroxidation (LPO). While short-term effects of thermal stress on antioxidant enzyme activities in insects are well understood, the long-term effects are less explored. We investigated both short-term (3 and 6 h) and long-term (24 h) effects of thermal stress on SOD, CAT and LPO activities in the Parthenium beetle, Zygogramma bicolorata Pallister at cold (15°C), control/optimal (25°C) and hot (35°C) temperatures. Although Z. bicolorata is an effective biocontrol agent for noxious Parthenium weed, no prior study assessed the impact of thermal stress on antioxidant enzyme activities in this beetle. Our results revealed that antioxidant enzymes activities increased above control levels in both larvae and adults when exposed to thermal stress for short durations. Under long-term thermal stress, CAT and LPO activities decreased below control levels, while SOD activity increased. Regardless of temperature conditions, early larval instars exhibited higher enzyme activities compared to later instars. In adults, males showed higher SOD and CAT activities, whereas LPO activity did not differ significantly between sexes. Our findings suggest that short-term thermal stress can stimulate protective enzyme activity in these beetles and help them adapt to suboptimal temperatures. However, prolonged exposure may lead to excessive stimulation, potentially inhibiting protective enzyme activity and causing the beetles to activate alternative pathways to manage thermal stress. Moreover, fourth instars and adult females are the most thermal stress-tolerant stages for Parthenium biocontrol.