Exposure of Helicoverpa punctigera pupae to extreme temperatures for extended periods negatively impacts on adult population dynamics and reproductive output

Abstract

<p>Understanding the impact that heat stress has on critical life stages of an organism is essential when assessing population responses to extreme events. Heat stress may occur as repeated small-scale events or as a single prolonged event, which may cause different outcomes to the organism. Here, we subjected <i>Helicoverpa punctigera</i> (Wallengren) pupae to two temperatures (44.2 ^◦C and 43 ^◦C) and two exposure treatments - a single 3-h prolonged exposure prolonged and three repeated 1-h exposure period with 24 h recovery time between bouts - to assess the biological traits of individuals. The maximum temperatures were used as they were just below the critical thermal maximum (CTmax) 47.3 ^◦C ± 0.3 ^◦C of pupae for which they could survive exposure. Adults in the prolonged and repeated heat-stressed treatments had 1.70 and 3.34 more days to emergence and 1.57 and 3.30 days extended life span compared to those kept under a constant 25 ^◦C temperature (control treatment). Both pre-oviposition and oviposition periods were extended in the heat-stressed groups. Fecundity in the prolonged and repeated heat-stressed females was reduced by 34.7% and 65.5% eggs in the 43 ^◦C treatment group and by 94.3% and 93.6% eggs in the 44.2 ^◦C treatment group compared to the control group. No eggs from females in either the prolonged and repeated heat-stress groups hatched. We establish that heat stress on pupae can influence the population dynamics of <i>H. punctigera</i> by reducing fecundity as well as extending the pre oviposition period, and affecting adult development. Also, as heat exposure on the parent generation resulted in no offspring production, it is critical to assess cross-generational responses to extreme heat stress.</p>