Effects of climate change on overwintering pupae of the cotton bollworm, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae).

Climate change significantly affects insects' behaviors. Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) is one of the most serious insect pests in the world. Much is known about the survival of the overwintering population and spring emergence of H. armigera. However, little is known about the effects of climate change on overwintering and spring emergence of H. armigera. This study investigated the effects of changes of air and soil temperatures and precipitation on overwintering pupae of H. armigera by analyzing historical data from Magaiti County in northwest China using statistical methods. The results showed that during the period of 1989-2006, the climate warming advanced the first-appearance date of overwintering pupae eclosion (FD) and end date of overwintering pupae eclosion (ED) by 1.276 and 0.193 days per year, respectively; the duration between the FD and ED (DFEPE) was prolonged by 1.09 days per year, which resulted in more eclosion of overwintering pupae. For a 1 °C increase in the maximum air temperature (Tmax) in winter, the FD became earlier by 3.234 days. Precipitation in winter delayed the FD and ED and produced little relative influence on DFEPE. A 1-mm increase of precipitation in winter delayed the FD and ED by 0.850 and 0.494 days, respectively. Mean air temperature (Tmean) in March, with a 41.3% relative influence, precipitation in winter, with a 49.0% relative influence, and T mean in March, with a 37.5% relative influence, were the major affecting factors on FD, ED, and DFEPE, respectively. T max in February with a 53.0% relative influence was the major affecting factor on the mortality of overwintering pupae (MOP). Increased soil temperatures in October and November and autumn and air temperatures in winter could decrease the MOP, though the relative influences were lower than T max in February. Increased precipitation in winter increased the MOP, but the relative influence was only 4.2% because of little precipitation. T mean in October had the greatest influence on the pre-wintering density of pupae (PDP). Increasing soil temperatures in October, November, and autumn increased PDP. A higher PDP increased overwintering survival and advanced FD and prolonged DFEPE. The overwintering boundary air temperatures of H. armigera should be expanded due to higher soil temperature and snow covering. Thus, climate warming helped to enhance the survival of overwintering pupae.