Temperature affects performance of Lymantria dispar larvae feeding on leaves of Quercus robur

Future climatic warming may modify insect development, sex ratio, quantitative changes in populations that could affect the frequency of outbreaks. Here we analyzed the influence of temperature on larval growth and development in the gypsy moth (Lymantria dispar L.). The larvae were reared at three constant temperatures: 15, 20 or 25°C, and fed with leaves of the English oak (Quercus robur L.). Larval mortality, duration of development (DD), relative growth rate (RGR), total mass of food eaten (TFE), and pupal mass (PM) were estimated. Larval mortality was lowest at 20°C, higher at 25°C, and highest at 15°C. DD significantly decreased with increasing temperature and depended on sex. The influence of temperature on the shortening of DD was stronger in males than in females. RGR significantlydepended on temperature and was the highest at 25°C, and lowest at 15°C. At 15°C, RGR did not change markedly with time. In contrast, RGR at 20°C was characterized by a continuous decreasing trend. At 25°C, RGR was very high for 2 weeks but quickly declined afterwards. Temperature did not affect the TFE. PM was significantly correlated with temperature and sex. PM of females was higher at 20°C than at 15 and 25°C, in contrast to that of males, which was similar at 20 and 25°C, and higher than at 15°C. For larval growth and development, the most favourable was the medium temperature (20°C). The least favourable temperature for females was 25°C, for males 15°C. The results suggest that global warming may modify the future sex ratio of gypsy moths that may affect insect development and outbreaks.