Effects of temperature on larval development of Asian gypsy moth (Lymantria dispar asiatica and L. dispar japonica): a laboratory study

The gypsy moth (Lymantria dispar L., Lepidoptera: Erebidae) is a polyphagous pest capable of major defoliation of numerous tree species in most of the northern hemisphere.  Episodic introduction of two subspecies of the Asian gypsy moth (AGM: Lymantria dispar asiatica and L.d. japonica) threatens North American forests and are the target of vigilant monitoring by the USDA.  If AGM should become established in the U.S., it has the potential to spread rapidly; in contrast to the European subspecies (L. d. dispar) that has been in the U.S. for over 100 years. We evaluated the development of eight strains of AGM from a broad geographic range at five constant temperatures (10-30 °C) in a laboratory environment, which revealed temperature-dependent differences in development rates.  The Russian strain from Siberia developed to adulthood the fastest.  While the majority of AGM strains pupated subsequent to the 5^th or 6^th instar, the Siberian strain sometimes pupated following the 4^th instar.  As expected, development rate was faster as temperature increased, however, many larvae experienced difficulty molting at 10 or 30 °C.  At 120 days following hatch only eight larvae reached 4^th instar at 10 °C and at 30 °C the percentage survival to pupation averaged 35% which was much lower than at the other temperatures. These findings are important for monitoring and management strategies as well as risk assessment since timing is critical for both biopesticide application and male trapping to delimit introductions.