Parasitism, development and adult longevity of the egg parasitoid Telenomus nawai (Hymenoptera: Scelionidae) on the eggs of Spodoptera litura (Lepidoptera: Noctuidae)

When Telenomus nawai Ashmead or Trichogramma ostriniae Pang & Chen (Hymenoptera: Trichogrammatidae) was inoculated into intact egg masses of Spodoptera litura (Fabricius) that were covered with a scale-hair layer, T. nawai emerged from 76% of the eggs, while emergence of T. ostriniae was from only 3% of the eggs. When the hair layer was removed before inoculation, the rate by the latter increased to 21%. These observations confirmed that the hair layer effectively protects S. litura egg masses from attack by T. ostriniae, and that T. nawai parasitism is more effective. In order to assess the feasibility of T. nawai as a biological control agent for S. litura, parasitism rate, development time and adult longevity were examined in the laboratory. Emergence of T. nawai was observed in more than 95% of 0- and 1-day-old separated eggs of S. litura, but the rate decreased to 60% and 0% for 2- and 3-day-old eggs, respectively. The emergence rates of T. nawai were near 95% for temperatures in a range from 25°C to 35°C, but decreased to 80% at 20°C. No parasitoids emerged at 15°C. The developmental periods decreased as temperature increased from 20°C to 35°C. The developmental threshold occurred at 13.7°C and 13.9°C, and the effective accumulative temperatures from egg to adult emergence were 149.3 and 147.1 degree-days for females and males, respectively. Mean longevity of the adult females decreased with increasing temperature; 87.0 days at 15°C and 9.5 days at 35°C. The feasibility of the use of T. nawai for controlling S. litura is discussed.