Performance of two dominant trichogrammatid species of fall armyworm from China and Africa under contrasted temperature and humidity regimes

The fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith), has become an international pest with its ability to spread rapidly. The FAW has successfully invaded Africa, Asia, and Australia, and recently China. It has become a serious threat to food security as a major pest of cereals and other crops. Trichogrammatid parasitoids are the dominant biological control agents that have been applied to control lepidopteran pests of crops, vegetables and forests worldwide. The aim of this study was to evaluate parasitism, development, and emergence of two trichogrammatid species, Trichogramma dendrolimi and Trichogrammatoidea lutea, from China and Africa on FAW at four temperatures (21, 25, 29, 33 degrees C) and three relative humidity (RH) (30, 60, 90 %) conditions. The temperature and humidity significantly affected the performance of the two trichogrammatid species on their host, including parasitic ability and development. The parasitism of T. dendrolimi was significantly higher than that of T. lutea (except for the treatment of 33 degrees C x RH 60 %) under various temperature and humidity conditions, however, T. lutea could not parasitize host eggs at 33 degrees C x RH 90 %. The higher parasitism was observed at 25 degrees C and 29 degrees C, while the lower at 21 degrees C and 33 degrees C for both two trichogrammatid species. The developmental time of T. dendrolimi and T. lutea significantly decreased with the increase of temperature under all three humidity treatments. The developmental time of T. dendrolimi under different temperature and humidity conditions (except for the treatment of 33 degrees C x RH 30 %), was significantly shorter than that of T. lutea. Temperature and humidity significantly influenced the sexual ratio of T. dendrolimi, the highest female ratio (94.6 %) was recorded at 33 degrees C x RH 60 %, while the lowest (79.5 %) was recorded at 25 degrees C x RH 60 %, but had no effect on T. lutea. The emergence rate of T. dendrolimi and T. lutea under different temperature and humidity conditions was only significantly different at 25 degrees C. Generally, T. dendrolimi had a better temperature and humidity adaptation than that of T. lutea, thus, T. dendrolimi appears to be a potential candidate for the control FAW under varying environmental conditions.