Effect of Soil Textures on Host Finding Behavior and Virulence of Heterorhabditis bacteriophora and Steinernema carpocapsae

Abstract

Spodoptera littoralis (Boisd Lepidoptera: Noctuidae) considered the main pest of several crops in Egypt. Entomopathogenic nematodes (EPNs) may be used to control this pest and exhibit different and unique abilities to search for their hosts. The movement of EPN in relation to S. littoralis and Galleria mellonella was evaluated. To test for vertical movement, a transparent enclosure tubes with different lengths filled with moistened sand and nematodes were placed at 5 cm of the entrance to the enclosure and the insect larvae were placed at 0,10,20,30,40, and 50 cm of the nematodes. The same maner was used to evaluate the movement in sandy clay soil. In general, the mortality and the penetration ratio were inversely proportional to the initial distance between host and nematodes. The most mortality and penetration ratio occurred at the distance 0, 10, and 20 cm in the two examined soil with the two insects, the percentages were decrease at 40, and 50 cm. Moreover, In sandy clay soil, at the last two distances infective juveniles were not able to kill G. mellonella and S. littoralis larvae, hence it was no penetration of S. carpocapsae in S. littoralis at 30 cm. Therefore, both nematodes were able to search out, infect and kill larvae of S. littoralis up to a distance of 50 and 30 cm in the sand and sandy clay soil, respectively, but the activity was higher in the sandy soil.