Bionomics of Entomopathogenic Nematode Steinernema siamkayai Stock, Somsook and Reid (n. sp.) and Its Efficacy Against Helicoverpa armigera Hübner (Lepidoptera: Noctuidae)

Abstract

The investigation on life cycle and development of Steinernema siamkayai in Helicoverpa armigera larva and its pathogenicity to insect comparing with other nematodes at various exposure times and concentrations was conducted under laboratory conditions. Life cycle of S. siamkayai in H. armigera was found to take 11 days to complete development at 30^oC. Two generations were able to develop in the host. Only the infective juveniles (IJs) were used in the experiments. The symbiotic bacteria Xenorhabdus sp. associated with S. siamkayai isolated from hemolymph of H. armigera 18 h after infection was noticed to yield perfect colonies on NBTA media. The optimal temperature for entomopathogenic nematode S. siamkayai to control H. armigera larvae were 25 and 30^oC, whereas 100 IJs per larva gave 91.66 and 89.58% larval mortalities, respectively, 72 h after infection. LC₅₀ of S. siamkayai, Steinernema carpocapsae and Steinernema riobrave onto H. armigera and Spodoptera litura were found to be 22.5, 1.2 and 1.2 IJs per larva and 18.0, 0.2 and 1.8 IJs per larva, respectively. While LT50 of S. siamkayai, S. carpocapsae and S. riobrave with 5 IJs per larva used to penetrate into H. armigera were 89.9, 22 and 39.8 h, those of and S. litura were 72.5, 11.46 and 39.8 h, respectively.