Bioefficacy of entomopathogenic nematode, Steinernema sp. isolated from Timor Island as bioinsecticide on sweet potato weevil, Cylas formicarius (Fabr.) (Coleoptera: Brentidae)

Bioefficacy of entomopathogenic nematode belongs to the genus Steinernema sp. were tested against mealworm Tenebrio mollitor with 50, 100, 150, 200 and 250 juveniles (IJs)/30 mealworm larvae. LC 50 value was 105 IJs/ml for mealyworm. The invasion efficiency was lower as the density of nematodes increased. At highest density (250 IJs/ml), the efficiency of invasion of nematodes was 24.5 % whereas at lowest density (50 IJs/ml) the invasion efficiency reached 33%. For LT 50 calculation, 30 larvae were put in contact with the nematode (density 250 IJs/ml) during 2, 4, 6, 8 and 10 hours. Mortality was recorded 48 hours after the contact periods, and LT 50 value was obtained at 7.7 hours. After two weeks, nematode population could reach ca. 40,000 IJs/larva, 35,000 IJs/pupa and 29,000 IJs/imago. When applied using density 50 IJs/ml against Cylas formicarius, the nematode population grew up to ca. 4000 IJs/larva, 3600 IJs/pupa and 3400 IJs/imago with invasion efficiency of 10%, 8% and 7% respectively. A series of nematode density 1.5, 2.0, 2.5 and 3.0 x 10 4 IJs were poured on the soil surface in the plastic container where sweet potato tuber were buried. The tubers were previously and artificially infested by five pairs of weevil. Although in general the difference between treatments is not significant, the result showed that high mortality (>70%) of larva, pupa and adult of C. formicarius was observed in each tuber. It is concluded that the isolated nematode was not difficult to propagate in vivo, and their mobility to search and kill the weevil seemed promising as bioinsecticide.