Pathogenicity of Selected Kenyan Entomopathogenic Nematodes of Genus Steinernema against Banana Weevil (Cosmopolites Sordidus)

Banana weevil is a pest with a great impact on banana production in the world. The objective of this study was to evaluate the pathogenicity of the Kenyan entomopathogenic nematodes (EPNs) of genus Steinernema against the weevil Cosmopolites sordidus (Germar) under laboratory conditions. Adult weevils were trapped from banana fields in Maragua, Central Kenya and larvae extracted from the infested banana rhizomes. The adults were treated with three Kenyan EPNs Steinernema weiseri, Steinernema yirgalemense and the new Steinernema spp and with Steinernema carpocapsae ALL strain as a standard and plain distilled water as a control in five replicates. The treatments were 500ijs, 750ijs and 1000ijs per adult on petri dishes and 1000ijs, 3000ijs and 5000ijs per adult on pseudo-stems. The treatments for larvae in petri dishes were 300ijs, 400ijs and 500ijs. The adults were not susceptible to all the nematodes at all doses and preparations while larvae were highly susceptible to the four test EPNs at all concentrations. There was a significant difference at P<0.05 in the mortality of larvae between nematode Steinernema carpocapsae and Steinernema weiseri. A significant difference was observed between nematode Steinernema carpocapsae and Steinernema yirgalemense. There was also a significant difference between the new Steinernema spp and Steinernema weiseri and finally in the two nematodes the new Steinernema spp and Steinernema yirgalemense. All the test nematodes caused over 90 % larval mortality within 48 hours. The mean percent mortality of larva increased with nematode concentration for all the test nematodes. The results indicated that the four test EPNs significantly (P<0.05) caused high mortality within 24-48 hrs. The findings indicate that the banana weevil larvae are susceptible to the local entomopathogenic nematodes and potentially useful in the management of the banana weevil. It is however recommended that more research be conducted on the formulation and application technology to enhance their effectiveness in the field.