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.

Bionomics of the entomopathogenic nematode, Steinernema weiseri (Rhabditida: Steinernematidae)

This study describes some important bio-ecological properties of Steinernema weiseri, a recently isolated entomopathogenic nematode species in Turkey. The effects of temperature on the infectivity and development of S. weiseri were determined at 5, 8, 10, 15, 20, 25 and 30°C. The greatest and the fastest mortality of Galleria mellonella larvae was observed at 20 and 25°C (ca 2 days) and the slowest at 5°C in 11.5 days. The emergence time of the new generation of infective juveniles (IJ) from the host cadaver was shortest at 20 and 25°C (ca 9 days) and the longest at 8°C (ca 40 days). No progeny were observed at 5 and 30°C. At the tested temperatures, the lowest number of new generation IJ was obtained at 8 and 10°C and the highest at 15 and 20°C. The life cycle, determined at 23-24°C under laboratory conditions using G. mellonella as a host, took 9 days to complete. Our study suggests that the Turkish isolate of S. weiseri is adapted to cold temperatures. Steinernema weiseri has a wide host range and infects and develops well in larvae of Agrotis sp., Ceratitis capitata, Cydia splendana, Synanthedon vespiformis and Hoplocampa flava, but it infects and develops poorly in Polyphylla fullo. Larval stages of C. cossus were divided into four groups based on the diameter of their head capsules. Steinernema weiseri developed well in larval stages in Group 1 (the smallest head capsule) and Group 2 of Cossus cossus but, interestingly, very low infection and nematode development occurred in the Group 3 and Group 4 larval stage of C. cossus. No nematode infection was observed in Gryllotalpa gryllotalpa either.