Isolation of entomopathogenic fungi and their pathogenicity against the Chili Thrips, Scirtothrips dorsalis
Mikunthan G1, Manjunatha M2
1Dept. Agricultural Biology, Faculty of Agriculture, University of Jaffna, Jaffna, Sri Lanka.
2Department of Entomology, College of Agriculture, Shimoga 577201, Karnataka, India
Correspondence: gunamiku@sify.com
The Chili Thrips, Scirtothrips dorsalis (Thysanoptera: Thripidae) is considered as a polyphagous insect pest causing severe upward leaf curl in chili (Capsicum annuum L.). This dreaded pest is being controlled by frequent use of selective and expensive systemic insecticides however, resistance developed in these insects limits the long term application and dependency on these chemicals in near future. Biological control is a viable alternative strategy that can be incorporated in to the integrated management of thrips to overcome this problem. However a sound knowledge of the natural enemy complex is very essential as an opted alternate choice to chemicals. Among the natural enemy complex, pathogens regulating the population of S. dorsalis have not been extensively studied. Added to this, there are no reports available on fungi infecting S. dorsalis. An attempt was made to isolate entomopathogenic fungi from chili fields and to evaluate their pathogenicity against S. dorsalis. A roving survey was conducted during 2002 to collect soil and foliage samples from chili fields representing ten agroclimatic zones of the Karnataka State of India. Entomopathogenic fungi were isolated from soil using a soil bait method (Zimmerman G. 1986. Journal of Applied Entomology 102: 213¨C215; Parker BL et al.1996. In: Tospoviruses and thrips, ISHS Acta Horticulturae 431: 521¨C534) and from infected cadavers collected from chili leaves. Larvae of Tribolium castaneum (Coleoptera: Tenebrionidae) and wax moth, Galleria melonella (Lepidoptera: Galleridae) were used as soil baits. Thirteen fungal isolates were recovered from soil using larvae of T. castaneum and G. melonella. However none of them were able to infect on any stages of S. dorsalis. Three fungi viz. Fusarium sp. isolate GM15 (ARSEF 7381), Neozygites floridana and Penicillium sp. were isolated from diseased cadavers of larvae of S. dorsalis and Fusarium semitectum (ARSEF 7233) from larvae of S. dorsalis, active stages of Polyphagotarsonemus latus (Acarina: Tarsonemidae) and nymphs and adults of Aphis gossypii (Hemiptera: Aphididae) from chili leaves. A local isolate of Metarhizium anisopliae was also found infective to adults of S. dorsalis and caused 13 per cent mortality. The isolation of entomopathogenic fungi from S. dorsalis and Fusarium species from S. dorsalis, P. latus and A. gossypii are new records. Koch¡¯s postulates confirmed the infectivity of Fusarium isolates on S. dorsalis and the pathogenicity studies revealed that F. semitectum and Fusarium sp. isolate GM15 caused 86 and 76 per cent mortality of larvae of S. dorsalis, respectively. N. floridana caused 82 per cent mortality. These results show the potential use of entomopathogenic fungi in controlling S. dorsalis. The identity of the Fusarium isolates was confirmed by Dr. D. M. Geiser, Pennsylvania State University and Neozygites floridana by Dr.R.A.Humber of USDA-ARSEF, Collection of Entomopathogenic Fungal Cultures.
