BIOEFFICACY OF ENTOMOPATHOGENIC FUNGI AND THEIR COMBINATIONS WITH SELECTIVE INSECTICIDES AGAINST SPODOPTERA LITURA F. (LEPIDOPTERA: NOCTUIDAE) ON COTTON

Abstract

The susceptibility of different biological stages of Spodoptera litura to various strains of entomopathogenic fungi was tested under laboratory conditions at Department of Agri. Entomology University of Agriculture, Faisalabad using the insect immersion method. All biological stages were susceptible to the fungal isolates in a dose dependent manner. All biological stages were not equally susceptible. Eggs and larvae were comparatively more susceptible to infections by entomopathogenic fungi, while pupae were less susceptible. The susceptibility of the insect to entomopathogenic fungi decreased with the advancement in age of larvae of target host. The LC50 values for eggs were 1.13×106, 4.82×106 and 2.45×107conidia ml-1 in M. anisopliae L6, P. fumosoroseus 32 and B. bassiana 25, respectively. The median lethal concentration (LC50) for 3rd instars larvae was1.11×107conidia ml-1 in B. bassiana 25 and 2.17×107conidia ml-1 in P. fumosoroseus 32. Mortality of the larvae increased with increase in conidial concentrations and time elapsed after treatment. Virulence of entomopathogenic fungi also varied from species to species and strain to strain against S. litura. Variations were observed in the susceptibility the insect to particular entomopathogenic fungus under laboratory and green house conditions. The use of fungi as alternative to insecticides and their combined application with selective insecticides is very useful strategy in integrated pest management program. It requires detailed compatibility studies. Therefore, investigations were carried out to evaluate in vitro influence of insect growth regulators and some other selective insecticides on vegetative growth and conidial germination of fungal pathogens, M. anisopliae, P. fumosoroseus and B. bassiana. All tested insecticides displayed significant potential to inhibit growth (6.84- 74.80%) and germination (19.35-85.43%) of the fungal pathogens. Lorsban was the most toxic insecticide to mycelial growth and conidial germination followed by Lannate, Larvin and Pirate. Cascade, Match, Steward and Proclaim were comparatively less toxic to mycelial growth (36.78-48.67% inhibition) and conidial germination (40.32-49.97% inhibition) of the fungal pathogens. Conversely, Runner, Capture, abamectin and Curacron were compatible with significantly lesser inhibition in growth (25.19-36.47%) and conidial germination (27.78-43.66%) of the fungi. Tracer was found safe to conidial germination and growth of the fungi. Effect of combined treatments of entomopathogenic fungi and insecticides against S. litura larvae was investigated under green house conditions at Entomological Research Institute, AARI, Faisalabad. Different insecticides exhibited additive to synergistic effects on toxicity against S. litura larvae, when they were mixed with B. bassiana and P. fumosoroseus under green house conditions. The combined treatment of the fungi and insecticide exhibited synergistic effects except Lannate and Lorsban that displayed additive effects. However, no antagonistic effects were found in any treatment combination. Joint application of the entomopathogenic fungi and Insect growth regulators: Runner Cascade, Abamectin, Capture and other insecticides like Tracer, Proclaim Curacron and Steward seems to be feasible for control of this polyphagus pest. However, it needs further investigations under field conditions