MSc

The present study entitled “Biocontrol of cowpea aphid, Aphis craccivora (Koch) using entomopathogenic fungi” was undertaken to identify the effective local isolates of entomopathogenic fungi (EPF) and to evaluate the pathogenicity of pure cultures and commercial formulations of Beauveria bassiana, Metarhizium anisopliae, Verticillium lecanii, Hirsutella thompsonii and local isolate on cowpea aphid, Aphis craccivora.

A survey was conducted at four locations of Thrissur district. During the survey, five fungal isolates were collected. Among the five isolates one pathogenic fungus, obtained from the Vellanikkara locality was identified as Cladosporium oxysporum. It is the first report from Kerala.

Laboratory bioassay studies were carried out with six different concentrations of B. bassiana, M. anisopliae, V. lecanii, H. thompsonii and C. oxysporum against the adults of A. craccivora. Among the five isolates tested, V. lecanii and H. thompsonii caused cent per cent mortality followed by B. bassiana with 96.66 per cent. It was revealed that V. lecanii and H. thompsonii showed higher virulence with the lowest LC50 value of 2.5x104 spores ml-1. At the highest concentration of 108 spores ml-1, the LT50 values ranged from 3.63 to 5.96 days in the different fungal isolates which was found increasing along with the decreasing concentrations.

The survival rate of nymphs was considerably reduced with in 24 hours after treatment. At the highest concentration (108 spores ml-1), all the isolates recorded less survival per cent of nymphs which ranged between 2.49 to 18.33 per cent. But even in the lower concentration (103 spores ml-1), H. thompsonii and B. bassiana exhibited low nymphal survivability (34.75 to 37.61%) as compared to other isolates.

Based on the bioassay studies a pot culture experiment was conducted to evaluate the efficacy of different fungal isolates against A. craccivora under field conditions. Among the different treatments, B. bassiana and V. lecanii @ 108 spores ml-1 and F. pallidoroseum @ 7x 106 spores ml-1 gave cent per cent mortality on 14th day after treatment. This was followed by the commercial formulations, Biopower and Biocatch (0.2%) and the chemical insecticide Malathion (0.05%) which recorded more than 90 per cent mortality.

The highest yield was obtained in plants treated with F. pallidoroseum @ 7x106 spores ml-1 which recorded the maximum number and weight of pods followed by V. lecanii and B. bassiana @ 108 spores ml-1. These treatments were statistically on par and were considerably increasing the yields upto 47.84, 47.14 and 45.10 per cent respectively.

From the study it is revealed that B. bassiana and V. lecanii @ 108 spores ml-1 were found to be as effective as the standard F. pallidoroseum @ 7x106 spores ml-1. These entomopathogenic fungi were found to be even more superior to the chemical insecticide, malathion based on the cumulative bioefficacy.