Influence of Plant Resistance in Certain Genotypes of Green Gram on Insecticide Tolerance on Spotted Pod Borer, Maruca vitrata (Geyer)

Ten genotypes of green gram viz., WGG-42, LGG-407, PM-115, MGG-360, PM-110, LGG-410, PM-112, TM-962, LGG-450 and LGG-460 were screened for their susceptibility to Spotted pod borer, Maruca vitrata (Geyer) infestation at wetland farm, S.V.Agricultural College, Tirupati in a randomized block design (RBD) during the late Kharif season of 2014. Two crops were raised one at during last week of August-2014 and second was raised durin second week of September-2014. Readings on the number of Maruca webbings per plant, total number of caterpillars per plant and per cent infestation were taken at weekly intervals. Field screening experiments which were conducted on green gram genotypes against M. vitrata infestation revealed that WGG-42, TM-962 and MGG-360 were observed resistant, moderately resistant and susceptible reaction based on number of webbings per plant and number of caterpillars per plant. Further investigation on feeding preference of Maruca by free-choice and no-choice techniques on selected genotypes of green gram in the laboratory to confirm the resistance ranking observed in the field screening have yielded similar resistance reaction to Maruca infestation. Larvae of the first instar were allowed to feed on the susceptible and resistant genotypes of green gram upto third instar. At the third instar stage, they were allowed for topical bioassay application with Chlorpyriphos insecticide after taking the larval weights. The larvae which fed on the WGG-42 (resistant) gave LC50 (Lethal Concentration) and LD50 (Lethal Dose) values of 1.39 µL/ml and 36.98 µg/g and the larvae which fed on the MGG-360 (susceptible) gave LC50 and LD50 values of 1.63 µL/ml and 36.85 µg/g. 