Insecticide resistance in spotted pod borer, Maruca vitrata (Fabricius) on vegetable cowpea and its management

Abstract

A study on “Insecticide resistance in spotted pod borer Maruca vitrata (Fabricius) on vegetable cowpea and its management” was undertaken at College of Agriculture, Vellayani and in the farmer’s field at Kalliyoor and Venganoor panchayaths during January, 2013 to May, 2014. The main objectives were to assess the insecticide resistance in field population of spotted pod borer, M. vitrata, evaluate the efficacy of new generation insecticides against the resistant population and determine the harvest time residues in cowpea pods. A preliminary survey conducted among cowpea growers in Kalliyoor and Venganoor panchayaths of Thiruvananthapuram district revealed control failures in the field population of spotted pod borer due to the continuous application of a single insecticide like chlorpyriphos or lambda cyhalothrin. The survey data served as the benchmark for further studies on the insecticide resistance in M. vitrata. Bioassay was carried out in CRD to assess insecticide resistance in populations of M.vitrata collected from three different locations (location I- field with no previous history of pesticide application, location II- field where less control failures and location III- field where more control failures) using two chemicals viz. chlorpyriphos and lambda-cyhalothrin at different doses. Results revealed that population collected from location-I was found to be susceptible for both the chemicals with resistance ratio-1, population collected from location-II to be moderately resistant with a resistant ratio of 2.28 and 2.38 and population from location-III to be resistant with resistance ratios of 2.93 and 7.94 for chlorpyriphos and lambda-cyhalothrin respectively. Laboratory experiments conducted to evaluate the efficacy of new generation insecticides viz. novaluron - 0.015 per cent, flubendiamide - 0.01 per cent, spinosad - 0.015 per cent, emamectin benzoate - 0.002 per cent, indoxacarb 14.5 per cent + acetamiprid 7.7 per cent SC- 0.09 per cent, acephate 50 per cent + imidacloprid 1.8 per cent SP - 0.20 per cent, chlorantraniliprole - 0.03 per cent, indoxacarb - 0.10 per cent and chlorpyriphos - 0.05 per cent (as check) against the resistant population of M.vitrata revealed that the per cent mortality of the second instar larvae treated with insecticides viz. emamectin benzoate, indoxacarb+acetamiprid and spinosad were 97.28, 97.28 and 90.90 per cent respectively after 6 hours of treatment. Hence, these insecticides were selected for further field trials against the resistant population of M .vitrata. The field experiment was conducted in RBD with four treatments viz. emamectin benzoate 0.002 per cent, indoxacarb+acetamiprid 0.09 per cent and spinosad 0.015 per cent including control against the resistant population of M.vitrata. Application of emamectin benzoate, indoxacarb + acetamiprid and spinosad resulted in a reduction of 81-100, 64-100 and 69.96 - 99.6 per cent respectively in the case of flower infestation and 83 -100, 23.38 - 98.40 and 55.26 – 100 per cent respectively in case of pod infestation. Harvest time residue estimation done on 7th day after the application of insecticides showed the residues below the quantitative limit of 0.05 mg kg-1 revealing its safety for consumption. The study could indicate the development of insecticide resistance in the field population of M.vitrata. On the basis of the present study it could be concluded that spraying of emamectin benzoate @ 10 g ai ha-1 or indoxacarb + acetamiprid @100 g ai ha-1 or spinosad @ 75 g ai ha-1 could effectively manage the resistant population of M. vitrata in cowpea. This study forms a maiden attempt in assessing the extent of insecticide resistance development in the populations of M. vitrata in Kerala. Further studies have to be taken up to develop and popularize an Insecticide Resistance Management (IRM) strategy against this devastating pest of cowpea.