Insecticide resistance in diamondback moth (DBM), Plutella xylostella (L.): status and prospects for its management in India

Insecticide resistance and concomittant field failure to control the diamondback moth (DBM), Plutella xylostella were first recorded in 1968 in Punjab. Studies carried out in different states like Tamil Nadu, Karnataka, Madhya Pradesh, Punjab, indicate that fenvalerate, quilnalphos and monocrotophos resistance are now ubiquitous in Plutella xylostella. In Tamil Nadu, the discriminating dose technique by vial assay is used to routinely monitor resistance in cabbage and cauliflower growing areas. Very high levels of resistance to fenvalerate (66–100%), significant OP resistance (quinalphos 45–81%; monocrotophos 33–86%) and low levels of resistance to cartap hydrochloride (18–53%) and carbosulfan (14–55%) are a feature of all regions monitored. The problems encountered in effective management of P. xylostella under Indian conditions are: 1. indiscriminate and over use of pesticides; 2. carry over of pest aided by staggered and repeated monocropping of cabbage and cauliflower and 3. nonavailability of effective biocontrol agents such as Cotesia plutella (Kurdjumov), Diadegma semiclausum (Horstmann), granulosis virus, etc. in sufficient quantities and high cost of B.t. formulations. The extent of natural parasitisation of P. xylostella by C. plutellae varied from 16 to 75% in tropical plains and that of D. semiclausum to the extent of 80% in hill/highland areas. The occurrence of granulosis virus (GV) highly pathogenic to P. xylostella was observed in lab. culture. Attempts are being made to mass multiply this virus. The following strategies are discussed: 1. create a network on resistance monitoring and management on the lines developed recently for Helicoverpa armigera, 2. obtaining base-line data for site specific IRM tactics and 3. developing and popularising available alternative control agents like parasitoids and the GV.