Resistance to carbamate insecticides in Helicoverpa armigera (Lepidoptera: Noctuidae) in Pakistan

The status of resistance to four carbamates viz, carbaryl, alanycarb, methomyl and thiodicarb was monitored in Pakistani populations of Helicoverpa armigera (Hubner) during 1994 to 1999 using an IRAC leaf-dip method. A general trend was that resistance to carbaryl, alanycarb and methomyl was high in 1994 and 1995, low in 1996 and 1997, and moderate to high in 1998 and 1999. Because of limited use of carbamates in Pakistan, this trend is not understood. It may be the consequence of cross-resistance from mechanisms developed for other insecticide groups. However, a broad cross-resistance was evident among carbaryl, alanycarb and methomyl. Surprisingly, a very low level of resistance to thiodicarb was found throughout this six-year study. No correlation of resistance factors existed between thiodicarb and carbaryl or methomyl. This lack of cross-resistance between thiodicarb and other carbamates in H. armigera is very encouraging for devising an insecticide resistance management strategy against this pest. (C) 2001 Elsevier Science Ltd. All rights reserved.