Abstract
A study was carried out to determine the development of resistance against synthetic pyrethroids in Conopomorpha cramerella (CPB). Samples of CPB were collected from six commercial cocoa fields in Tawau, Malaysia, which had been treated with synthetic pyrethroids for many years and from one cocoa field in which no chemicals had been used for over two years. Adults of CPB were treated with 0.5 mul of fenvalerate or deltamethrin solutions applied to the thorax with a 25 mul Hamilton microsyringe in arepeating dispenser. The results indicated that the CPB had developed a certain degree of resistance to the synthetic pyrethroid. The LD50 for fenvalerate was 0.128 mug per moth in the unsprayed field and 0.248 to 0.343 mug per moth in the cocoa field treated with synthetic pyrethroids. The resistance ratio of CPB in the sprayed field was estimated as 1.93 to 2.68. By comparison, the LD50 for deltamethrin was 0.0020 mug per moth in the unsprayed field and 0.0055 to 0.0089 mug per moth in the fields sprayed with synthetic pyrethroids. The resistance ratio was 2.75 to 4.45. A strategy for preventing the development of insecticide resistance in CPB is presented.A study was carried out to determine the development of resistance against synthetic pyrethroids in Conopomorpha cramerella (CPB). Samples of CPB were collected from six commercial cocoa fields in Tawau, Malaysia, which had been treated with synthetic pyrethroids for many years and from one cocoa field in which no chemicals had been used for over two years. Adults of CPB were treated with 0.5 mul of fenvalerate or deltamethrin solutions applied to the thorax with a 25 mul Hamilton microsyringe in arepeating dispenser. The results indicated that the CPB had developed a certain degree of resistance to the synthetic pyrethroid. The LD50 for fenvalerate was 0.128 mug per moth in the unsprayed field and 0.248 to 0.343 mug per moth in the cocoa field treated with synthetic pyrethroids. The resistance ratio of CPB in the sprayed field was estimated as 1.93 to 2.68. By comparison, the LD50 for deltamethrin was 0.0020 mug per moth in the unsprayed field and 0.0055 to 0.0089 mug per moth in the fields sprayed with synthetic pyrethroids. The resistance ratio was 2.75 to 4.45. A strategy for preventing the development of insecticide resistance in CPB is presented.