Susceptibility of Dysdercus spp.Boisdural (Hemiptera: Pyrrhocoridae)to selected synthetic pyrethroid insecticides

Dysdercus species are important pests of cotton because of their staining effect on cotton lint. Chemical control, using the newer generation of insecticides known as the synthetic pyrethroids, is the most important method of control of these pests on cotton in Kenya at present. Susceptibility studies were conducted using three pyrethroids, namely Cypermethrin, Fenvalerate and permethrin against strains of Dysdercus fasciatus Sign., D. nigrofasciatus (Stal.), D. cardinalis (Gerst.) and D. superstitiosus (F.) collected from the field and raised in the laboratory to obtain test strains. Laboratory observations showed that there were differences in the susceptibility levels of the four species studied. The most susceptible species to the three insecticides was D. fasciatus. On the other hand D. cardinalis and D. nigrofasciatus displayed the least susceptibility to the test insecticides. It was also observed that there were differences in the susceptibilities of different strains of the four Dysdercus species to the chemicals tested. The most susceptible strain to all the insecticides used was that of D. fasciatus collected from Masongoleni in Machakos District. Among the D. fasciatus strains, the most resistant strain was that which was collected from Kibos. Among the rest of the species, the D. nigrofasciatus strain collected from Homabay and the D. cardinalis strain collected from Kibos were the Wkle^ most resistant to the test insecticides. The toxicity of the three «• insecticides based on the topical application technique was found to be in descending order of effectiveness-.Cypemethrin, fenvaierate