Role of spatial and temporal refuges in the evolution of pest resistance to toxic crops.

Toxic plants have been used for years in agriculture to control major crop pests. However, the continuous exposure of targeted pests to toxins dramatically increases the rate of resistance evolution (Gassman et al. in Annu Rev Entomol 54:147-163, 2009a; Tabashnik et al.

Variation in resistance to pyrethroids in Helicoverpa armigera from Benin Republic, West Africa.

Pyrethroid resistance in Helicoverpa armigera (Hübner) field populations was investigated in Benin over several years by using third- and fourth-instar larval topicalbioassays. H. armigera was resistant to pyrethroids tested as cypermethrin, deltamethrin, bifenthrin, and fenvalerate.

Esterase-mediated resistance to pyrethroids in field populations of Helicoverpa armigera (Lepidoptera: Noctuidae) from Central Africa.

Background: Evolution of pyrethroid resistance in the cotton bollworm Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) threatens continued cotton production in Central Africa. Dose-response bioassays were conducted on area-wide collection of bollworm populations from major host plants, while biochemical techniques were used to evaluate basic mechanisms underlying resistance.

Results: Pyrethroid resistance is primarily associated with detoxification by enhanced esterase activity.

Organophosphorus insecticides synergize pyrethroids in the resistant strain of cotton bollworm, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) from West Africa.

Helicoverpa armigera (Hübner) populations from West Africa recently developed resistance to pyrethroid insecticides through enhanced metabolism by mixed-function oxidases. The combination index method was used to study the synergism of pyrethroids by organophosphorus insecticides. Several mixtures of insecticides currently registered to control cotton pest complex in West Africa were tested, including: cypermethrin/ethion, cypermethrin/profenofos, deltamethrin/ triazophos, deltamethrin/chlorpyriphos, cyfluthrin/chlorpyriphos, and betacyfluthrin/chlorpyriphos.

Oxidases responsible for resistance to pyrethroids sensitize Helicoverpa armigera (Hübner) to triazophos in West Africa.

Helicoverpa armigera (Hübner) is the major insect pest of cotton in Africa, Turkey, Asia, India, Indonesia and Australia. Populations recently developed resistance to pyrethroids in West Africa via the overproduction of cytochrome P450 (oxidases) increasing pyrethroid metabolism. One way to overcome pyrethroid resistance is to use compounds that show negative cross-resistance to pyrethroids.