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. High resistance to cypermethrin (RF = 67-1771), cross-resistance to deltamethrin (RF = 60-2972) and lack of cross-resistance to the non-ester pyrethroid etofenprox (RF = 2-10) were observed among H. armigera field populations and laboratory-selected strains. Enzymatic assays showed that esterase activity, but not oxidase content or glutathione-S-transferase activity, was positively correlated with resistance to cypermethrin. Pretreatment with piperonyl butoxide (PBO) resulted in significant synergism with cypermethrin in 6/10 field populations, but not in the laboratory-selected strain, indicating that additional mechanisms such as mixed-function oxidase (MFO) may be involved in field resistance. The absence of cross-resistance to DDT ruled out a possible target-site modification.


CONCLUSIONS
Knowledge of the mechanisms involved in pyrethroid resistance and the lack of cross-resistance to spinosad and indoxacarb is a key to devising new resistance management strategies aimed at restoring the efficacy of pyrethroid-based programmes.
Achaleke
Joseph
J
IRAD, PRASAC-ARDESAC, Cotton Programme, Garoua, Cameroon.
Martin
Thibaud
T
Ghogomu
Richard T
RT
Vaissayre
Maurice
M
Brévault
Thierry
T
D000350:Africa, Central; D000818:Animals; D004950:Esterases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D003368:Gossypium / Q000469:parasitology; D019476:Insect Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D007305:Insecticide Resistance; D007306:Insecticides / Q000494:pharmacology; D009036:Moths / Q000187:drug effects / Q000201:enzymology*; D010935:Plant Diseases / Q000469:parasitology; D011722:Pyrethrins / Q000494:pharmacology*
D019476:Insect Proteins; D007306:Insecticides; D011722:Pyrethrins; D004950:Esterases