title: Variation in resistance to pyrethroids in Helicoverpa armigera from Benin Republic, West Africa.
abstract: 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. Pretreatment with piperonyl butoxide significantly decreased the LD50 value of cypermethrin and deltamethrin, and the resistance suppression by this synergist effect was observed. No significant decrease in the LD50 value was obtained when S,S,S-tributyl phosphoro-trithioate was applied before deltamethrin. In the field, cypermethrin's LD50 value varied, and the highest LD50 values were observed during the rainy season, the cotton, Gossypium hirsutum L., crop period, when pyrethroids are extensively used. In the dry season when there was no cotton cultivation, the lowest LD50 values were obtained. However, reversion was never total in the field; resistance did not revert to the level we observed in the susceptible strain. In the laboratory, when field populations were reared in insecticide-free conditions, resistance decreased and total reversion was observed. Results are discussed with regard to insecticide resistance fitness cost and resistance management strategies.
authors.affiliation: Laboratoire de Defense des Cultures, Institut National des Recherches Agricoles du Bénin, 01 BP 128 Porto-Novo, Republique du Bénin. djihinto@yahoo.com
authors.forename: Angelo C
authors.initials: AC
authors.lastname: Djihinto
authors.forename: André
authors.initials: A
authors.lastname: Katary
authors.forename: Patrick
authors.initials: P
authors.lastname: Prudent
authors.forename: Jean-Michel
authors.initials: JM
authors.lastname: Vassal
authors.forename: Maurice
authors.initials: M
authors.lastname: Vaissayre
mesh_terms: D000818:Animals; D001541:Benin; D004351:Drug Resistance / Q000235:genetics*; D003368:Gossypium / Q000469:parasitology; D007313:Insecta / Q000187:drug effects*; D007306:Insecticides / Q000633:toxicity*; D007928:Lethal Dose 50; D018551:Solanum lycopersicum / Q000469:parasitology; D009570:Nitriles / Q000633:toxicity; D010571:Pest Control / Q000379:methods; D011722:Pyrethrins / Q000494:pharmacology* / Q000633:toxicity
chemical_list: D007306:Insecticides; D009570:Nitriles; D011722:Pyrethrins; C017160:cypermethrin; C017180:decamethrin; C099952:bifenthrin; C017690:fenvalerate