Genetics and mechanism of resistance to deltamethrin in a field population of Spodoptera litura (Lepidoptera: Noctuidae).
BACKGROUND
Spodoptera litura (F.) causes enormous losses in many economically important crops. The genetics of insecticide resistance has been extensively studied in several insect pests, but there is a lack of information on S. litura. Therefore, the genetics and mechanisms of the resistance of S. litura to deltamethrin were investigated.


RESULTS
Bioassays at generation G1 gave resistance ratios of 9, 5, 41, 52 and 49 for deltamethrin, cypermethrin, profenofos, chlorpyrifos and triazofos respectively, when compared with the susceptible Lab-PK strain. Bioassays at G4 with a deltamethrin-selected population (Delta-SEL) showed that selection gave resistance ratios of 63 and 7 for deltamethrin when compared with the Lab-PK and UNSEL strains respectively. Cross-resistance to other insecticides tested was observed in the selected population. A notable feature of the Delta-SEL strain was that resistance to deltamethrin, cypermethrin, profenofos and chlorpyrifos did not decline over the course of five generations. Synergism tests with microsomal oxidase (MO) and esterase-specific inhibitors indicated that the deltamethrin resistance was associated with MO and, possibly, esterase activity. Reciprocal crosses between the Delta-SEL and Lab-PK strains indicated that resistance was autosomal and incompletely dominant. A direct test of monogenic inheritance suggested that resistance to deltamethrin was controlled by more than one locus.


CONCLUSIONS
Stability and dominance of resistance and cross-resistance suggest that insecticides with different modes of action should be recommended to reduce pyrethroid selection pressure.
Department of Entomology, University College of Agriculture, Bahauddin Zakariya University, Multan, Pakistan.
Munir
M
Ahmad
Ali H
AH
Sayyed
Neil
N
Crickmore
Mushtaq A
MA
Saleem
D000818:Animals; D005260:Female; D017344:Genes, Insect; D007305:Insecticide Resistance / Q000235:genetics; D007306:Insecticides; D008297:Male; D009570:Nitriles; D063086:Organothiophosphates; D010574:Pesticide Synergists; D010882:Piperonyl Butoxide; D011722:Pyrethrins; D012641:Selection, Genetic; D018411:Spodoptera / Q000235:genetics*
D007306:Insecticides; D009570:Nitriles; D063086:Organothiophosphates; D010574:Pesticide Synergists; D011722:Pyrethrins; C017180:decamethrin; C006863:butyl phosphorotrithioate; D010882:Piperonyl Butoxide