Cross-resistance, mode of inheritance and stability of resistance to emamectin in Spodoptera litura (Lepidoptera: Noctuidae).
BACKGROUND
Spodoptera litura (F.) is a cosmopolitan pest that has developed resistance to several insecticides. The aim of the present study was to establish whether an emamectin-selected (Ema-SEL) population could render cross-resistance to other insecticides, and to investigate the genetics of resistance.


RESULTS
Bioassays at G(1) gave resistance ratios (RRs) of 80-, 2980-, 3050- and 2800-fold for emamectin, abamectin, indoxacarb and acetamiprid, respectively, compared with a laboratory susceptible population Lab-PK. After three rounds of selection, resistance to emamectin in Ema-SEL increased significantly, with RRs of 730-fold and 13-fold compared with the Lab-PK and unselected (UNSEL) population respectively. Further studies revealed that three generations were required for a tenfold increase in resistance to emamectin. Resistance to abamectin, indoxacarb, acetamiprid and emamectin in UNSEL declined significantly compared with the field population at G(1). Furthermore, selection with emamectin reduced resistance to abamectin, indoxacarb and acetamiprid on a par with UNSEL. Crosses between Ema-SEL and Lab-PK indicated autosomal and incomplete dominance of resistance. A direct test of a monogenic model and Land's method suggested that resistance to emamectin was controlled by more than one locus.


CONCLUSIONS
Instability of resistance and lack of cross-resistance to other insecticides suggest that insecticides with different modes of action should be recommended to reduce emamectin selection pressure.
Shad
Sarfraz Ali
SA
Department of Entomology, University College of Agriculture, Bahauddin Zakariya University, Multan, Pakistan.
Sayyed
Ali H
AH
Saleem
Mushtaq A
MA
D000818:Animals; D018556:Crops, Agricultural; D004187:Disaccharides / Q000633:toxicity*; D004305:Dose-Response Relationship, Drug; D005260:Female; D003368:Gossypium; D040582:Inheritance Patterns / Q000235:genetics*; D007300:Insect Control; D007305:Insecticide Resistance / Q000187:drug effects / Q000235:genetics; D007306:Insecticides / Q000633:toxicity*; D007559:Ivermectin / Q000031:analogs & derivatives* / Q000633:toxicity; D008297:Male; D009035:Mothers; D020412:Multifactorial Inheritance; D012730:Sex Chromosomes / Q000235:genetics; D018411:Spodoptera / Q000187:drug effects / Q000235:genetics* / Q000502:physiology*
D004187:Disaccharides; D007306:Insecticides; D007559:Ivermectin; C443359:emamectin