Dominant fitness costs of abamectin resistance in Plutella xylostella

BACKGROUNDThe TH-Abm strain of Plutella xylostella, exhibiting 23 670-fold resistance to abamectin, was selected from a field-evolved multiresistant population. By repeated backcrossing to a susceptible strain (Roth) and selection with abamectin, the resistance trait of TH-Abm was introgressed into Roth to generate a near-isogenic strain (Roth-Abm). Fitness costs associated with abamectin resistance were examined in Roth-Abm. RESULTSCompared with Roth, Roth-Abm obtained 11 500-fold resistance to abamectin and 364 000-, 12- and 12-fold cross-resistance to emamectin benzoate, spinosad and fipronil respectively. Roth-Abm has a significantly longer pupal development time, lesser female pupal weight and lower larval survival than Roth. Female fecundity and egg viability are significantly lower in Roth-Abm than in Roth. All of the above fitness components of the F-1 progeny from Roth x Roth-Abm are similar to those of Roth-Abm and are significantly lower than those of Roth. By comparing with the net replacement rate (R-0) of Roth, the fitness of Roth-Abm, F-1a (Roth male x Roth-Abm) and F-1b (Roth female x Roth-Abm) are 0.50, 0.50 and 0.53 respectively. CONCLUSIONAbamectin resistance in Roth-Abm results in significant fitness costs, and the fitness costs are autosomal and dominant. Rotation of abamectin with other insecticides without cross-resistance could be especially useful for delaying abamectin resistance in P. xylostella. (c) 2014 Society of Chemical Industry