Efficient elimination of insecticide-susceptible diamondback moth (DBM), Plutella xylostella (L.) by esfenvalerate from a population generates high esfenvalerate-resistance in the DBM
The study was undertaken at Nagoya University, Nagoya, Japan, to determine in what way the low selection concentration of esfenvalerate influenced the speed and magnitude of resistance development in the DBM. KOBII-esfenvalerate selected strain and KOBII-nonselected strain, which were developed from the KOBII population, esfenvalerate 50 g/l EC and the leaf-dipping method was used for the study. The esfenvalerate concentration that caused hundred percent mortality in the KOBII-nonselected strain, which is homogenous in homozygous susceptible (ss) individuals, was used to estimate the proportion of ss individuals in the esfenvalerate selected strain. Concentration of 6.25 mg/l esfenvalerate eliminated all ss individuals from the KOBII-nonselected strain. The 6.25 mg/l esfenvalerate showed that there was about 2.5 percent ss individuals in the KOBII-esfenvalerate selected strain. Two generations after selection with the 10 mg/l esfenvalerate, which yielded 273-fold resistance, up to 97.5 percent of the individuals in the esfenvalerate-selected strain were heterozygous resistant (rs) and homozygous resistant (rr). A field population of DBM, exposed to the recommended insecticide dilution for field application against DBM in Japan, which is 1,000 – 2,000 times dilution and translated into 25 mg/l – 50 mg/l esfenvalerate, a high frequency of rr individuals accumulated and generated a DBM population resistant to esfenvalerate in the field. Proactive management of the development of insecticide resistance is important.