Fenpropathrin [OVA]

The mirid bug, Apolygus lucorum Meyer-Dur, has been an important pest of cotton crop in China, and is primarily controlled with insecticides, such as pyrethroids. To elucidate the potential resistant mechanisms of A. lucorum to lambda-cyhalothrin, a series of biological, biochemical, and molecular assays were conducted in the reference (AL-S) and lambda-cyhalothrin-resistant (AL-R) populations. Comparison of the molecular target of pyrethroid insecticides, voltage-gated sodium channel, revealed that there were no mutation sites in the resistant population, indicating target insensitivity is not responsible for increased resistance of AL-R to lambda-cyhalothrin. Furthermore, the synergism assays and the activities of detoxification enzymes were performed to determine detoxification mechanism conferring the lambda-cyhalothrin resistance. In the tested synergists, the piperonyl butoxide had the highest synergism ratio against lambda-cyhalothrin, which was up to five-fold in both populations. In addition, the result also showed that only cytochrome P450 had significantly higher O-deethylase activity with 7-ethoxycoumarin (1.78-fold) in AL-R population compared with AL-S population. Seven cytochrome P450 genes were found to be significantly overexpressed in the resistant AL-R population compared with AL-S population. Taken together, these results demonstrate that multiple over-transcribed cytochrome P450 genes would be involved in the development of lambda-cyhalothrin resistance in AL-R population.

The European red mite Panonychus ulmi (Koch) is a major pest of apple trees worldwide and causes significant damage to apple orchards in Iran. Pyrethroid insecticides/acaricides, such as fenpropathrin and fenvalerate, are widely used to control P. ulmi, but their long-term use may lead to low efficacy. Earlier studies investigating pyrethroid resistance in closely related mites such as Tetranychus urticae revealed that pyrethroid resistance was associated with point mutations in the voltage-gated sodium channel gene (vgsc). The aim of this study was to investigate the biochemical and molecular mechanisms of fenpropathrin and fenvalerate resistance in Iranian populations of P. ulmi. Pyrethroid toxicity bioassays were carried out on different P. ulmi field populations. Marand (resistance ratio, RR = 149), Maracieh (RR = 90) and Mianeh2 (RR = 71) populations exhibited high levels of resistance to fenpropathrin, compared to a susceptible field population (Shahin Dej). Resistance was also observed for fenvalerate with resistance ratio's ranging from 2- to 20-fold. Synergism experiments and enzyme activity assays predicted a minor role for classical detoxification enzymes. In contrast, two amino acid substitutions in the VGSC, L1024V and F15381, that were previously shown to confer pyrethroid resistance, were detected in all three resistant P. ulmi populations and point towards target-site insensitivity as the most likely resistance mechanism. Furthermore, sequencing after cloning of vgsc fragments from single haploid males revealed the presence of multiple copies of vgsc in a highly resistant strain. The link between resistance mutations and vgsc copy number variation should be the subject of future study, as this might be used to develop molecular markers for monitoring pyrethroid resistance of P. ulmi in the field.