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Dryad

Association between susceptibility of Thrips palmi to spinetoram and frequency of G275E mutation provides basis for molecular diagnostics of field-evolved resistance

Abstract

Background: Spinosyn resistance is an increasing problem in field control of targeted pests. While putative mechanisms underlying spinosyn resistance have been identified in controlled studies on many species, mechanisms underlying field-evolved resistance and the development of a molecular diagnostic method for monitoring field resistance have lagged behind. Here, we examined levels of resistance of melon thrips, Thrips palmi, to spinetoram as well as target site mutations in field populations across China to identify potential mechanisms and useful molecular markers for diagnostic purposes.

Results: LC50 of 16 field-collected populations to the spinetoram varied from 0.12 to 759.34 mg L-1. In resistant populations, we identified the G275E mutation, which has previously been linked to spinosyns resistance, as well as another nonsynonymous mutation, F314V, both located in the α6 subunit of the nicotinic acetylcholine receptor. There was a strong correlation between levels of spinetoram resistance and allele frequency of G275E mutation in field-collected populations (r2 = 0.84) and those reared under laboratory conditions for two to five generations (r2 = 0.91). LC50 ranged from 0.12 to 0.66 mg L-1 in populations without G275E mutation, while it ranged from 33.12 to 39.91 mg L-1 in most populations with a G275E mutation frequency > 90%, with the exception of one field-collected population which had an G275E frequency of 92% and a very high LC50 value of 759.34 mg L-1, suggesting additional mechanisms.

Conclusions: Our results indicate that field-evolved resistance of T. palmi to spinetoram in China is mainly conferred by the G275E mutation, with other mechanisms contributing to a higher level of resistance. The frequency of the G275E mutation provides a useful diagnostic for quantifying resistance levels in field populations of T. palmi.