Nicotinic acetylcholine receptor α6 subunit mutation (G275V) found in a spinosad-resistant strain of the flower thrips, Frankliniella intonsa (Thysanoptera: Thripidae)

The flower thrips Frankliniella intonsa strain showing resistance to spinosad was established in the laboratory. The resistant strain showed an LC₅₀ value of 1398.7 mg/L in a leaf dipping/contact assay. The LC₅₀ value was ca. 280 times higher than that of the most susceptible strain. An insecticidal assay using synergists suggested no involvement of degradation enzymes, such as cytochrome P450, glutathione S-transferase, and carboxyl esterase, in the resistance. Glycine at amino acid position 275 of the nicotinic acetylcholine receptor (nAChR) α6 subunit was mutated to valine in the resistant strain. These results suggest that spinosad resistance in F. intonsa is conferred by the reduced sensitivity of nAChR.

Spinosad resistance of melon thrips, Thrips palmi, is conferred by G275E mutation in α6 subunit of nicotinic acetylcholine receptor and cytochrome P450 detoxification

To examine the resistance mechanisms of Thrips palmi against spinosad, we cloned partial nucleotide sequences of the nicotinic acetylcholine receptor α6 subunit (TPα6) gene from susceptible (OK) and resistant (TS1 and TS5) strains and compared the deduced amino acid sequences among the three strains. The OK, TS1, and TS5 strains respectively showed LC50 values of 3.4mg/L, 2838.5mg/L, and 6655.5mg/L. The deduced amino acid sequence of TPα6 gene showed 96% identity with that of Frankliniella occidentalis. Comparison of the deduced amino acid sequences of TPα6 gene among the three strains showed that the TS1 and TS5 strains had a resistant amino acid, Glu, at amino acid position 275. On the other hand, a susceptible amino acid, Gly, was encoded at the corresponding amino acid position for the OK strain. The synergist, piperonyl butoxide, respectively caused 1.1-fold , 5.8-fold , and 9.0-fold decreases in the resistance ratios of the OK, TS1, and TS5 strains. These results suggest that spinosad resistance of T. palmi is conferred by reduced sensitivity of TPα6 and cytochrome P450-mediated detoxification.