| In order to understand the resistance level and mechanism of P. xylostella to indoxacarb,5 field populations of diamondback moth were monitored in 3 province (2014-2015). A susceptible population of P. xylostella was selected with indoxacarb for thirty-eight generations under controlled laboratory conditions to study the cross resistance, biological characteristic and mechanism of indoxacarb resistance in P. xylostella. The main results were as follows:To provide a basis for future resistance management strategies, the resistance of P. xylostella to indoxacarb was evaluated in centrol China from 2014 to 2015 with 5 field populations. The results showed that the diamondback moth field populations generally had moderate resistance to indoxacarb from 2014 to 2015 in Yueyang, and the resistance to indoxacarb of diamondback moth reach up to 45.8-fold.The resistance to indoxacarb in P. xylostella (WH-RR) reached up to 1069.30-fold after thirty-eight generation selection with indoxacarb as compared to a susceptible population (WH-SS) of P. xylostella. This selected-population also developed moderate levels of cross-resistance to metaflumizone (20.9-fold), beta-cypermethrin (8.7-fold) and chlorfenapyr (8.3-fold), but has no cross resistance to abamectin, chlorantraniliprole, diafenthiuron, chlorfluazuron, spinosad and cyantraniliprole compared with the susceptible population. The egg, larva and pupa of WH-RR strain had a low survival rate compared to WH-SS strain. There were significant differences in the development of egg, 1st instar larvae,2st instar larvae,4st instar larvae and pupa between WH-RR strain and WH-SS strain. The development periods of egg and 2st instar larvae of WH-RR strain were 0.5 d shorter than that of WH-SS strain. The development periods of 1st instar larvae, 4st instar larvae, pupa and the mean generation time of WH-RR strain were 0.6d,0.5d, 0.5d and 1.2 d longer than that of WH-SS strain. However, the WH-RR strain did not have a fitness value to the WH-SS strain.To study the synergistic mechanism and biochemical mechanism of indoxacarb resistance in P. xylostella three synergists, Piperonyl butoxide (PBO), diethyl-maleate (DEM) and triphenyl phosphate (TPP) and three enzymes activity including Esterase (CarE), Glutathione S-transferase (GSTs) and P450 monooxygenase (MFO) were tested on the WH-SS and WH-RR strains. The study showed that the synergism and CarE activity increased with the resistance ratio. When the WH-RR strains (F58) exhibited 1069.3-fold resistance to indoxacarb, the toxicity of indoxacarb was synergised by known metabolic inhibitors DEM (synergistic ratio, SR= 3.5), and GSTs activities of the WH-RR strain was 5.82-fold greater than that of the WH-SS strain (P< 0.05). So, we can think that the GSTs activity enhancement may be one of the main reasons for diamondback moth produce the resistance to indoxacarb.Through cloning the cDNA sequence which encoding the sodium channel genes of WH-RR and WH-SS strain, we obtained a length of 5807 bp and 5717 bp sequence. Comparison of cDNA sequences encoding the sodium channel genes of WH-RR and WH-SS revealed one point mutations (A1376T) in the domain ES3,69 bases were inserted in domain I S5-S6 and 18 bases were deleted in the link of domain Ⅱ to Ⅲ of the P. xylostella sodium channel protein in the WH-RR population. These could be the main molecular mechanisms of P. xylostella to indoxacarb. And we also found that amino acid sequences encoding the sodium channel genes of P. xylostella had high homology with silkworm (90.0%), German cockroach (82.0%) and houseflies (77.0%). |
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