Selection for imidacloprid resistance in silverleaf whiteflies from the Imperial Valley and development of a hydroponic bioassay for resistance monitoring

Abstract

: A Ðeld-collected population of the silverleaf whiteÑy, Bemisia argentifolii, was selected with the nicotinyl compound, imidacloprid, over 32 generations to determine if resistance would develop when maintained under continuous selection pressure in a greenhouse. Resistance was slow to increase at Ðrst with low to moderate levels of resistance (RR from 6-to 17-fold) in the Ðrst 15 generations of selection. Further selection steadily led to higher levels of resistance, with the greatest resistance ratio at 82-fold, the gradual rise suggesting the involvement of a polygenic system. At the end of the selection, slopes of probit regressions were substantially steeper than earlier, indicating increased homogeneity of imidacloprid resistance in this strain.A hydroponic bioassay featuring systemic uptake of imidacloprid through roots was developed to monitor the changes in resistance to imidacloprid in the selected whiteÑy strain and in seven Ðeld-collected strains from Imperial Valley, California. Six out of seven Ðeld-collected strains exhibited low values LC 50 (0É002 to 0É512 mg ml~1) compared to the selected resistant strain, with one exception where the was 0É926 mg ml~1 (RR \ 15É0). Variation in LC 50 responses to imidacloprid in the Ðeld strains suggest that this technique is sufficiently sensitive to detect di †erences in susceptibilities of whiteÑy populations. The imidacloprid-resistant strain showed no cross-resistance to endosulfan, chlorpyrifos or methomyl (RR ranging from 0É4-to 1É5-fold). A low level of cross-resistance was observed to bifenthrin in the IM-R strain at 7-fold. The success of selection for resistance to imidacloprid has serious implications for whiteÑy control programs that rely heavily on imidacloprid.

A nicotinic acetylcholine receptor mutation conferring target-site resistance to imidacloprid inNilaparvata lugens(brown planthopper)

“…Resistance to imidacloprid has been reported in a range of species including western flower thrips, Colorado potato beetle, German cockroach, and house fly (39,40). In silverleaf whitefly and green peach aphid, high resistance was obtained by continuous selection in the greenhouse (41,42). Previous studies from this laboratory also have shown that the brown planthopper (N. lugens) developed high resistance to imidacloprid after continuous selection (19,20).…”

“…Previous studies from this laboratory also have shown that the brown planthopper (N. lugens) developed high resistance to imidacloprid after continuous selection (19,20). In some species with high resistance to imidacloprid, piperonyl butoxide had very strong synergistic effects on imidacloprid, suggesting that P450 monooxygenases may play important roles in imidacloprid resistance (41,42). Our previous studies of resistance to imidacloprid in N. lugens (19) revealed significant cross-resistance only to the insecticides that target nAChRs, suggesting that target insensitivity might play an important role in imidacloprid resistance.…”

Challenges with managing insecticide resistance in agricultural pests, exemplisfied by the whitefly Bemisia tabaci

“…Their structural similarity, coupled with a likely common target site, nicotinic acetylcholine receptors in the post-synaptic region of insect nerves (Bai et al 1991), also raises the spectre of cross-resistance a¡ecting the group as a whole (Elbert et al 1996;. The risk of resistance is therefore considerable, and reinforced by the speed with which resistance to imidacloprid has developed in B. tabaci under sustained exposure to this chemical in the laboratory (Prabhakar et al 1997) and in greenhouses in southern Europe (Cahill et al 1996b). Given the current scale of imidacloprid use, further resistance outbreaks seem inevitable and it is essential to exploit these for de¢ning conditions under which chloronicotinyls might be used sustainably.…”

Mutations in Dα1 or Dβ2 nicotinic acetylcholine receptor subunits can confer resistance to neonicotinoids in Drosophila melanogaster

“…Neonicotinoid resistance by metabolic detoxification of the insecticide, arising initially due to selection by DDT, has been found in D. melanogaster (Daborn et al, 2002). Long-term selection in Bemisia tabaci produced strains up to 82-fold resistant (Prabhaker et al, 1997). A mutation in two nAChR asubunits of Nilaparvata lugens reduced radiolabelled insecticide binding in assays with vertebrate b-subunits (Liu et al, 2005).…”