Deltamethrin selection with

Figure 10.9 Resistance ratios in successive generations of Aedes aegypti larvae subjected to different selection pressures. Open circle, selection with deltamethrin alone Triangle, selection of the parent susceptible strain with deltamethrin plus PBO (1 5) Solid circles, selection of F24 deltame-thrin-selected strain with deltamethrin plus PBO (1 5). (From Kumar, S., et al., Arch. Insect Biochem. Physiol., 50,1, 2002. With permission.)...

The field nontarget arthropod data for pyrethroids summarized in Table 9 indicate that for all pyrethroids there was an initial reduction in abundance for some species shortly after application. There was a trend of more marked effects at the higher full field application rates with less marked affects at the lower drift rates tested (e.g., Deltamethrin, bifenthrin, and esfenvalerate). Also there was a trend of greater selectivity (i.e., fewer taxa affected) at lower drift rates (e.g., /amMa-cyhalothrin and Deltamethrin). For nearly all the pyrethroid field studies, either full or partial recovery of affected taxa was reported by the end of the field study or growing season, and in some cases for certain taxa, recovery occurred within 1-3 weeks. 

In a parallel selection study, a 137-fold deltamet hi in-resistant strain when subject to continuous selection pressure with synergized della me thrin, showed 76 reversion in resistance in the lirst generation and significantly retarded the development of resistance in subsequent generations. Thomas ef al. concluded that even though high larval resistance develops under intense laboratory selection. the addition of PBO can drastically reduce the speed of development of deltamethrin resistance in this species of mosquito. 

DDT significantly enhanced veratridine-dependent uptake at all veratridine concentrations above 10 pM, and maximum sodium uptake in the presence of both compounds was achieved at 50 pM, which is the approximate for veratridine alone These findings suggest that , -DDT notuonly enhances veratridine-dependent activation but also increases the potency of veratridine. This result contrasts with the interaction of deltamethrin and veratridine in mouse brain synaptosomes (Figure 1) where the insecticide enhanced activation but did not affect the potency of the activator The only previous report of insecticide-dependent potency shifts in sodium channel activation is in neuroblastoma cells, where pyrethroids increase the potency of batrachotoxin and dihydrograyanotoxin II as sodium channel activators, but do not alter the potency of veratridine (5). These experiments provide the basis for further studies to compare directly the selectivity and sensitivity of sodium channels from mammalian and fish brain in their interactions with insecticides ... 

The 3D QSAR pharmacophore model selected very fast and very slow metabolizers, leaving the catalytic hydrolysis rates in the middle group as being questionable. Catalytic rates ( cat) for the pyrethroids that were outside of the training set (8-25 h ) were obtained by extrapolation. Less confidence should be placed on these predicted values. The hydrolysis rate for deltamethrin (IR, cis, aS) fell into the middle group and was not included in Table 19. However, catalytic rates (rat serum carboxylesterases) for two trans deltamethrin (1R,3S, aR lS,3R,oR) isomers were included in the table and compared favorably with the rat hydrolase A and B values in Table 11. Cypermethrin (IR, trans, aR), cyfluthrin (IR, trans, oR IR, trans, oR), and permethrin (IR, trans IS, trans) were fast metabolizers. Among the slow metabolizers were permethrin (IS, cis), cyfluthrin (IS, cis, aS) and cypermethrin (IR, trans, aS). 

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