Temperature,deltamethrin-resistance status and performance measures of Plutella xylostella: complex responses of insects to environmental variables

1. Worldwide, the excessive use of insecticides has resulted in field-evolved insecticide-resistant populations of diamondback moth (DBM), Plutella xylostella. A deltamethrin-resistant DBM population from the field was divided into two subpopulations in the laboratory. One population (S-strain) was maintained with no further exposure to insecticides, whereas the other population (R-strain) was maintained under a regime of intermittent selection with deltamethrin. 2. Individuals from both strains were reared at constant temperatures in the range 10–35 °C in the absence of deltamethrin, and the effects of rearing temperature on various traits were investigated. At the time of experimentation, the R-strain was 20-fold more resistant to deltamethrin than the S-strain. 3. Temperature differentially affected developmental time, adult life span, pupal weight, and fecundity of both strains. Although both strains laid eggs after being reared at 10 °C, few of these eggs were fertile. The R-strain developed significantly faster than the S-strain. The integrated performance of the S-strain and R-strain was greatest at 25 and 15 °C, respectively. 4. The present study provides important information on the complexities of the outcomes of the interactions between ectotherms and temperature. Specifically, temperature-trait relationships may not be unimodal, and ectotherm genotypes (in this case insecticide-resistance status) and abiotic stresses can interact with unpredictable outcomes. 5. Current models predicting DBM population dynamics and relative abundance in different locations do not consider different thermal biologies of different genotypes. The present study shows the dramatic effects of environment on many parameters used in these models and will help to enhance their accuracy, and thus their utility.     

Relative contribution of detoxifying enzymes to pyrethroid resistance in a resistant strain of Helicoverpa armigera

Abstract:  The relative contribution of oxidases and esterases to pyrethroid resistance was studied in a YS-FP strain of Helicoverpa armigera from China. The YS-FP strain was derived from a field-collected strain (YS) by 16 generations of selection with a mixture of fenvalerate and phoxim. Compared with the YS strain, the YS-FP strain showed 1850- to >7140-fold resistance to four ester-bonded phenoxybenzyl alcohol pyrethroids (fenvalerate, deltamethrin, cypermethrin and cyhalothrin), >205-fold resistance to a non-ester phenoxybenzyl alcohol pyrethroid (etofenprox) and only 19-fold resistance to an ester-bonded methylated biphenyl alcohol pyrethroid (bifenthrin). The oxidase inhibitor piperonyl butoxide eliminated most the of resistance to fenvalerate, deltamethrin, cypermethrin, cyhalothrin and etofenprox, whereas the esterase inhibitor S,S,S -tributylphosphorothioate had a small synergistic effect for fenvalerate and cyhalothrin only. This suggests that the resistance to these pyrethroids in the YS-FP strain was mainly because of enhanced oxidative detoxification. The monooxygenase activities of the midguts of sixth-instar larvae of the YS-FP strain to substrates p -nitroanisole, ethoxycoumarin and methoxycoumarin were 3.7-, 4.7- and 10-fold, respectively, compared with that of the YS strain. Glutathione S -transferase activity and esterase activity were not significantly altered in the YS-FP strain. This confirms that enhanced oxidative detoxification was a major mechanism contributing to pyrethroid resistance in the YS-FP strain.     

Frequency of pyrethroid resistance in Aedes aegypti and Aedes albopictus (Diptera: Culicidae) in Thailand

Thirty‐two Aedes aegypti populations collected throughout Thailand and five populations of Aedes albopictus from southern Thailand were subjected to standard WHO contact bioassays to assess susceptibility to three commonly used synthetic pyrethroids: permethrin, deltamethrin, and lambda‐cyhalothrin. A wide degree of physiological response to permethrin was detected in Ae. aegypti, ranging from 56.5% survival (Lampang, northern Thailand) to only 4% (Kalasin in northeastern and Phuket in southern Thailand). All 32 populations of Ae. aegypti were found to have evidence of incipient resistance (62.5%) or levels of survival deemed resistant (37.5%) to permethrin. Four populations of Ae. albopictus were found with incipient resistance (97 – 80% mortality) and one with resistance (< 80%) to permethrin. The majority of Ae. aegypti populations (68.7%) was susceptible (> 98% mortality) to deltamethrin, with incipient resistance (observed 97–82% mortality) in other localities. In contrast, all populations of Ae. aegypti were completely susceptible (100% mortality) to the recommended operational dosage of lambda‐cyhalothrin. All five populations of Ae. albopictus were found completely susceptible to both deltamethrin and lambda‐cyhalothrin. Evidence of defined incipient or resistance to synthetic pyrethroids mandates appropriate response and countermeasures to mitigate further development and spread of resistance. In light of these findings, we conclude that routine and comprehensive susceptibility monitoring of dengue mosquito vectors to synthetic pyrethroids should be a required component of resistance management policies and disease control activities.     

The Influence of Physical Habitat,Pyrethroids, and Metals on Benthic Community Condition in an Urban and Residential Stream in California

This study was designed to characterize benthic communities and physical habitat in both an urban (Kirker Creek) and residential (Pleasant Grove Creek) stream in California in late spring of 2006 and 2007. Concurrent water quality evaluations, physical sediment parameters, pyrethroids, bulk metals, and SEM/AVS ratios were also measured during both years of this study. The relationship of various benthic metrics to physical habitat metrics, pyrethroids, and metals was evaluated for each stream using stepwise multiple linear regressions with both years combined for each stream, as well as both years and both streams combined, to increase the statistical power for determining significant relationships. Physical habitat was determined to be poor in each stream during both years of sampling. More than 100 benthic taxa were reported annually for both streams based on 2006 and 2007 sampling. A significant result from the stepwise regression analysis combining data for 2 years across both streams is that when habitat metrics and to a lesser degree metals are considered in the statistical models pyrethroids do not display any significant relationships to the benthic metrics. In summary, it is apparent from this analysis that the health of benthic communities in both streams is primarily affected by habitat metrics.     

家蝇对拟除虫菊酯抗性机理研究进展

本文概述了家蝇对拟除虫菊酯的抗性机制 ,特别是结合我国室内培育的抗拟除虫菊酯家蝇品系 (Dec R和 2Cl R) ,探讨了Na+通道、神经递质释放、ATPase、蛋白质磷酸化等与家蝇Kdr抗性的关系 ,从多方面证明了神经敏感性降低是家蝇对拟除虫菊酯产生抗性的重要机制。     

Evidence for Dual Binding Sites for 1,1,1-Trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) in Insect Sodium Channels

1,1,1-Trichloro-2,2-bis(p-chlorophenyl)ethane (DDT), the first organochlorine insecticide, and pyrethroid insecticides are sodium channel agonists. Although the use of DDT is banned in most of the world due to its detrimental impact on the ecosystem, indoor residual spraying of DDT is still recommended for malaria control in Africa. Development of resistance to DDT and pyrethroids is a serious global obstacle for managing disease vectors. Mapping DDT binding sites is necessary for understanding mechanisms of resistance and modulation of sodium channels by structurally different ligands. The pioneering model of the housefly sodium channel visualized the first receptor for pyrethroids, PyR1, in the II/III domain interface and suggested that DDT binds within PyR1. Previously, we proposed the second pyrethroid receptor, PyR2, at the I/II domain interface. However, whether DDT binds to both pyrethroid receptor sites remains unknown. Here, using computational docking of DDT into the K_v1.2-based mosquito sodium channel model, we predict that two DDT molecules can bind simultaneously within PyR1 and PyR2. The bulky trichloromethyl group of each DDT molecule fits snugly between four helices in the bent domain interface, whereas two p-chlorophenyl rings extend into two wings of the interface. Model-driven mutagenesis and electrophysiological analysis confirmed these propositions and revealed 10 previously unknown DDT-sensing residues within PyR1 and PyR2. Our study proposes a dual DDT-receptor model and provides a structural background for rational development of new insecticides.     

Pyrethroid resistance in tropical bedbugs,Cimex hemipterus,associated with use of treated bednets

When Tanzanian villages were provided with pyrethroid-treated bednets, bedbugs (Cimicidae) disappeared; however, after about 6 years they have re-appeared in these villages. Using a newly devised test-kit, susceptibility tests of bedbugs Cimex hemipterus (Fabricius) from five of these villages showed that there is resistance to permethrin and alphacypermethrin in bedbugs from each of the villages, in contrast to those from five villages without treated nets. Circumstantial evidence indicates that bedbug resistance to pyrethroid insecticides may evolve more readily in villages with incomplete coverage rates of treated bednets, allowing bedbug infestations to become re-established. Bedbugs have not returned to a village where nearly all the beds have been provided with pyrethroid-treated bednets for 14 years.     

Comparative insecticidal power of three pyrethroids on netting

Adult mosquitoes, Anopheles gambiae Giles and Culex quinquefasciatus Say (Diptera: Culicidae), were exposed for 3 min to replicate samples of polyester netting cut from replicate bednets treated with pyrethroid insecticide formulations at the recommended concentration (alphacypermethrin SC at 40mg ai/m2; cyfluthrin EW at 50 mg ai/m2; deltamethrin WT at 25 mg ai/m2), or treated with only a quarter of those dosages. After 4 months domestic use of the bednets in Malawi, chemical assays showed that pyrethroid deposits on the netting were somewhat less than the target concentrations. Comparing the pyrethroid bioassay results with Anopheles at both treatment concentrations, deltamethrin gave significantly higher mortality (99.7-100%) than the other compounds (alphacypermethrin 94-96%, cyfluthrin 80-89%). Culex bioassay mortality was lower (alphacypermethrin 56-74%; cyfluthrin 63-65%; deltamethrin 50-81 %) and results with the three pyrethroid insecticides at their recommended doses did not differ significantly.     

A high incidence of parasitism ofHeliothis SPP. [Lep.: Noctuidae] larvae in cotton in Southeastern Arkansas

During 1981 and 1982, bollworm,Heliothis zea (Boddie), and tobacco budworm,H. virescens (F.), larvae (n=3,666) were collected from 41 cotton fields near Portland, Arkansas (USA) to assess the occurrence of parasitism. Three strategies were employed to controlHeliothis spp. in these fields: (1) release ofTrichogramma pretiosum Riley; (2) insecticidal control; or (3) inaction (check). Insecticide use in nonchemical control fields was reduced, but not eliminated.Heliothis spp. larvae collected in cotton had higher parasitism rates in 1981 (30.9%) and 1982 (50.1%) than had been reported for cotton since the advent of organochlorine insecticide usage. Four species of larval parasites and 1 species of larval-pupal parasite were recorded. The larval parasiteMicroplitis croceipes (Cresson) comprised 90.6% and 94.5% of all parasitic insects reared from field collectedHeliothis spp. in 1981 and 1982, respectively. No difference (P>0.05) in level of parasitism existed betweenH. zea andH. virescens. Differences between treatments occurred only in 1982 whenH. zea larvae were parasitized at a greater (P<0.05) rate in check fields (68.3%) than in insecticidal control fields (44.3%). Higher levels of larval parasitism in cotton fields may be a consequence of reduced insecticide usage and changes in materials applied, particularly the pyrethroids. Mention of a trademark or proprietary product does not constitute a guarantee or warranty of the product by the U.S. Dept. of Agriculture and does not imply its approval to the exclusion of other products that may also be suitable.