Measuring cypermethrin resistance in the German cockroach (Orthoptera: Blattellidae).

Cypermethrin resistance in the German cockroach, Blattella germanica (L.), was assessed by tests of surface contact and topical application. Topical application provided the most sensitive measure of resistance in a field strain. The resistance ratio (RR) measured by topical application was 122.6 for cypermethrin at LD50. As measured by surface contact, the resistance ratio at KT50 was 2.9. Differences between the walking movement of cockroaches of susceptible (VPI) and field (RHA) strains on deposits of cypermethrin influenced KT50 values. A bioassay with unrestricted movement resulted in RHA strain cockroaches accumulating a larger dose on the tarsal pads and subsequent reduction of the resistance ratio at KT50. Less walking by the VPI strain resulted in less insecticide accumulation on their tarsal pads. On a bioassay in which movement was restricted, the amount of insecticide accumulating on the tarsi was equalized, resulting in an increased resistance ratio at KT50. Differences in susceptibility were more accurately measured when the two strains were topically treated (either on the thorax or the tarsal pads) with known doses of insecticide.     

Evaluation of three methods for detecting permethrin resistance in adult and nymphal Blattella germanica (Dictyoptera: Blattellidae).

The insecticide resistance status of the German cockroach, Blattella germanica (L.), against permethrin was evaluated with three different bioassay methods. The LT50 and KT50 in adults were measured by glass jar test, the LT50 and KT50 in nymphs were assessed by glass petri dish-test, and the LD50 in adults and nymphs was measured by topical application. The results indicate that in all three bioassays, cockroaches showed different degrees of resistance to permethrin. Resistance ratios of 6.7-, 12.8-, and 7.5-fold for KT50, LD50, and LT50, respectively, were obtained for adult cockroaches compared with those from a susceptible strain. Similarly, resistance ratio values of 17-fold for KT50, 8-fold for LD50, and 6.4-fold for LT50 were obtained for nymphs compared with those from a susceptible strain. Although both adults and nymphs exhibited a similar level of susceptibility to permethrin, adults showed a higher degree of susceptibility to topical application than to the other exposure method. The order of sensitivity (based on resistance ratio values) was topical application (LD50) > LT50 > KT50 in adults. For nymphs, the resistance ratio in the knockdown test was higher than in other tests (resistance ratio = 17-fold). Therefore, the order of test sensitivity based on comparisons of resistance ratio values was KT50 > topical application (LD50) > LT50 in nymphs. Topical application exhibited a higher sensitivity than the LT and KT methods in adults. Thus, the results suggest that topical application and knockdown testing methods are the most sensitive assays for measuring resistance of adult and nymphal German cockroaches, respectively, to permethrin.     

Modifications of pyrethroid effects associated with kdr mutation in Anopheles gambiae

Effects of knockdown resistance (kdr) were investigated in three pyrethroid‐resistant (RR) strains of the Afrotropical mosquito Anopheles gambiae Giles (Diptera: Culicidae): Kou from Burkina Faso, Tola and Yao from Côte d'Ivoire; compared with a standard susceptible (SS) strain from Kisumu, Kenya. The kdr factor was incompletely recessive, conferring 43‐fold resistance ratio at LD₅₀ level and 29‐fold at LD₉₅ level, as determined by topical application tests with Kou strain. When adult mosquitoes were exposed to 0.25% permethrin‐impregnated papers, the 50% and 95% knockdown times (KdT) were 23 and 42 min for SS females, compared with 40 and 62 min for RS (F₁ Kou × Kisumu) females. On 1% permethrin the KdT₅₀ and KdT₉₅ were 11 and 21 min for SS compared with 18 and 33 min for RS females. Following 1 h exposure to permethrin (0.25% or 1%), no significant knockdown of Kou RR females occurred within 24 h. Permethrin irritancy to An. gambiae was assessed by comparing ‘time to first take‐off’ (TO) for females. The standard TO₅₀ and TO₉₅ values for Kisumu SS on untreated paper were 58 and 1044 s, respectively, vs. 3.7 and 16.5 s on 1% permethrin. For Kou RR females the comparable values were 27.3 s for TO₅₀ and 294 s for TO₉₅, with intermediate RS values of 10.1 s for TO₅₀ and 71.9 s for TO₉₅. Thus, TO values for RS were 2.7–4.4 times more than for SS, and those for RR were 7–18 times longer than for SS. Experiments with pyrethroid‐impregnated nets were designed to induce hungry female mosquitoes to pass through holes cut in the netting. Laboratory ‘tunnel tests’ used a bait guinea‐pig to attract mosquitoes through circular holes (5 × 1 cm) in a net screen. With untreated netting, 75–83% of laboratory‐reared females passed through the holes overnight, 63–69% blood‐fed successfully and 9–17% died, with no significant differences between SS and RR genotypes. When the netting was treated with permethrin 250 mg ai/m² the proportions that passed through the holes overnight were only 10% of SS vs. 40–46% of RR (Tola & Kou); mortality rates were 100% of SS compared with 59–82% of RR; bloodmeals were obtained by 9% of Kou RR and 17% of Tola RR, but none of the Kisumu SS females. When the net was treated with deltamethrin 25 mg ai/m² the proportions of An. gambiae that went through the holes and blood‐fed successfully were 3.9% of Kisumu SS and 3.5% of Yaokoffikro field population (94% R). Mortality rates were 97% of Kisumu SS vs. 47% of Yaokoffikro R. Evidently this deltamethrin treatment was sufficient to kill nearly all SS and half of the Yaokoffikro R An. gambiae population despite its high kdr frequency. Experimental huts at Yaokoffikro were used for overnight evaluation of bednets against An. gambiae females. The huts were sealed to prevent egress of mosquitoes released at 20.00 hours and collected at 05.00 hours. Each net was perforated with 225 square holes (2 × 2 cm). A man slept under the net as bait. With untreated nets, only 4–6% of mosquitoes died overnight and bloodmeals were taken by 17% of SS vs. 29% of Yaokoffikro R (P < 0.05). Nets treated with permethrin 500 mg/m² caused mortality rates of 95% Kisumu SS and 45% Yao R (P < 0.001) and blood‐feeding rates were reduced to 1.3% of SS vs. 8.1% of Yao R (P < 0.05). Nets treated with deltamethrin 25 mg/m² caused mortality rates of 91% Kisumu SS and 54% Yao R (P < 0.001) and reduced blood‐feeding rates to zero for SS vs. 2.5% for Yao R (P > 0.05). Pyrethroid‐impregnated bednets in experimental huts and ‘tunnel tests’ gave equivalent results, showing that nets impregnated with permethrin or deltamethrin provided good levels of protection against kdr homozygous strains of An. gambiae (Kou and Tola), and against the field population at Yaokoffikro with 94% kdr frequency. The explanation seems to be that (a) high proportions of kdr females are killed by prolonged contact with pyrethroids through diminished sensitivity to the usual irritant and repellent effects, and (b) relatively few kdr females take advantage of this prolonged contact to ingest a bloodmeal.     

Effect of sub-lethal concentrations of permethrin on ovary activation in the predator Supputius cincticeps (Heteroptera: Pentatomidae).

Insecticides may cause mortality and deleterious effects on predatory stinkbugs. For this reason, the effect of five concentrations of permethrin applied on third instar nymphs of Supputius cincticeps (St?l) (Heteroptera: Pentatomidae) was investigated on ovary activation in this predator. The nymphs received topical application of permethrin in the following concentrations (mg a.i./ml): 10(-7), 10(-6), 10(-5), 10(-4), and 10(-3). Ovary lengths and oocyte numbers were quantified following first egg mass. Ovary length of S. cincticeps varied from 5.7 mm with 10(-4) mg a.i./ml, to 6.4 mm with 10(-7) mg a.i./ml, with similar values for the other permethrin concentrations and for the control. The number of oocytes per female varied from 13.5 with 10(-3) mg a.i./ml, to 29.2 for the control, with significant differences. The number of oocytes per female of nymphs exposed to a permethrin concentration of 10(-5) mg a.i./ml was similar to that of the control. However, the lower number of oocytes per female from nymphs exposed to other concentrations of permethrin suggests that this insecticide may affect the reproductive capacity of this predator. The results obtained are discussed in relation to tolerance of Heteroptera predators to insecticides and possible hormesis occurrence.     

Third instar nymphs of Rhodnius prolixus exposed to alpha-cyanopyrethroids: from hyperactivity to death

The hyperactivity, incoordination, recovery, and mortality produced by four alpha-cyanopyrethroids usually used for Chagas disease vector control (beta-cypermethrin, beta-cyfluthrin, lambda-cyhalothrin, and deltamethrin) were evaluated on third instar nymphs of Rhodnius prolixus. All pyrethroids modified the locomotor activity of the nymphs, which increased linearly as a function of the log of insecticide concentration. lambda-Cyhalothrin showed the lowest values of Effective Concentration 50%, Lethal Concentration 50%, Effective Time 50%, and Lethal Time 50% when insecticides were applied by contact with treated filter papers. Recovery from incoordination was observed after topical application of the insecticides. The recovery was inhibited by the simultaneous application of piperonyl butoxide, suggesting that biotransformation by mixed-function microsomal oxidases is involved in the process of recovery.     

Monitoring pyrethroid resistance in field collected Blattella germanica Linn. (Dictyoptera: Blattellidae) in Indonesia

The German cockroach, Blattella germanica , is a major and the most common pest in public areas in Indonesia. Although intensive control measures have been carried out to control the populations of this pest, results have been far from successful, which is believed to be because of its resistance to insecticides. A standard World Health Organization (WHO) glass jar test was carried out to determine the resistance level of this insect to pyrethroid insecticides, the most commonly used insecticides for cockroach control in Indonesia. A susceptible S1 strain collected from Tembagapura Papua was compared with four strains collected from Bandung, West Java: strain S2, from a local restaurant; strain S3, from the Bandung train station; and strains S4 and S5, from two different hotels. All strains showed low resistance to the pyrethroid, except the S5 strain, which had a Resistance Ratio (RR)₅₀ of 95 for permethrin. The addition of piperonyl butoxide (PBO) suggests that the detoxifying enzyme mixed function oxidases (MFO) played an important role in the development of resistance to permethrin in the S5 strain, suggested by the high Synergist Ratio (SR) of 70.4. However, the low level of resistance to cypermethrin was not affected by PBO, suggesting that other mechanisms of pyrethroid resistance are involved. Our study is the first report of German cockroach resistance to permethrin in Indonesia, and the findings can be used in formulating potential strategies for cockroach resistance management.     

Effects of permethrin at different temperatures on pyrethroid-resistant and susceptible strains of Anopheles

The influence of temperature (16, 22, 28, 37 degrees C) on effects of permethrin was investigated for susceptible and pyrethroid-resistant strains of the mosquitoes Anopheles gambiae and An. stephensi (Diptera: Culicidae). Young unfed female adult mosquitoes were exposed to 0.25% permethrin test papers or to polyester netting treated with permethrin 500mg a.i./m2. The time to 50% knockdown (KT50) declined as temperature increased, i.e. there was a positive temperature coefficient of this effect of the pyrethroid. Resistance ratios (comparing KT50 values) between resistant and susceptible An. stephensi ranged between 2.5 and 4.4 at the different temperatures. Comparative tests of pyrethroid tolerance of different strains would be valid over the 22-28 degrees C range but, when using a discriminating dose to detect resistance, more precise temperature control is desirable. Mortality 24h after exposure to 0.25% permethrin of both susceptible and resistant strains of An. stephensi showed a negative correlation with temperature between 16 and 22 degrees C and a positive correlation at higher temperatures. In An. gambiae, however, the correlation was positive over the whole range. Irritancy of permethrin-treated netting to Anopheles females (measured as time lapse until first flight take-off, and the number of take-offs during 7.5 min exposure) was positively correlated with temperature in all four strains and was much greater for the susceptible than the resistant strains.     

Resistance of the German cockroach (Blattella germanica) to bendiocarb

Two field strains of the German cockroach Blattella germanica (L.) were collected in England from survivors of treatments with bendiocarb wettable powder, and bred in the laboratory. These and a laboratory susceptible strain were compared by a tarsal contact method to test for resistance to bendiocarb, fenitrothion and dieldrin. The field strains after exposure to the insecticide for 24 h were resistant to bendiocarb in terms of mortality by factors of 5.6 and 6.2 at the LC₅₀ level, but at the LC₉₅ level the resistance factors were only 1.7 and 2.0; however knockdown resistance was detected, with resistance factors at the KD₅₀ level of 10.6 and 8.1. At shorter exposure times of 5 min and 60 min, 2–20% of cockroaches from the field strains survived 55 or 110 mg bendiocarb/m²; there were no survivors from the susceptible strain. Some cockroaches from the field strains were able to recover from knockdown after and during exposure to 110 mg bendiocarb/m². Both field strains showed some resistance to dieldrin; however, there was no resistance to fenitrothion. When all three strains were exposed to 55 mg fenitrothion/m² for 5 min, all the insects were knocked down within 3 h, and all had died within 96 h. There was no recovery from knockdown to fenitrothion or dieldrin.     

Comparison of two bioassay methods for determining deltamethrin resistance in German cockroaches (Blattodea: Blattellidae)

Susceptibility to deltamethrin of 10 strains of the German cockroach, Blattella germanica (L.), trapped in hotel kitchens in Singapore was determined. Two resistance detection bioassay methods (topical application and World Health Organization glass jar method) were compared. Resistance ratios based on 50% knockdown, obtained by comparison with the S strain, ranged from 17.7 to 4,235 for topical application and from 2.2 to 22 for the glass jar method. A field strain, with consistently low resistance ratios (topical method = 17.7, glass jar method = 2.2), was identified as a potential field strain to be used as a baseline for comparison with other field strains. Resistance ratios for the other field strains obtained by comparison with the R5 strain ranged from 24.5 to 239 for topical application and from 1.2 to 9.8 for the glass jar method. The results of our study demonstrate that deltamethrin-resistant German cockroaches are numerous in Singapore. Comparison between the two bioassay methods showed that there was significant correlation between KD50 and KT50 values. The glass jar method is similar to field situations but topical application is sensitive enough to define the magnitude of resistance. Differences between the two detection bioassays and the factors governing the choice of bioassay in monitoring resistance in German cockroaches are discussed.     

Strain differences in the response of German cockroaches (Dictyoptera: Blattellidae) to emulsifiable concentrates.

The response of a susceptible and two pyrethroid-resistant field strains of the German cockroach, Blattella germanica, to four emulsifiable concentrates (ECs)--Tempo (cyfluthrin), Demon (cypermethrin), Dursban (chlorpyrifos) LO, and XRM 5184 (chlorpyrifos)--was investigated. Application rates were 0.4, 0.1, 0.5, and 0.5%, respectively. Susceptible cockroaches avoided dried formulations of the pyrethroids Tempo and Demon, but resistant cockroaches did not; avoidance was greater with Demon than with Tempo. Filter papers freshly impregnated (wet) with Demon and Tempo flushed susceptible cockroaches (Demon greater than Tempo). Resistant cockroaches were flushed only by Demon, but less so than susceptible strain cockroaches. No mortality occurred in experiments with the pyrethroids. Dried formulations of Dursban LO and XRM 5184 had little, if any, repellency to nymphs of either the susceptible or resistant strains. Initially (1-3 h), most cockroaches settled on treated papers. Subsequent movement off treated papers was a step in the process leading to knockdown. At 24 h, mortality of susceptible cockroaches was 100% in the experiment with Dursban LO and 95% in the experiment with XRM 5184. Highest mortality in a resistant strain (40%) was in the contact experiment with Dursban LO. In contact repellency and flushing experiments, mortality was higher with Dursban LO than with XRM 5184. Neither chlorpyrifos formulation flushed cockroaches effectively. Mortality in flushing experiments was less than in the contact repellency experiments.     

Excito-Repellent Responses between <Emphasis Type="Italic">Culex quinquefasciatus</Emphasis> Permethrin Susceptible and Resistant Mosquitoes

The behavioral responses exhibited between four permethrin-resistant field-derived populations and a long-established, permethrin susceptible colony population of Culex quinquefasciatus mosquitoes was assessed for behavioral responses to permethrin in an excito-repellency (ER) test system. After a 30-min exposure to two different insecticide concentrations (200 and 500 mg/m²) in paired contact and noncontact test designs, the initial knockdown and escape (exit) responses were recorded followed by mortality after 24-h. All five test populations rapidly escaped from the chambers treated with permethrin regardless of background insecticide susceptibility status or chemical concentration. The greatest contact escape response was seen from the colonized population with 88 % of specimens escaping the chamber within 30-min. Contact irritancy was the predominant response compared to relatively weak noncontact spatial repellency in all test populations at both low and high concentrations. At the lower concentration, the contact escape responses did not appear influenced by background susceptibility status, whereas at the higher concentration the permethrin-resistant field populations exhibited significantly reduced avoidance behavior compared to the laboratory susceptible strain.     

Resistance status of house flies (Diptera: Muscidae) from southeastern Nebraska beef cattle feedlots to selected insecticides

The status of resistance to three insecticides (permethrin, stirofos, and methoxychlor), relative to a laboratory-susceptible colony, was evaluated in field populations of house flies, Musca domestica L., collected from two beef cattle feedlots in southeastern Nebraska. Topical application and residual exposure to treated glass surfaces were suitable methods for determining the resistance status of house flies to permethrin, stirofos, or methoxychlor. However, in most cases, residual exposure was more sensitive in resistance detection (i.e., higher resistance ratios). The field populations tested were moderately resistant to permethrin (RR = 4.9-fold and RR = 7.3-fold, for topical application and residual exposure, respectively) and extremely resistant to stirofos and methoxychlor (not accurately quantifiable because of low mortality at the highest possible concentrations or doses). Probable explanations for the resistance status of these house fly populations and implications for global feedlot fly management are discussed.     

神经递质释放与家蝇对拟除虫菊酯抗性关系研究

通过生物测定比较溴氰菊酯、氯菊酯和DDT对Dec-R,2C1-R,DDT-R和敏感(SP)家蝇Musca domestica vicina的毒力,表明三个抗性品系对溴氰菊酯、氯菊酯和DDT均有很高的抗性,抗性倍数分别达120 912,6 032和112.2倍,并对上述三种杀虫剂有明显的交互抗性和抗击倒效应。杂交试验表明Dec-R对溴氰菊酯的抗性是一个隐性基因,电生理试验表明抗性家蝇中枢神经系统(CNS)对药剂敏感度的降低是其产生抗性和交互抗性的重要机制。研究结果表明Dec-R和2CLR家蝇品系中存在有击倒抗性因子(Kdr)。当用1×10^-7mol/L溴氰菊酯对SP家蝇脑突触体在提高K+浓度去极化后,可加强3H-胆碱的释放,而在Dec-R品系中,溴氰菊酯浓度提高到1×10^-4m0l/L也未能加强³H-胆碱的释放,表明溴氰菊酯与神经递质的释放和钠通道亲和性的降低是抗性的主要机制。     

Synergism between permethrin and propoxur against Culex quinquefasciatus mosquito larvae

To see if synergism occurs between carbamate and pyrethroid insecticides, we tested permethrin and propoxur as representatives of these two classes of compounds used for mosquito control. Larvicidal activity of both insecticides was assessed separately and together on a susceptible strain of the mosquito Culex quinquefasciatus (Diptera: Culicidae) by two methods. When mixed at a constant ratio (permethrin : propoxur 1 : 60 based on LC50) and tested at serial concentrations to plot dose/mortality regression, significant synergy occurred between them (co-toxicity coefficient = 2.2), not just an additive effect. For example, when the mixture gave 50% mortality, the same concentrations of permethrin and propoxur alone would have given merely 2 x 1% mortality. When a sublethal dose (LC0) of permethrin or propoxur was added to the other (range LC10-LC95), synergism occurred up to the LC80 level. Synergistic effects were attributed to the complementary modes of action by these two insecticide classes acting on different components of nerve impulse transmission. Apart from raising new possibilities for Culex control, it seems appropriate to consider using such mixtures or combinations for insecticide-treated mosquito nets in situations with insecticide-resistant Anopheles malaria vectors.     

Dosage differential effects of permethrin impregnated into bednets on pyrethroid resistant and susceptible genotypes of the mosquito Anopheles stephensi

Abstract Effects of bednets impregnated with permethrin 200 mg and 500mg/m² on pyrethroid resistant and susceptible strains of Anopheles stephensi and their F hybrid progeny were studied, using free-flying female mosquitoes of these three genotypes, in a room with a human subject under a polyester net, having one of his arms in contact with the treated netting. Unexpectedly an apparently higher feeding rate, but lower knockdown and mortality rates, of mosquitoes were obtained for each of the three genotypes with the higher concentration of 500mg/m² compared with the lower dose of 200mg/m². At the lower dose there was 100% mortality 24 h after exposure of all three genotypes, suggesting that there would not be selection for resistance at this dose. However, at the higher dose there was significantly higher mortality of the susceptible strain than of the F hybrids, suggesting incomplete recessiveness of this resistance and that there would therefore be effective selection for resistance by this dose.
When female mosquitoes were confined in bioassay cones on treated netting, the resistant strain of An.stephensi showed significantly less irritability (scored as the time until first flight take-off) in response to each dose, as compared with the susceptible strain and F, hybrids. The higher dose provoked more irritation of each genotype; this could explain the greater knockdown and mortality rates of mosquitoes exposed to the lower dose which was less irritating and hence more effectively insecticidal. Thus a dose of 200mg/m² is preferable to 500mg/m² for malaria vector control.     

Monitoring of Insecticide Resistance in Field-Collected Populations of Culex pipiens pallens (Diptera: Culicidae)

A susceptible strain and six field populations of the northern house mosquito, Culex pipiens pallens Coquillett, were collected in Seoul, Paju, Daejeon, Heongseong, Jinhae, and Buan, and tested for their susceptibility to seven insecticides by topical application. In tests with female Cx. pipiens pallens, marked regional variations of insecticide susceptibility were observed. Five field-collected populations of Cx. pipiens pallens, except for the Seoul colony, exhibitedhightoveryhighlevelsofresistanceto cyfluthrin [resistance ratio (RR), 96–554] and deltamethrin (RR, 192–959). Low to moderate levels of resistance were observed in bendiocarb (RR, 14–46), chlorpyrifos [RR, 7–38; exceptions: Buan (RR, 63) and Jinhae (RR, 80) colonies], λ-cyhalothrin (RR, 5–23), S-bioallethrin (RR, 1–47), and permethrin [RR, 2–27; exception: Jinhae colony (RR, 247)]. These results indicate that careful selection and rotational use of these insecticides should result in continued satisfactory control against field populations of Cx. pipiens pallens.     

Insecticide Susceptibility of Field‐collected Blattella germanica (Blattaria: Blattalidae) in Busan,Republic of Korea during 2014

The susceptibility values for field‐collected (BG‐BG) and laboratory (KS‐BG) strains of German cockroaches (BS‐BG), Blattella germanica (L.) to five synthetic pyrethroid and three organophosphate insecticides were assessed by topical application. Both KS‐BG and BS‐BG strains demonstrated the highest levels of susceptibility to deltamethrin with LD₅₀ values of 0.0035 μg/female and 1.5744 μg/female, respectively. The KS‐BG strain demonstrated the lowest susceptibility level to fenthion with an LD₅₀ value of 0.0698 μg/female, while the BS‐BG field population showed the lowest susceptibility to bifenthrin with 4.6811 μg/female. The BS‐BG field population showed resistance levels of 50 to 640 fold higher against the eight pesticides evaluated compared to the KS‐BG strain. The resistance ratios (RR) of the eight pesticides were compared using populations of B. germanica that were collected from the same locality during 2007 and 2014. The field population of B. germanica collected during 2014 demonstrated significantly high resistance to an organophosphates and all pyrethroids when compared with those collected during 2007, but RR values were <10 except for chlorpyrifos‐methyl and chlorpyrifos with RR values of 74 and 104, respectively.     

Release of piperonyl butoxide and permethrin from synergized ear tags on cattle and effects on horn fly mortality

A study was conducted to determine the release rates of piperonyl butoxide (PBO) and permethrin from synergized insecticidal cattle ear tags and their effects on mortality of the horn fly, Hematobia irritans irritans (L.) (Diptera: Muscidae). PBO was released from the ear tags at a higher rate than permethrin in both winter and summer trials. The cumulative release of PBO and permethrin from the ear tags at the end of 18 wk in the winter trial was 50.4 and 30.3%, respectively. The cumulative release of PBO and permethrin from the ear tags at the end of 18 wk in the summer trial was 66.7 and 44.7%, respectively. There was a significant correlation between the cumulative daily high ambient temperature (degrees C) and the cumulative release of both PBO and permethrin. Compared with the susceptible horn fly strain, the permethrin-resistant strain demonstrated 7.9- and 12.8-fold resistance to permethrin at the levels of LC50 and LC90, respectively. When exposed to filter paper wipes taken from the shoulders of cattle treated with the PBO-synergized permethrin tags from the summer trial, the resistant strain demonstrated reduced mortality compared with the susceptible strain. The mortality of the resistant strain at 2- and 3-h exposure exhibited a pattern of declining fly mortalities as a result of the decreased release of PBO and permethrin, as well as the decline in the ratio of PBO:permethrin released from the tags after 8 wk. A similar decline in horn fly mortalities was observed in the susceptible strain at 30-min exposure time that coincided with the pattern of reduced release of PBO and permethrin from the ear tags over the course of summer trial.     

拟除虫菊酯抗性家蝇的交互抗药性研究

拟除虫菊酯的广泛使用使家蝇普遍产生了抗药性,为有效的控制家蝇的危害,需要了解家蝇对轮换或新杀虫剂的交互抗性状况。作者用点滴法测定了两个实验室汰选的拟除虫菊酯抗性家蝇品系对几种杀虫剂的交互抗性,结果表明:二氯苯醚菊酯和溴氰菊酯之间存在较高程度的交互抗药性;拟除虫菊酯抗性较高的家蝇对作用机制不同的新农药(多杀菌素、氟虫腈)表现较低程度的交互抗性。     

Essential oils enhance the toxicity of permethrin against Aedes aegypti and Anopheles gambiae

Insecticide resistance and growing public concern over the safety and environmental impacts of some conventional insecticides have resulted in the need to discover alternative control tools. Naturally occurring botanically‐based compounds are of increased interest to aid in the management of mosquitoes. Susceptible strains of Aedes aegypti (Linnaeus) (Diptera: Culicidae) and Anopheles gambiae (Meigen) (Diptera: Culicidae) were treated with permethrin, a common type‐I synthetic pyrethroid, using a discriminate dose that resulted in less than 50% mortality. Piperonyl butoxide (PBO) and 35 essential oils were co‐delivered with permethrin at two doses (2 and 10 µg) to determine if they could enhance the 1‐h knockdown and the 24‐h mortality of permethrin. Several of the tested essential oils enhanced the efficacy of permethrin equally and more effectively than piperonyl butoxide PBO, which is the commercial standard to synergize chemical insecticide like pyrethroids. PBO had a strikingly negative effect on the 1‐h knockdown of permethrin against Ae. aegypti, which was not observed in An. gambiae. Botanical essential oils have the capability of increasing the efficacy of permethrin allowing for a natural alternative to classic chemical synergists, like PBO.