Novel Kdr mutations (K964R and A943V) in pyrethroid‐resistant populations of Triatoma mazzottii and Triatoma longipennis from Mexico and detoxifying enzymes

Although having five different ways of transmission the vector-borne is the principal way of transmission of Chagas disease, which involves insects of the subfamily Triatominae (Hemiptera: Reduviidae). Nineteen of the 31 species that occur in Mexico are associated with humans, and all are capable of transmitting the disease. Pyrethroids are the insecticides recommended for the control of these vectors in Mexico. We determined the susceptibility to the pyrethroids dcltamethrin and permethrin of peridomestic populations of Triatoma mazzottii Usinger and two populations of Triatoma longipetmis Usinger in comparison with a reference strain for each species. Bioassays were performed for the determination of the LD50 for both field populations and reference strains. A maximum of 27 fold resistance to deltamethrin was observed in T. mazzottii, meanwhile, for permethrin, T. longipennis from Jalisco show the highest value of 3.19 fold. There was significantly increased activity of esterases in field populations in comparison with their corresponding reference strain. The results of the search of kdr mutations related to the resistance to deltamethrin and permethrin in the evaluated species show the presence of mutations in the field populations, as is the case with individuals of T. mazzottii, for which the mutation was found A943V, and for the two populations of T. longipennis included in this study, we report the presence of the kdr mutation K964R. Evaluation of the various mechanisms involved in resistance to pyrethroids in triatomines from Mexico could guide us to the real justification for insecticide resistance monitoring.     

Naturally occurring Trichogramma species in olive farms in Egypt

A survey of two-year studies (2001-2003) was carried out in two olive groves sited at two representative olive growing areas, namely Paradise Park (arid area) and Burg E1-Arab farm (semi-arid area) to monitor the frequency of endemic Trichogramma species on olive moth (Prays oleae) and jasmine moth (Palpita unionalis). The suspended host bait traps were found to be a more practical and effective tool for collecting Trichogramma wasps than the attached ones. Four naturally occurring Trichogramma species were collected for the first time in Egypt from the olive groves, where releases have never been conducted. T.bourarachae was collected exclusively from Burg El-Arab farm. It seems that this wasp species adapts well to the semi-arid area. Three species, namely T. cordubensis, T. nr.pretiosum and T. cacociae were isolated from Paradise Park farm. All of these wasps were also bred from naturally parasitized host eggs during favorable and even at unfavorable temperature conditions of June-August. However, these endemic species did not occur naturally in sufficient numbers to keep the pest populations from reaching damaging levels.The excessive usage of insecticides and the oophagous predators (e.g., ants and lacewing larvae) are some factors that affect the performance of Trichogramma wasps in olive farms.The presence of warm weather wasp strains suggests the existence of well-adapted wasp species or swains which may be appropriate candidates for the control of target pests in olive groves. Additional study is required to determine the best “habitat-specific” species/strains of Trichogramma for augmentative release of naturally occurring wasps and to incorporate them into integrated pest management programs. Efforts should be made to conserve these endemic species from oophagous predators, hot weather and insecticides.The olive and jasmine moth-larvae and pupae found under tree canopies were bred and emerged parasitoids were listed.     

Sodium channel gene expression in mosquitoes, Aeries albopictus （S.）

A mosquito strain of Aedes albopictus, HAmAal^G0, from Huntsville, Alabama, USA, showed a normal susceptibility and low tolerance to permethrin and resmethrin （pyrethroid insecticides） compared to a susceptible Ikaken strain, even though these pyrethroid insecticides have been used in the field for a long period of time in Alabama. Recently, we treated HAmAal^G0 in the laboratory with permethrin for five generations and detected no significant change in the level of resistance to permethrin in the selected mosquitoes, HAmAal^G0, compared with the parental strain HAmAal^G0. We then examined the allelic expression at the L-to-F kdr site of the sodium channel gene in the Aedes mosquitoes to address our hypothesis that the L-to-F kdr mutation was not present in HAmAal^G0 and HAmAal^G5 mosquitoes. We found that every tested individual in Ikaken, HAmAal^G5, and HAmAal^G5 populations expressed a codon of CTA at the L-to-F kdr site encoding Leu, strongly corresponding to their susceptibility to insecticides.     

Nucleopolyhedrovirus Introduction in Australia

Nucleopolyhedrovirus (NPV) has become an integral part of integrated pest management (IPM) in many Australian agricultural and horticultural crops. This is the culmination of years of work conducted by researchers at the Queensland Department of Primary Industries and Fisheries (QDPI&F) and Ag Biotech Australia Pty Ltd. In the early 1970’s researchers at QDPI&F identified and isolated a virus in Helicoverpa armigera populations in the field. This NPV was extensively studied and shown to be highly specific to Helicoverpa and Heliothis species. Further work showed that when used appropriately the virus could be used effectively to manage these insects in crops such as sorghum, cotton, chickpea and sweet corn. A similar virus was first commercially produced in the USA in the 1970’s. This product, Elcar?, was introduced into Australia in the late 1970’s by Shell Chemicals with limited success. A major factor contributing to the poor adoption of Elcar was the concurrent enormous success of the synthetic pyrethroids. The importance of integrated pest management was probably also not widely accepted at that time. Gradual development of insect resistance to synthetic pyrethroids and other synthetic insecticides in Australia and the increased awareness of the importance of IPM meant that researchers once again turned their attentions to environmentally friendly pest management tools such NPV and beneficial insects. In the 1990’s a company called Rhone-Poulenc registered an NPV for use in Australian sorghum, chickpea and cotton. This product, Gemstar?, was imported from the USA. In 2000 Ag Biotech Australia established an in-vivo production facility in Australia to produce commercial volumes of a product similar to the imported product. This product was branded, ViVUS?, and was first registered and sold commercially in Australia in 2003. The initial production of ViVUS used a virus identical to the American product but replicating it in an Australian Helicoverpa species, H. armigera. Subsequent research collaboration between QDPI&F and Ag Biotech reinvigorated interest in the local virus strain. This was purified and the production system adapted to produce it on a commercial scale. This new version of ViVUS, which was branded ViVUS Gold?, was first registered and sold commercially in 2004. Widespread insect resistance to insecticides and a greater understanding of integrated pest management is leading to increased adoption of technologies such NPV in Australian agriculture.     

Current susceptibilities of brown planthopper Nilaparvata lugens to triflumezopyrim and other frequently used insecticides in China

The brown planthopper is a notorious rice pest in many areas of Asia.The evolution of insecticide resistance in Nilaparvata lugens has become a serious problem in the effective control of this pest in the paddy field.In this article,the current susceptibility of N.lugens field populations to novel mesoionic insecticide triflumezopyrim and major classes of chemical insecticides was determined and compared.The monitoring results indicated that field populations of N.lugens had developed low resistance to triflumezopyrim(resistance ratio,RR:1.3-7.3-fold)during 2015-2018 in China,and the median lethal concentration values varied from 0.05 to 0.29 mg/L.Additionally,during 2017 to 2018,field populations of N.lugens showed high resistance levels to thiamethoxam(RR:456.1-1025.6-fold),imidacloprid(RR:2195.3-6899.0-fold)and buprofezin(RR:1241.57521.7-fold),moderate to high resistance levels to dinotefuran(RR:97.6-320.1-fold),clothianidin(RR:69.4-230.1-fold)and isoprocarb(RR:44.1-108.0-fold),and low to moderate levels of resistance to chlorpyrifos(RR:12.0-29.7-fold)and nitenpyram(RR:6.9-24.1-fold).In contrast,N.lugens just showed low resistance to sulfoxaflor(RR:3.3-8.5-fold)and etofenprox(RR:5.0-9.1-fold)in the field.Additionally,the P450 gene CYP6ER1 was found to be significantly overexpressed in all five field populations of N.lugens collected in 2018 when compared with a laboratory susceptible strain.Our findings will provide useful information to delay the evolution of insecticide resistance in N.lugens.     

Sublethal effects of imidacloprid and pymetrozine on population growth parameters of cabbage aphid, Brevicoryne brassicae on rapeseed, Brassica napus L.

Efficiency of imidacloprid and pymetrozine on population growth parameters of cabbage aphid, Brevicoryne brassicae L. （Homoptera： Aphididae） was determined using demographic toxicology by leaf dip method. At first, bioassay tests were performed. The LC50 value and confidence limit for imidacloprid and pymetrozine were 1.61 × 10^-5 mol/L （0.74 × 10^-5-2.66 × 10^-5） and 2.14 × 10^-4 mol/L （1.24 × 10^-4-3.40 × 10^-4）, respectively. To evaluate the sublethal effect of two insecticides on population growth parameters of cabbage aphid, LC30 concentrations of imidacloprid and pymetrozine were used at 5 mol/L and 30 mol/L. The experiments were carried out in a incubator at 20±1℃, 60% ± 5% RH and 16：8 （L：D） photoperiod on canola seedlings, Brassica napus L. var. ＇PF＇. Net fecundity rate decreased in both insecticide-treated populations. Intrinsic rates of increase （rm） were lower in imidacloprid and pymetrozine treatments than in controls. Intrinsic birth rates also decreased in treated populations. There was a relative increase in intrinsic death rates of treated populations. The mean generation times and doubling time were also lower in populations treated with insecticides than in controls. There was a considerable reduction in the average numbers of nymphs reproduced per female as compared with the control. The average longevity of female adults in the control was significantly different from those treated with imidacloprid and pymetrozine. However, there was no significant differences in aphid life-table parameters between the two insecticide-treated populations （P 〉 0.01）.     

Impact of insect-resistant transgenic rice on target insect pests and non-target arthropods in China

Progress on the research and development of insect-resistant transgenic rice, especially expressing insecticidal proteins from Bacillus thuringiensis （Bt）, in China has been rapid in recent years. A number of insect-resistant transgenic rice lines/varieties have passed restricted and enlarged field testing, and several have been approved for productive testing since 2002 in China, although none was approved for commercial use until 2006. Extensive laboratory and field trials have been conducted for evaluation of the efficiency of transgenic rice on target lepidoteran pests and potential ecological risks on non-target arthropods. The efficacy of a number of transgenic rice lines currently tested in China was excellent for control of the major target insect pests, the rice stem borers （Chilo suppressalis, Scirpophaga incertulas, Sesamia inferens） and leaffolder （ Cnaphalocrocis medinalis）, and was better than most insecticides extensively used by millions of farmers at present in China. No significantly negative or unintended effects of transgenic rice on non-target arthropods were found compared with non-transgenic rice. In contrast, most of the current insecticides used for the control of rice stem borers and leaffolders proved harmful to natural enemies, and some insecticides may directly induce resurgence of rice planthoppers. Studies for developing a proactive insect resistance management of transgenic rice in the future are discussed to ensure the sustainable use of transgenic rice.     

The evolutionary ecology of symbiont-conferred resistance to parasitoids in aphids

Abstract Aphids may harbor a wide variety of facultative bacterial endosymbionts. These symbionts are transmitted maternally with high fidelity and they show horizontal trans-mission as well, albeit at rates too low to enable infectious spread. Such symbionts need to provide a net fitness benefit to their hosts to persist and spread. Several symbionts haveachieved this by evolving the ability to protect their hosts against parasitoids. Reviewing empirical work and some models, I explore the evolutionary ecology of symbiont-conferredresistance to parasitoids in order to understand how defensive symbiont frequencies are maintained at the intermediate levels observed in aphid populations. I further show thatdefensive symbionts alter the reciprocal selection between aphids and parasitoids by augmenting the heritable variation for resistance, by increasing the genetic specificity of thehost-parasitoid interaction, and by inducing environment-dependent trade-offs. These effects are conducive to very dynamic, symbiont-mediated coevolution that is driven by frequency-dependent selection. Finally I argue that defensive symbionts represent a problem for biological control of pest aphids, and I propose to mitigate this problem byexploiting the parasitoids＇ demonstrated ability to rapidly evolve counteradaptations to symbiont-conferred resistance.     

Development and Characterization of 15 Polymorphic Micro satellite Markers for a Highly Adaptive and Wide-range Frog （Microhyla fissipes）

In order to analyze population genetic structure at multiple spatial scales, microsatellite loci were developed for the ornamented pygmy flog （Microhylafissipes）, and 15 polymorphic microsatellite loci were successfully screened from 105 individuals, of which 82 from four populations distributed in the Sichuan Basin and 23 from the Sangzhi population in western Hunan. Five loci were found to deviate significantly from Hardy-Weinberg equilibrium in one to three popu lations, probably due to small sample size or null alleles. The average number of alleles in all loci was 8.5, ranging from 4 to 13, and the observed and expected heterozygosity ranged from 0.26 to 0.90 and 0.63 to 0.90, respectively. The Sangzhi population and the remaining four populations can be clearly separated using Bayesian clustering methods, showing that the genetic structure of M. fissipes was probably affected by the topography, especially mountain barriers. These polymorphic microsatellite loci could be used for further study on the landscape genetics of this highly adaptive and widely distributed species.     

Detection and monitoring of insect resistance to transgenic Bt crops

Transgenic crops expressing Bacillus thuringiensis （Bt） endotoxins havebecome one of the most important tools for managing corn and cotton insect pests in the US and other countries. The widespread adoption of transgenic Bt crops could place a high degree of selection pressure on the target insect populations and accelerate development of resistance, raising concerns about the long-term durability of Bt plants as an effective pest management tool. Conservation of Bt susceptibility in insects has become one of the most active research areas in modern agriculture. One of the key factors for a successful Bt resistance management plan is to have a cost-effective monitoring system that can provide information on. （i） the initial Bt resistance allele frequencies at low levels in field insect populations; and （ii） early shifts in Bt resistance allele frequencies so that proactive measures for managing resistance can be deployed well before field control failures. Developing such a monitoring program has been difficult because： （i） resistance traits that occur at very low frequencies are hard to detect; （ii） many factors affect the sensitivity and accuracy of a Bt resistance monitoring program; and （iii） monitoring resistance is costly. Several novel methods for detecting Bt resistance alleles developed during the last decade have made a cost-effective monitoring system possible. Future studies should focus on how to improve and standardize the methodologies for insect sampling and Bt resistance detection.     

菜蚜茧蜂对六种杀虫剂抗药性的季节性变化

采用药膜法研究了福州建新和闽侯上街菜蚜茧蜂Diaeretiella rapae对杀虫剂抗药性的季节性变化。田间菜蚜茧蜂种群在网室内脱离选择压力后对杀虫剂敏感性显著升高。与敏感的F₂₁子代的LC₅₀相比,2002年6月8日至2004年11月18日期间,建新菜区菜蚜茧蜂对甲胺磷、氟虫腈、阿维菌素、氰戊菊酯和吡虫啉的抗性倍数分别为11.8～31.2,9.3～14.7,9.3～35.7,7.0～16.6,和13.3～30.1倍;2003年6月5日至2004年12月17日期间,上街菜区菜蚜茧蜂对甲胺磷、氟虫腈、阿维菌素、氰戊菊酯和吡虫啉的抗性倍数分别为7.5～34.9,4.0～14.3,9.2～38.6,7.8～18.9和12.1～24.2倍。田间菜蚜茧蜂种群在5月份和6月初抗性水平最高,12月份较低,6月末最低,尤其在6月份期间20天内抗性水平急剧下降。研究结果表明,田间菜蚜茧蜂对6种杀虫剂的抗性水平在脱离选择压力后不稳定,且呈显著的季节性变化。表2参25     

Effects of synergists on toxicity of six insecticides in parasitoid Diaeretiella rapae (Hymenoptera: Aphidiidae)

The resistance to and the effects of synergists on the toxicity of six insecticides in Diaeretiella rapae (M'Intosh) (Hymenoptera: Aphidiidae), a parasitoid of vegetable aphid collected in Jianxin at Fuzhou-City, Fujian, China, were studied. In comparison with susceptible F21 progeny, the resistance ratios in resistant F0 parents were 27.6 for methamidophos, 20.8 for fipronil, 47.5 for avermectin, 3.3 for fenvalerate, 4.5 for cypermethrin, and 74.7 for imidacloprid. Piperonyl butoxide (PB), triphenyl phosphate (TPP), and diethyl maleate (DEM) were chosen to be applied in susceptible F21 progeny, as well as in resistant F11 progeny and F0 parents. Significant synergistic effects on the toxicity of the six insecticides were found by using PB, TPP, and DEM in F0 parents; on methamidophos, avermectin, and imidacloprid by PB, TPP, and DEM in F11 progeny; on fipronil by PB and DEM in F11 progeny; and on fenvalerate and cypermethrin by PB in F11 progeny. PB also showed significant synergism on the six insecticides in susceptible F21 progeny, although the synergism was far less in F21 progeny than those in resistant F0 parents. TPP and DEM showed little or no synergistic effects on the toxicity of the six insecticides in F21 progeny. Compared with TPP and DEM, the highest synergistic ratios of PB for methamidophos, fipronil, avermectin, fenvalerate, cypermethrin, and imidacloprid were observed in F0 parents, and F11 and F21 progeny. The resistance levels to methamidophos, fipronil, avermectin, fenvalerate, and cypermethrin could be inhibited strongly by applying PB in F0 parents. From the results, oxidative degradation is believed to play a critical role in resistance to methamidophos, fipronil, avermectin, fenvalerate, and cypermethrin in D. rapae. To a lesser extent, hydrolytic reactions also were partially involved in the resistance to these five insecticides by using the synergists PB, TPP, and DEM. However, although high synergism of PB, TPP, and DEM on imidacloprid was found, the resistance levels to imidacloprid remained high in the presence of PB, TPP, and DEM. The mediated detoxification of oxidative degradation and hydrolytic reactions was thought to be involved in the resistance to imidacloprid in F0 parents.     

First report of amitraz and cypermethrin resistance in Rhipicephalus sanguineus sensu lato infesting dogs in Mexico

Engorged female Rhipicephalus sanguineus sensu lato (Ixodida: Ixodidae) were collected from dogs in the state of Yucatán, Mexico. Fourteen tick populations were collected from dogs at seven veterinary clinics, four residential homes and three cattle farms. The larval immersion test was used in the progeny of collected adult females to test susceptibility to amitraz and cypermethrin. Dose–mortality regressions, 50% lethal concentrations (LC₅₀), confidence intervals and slope were estimated by probit analysis. For amitraz, 12 tick populations (85.7%) were classified as resistant and low inter‐population variation in the phenotypic level of resistance was evident [resistance ratios (RRs) at LC₅₀: 1.0–13.0]. For cypermethrin, 12 tick populations (85.7%) were classified as resistant and substantial inter‐population variation in the phenotypic level of resistance was evident (RRs at LC₅₀: 1.0–104.0). Thus, amitraz resistance in R. sanguineus s.l. is common, but generally occurs at low levels; however, alarmingly high levels of cypermethrin resistance are present in R. sanguineus s.l. populations in dogs in Yucatán, Mexico. The intensive use of both acaricides to control ectoparasites on dogs is likely to lead to more serious resistance problems that may cause high levels of control failure in the future.     

Insecticide Susceptibilities of Anopheles sinensis (Diptera: Culicidae) Larvae from Paju-shi, Korea

A study was conducted to determine the susceptibility of Anopheles sinensis larvae, malaria vector, from Paju‐shi (Gyonggi‐do) to 24 pesticides including 11 pyrethroids, 11 organophosphates, 1 pyrazole analogue and another pesticide. The mosquito larvae showed the most highly susceptible to chlorfenapyr with LC₅₀ of 0.0063 ppm followed by spinosad, temephos, fenthion and beta‐cyfluthrin with 0.03, 0.0366, 0.0367 and 0.0998 ppm, respectively, and fluvalinate (>128 ppm) was the least susceptible. Also, 11 pesticides of them were compared with Goyang strain (Gyonggi‐do) of data 1992. The development of resistance was noticed to cypermethrin and permethrin as much of 73.59 and 6.23 folds at LC₅₀, respectively, and also fluvalinate was showed high resistance development. In generally, the pyrethroid insecticides were showed higher development of resistance than organophosphorus insecticides.     

Effect of insecticides on the emergence ofTrichogramma Brasiliensis [Hymenoptera: Trichogrammatidae] from parasitized host eggs

The effect of 9 insecticides recommended for the control of cotton bollworms was studied, under laboratory conditions, on the emergence ofTrichogramma brasiliensis Ashmead from the parasitized eggs ofCorcyra cephalonica (Stainton) of different age groups. The insecticide concentrations tested were equivalent to those recommended for field application viz. phenthoate 0.14%, phosalone 0.15%, endosulfan 0.25%, permethrin 0.014%, monocrotophos 0.13%, fenvalerate 0.014%, cypermethrin 0.014%, fenitrothion 0.30% and quinalphos 0.14%, quinalphos and fenitrothion caused complete inhibition of emergence of the parasitoid from parasitized host eggs of all ages (1 to 7 days); but in general, adverse effect of insecticides on the disruption of emergence decreased with the advancement in the age of the parasitized eggs. For 1 day old parasitized host eggs, emergence ofT. brasiliensis adults varied from 33 to 57% for the remaining 7 treatments. For the 7 days old parasitized host eggs, emergence of parasitoids from the treatments with endosulfan, phosalone and phenthoate was similar to that from control. However, 46 to 59% inhibition of emergence was observed for permethrin, monocrotophos and cypermethrin. Fenvalerate treatment also significantly inhibited the emergence but at a comparatively lower level (40%). Out of 9 insecticides tested, phosalone and fenvalerate were considered to be relatively safe toT. brasiliensis.      

Organophosphate and pyrethroid resistances in the tomato leaf miner Tuta absoluta (Lepidoptera: Gelechiidae) from Iran

The tomato leafminer, Tuta absoluta (Meyrich) (Lepidoptera: Gelechiidae), is a serious pest of tomato crops worldwide. The intensive use of chemical pesticides to control it has led to the selection of resistant populations. This study investigated the resistance of T. absoluta populations to pyrethroid and the organophosphate insecticides from ten regions of Iran. The resistance ratios at LC₅₀ for chlorpyrifos and diazinon varied among populations from 4.3 to 12 and from 1.4 to 9.0, respectively. The resistance ratios of the pyrethroids cypermethrin, deltamethrin and permethrin varied from 1.3 to 3.7, 2.7 to 13 and 1.2 to 4.3, respectively. Inclusion of synergists in toxicological bioassays and the variation observed in the activity of esterases, glutathione S‐transferase and cytochrome P450‐dependent monooxygenase suggest the existence of metabolically based resistance. Esterase and P450 biochemical assays were positively correlated with deltamethrin, and cypermethrin tolerance and diazinon tolerance correlated with esterase activity. The genes encoding the organophosphate and pyrethroid target sites acetylcholinesterase (ace1) and sodium channel (kdr) were partly sequenced. The genotyping revealed mutations in high frequencies in all populations leading to an A201S substitution in ace1 and three substitutions in the sodium channel gene L1014F, M918T, T929I. In summary, our results indicate the presence of organophosphate and pyrethroid resistance in Iranian T. absoluta populations with involvement of both detoxification enzymes and target site alterations. Most likely the populations of T. absoluta imported to Iran were resistant upon arrival.     

Reduced insecticide susceptibility among populations of Scirtothrips dorsalis Hood (Thysanoptera: Thripidae) in strawberry production

Chilli thrips, Scirtothrips dorsalis Hood (Thysanoptera: Thripidae) is a major, economically important, and recent invasive pest of strawberries and other horticultural crops in United States. Several conventional insecticides are used for S. dorsalis management, and resistance development threatens loss of few available tools. Hence, our objectives were to: (1) determine the susceptibility of S. dorsalis to commonly used conventional insecticides: spinetoram, acetamiprid, cyantraniliprole and bifenthrin, and (2) establish LC₅₀ and LC₉₀ dosages for spinetoram against S. dorsalis. Sampling of S. dorsalis populations was conducted twice in seven strawberry fields in Florida during the strawberry field season between 2019 and 2020. Leaf-disc bioassays were performed with field collected populations along with a susceptible 2-year-old laboratory culture of S. dorsalis. Overall, at highest recommended rate the percent mortality of late season S. dorsalis populations from five out of seven collection sites was lower (~41%) than average mortality observed with early season populations (~72%). Populations from at least four out of seven sampling sites exhibited significantly lower mortality than the laboratory susceptible culture in late season. The LC₅₀ and LC₉₀ values for spinetoram for the susceptible laboratory population were 0.026 and 8.64 ppm, respectively. On the other hand, LC₅₀ values of field collected populations to spinetoram varied with resistance ratios ranging from 6 to 269 fold as compared against the laboratory strain. Our results suggest that susceptibility of S. dorsalis to commonly used insecticides in strawberries varies significantly between early and late season populations within the same crop season. The efficacy of bifenthrin against S. dorsalis was particularly low (~ reduced to half in late season), especially among field collected populations. Our results indicate an urgent need to incorporate other pest management strategies, as well as effective rotation programs to reduce selection for resistance among populations of S. dorsalis in strawberry production.     

Insecticide Mixtures Could Enhance the Toxicity of Insecticides in a Resistant Dairy Population of Musca domestica L

House flies, Musca domestica L., are important pests of dairy operations worldwide, with the ability to adapt wide range of environmental conditions. There are a number of insecticides used for their management, but development of resistance is a serious problem. Insecticide mixtures could enhance the toxicity of insecticides in resistant insect pests, thus resulting as a potential resistance management tool. The toxicity of bifenthrin, cypermethrin, deltamethrin, chlorpyrifos, profenofos, emamectin benzoate and fipronil were assessed separately, and in mixtures against house flies. A field-collected population was significantly resistant to all the insecticides under investigation when compared with a laboratory susceptible strain. Most of the insecticide mixtures like one pyrethroid with other compounds evaluated under two conditions (1∶1-“A” and LC₅₀: LC₅₀-“B”) significantly increased the toxicity of pyrethroids in the field population. Under both conditions, the combination indices of pyrethroids with other compounds, in most of the cases, were significantly below 1, suggesting synergism. The enzyme inhibitors, PBO and DEF, when used in combination with insecticides against the resistant population, toxicities of bifenthrin, cypermethrin, deltamethrin and emamectin were significantly increased, suggesting esterase and monooxygenase based resistance mechanism. The toxicities of bifenthrin, cypermethrin and deltamethrin in the resistant population of house flies could be enhanced by the combination with chlorpyrifos, profenofos, emamectin and fipronil. The findings of the present study might have practical significance for resistance management in house flies.     

Are Helicoverpa armigera and Tetranychus spp. populations still susceptible to pesticides? A Zimbabwean study

The African bollworm, Helicoverpa armigera (Hübner), and the cotton red spider mite, Tetranychus spp., are important pests of cotton in Zimbabwe. A study to assess H. armigera resistance to fenvalerate 20 EC (Cyano (3-phenoxyphenyl) methyl 4-chloro-α-(1-methylethyl)benzene acetate) and Tetranychus spp. resistance to amitraz 20 EC (n’-(2,4-dimethylphenyl)-n-[[(2,4-dimethylphenyl)imino]methyl]-n-) was conducted at the Cotton Research Institute (CRI) during the 2005/06 cotton-growing season. Field populations of H. armigera and Tetranychus spp. were collected from some of Zimbabwe’s major cotton-growing areas of Sanyati, Umguza, Chisumbanje, Chinhoyi and the CRI in Kadoma and exposed to bioassays. The African bollworm leaf disc technique and the red spider mite attached leaf-dipping technique were used to assess responses of the African bollworm and red spider mite to the pesticides. Susceptible laboratory populations served as the standard populations and their responses were compared with those of the field populations. The graphical method and MSTAT-C probit analysis computer program were used to calculate LC₅₀ values. Although the CRI field population, used as a reference population for the registration of H. armigera insecticides, had the highest LC₅₀ value (graphical?=?0.000100000; MSTAT-C?=?0.000088195) compared with all the other field populations, overall log-dose probit bioassays on all field-collected strains of the bollworm showed no resistance to the pyrethroid (RFs?=?0.04–0.54-fold). Tetranychus spp. showed very low levels of resistance (RFs?=?1.26–2.00-fold). Continuous monitoring of major cotton pests, especially H. armigera and Tetranychus spp., from all cotton districts of Zimbabwe is vital for early detection of resistance development.