Frequency Of Resistance Alleles Research Articles

Pyrethroid Resistance and Fitness Cost Conferred by the super-kdr Mutation M918L in Rhopalosiphum padi (Hemiptera: Aphididae).

Pyrethroid insecticides have been widely utilized for insect pest control. Target-site resistance is one of the major mechanisms explaining pest resistance to pyrethroids. This study quantified pyrethroid resistance and fitness cost conferred by the voltage-gated sodium channel (VGSC) M918L mutation in Rhopalosiphum padi. Six s-kdr-SS and six s-kdr-RS parthenogenetic lineages were established from the same field population and were reared in the laboratory without exposure to pesticides for more than one year. Enzyme activity analysis demonstrated that metabolic resistance had no impact on these lineages. Bioassays showed that the M918L mutation strongly affected pyrethroid efficiency, conferring moderate resistance to bifenthrin (type I) (39.0-fold) and high resistance to lambda-cyhalothrin (type II) (194.7-fold). Compared with the life table of s-kdr-SS lineages, s-kdr-RS lineages exhibited a relative fitness cost with significant decreases in longevity and fecundity. Meanwhile, competitive fitness was measured by blending various ratios of s-kdr-SS and s-kdr-SS aphids. The results indicated that M918L-mediated resistance showed a significant fitness cost in the presence of wild aphids without insecticide pressure. The fitness cost strongly correlated with the initial resistance allele frequency. This work characterized the novel s-kdr M918L mutation in R. padi, defined its function in resistance to different types of pyrethroids, and documented that the M918L-mediated resistance has a significant fitness cost.

Genome-wide association mapping identifies yellow rust resistance loci in Ethiopian durum wheat germplasm.

Durum wheat is an important cereal grown in Ethiopia, a country which is also its center for genetic diversity. Yellow (stripe) rust caused by Puccinia striiformis fsp tritici is one of the most devastating diseases threatening Ethiopian wheat production. To identify sources of genetic resistance and combat this pathogen, we conducted a genome wide association study of yellow rust resistance on 300 durum wheat accessions comprising 261 landraces and 39 cultivars. The accessions were evaluated for their field resistance using a modified Cobb scale at Meraro, Kulumsa and Chefe Donsa in the 2015 and 2016 main growing seasons. Analysis of the 35K Axiom Array genotyping data of the panel resulted in a total of 8,797 polymorphic SNPs of which 7,093 were used in subsequent analyses. Population structure analysis suggested two groups in which the cultivars clearly stood out separately from the landraces. Eleven SNPs significantly associated with yellow rust resistance were identified on four chromosomes (1A, 1B, 2B, and 5A) which defined at least five genomic loci. Six of the SNPs were consistently identified on chromosome 1B singly at each and combined overall environments which explained 62.6-64.0% of the phenotypic variation (R2). Resistant allele frequency ranged from 14.0-71.0%; Zooming in to the identified resistance loci revealed the presence of disease resistance related genes involved in the plant defense system such as the ABC transporter gene family, disease resistance protein RPM1 (NBS-LRR class), Receptor kinases and Protein kinases. This study has provided SNPs for tracking the loci associated with yellow rust resistance and a diversity panel which can be used for association study of other agriculturally important traits in durum wheat.

Insecticide resistance trait may contribute to genetic cluster change in Bemisia tabaci MED (Hemiptera: Aleyrodidae) as a potential driving force.

Previously, we reported that the majority of the Bemisia tabaci Mediterranean (MED) populations converged from two dominant genetic clusters (cluster 1 and 2) to one (cluster 2) during 1 year in greenhouse tomatoes in Korea. To find possible mechanisms for this phenomenon, we investigated the concurrent changes in resistance traits of the two clusters for three insecticide classes (organophosphate, pyrethroid, and neonicotinoid). Since the resistance mutation frequencies in regional samples were either high (i.e. the voltage-sensitive sodium channel L925I/T929V mutations and the F392 acetylcholinesterase 1 mutation) or zero (the nicotinic acetylcholine receptor R81T mutation), no meaningful correlation between the resistance allele frequency and genetic cluster was deduced. However, the actual resistance levels to all three insecticide classes were significantly higher in cluster 2 than in cluster 1, suggesting that cluster 2 has a higher resistance potential. Furthermore, thiamethoxam treatment to the mixed population of clusters 1 and 2 over three generations exhibited a strong tendency of population change from cluster 1 to cluster 2. Our results demonstrated that the insecticide resistance trait is one of the driving forces for rapid genetic cluster change in B. tabaci MED populations. © 2021 Society of Chemical Industry.

Intensity and mechanisms of deltamethrin and permethrin resistance in Anopheles gambiae s.l. populations in southern Benin

BackgroundInsecticide resistance is threatening the effectiveness of efforts to control malaria vectors in Benin. This study explores the levels and mechanisms of insecticide resistance in An. gambiae s.l. to pyrethroids.MethodsLarvae were collected from August 2017 to July 2018 in five communes in southern Benin (Adjohoun, Allada, Bohicon, Cotonou, and Porto-Novo) representing diverse ecological regions, and were reared in Benin’s insectary. Two- to five-day-old female mosquitoes from each district were exposed to multiple doses of deltamethrin and permethrin (1×, 2×, 5×, and 10×) using the WHO insecticide resistance intensity bioassay. The effect of pre-exposure to the synergist, piperonyl butoxide (PBO), was also tested at different pyrethroid doses. Molecular allele frequencies of kdr (1014F) and ace-1R (119S) insecticide resistance mutations and levels of detoxification enzymes were determined for mosquitoes sampled from each study area.ResultsAn. gambiae s.l. were resistant to pyrethroid-only exposure up to 10× the diagnostic doses in all the study sites for both deltamethrin and permethrin. Mortality was significantly higher in An. gambiae s.l. pre-exposed to PBO followed by exposure to deltamethrin or permethrin compared to mosquitoes exposed to deltamethrin or permethrin only (p < 0.001). The difference in mortality between deltamethrin only and PBO plus deltamethrin was the smallest in Cotonou (16–64%) and the greatest in Bohicon (12–93%). The mortality difference between permethrin only and PBO plus permethrin was the smallest in Cotonou (44–75%) and the greatest in Bohicon (22–72%). In all the study sites, the kdr resistance allele (1014F) frequency was high (75–100%), while the ace-1 resistance allele (G119S) frequency was low (0–3%). Analysis of the metabolic enzymatic activity of An. gambiae s.l. showed overexpression of nonspecific esterases and glutathione S-transferases (GST) in all study sites. In contrast to the PBO results, oxidase expression was low and was similar to the susceptible An. gambiae s.s. Kisumu strain in all sites.ConclusionThere is high-intensity resistance to pyrethroids in southern Benin. However, pre-exposure to PBO significantly increased susceptibility to the pyrethroids in the different An. gambiae s.l. populations sampled. The use of PBO insecticide-treated bed nets may help maintain the gains in An. gambiae (s.l.) control in southern Benin.Graphical

Recurrent selection for resistance to Thrips tabaci in a tropical onion population

Recurrent selection for resistance to onion Thrips tabaci has not been well studied by breeding programmes. Onion thrips is a pest of major concern and is controlled by insecticide spraying, raising production costs and potentially damaging the environment. This study aimed to estimate onion bulb yield genetic gain through six cycles in the ‘BRS Alfa São Francisco’ developed by recurrent selection for T. tabaci resistance. Experiments were carried out in a randomised block design, with three replications, in two locations. The degree of infestation in plants was evaluated five times after transplanting, as well as plant architecture traits and bulb yield. The latest selection cycle presented bulb commercial yield of 32.1 t.ha-1, while the base population ‘Alfa Tropical’ and IPA 10 check cultivar 15.9 and 14.0 t.ha-1, respectively (p&lt;0.01). The broad sense heritability values ranged from 0.65 to 0.74 for bulb yield. The mean genetic gain was 1.0 t.ha-1 or 6% per selection cycle, indicating the efficiency of the method to increase the frequency of favourable alleles for thrips resistance and the possibility of onion cultivation in the total absence of insecticide applications to control this pest, or a reduction in their number

Fitness Costs Associated with Pyrethroid Resistance in Halotydeus destructor (Tucker) (Acari: Penthaleidae) Elucidated Through Semi-field Trials.

Pyrethroid resistance in the redlegged earth mite, Halotydeus destructor (Tucker), is primarily attributed to a kdr (knockdown resistance) mutation in the parasodium channel gene. To assess fitness costs associated with this resistance, adult resistant and susceptible populations were mixed in different proportions in microcosm tubs and placed in a shade-house simulating field conditions. Three separate experiments were undertaken whereby parental mites were collected from the field and offspring were followed for two to three generations. The association between fitness costs and kdr-mediated resistance was investigated by examining differences in mite numbers and changes in resistant allele frequencies across generations. In two (of the three) experiments, the population fitness measure of mites was significantly lower in microcosms containing a higher proportion of resistant individuals compared with treatments containing susceptible mites. No differences in mite fitness were observed between treatments in the third experiment; in this instance, the starting proportion of individuals homozygous for the resistant mutation was much lower (~40%) than in the other experiments (>90%). In all three experiments, a decrease in the resistant allele frequency across mite generations was observed. These findings indicate a potential deleterious pleiotropic effect of the kdr mutation on the fitness of H. destructor and have implications for resistance management strategies aimed at this important agricultural pest. Further experiments investigating fitness costs directly in the field are warranted.

Frequency of resistance alleles to Cry1Ac toxin from cotton bollworm, Helicoverpa armigera (Hübner) collected from Bt-cotton growing areas of Telangana state of India

Transgenic cotton expressing Bacillus thuringiensis (Bt) cry1Ac and cry2Ab toxin genes is widely cultivated to manage bollworm complex in India. Cotton bollworm Helicoverpa armigera (Hübner) is one of the most serious of this complex. It is likely to evolve resistance to Cry toxins in view of continual selection pressure due to extensive cultivation of Bt cotton. Monitoring susceptibility of cotton bollworm using conventional bioassays is reported to have shown its increasing tolerance to Cry1Ac over the years. We report using an F2 screen Cry1Ac resistance allele frequencies of 0.050 (95% CI 0.022–0.076) and 0.056 (95% CI 0.035–0.075) in the insect populations collected from pigeon pea grown alongside Bt cotton in the respective years of 2016 and 2017 in the Telangana state of India. Compared to our earlier studies for 2013 and 2014, resistance allele frequency to Cry1Ac in the cotton bollworm in the following two years remains unchanged. The significance of these results is discussed in the context of non-Bt host crops acting as refuge for cotton bollworm for ensuring sustainable resistance management.

Baseline Response, Monitoring, and Cross-Resistance of Spodoptera frugiperda (Lepidoptera: Noctuidae) to Sodium Channel Blocker Insecticides in Brazil

Spodoptera frugiperda (J.E. Smith) is one of the key cross-crop pests in Brazilian agroecosystems. Field-evolved resistance of S. frugiperda to some conventional insecticides and Bt proteins has already been reported. Thus, the use of insecticides with new mode of action such as sodium channel blockers (indoxacarb and metaflumizone) could be an important tool in insecticide resistance management (IRM) programs. To implement a proactive IRM, we conducted baseline response and monitoring to indoxacarb and metaflumizone in 87 field populations of S. frugiperda collected from major maize-growing regions of Brazil from 2017 to 2020, estimated the frequency of resistance alleles to indoxacarb, and evaluated cross-resistance of indoxacarb and metaflumizone to some selected insecticides and Bt proteins. Low variation in susceptibility to indoxacarb (4.6-fold) and metaflumizone (2.6-fold) was detected in populations of S. frugiperda in 2017. The frequency of the resistance allele to indoxacarb was 0.0452 (0.0382-0.0527 CI 95%), by using F2 screen method. The mean survival at diagnostic concentration, based on CL99, varied from 0.2 to 12.2% for indoxacarb and from 0.0 to 12.7% for metaflumizone, confirming high susceptibility of S. frugiperda to these insecticides in Brazil. No cross-resistance was detected between sodium channel blocker insecticides and other insecticides (organophosphate, pyrethroid, benzoylurea, spinosyn, and diamide) and Bt proteins. These findings showed that sodium channel blocker insecticides are important candidates to be exploited in IRM strategies of S. frugiperda in Brazil.

Distribution of CCR5 Δ32 HIV-1 resistance allele frequency at Zanjan province in Iran

Introduction: The CC chemokine receptor 5 (CCR5) is known as the main co-receptor in human immunodeficiency virus (HIV) infection. Accumulating evidence verified 32bp deletion in both alleles of CCR5 provides natural resistance to HIV infection. Accordingly, recent therapeutic approaches are based on gene and cell therapies by inducing this resistance. Allogeneic transplantation of stem cells with CCR5Δ32 homozygous to HIV infected people has been considered as an efficient strategy. Objectives: The aim of this study was to determine CCR5 Δ32 mutation frequency in healthy and HIV-infected individuals in Zanjan province, in Iran and also detecting appropriate candidate for future therapeutic approaches. Patients and Methods: In this study, blood samples were collected from 102 HIV infected patients and 204 healthy controls in ethylene diamine tetra-acetic acid (EDTA) pre-coated tubes. DNA extraction was performed and analyzed for CCR5Δ32 mutation by GAP-PCR in both groups and followed by 2% gel agarose electrophoresis. The Δ32 genotype frequency was statistically determined. Results: Our finding demonstrated that 3 HIV infected patients displayed CCR5 mutation, while 204 healthy controls showed one CCR5 Δ32/Δ32 homozygote mutation. We observed that Δ32 mutation frequency is 0.82% in Zanjan province (χ2 =47.58, P&lt;0.001). Conclusion: Reduction in CCR5 mutation frequency as well as the other polymorphisms related to HIV resistance, can lead to the development of HIV infection epidemiology. Migration, natural selection and genetic admixture can elucidate various distribution of Δ32 allele frequency in different populations, like as north Europeans that reduce gradually to south. The result of this study can facilitate the presentation of suitable Δ32 donors to HIV infected patients in therapeutic approaches.

Estimation of Cry3Bb1 resistance allele frequency in field populations of western corn rootworm using a genetic marker.

Following the discovery of western corn rootworm (WCR; Diabrotica virgifera virgifera) populations resistant to the Bacillus thuringiensis (Bt) protein Cry3Bb1, resistance was genetically mapped to a single locus on WCR chromosome 8 and linked SNP markers were shown to correlate with the frequency of resistance among field-collected populations from the US Corn Belt. The purpose of this paper is to further investigate the relationship between one of these resistance-linked markers and the causal resistance locus. Using data from laboratory bioassays and field experiments, we show that one allele of the resistance-linked marker increased in frequency in response to selection, but was not perfectly linked to the causal resistance allele. By coupling the response to selection data with a genetic model of the linkage between the marker and the causal allele, we developed a model that allowed marker allele frequencies to be mapped to causal allele frequencies. We then used this model to estimate the resistance allele frequency distribution in the US Corn Belt based on collections from 40 populations. These estimates suggest that chromosome 8 Cry3Bb1 resistance allele frequency was generally low (<10%) for 65% of the landscape, though an estimated 13% of landscape has relatively high (>25%) resistance allele frequency.

Phenotypic and genotypic approaches for detection of anthelmintic resistant sheep gastrointestinal nematodes from Brazilian northeast.

The aim of this study was to characterize the anthelmintic resistance (AR) of a sheep gastrointestinal nematode population, named Caucaia, from northeastern Brazil. Phenotypic tests performed were: egg hatch (EHT), larval development (LDT) and fecal egg count reduction (FECRT). Benzimidazoles (BZs) genotypic evaluation was by frequency of single nucleotide polymorphisms (SNPs) F200Y, F167Y and E198A, and for levamisole (LEV), by frequency of resistance alleles of Hco-acr-8 gene. The primers were designed specifically for Haemonchus contortus. Effective concentrations 50% (EC50) for BZs (EHT), and for macrocyclic lactones (MLs) and LEV (LDT) were 1.02 µg/mL, 1.81 ng/mL and 0.04 µg/mL, respectively. Resistance ratios for MLs and LEV were 0.91 and 3.07, respectively. FECRT efficacies of BZs, MLs, monepantel (MPTL) and LEV were 52.4; 87.0; 94.5 and 99.6%, respectively. qPCR for BZs demonstrated resistance allele frequencies of 0%, 26.24% and 69.08% for SNPs E198A, F200Y and F167Y, respectively. For LEV, 54.37% of resistance alleles were found. There was agreement between EHT, FECRT and qPCR for BZs, and agreement between LDT and qPCR for LEV. Thus, based on higher sensitivity of qPCR, and phenotypic evaluation, the Caucaia population was considered resistant to BZs, MLs, LEV and suspect for MPTL.

Empowering Australian insecticide resistance research with genetic information: the road ahead

AbstractInsecticides are important for chemical control of arthropod pests in agricultural systems but select for resistance as an adaptive trait. Identifying the genetic mechanism(s) underpinning resistance can facilitate development of genetic markers, which can be used in monitoring programs. Moreover, understanding of genetic mechanisms in a broader population genetic context can be used to infer the origins of resistance, predict the dynamics of resistance evolution and evaluate the efficacy of different management strategies. Transitioning genetic information successfully into practical solutions requires overcoming two major hurdles. Firstly, genetic mechanisms must be identified to develop genetic markers. Secondly, routine use of genetic markers is required to build substantial spatio‐temporal data on the distribution and frequency of resistance alleles. In this study, we demonstrate large knowledge gaps on the genetic mechanisms of insecticide resistances in Australia using eight established arthropod pests important to the grains industry: Bemisia tabaci (silverleaf whitefly), Frankliniella occidentalis (western flower thrips), Halotydeus destructor (redlegged earth mite), Helicoverpa armigera (cotton bollworm), Myzus persicae (green peach aphid), Plutella xylostella (diamondback moth), Tetranychus urticae (two‐spotted spider mite) and Thrips tabaci (onion thrips). Many resistances have not been characterised at the genetic level in most pests, even for chemical MoA groups with a long history of use in Australia. Moreover, monitoring of resistance is spatio‐temporally patchy, which precludes examination of long‐term trends or predictive modelling. We suggest that leveraging cumulative global knowledge of resistances to develop a priori candidate genes, and incorporation of genomic approaches, can help overcome the hurdles of embracing genetic information in resistance management. We highlight the recently invasive Spodoptera frugiperda (fall armyworm) as a case study where genetic markers and genomic approaches should prove useful in rapidly assessing the risk of this species to the Australian grains industry and other agricultural commodities. The uptake of genetic information into management can only occur once its benefit to empower insecticide resistance research is fully realised. Ultimately, the road ahead requires amalgamation of multifaceted data (genes, environment and spatio‐temporal replication) to better understand and predict the dynamics of resistance evolution.

Haemonchus sp. in beef cattle in Brazil: species composition and frequency of benzimidazole resistance alleles

The aim of the present study was to investigate the occurrence of Haemonchus contortus and Haemonchus placei in beef cattle and the frequency of single nucleotide polymorphisms associated with benzimidazole (BZ)-resistance in Haemonchus spp. in Brazil. For such, fecal samples were collected from 61 beef cattle ranches in 11 Brazilian states. Third-stage larvae (L3) were produced for morphological species identification and DNA extraction. PCR was performed for the analysis of the isotype 1 β-tubulin gene and the products were sequenced to confirm the presence of H. placei and H. contortus. For each field population, pyrosequencing assays were performed to quantify the frequency of the F167Y, E198A and F200Y polymorphisms in the isotype-1 β-tubulin gene. The results of the morphometric analysis of 2345 larvae showed that H. placei was present on all ranches. The analysis of the isotype 1 β-tubulin gene confirmed 100% prevalence for H. placei and 23.7% for H. contortus. Pyrosequencing assays demonstrated single-nucleotide polymorphisms (SNPs) associated with BZ-resistance in all three codons (F167Y, E198A and F200Y) of the isotype 1 β-tubulin gene in H. placei field populations. Frequencies of resistance-associated alleles above background (≥ 15%) were found for at least one codon in 11.4% of the field isolates and maximum frequencies of 30, 21 and 29% were found for codons 167, 198 and 200, respectively, on individual ranches. This study confirms the presence of H. contortus in beef cattle in the major livestock farming states in Brazil and demonstrates that genotypes associated with BZ resistance are present in field populations of Haemonchus spp..

Assessment of the 2018 post‐market environmental monitoring report on the cultivation of genetically modified maize MON 810 in the EU

Following a request from the European Commission, the EFSA assessed the 2018 post‐market environmental monitoring (PMEM) report on the cultivation of Cry1Ab‐expressing maize event MON 810. Like previous years, there was partial compliance with refuge requirements by Spanish farmers growing MON 810 varieties. European and Mediterranean corn borer populations collected from north‐eastern Spain during the 2018 maize growing season and tested for Cry1Ab susceptibility show no symptoms of resistance to maize MON 810. The assessment of farmer questionnaires and relevant scientific publications does not indicate any unanticipated adverse effects on human and animal health or the environment arising from the cultivation of maize MON 810. The report does not provide information about the use of existing networks involved in environmental monitoring. Overall, EFSA concludes that the evidence reported in the 2018 PMEM report does not invalidate previous EFSA evaluations on the safety of maize MON 810. However, as in previous years, EFSA identifies shortcomings on resistance monitoring that need revision in future reports. In particular, the monitoring plan, as implemented in 2018, is not sufficiently sensitive to detect the recommended 3% resistance allele frequency. Consequently, EFSA strongly recommends the consent holder to: (1) achieve full compliance with refuge obligations in areas where adoption of maize MON 810 is high; (2) increase the sensitivity of the monitoring plan and address previously mentioned limitations for resistance monitoring; and (3) perform an F2 screen on corn borer populations from north‐eastern Spain. A fit‐for‐purpose farmer alert system may help to detect unexpected adverse effects associated with the cultivation of MON 810 varieties and be an alternative to the current farmer survey system. Moreover, relevant stakeholders should implement a methodological framework to enable making the best use of existing networks involved in environmental monitoring for the general surveillance of genetically modified plants.

Origin, selection, and spread of diamide insecticide resistance allele in field populations of diamondback moth in east and southeast Asia.

The investigation of molecular mechanisms and evolution of resistance to insecticides is an ongoing challenge, as researchers must provide guidance to manage the resistance to achieve sustainable production in agriculture. Predicting, monitoring, and managing insecticide resistance requires information on the origins, selection, and spread of resistance genes. The resistance of Plutella xylostella (L.) against diamide insecticides is becoming an increasingly severe problem in east and southeast Asia. In this study, the evolution of resistance was investigated using a resistance allele [ryanodine receptor (RyR); G4946E mutation] and its flanking regions, as well as mitochondrial cytochrome c oxidase subunit I (mtCOI). The sequences of the flanking region of the G4946E and mtCOI suggested that the G4946E mutation has a key role in resistance. Furthermore, the G4946E mutation has multiple origins, and congenic resistant mutations have spread across east and southeast Asia, despite substantial geographical barriers. In addition, the susceptibility of field populations partially recovered during winter, based on the observed decrease in the G4946E (resistant allele) frequency. Finally, the resistance level indexed by the frequency of the E4946 allele was significantly lower in non-overwintering regions than in overwintering regions. The information of the present study is useful to monitor resistance using molecular markers and to develop strategies to delay the evolution of diamide resistance.

Frequency of kdr mutations in the voltage-sensitive sodium channel (VSSC) gene in Aedes aegypti from Yogyakarta and implications for Wolbachia-infected mosquito trials

BackgroundIn the inner city of Yogyakarta, Indonesia, insecticide resistance is expected in the main dengue vector, Aedes aegypti, because of the intensive local application of pyrethroid insecticides. However, detailed information about the nature of resistance in this species is required to assist the release of Wolbachia mosquitoes in a dengue control program, so that we can ensure that insecticide resistance in the strain of Ae. aegypti being released matches that of the background population.MethodsHigh-resolution melt genotyping was used to screen for kdr mutations associated with pyrethroid resistance in the voltage-sensitive sodium channel (VSSC) gene in Ae. aegypti of some areas in the inner city of Yogyakarta.ResultsThe results show that the V1016G mutation predominated, with individuals homozygous for the 1016G allele at a frequency of 82.1% and the mutant allele G at a frequency of 92%. Two patterns of co-occurrence of mutations were detected in this study, homozygous individuals V1016G/S989P; and heterozygous individuals V1016G/F1534C/S989P. We found the simultaneous occurrence of kdr mutations V1016G and F1534C at all collection sites, but not within individual mosquitoes. Homozygous mutants at locus 1016 were homozygous wild-type at locus 1534 and vice versa, and heterozygous V1016G were also heterozygous for F1534C. The most common tri-locus genotype co-occurrences were homozygous mutant 1016GG and homozygous wild-type FF1534, combined with homozygous mutant 989PP (GG/FF/PP) at a frequency of 38.28%.ConclusionsGiven the relatively small differences in frequency of resistance alleles across the city area, locality variations in resistance should have minor implications for the success of Wolbachia mosquito trials being undertaken in the Yogyakarta area.

An agent-based model of insect resistance management and mitigation for Bt maize: a social science perspective.

Farmers around the world have used Bt maize for more than two decades, delaying resistance using a high-dose/refuge strategy. Nevertheless, field-evolved resistance to Bacillus thuringiensis (Bt) toxins has been documented. This paper describes a spatially explicit population genetics model of resistance to Bt toxins by the insect Ostrinia nubilalis and an agent-based model of farmer adoption of Bt maize incorporating social networks. The model was used to evaluate multiple resistance mitigation policies, including combinations of increased refuges for all farms, localized bans on Bt maize where resistance develops, area-wide sprays of insecticides on fields with resistance and taxes on Bt maize seed for all farms. Evaluation metrics included resistance allele frequency, pest population density, farmer adoption of Bt maize and economic surplus. The most effective mitigation policies for maintaining a low resistance allele frequency were 50% refuge and localized bans. Area-wide sprays were the most effective for maintaining low pest populations. Based on economic surplus, refuge requirements were the recommended policy for mitigating resistance to high-dose Bt maize. Social networks further enhanced the benefits of refuges relative to other mitigation policies but accelerated the emergence of resistance. These results support using refuges as the foundation of resistance mitigation for high-dose Bt maize, just as for resistance management. Other mitigation policies examined were more effective but more costly. Social factors had substantial effects on the recommended management and mitigation of insect resistance, suggesting that agent-based models can make useful contributions for policy analysis.

Baseline susceptibility and resistance allele frequency in Ostrinia furnacalis related to Cry1 toxins in the Huanghuaihai summer corn region of China

Ostrinia furnacalis (Guenée) is one of the most destructive pests of corn and is a major target of transgenic corn expressing Bt (Bacillus thuringiensis) toxins in the Huanghuaihai summer corn region of China. Prior to the widespread commercialization of transgenic Bt corn, it is necessary to estimate baseline susceptibility to Bt toxins and Bt toxin resistance allele frequencies in O. furnacalis. The median lethal concentration (LC50 ) values of the Bt toxins Cry1Ab, Cry1Ac and Cry1F for 15 different populations ranged from 0.887 to 1.617, 1.251 to 2.594 and 4.146 to 6.465 ng cm-2 , respectively. The LC99 values of 93, 45, and 197 ng cm-2 for Cry1Ab, Cry1Ac and Cry1F, respectively, killed > 99% of individuals of eight O. furnacalis populations collected in 2017 and were identified as diagnostic concentrations for monitoring susceptibility in O. furnacalis populations in this region. Using the F2 screening method with these diagnostic concentrations, the resistance allele frequencies related to Cry1Ab, Cry1Ac and Cry1F were found to be 0.002 (0.000283-0.006484), 0.001 (0.000030-0.004295) and 0.001 (0.000030-0.004295), respectively, in 2018. Fifteen populations of O. furnacalis collected in the Huanghuaihai summer corn region of China were all susceptible to Cry1Ab, Cry1Ac and Cry1F toxins, and the susceptibility showed no significant variation among these O. furnacalis populations. The estimated resistance allele frequency to Cry1Ab, Cry1Ac and Cry1F was rare in this region. This provided essential knowledge for making the decision to commercialize Bt maize, and monitoring resistance development and evaluating resistance management strategies in the future in the Huanghuaihai summer corn region of China. © 2020 Society of Chemical Industry.

Multiple anthelmintic resistance in gastrointestinal nematodes of Caprines on Mountain Research Centre for Sheep and Goat at Kashmir Valley, India

The study was conducted to evaluate the status of anthelmintic resistance in Gastro-Intestinal Nematodes (GINs) of goats at an organized farm located in Kashmir, as there is no report of resistance against these parasites of goats from this temperate region, although it has been reported worldwide including India. Caprines reared at this farm exhibited reduced efficacy to multiple anthelmintics following treatments with Fenbendazole (FBZ), Closantel and Ivermectin (IVM) in Faecal Egg Count Reduction Test (FECRT). The results suggested that the overall efficacy was highest for IVM at 83.5% and 90.0% on 7th and 14th day post-treatment, respectively and least for FBZ at 44.3% and 62.5%, respectively, whereas the corresponding figures for closantel were 68.3% and 86.2%, respectively. The pre-treatment faecal culture revealed Haemonchus contortus, Teladorsagia circumcincta and Trichostrongylus colubriformis as predominant strongyles, however, in post-treatment samples, only H. contortus was observed. Further, the infective larvae were subjected to Allele specific PCR (AS-PCR) for accurate diagnosis of BZ resistance. The AS-PCR revealed 52% of H. contortus were homozygous resistant (rr) and 17% were heterozygous (rS) on day “0” before treatment and 100% homozygous resistant (rr) on 7th day post treatment. In both T. colubriformis and T. circumcincta, 100% population was homozygous susceptible (SS) at day “0” before treatment. The overall frequency of resistant (r) allele for H. contortus was 60.5% and for susceptible allele (s) was 39.5%. For T. colubriformis and T. circumcincta the frequency of susceptible allele (s) was 100%. The survey indicated that the GINs of goats on the farm have developed multiple anthelmintic resistance to FBZ, closantel and IVM and the condition is alarming in the farm. Moreover surveillance studies about status of anthelmintic resistance in other farms (Govternment as well as Private) of Kashmir valley should be carried out at large scale to develop effective and sustainable control strategies against GI Nematodes.

Field-evolved resistance to chitin synthesis inhibitor insecticides by soybean looper, Chrysodeixis includens (Lepidoptera: Noctuidae), in Brazil

Soybean looper (SBL), Chrysodeixis includens (Walker), is an economically important soybean and cotton pest in Brazil. Here, we selected an SBL strain resistant to teflubenzuron using F2 screening, estimated the resistance allele frequency, characterized the inheritance of resistance, investigated fitness costs, evaluated patterns of cross-resistance, and determined the magnitude of resistance. The teflubenzuron-resistant strain (Teflu-R) was selected from field-collected populations with an estimated allele frequency of 0.1700. Estimated LC50 values were 0.010 and 363.61 μg a.i. cm−2 for the susceptible (Sus) and Teflu-R strains, respectively, representing a 36,361-fold resistance ratio (RR). The LC50 values of reciprocal crosses were 1.02 and 0.59 μg a.i. cm−2, suggesting that resistance is autosomally inherited. The low survival of reciprocal crosses (16 and 20%) on teflubenzuron-sprayed leaves indicates incomplete recessive resistance. The number of segregations influencing resistance was 2.72, suggesting a polygenic effect. The Teflu-R strain showed longer development periods as well as lower survival and population growth than the Sus strain, revealing fitness costs. The Teflu-R strain also showed high cross-resistancesto other chitin inhibitor insecticides, such as novaluron (RR = 6147-fold) and lufenuron (RR = 953-fold), but low cross-resistance to methoxyfenozide, flubendiamide, and indoxacarb (RR < 3.45-fold). On discriminatory concentrations of teflubenzuron and novaluron, populations of SBL showed survival rates from 15 to 52%, indicating field resistance to these insecticides. Our findings indicated that resistance to teflubenzuron in SBL is autosomal, recessive, polygenic, and associated with fitness cost. We also found a high cross-resistance to other benzoylphenylureas and a high frequency of resistance to this mode-of-action in SBL in Brazil.