Insecticide Resistance Management Strategies Research Articles

Mapping malaria vectors and insecticide resistance in a high-endemic district of Haryana, India: implications for vector control strategies

BackgroundAchieving effective control and elimination of malaria in endemic regions necessitates a comprehensive understanding of local mosquito species responsible for malaria transmission and their susceptibility to insecticides.MethodsThe study was conducted in the highly malaria prone Ujina Primary Health Center of Nuh (Mewat) district of Haryana state of India. Monthly entomological surveys were carried out for adult mosquito collections via indoor resting collections, light trap collections, and pyrethrum spray collections. Larvae were also collected from different breeding sites prevalent in the region. Insecticide resistance bioassay, vector incrimination, blood meal analysis was done with the collected vector mosquitoes.ResultsA total of 34,974 adult Anopheles mosquitoes were caught during the survey period, out of which Anopheles subpictus was predominant (54.7%). Among vectors, Anopheles stephensi was predominant (15.5%) followed by Anopheles culicifacies (10.1%). The Human Blood Index (HBI) in the case of An. culicifacies and An. stephensi was 6.66 and 9.09, respectively. Vector incrimination results revealed Plasmodium vivax positivity rate of 1.6% for An. culicifacies. Both the vector species were found resistant to DDT, malathion and deltamethrin.ConclusionThe emergence of insecticide resistance in both vector species, compromises the effectiveness of commonly used public health insecticides. Consequently, the implementation of robust insecticide resistance management strategies becomes imperative. To effectively tackle the malaria transmission, a significant shift in vector control strategies is warranted, with careful consideration and adaptation to address specific challenges encountered in malaria elimination efforts.

Insecticide Susceptibilities and Enzyme Activities of Four Stink Bug Populations in Mississippi, USA.

In Mississippi, the Pentatomidae complex infesting soybean is primarily composed of Euschistus servus, Nezara viridula, Chinavia hilaris, and Piezodorus guildinii. This study employed spray bioassays to evaluate the susceptibilities of these stink bugs to seven commonly used formulated insecticides: oxamyl, acephate, bifenthrin, λ-cyhalothrin, imidacloprid, thiamethoxam, and sulfoxaflor. Stinks bugs were collected from soybeans in Leland, MS, USA during 2022 and 2023, as well as from wild host plants in Clarksdale, MS. There was no significant difference in the susceptibility of C. hilaris to seven insecticides between two years, whereas P. guildinii showed slightly increased susceptibility to neonicotinoids in 2023. Among all four stink bug species, susceptibility in 2022 was ranked as P. guildinii ≤ C. hilaris ≈ N. viridula, while in 2023, it was ranked as P. guildinii ≤ C. hilaris ≤ E. Servus. Additionally, populations of E. servus and P. guildinii collected from Clarksdale exhibited high tolerance to pyrethroids and neonicotinoids. Moreover, populations of E. servus and P. guildinii from SIMRU-2022 and Clarksdale-2023 showed elevated esterase and cytochrome P450 activity, respectively. These findings from spray bioassays and enzyme activity analyses provide a baseline for monitoring insecticide resistance in Pentatomidae and can guide insecticide resistance management strategies for Mississippi soybean.

Field-evolved pyrethroid resistance in Tychius picirostris (Coleoptera: Curculionidae) populations in Oregon white clover seed crops.

The clover seed weevil, Tychius picirostris Fabricius, a serious pest of white clover, Trifolium repens L., grown for seed in western Oregon, causing feeding damage to flowers and developing seeds. Since 2017, white clover seed producers have anecdotally reported T. picirostris control failures using foliar pyrethroid insecticide applications. This mode of action (MoA) is an important chemical control option for T. picirostris management. To evaluate insecticide resistance selection to pyrethroids (bifenthrin) and other MoAs labeled for T. picirostris management (malathion and chlorantraniliprole), adult populations were collected from 8 commercial white clover grown for seed fields in the Willamette Valley, OR, in 2022 and 2023. Among collected Oregon populations, very high resistance ratios (RR50 = 178.00-725.67) were observed to technical grade bifenthrin and low to high resistance ratios (RR50 = 7.80-32.80) to malathion in surface contact assays compared to a susceptible Canadian field population. Moreover, >2.73 times the labeled rate of formulated product containing bifenthrin as the sole MoA was required to kill >50% of T. picirostris in topical assays. Synergistic assays with a mixed-function oxidase inhibitor, an esterase inhibitor, and a glutathione-S-transferase inhibitor revealed phase I and II detoxification enzymes are present in Oregon T. picirostris populations and confer metabolic resistance to bifenthrin. This is the first report of T. picirostris insecticide resistance selection to pyrethroid and organophosphate insecticides. Results will inform continued monitoring and insecticide resistance management strategies to slow the evolution of T. picirostris insecticide resistance selection in Oregon's white clover seed production.

Pyrethroid susceptibility reversal in Aedes aegypti: A longitudinal study in Tapachula, Mexico.

Pyrethroid resistance in Aedes aegypti has become widespread after almost two decades of frequent applications to reduce the transmission of mosquito-borne diseases. Because few insecticide classes are available for public health use, insecticide resistance management (IRM) is proposed as a strategy to retain their use. A key hypothesis of IRM assumes that negative fitness is associated with resistance, and when insecticides are removed from use, susceptibility is restored. In Tapachula, Mexico, pyrethroids (PYRs) were used exclusively by dengue control programs for 15 years, thereby contributing to selection for high PYR resistance in mosquitoes and failure in dengue control. In 2013, PYRs were replaced by organophosphates-insecticides from a class with a different mode of action. To test the hypothesis that PYR resistance is reversed in the absence of PYRs, we monitored Ae. aegypti's PYR resistance from 2016 to 2021 in Tapachula. We observed significant declining rates in the lethal concentration 50 (LC50), for permethrin and deltamethrin. For each month following the discontinuation of PYR use by vector control programs, we observed increases in the odds of mosquitoes dying by 1.5% and 8.4% for permethrin and deltamethrin, respectively. Also, knockdown-resistance mutations (kdr) in the voltage-gated sodium channel explained the variation in the permethrin LC50s, whereas variation in the deltamethrin LC50s was only explained by time. This trend was rapidly offset by application of a mixture of neonicotinoid and PYRs by vector control programs. Our results suggest that IRM strategies can be used to reverse PYR resistance in Ae. aegypti; however, long-term commitment by operational and community programs will be required for success.

Identification of inducible CYP3 and CYP4 genes associated with abamectin tolerance in the fat body and Malpighian tubules of Spodoptera litura

Abamectin, as a broad-spectrum bioinsecticide, has been widely used for the control of Lepidoptera insects, resulting in different levels of resistance to abamectin in Spodoptera litura. Cytochrome P450 monooxygenases (P450s) are known for their important roles in insecticide detoxification. In this study, the expression of SlCYP6B40, SlCYP4L12 and SlCYP9A32 in the fat body, and SlCYP4S9, SlCYP6AB12, SlCYP6AB58, SlCYP9A75a and SlCYP9A75b in Malpighian tubules was found to be significantly upregulated after abamectin exposure. SlCYP6AE44 and SlCYP6AN4 were simultaneously upregulated in these two tissues after abamectin exposure. Ectopically overexpressed SlCYP6AE44, SlCYP9A32 and SlCYP4S9 in transgenic Drosophila conferred tolerance to abamectin. In addition, homology modeling and molecular docking results suggested that SlCYP6AE44, SlCYP9A32 and SlCYP4S9 may be capable of binding with abamectin. These results demonstrate that upregulation of CYP3 and CYP4 genes may contribute to abamectin detoxification in S. litura and provide information for evidence-based insecticide resistance management strategies.

Integrated resistance management for acaricide use on Varroa destructor

The global beekeeping industry faces an escalating challenge in the form of Varroa destructor. Synthetic chemicals serve as a cornerstone for varroa management, although they face a major challenge in the form of acaricide resistance. Here, I examine acaricide resistance in varroa under the framework of Insecticide Resistance Management (IRM). I assess the potential of diverse IRM strategies, such as pesticide rotation and mixtures, refuge utilization, synergists and the integration of non-persistent chemicals. The peculiar life history of varroa, characterized by its incestuous breeding system, challenges conventional IRM strategies. There is little published evidence that pesticide rotation is beneficial for resistance management in varroa, with several studies showing resistance is maintained despite rotation. Fitness costs associated with pesticide resistance are often an essential component for IRM strategies, but there are no current data from varroa demonstrating such specific fitness costs (e.g., a reduced relative oviposition rate) associated with resistance. The single published experimental study directly examining relative fitness found that here was little or no reproductive fitness cost associated with pyrethroid resistance. More work is needed on fitness effects of the key acaricides, which would better guide the use of rotation and refuge strategies. A key prospect for future work that has been identified through simulation modeling is offered by pesticide mixtures and the role of synergists to elevate acaricide efficacy. Additional tools for varroa IRM include ‘soft’ acaricides, including oxalic acid, and biopesticides such as dsRNA. In light of the widespread prevalence of acaricide resistance and an increasing varroa problem, there is an urgent need for nuanced, data-driven varroa IRM strategies.

Anopheles gambiae s.s. resistance to pyrethroids and DDT in semi-urban and rural areas of the Moyen-Ogooué Province, Gabon

BackgroundPyrethroids are the main insecticides used in vector control for malaria. However, their extensive use in the impregnation of long-lasting insecticidal nets (LLINs) and indoor residual spraying has led to the development of resistance, threatening its success as a tool for malaria control. Baseline data prior to large scale distribution of LLINs are important for the implementation of efficient strategies. However, no data on the susceptibility of malaria vectors is available in the Moyen-Ogooué Province in Gabon. The aim of this study was to assess the susceptibility to pyrethroids and organochlorides of malaria vectors from a semi-urban and rural areas of the province and to determine the frequency of insecticide resistance genes.MethodsLarvae were collected from breeding sites in Lambaréné and Zilé and reared to adults. Three to five-day old female Anopheles gambiae sensu lato mosquitoes were used in cone tube assays following the WHO susceptibility tests protocol for adult mosquitoes. A subsample was molecularly identified using the SINE200 protocol and the frequency of Vgsc-1014 F and − 1014 S mutations were determined.ResultsAnopheles gambiae sensu stricto (s.s.) was the sole species present in both Lambaréné and Zilé. Mosquito populations from the two areas were resistant to pyrethroids and organochlorides. Resistance was more pronounced for permethrin and DDT with mortality lower than 7% for both insecticides in the two study areas. Mosquitoes were statistically more resistant (P < 0.0001) to deltamethrin in Lambaréné (51%) compared to Zilé (76%). All the mosquitoes tested were heterozygous or homozygous for the knockdown resistance (Kdr) mutations Vgsc-L1014F and Vgsc-L1014S with a higher proportion of Vgsc-L1014F homozygous in Lambaréné (76.7%) compared to Zilé (57.1%).ConclusionThis study provides evidence of widespread resistance to pyrethroids in An. gambiae s.s., the main malaria vector in the Moyen-Ogooué Province. Further investigation of the mechanisms underlining the resistance of An. gambiae s.s. to pyrethroids is needed to implement appropriate insecticide resistance management strategies.

Frequency and diversity of indoxacarb resistance in Australian Helicoverpa armigera (Lepidoptera: Noctuidae).

Annual indoxacarb resistance in Helicoverpa armigera (Hübner) populations collected from various crops in Australia was monitored between 2013 and 2023. Resistance frequency determined by F2 screening using a predetermined discriminating dose of indoxacarb, was lowest in the 2013-2014 and 2015-2016 seasons at 0.0164 and 0.0246, respectively. Resistance then increased significantly to a ten-year high of 0.0869 in 2018-2019 but declined to 0.0557 in 2019-2020 during a severe drought, remaining relatively stable thereafter to 2023. Indoxacarb resistance was first detected in H. armigera collected from maize in the Gwydir valley, New South Wales, in 2013 (strain GY7-39). In 2017, a second indoxacarb resistant H. armigera strain (UN1U3-10) was isolated from a population collected in chickpeas in the Liverpool Plains, New South Wales. Indoxacarb resistance of this strain was characterized to evaluate its potential to compromise the ongoing effectiveness of insecticide resistance management strategies in Australian farming systems. Survival at the discriminating dose of indoxacarb in UN1U3-10 was 28.9, 52.6, 86.7, and 92.9% in the F2, F3, F4, and F5, respectively. Following introgression with a susceptible strain and reselection with the discriminating dose of indoxacarb, the resistance ratio of UN1U3-10 was approximately 800-fold. Resistance was autosomal, incompletely dominant and conferred by more than 1 locus. While indoxacarb resistance in UN1U3-10 did not confer to emamectin benzoate or spinetoram and there was no evidence of major cross-resistance to the Bt toxins Cry1A, Cry2A or Vip3A, there was 5-fold reduced sensitivity to chlorantraniliprole. Indoxacarb resistance was suppressed by approximately 10-fold by PBO with no synergism by TPP or DEM, suggesting the involvement of cytochrome P450 enzymes. A stability analysis indicated a fitness cost may be associated with the genes that confer resistance in the UN1U3-10 strain. The potential risk for diverse indoxacarb resistance in the Australian H. armigera population is discussed.

The insecticidal activity and mechanism of tebuconazole on Nilaparvata lugens (Stål).

Previous studies have shown that fungicides have insecticidal activity that can potentially be used as an insecticide resistance management strategy in the brown planthopper Nilaparvata lugens (Stål). However, the mechanism that induces mortality of N. lugens remains elusive. In the present study, the insecticidal activities of 14 fungicides against N. lugens were determined, of which tebuconazole had the highest insecticidal activity compared with the other fungicides. Furthermore, tebuconazole significantly inhibited the expression of the chitin synthase gene NlCHS1; the chitinase genes NlCht1, NlCht5, NlCht7, NlCht9, and NlCht10; and the β-N-acetylhexosaminidase genes NlHex3, NlHex4, NlHex5 and NlHex6; it significantly suppressed the expression of ecdysteroid biosynthetic genes as well, including SDR, CYP307A2, CYP307B1, CYP306A2, CYP302A1, CYP315A1 and CYP314A1 of N. lugens. Additionally, tebuconazole affected the diversity, structure, composition, and function of the symbiotic fungi of N. lugens, as well as the relative abundance of saprophytes and pathogens, suggesting that tebuconazole reshapes the diversity and function of symbiotic fungi of N. lugens. Our findings illustrate the insecticidal mechanism of tebuconazole, possibly by inhibiting normal molting or disrupting microbial homeostasis in N. lugens, and provide an important rationale for developing novel insect management strategies to delay escalating insecticide resistance. © 2023 Society of Chemical Industry.

Insecticide resistance management strategies for public health control of mosquitoes exhibiting polygenic resistance: Acomparison of sequences, rotations, and mixtures.

Malaria control uses insecticides to kill Anopheles mosquitoes. Recent successes in malaria control are threatened by increasing levels of insecticide resistance (IR), requiring insecticide resistance management (IRM) strategies to mitigate this problem. Field trials of IRM strategies are usually prohibitively expensive with long timeframes, and mathematical modeling is often used to evaluate alternative options. Previous IRM models in the context of malaria control assumed IR to have a simple (monogenic) basis, whereas in natural populations, IR will often be a complex polygenic trait determined by multiple genetic variants. A quantitative genetics model was developed to model IR as a polygenic trait. The model allows insecticides to be deployed as sequences (continuous deployment until a defined withdrawal threshold, termed "insecticide lifespan", as indicated by resistance diagnosis in bioassays), rotations (periodic switching of insecticides), or full-dose mixtures (two insecticides in one formulation). These IRM strategies were compared based on their "strategy lifespan" (capped at 500 generations). Partial rank correlation and generalized linear modeling was used to identify and quantify parameters driving the evolution of resistance. Random forest models were used to identify parameters offering predictive value for decision-making. Deploying single insecticides as sequences or rotations usually made little overall difference to their "strategy lifespan", though rotations displayed lower mean and peak resistances. Deploying two insecticides in a full-dose mixture formulation was found to extend the "strategy lifespan" when compared to deploying each in sequence or rotation. This pattern was observed regardless of the level of cross resistance between the insecticides or the starting level of resistance. Statistical analysis highlighted the importance of insecticide coverage, cross resistance, heritability, and fitness costs for selecting an appropriate IRM strategy. Full-dose mixtures appear the most promising of the strategies evaluated, with the longest "strategy lifespans". These conclusions broadly corroborate previous results from monogenic models.

Functional characterization of cytochrome P450s associated with pyrethroid resistance in the olive fruit fly Bactrocera oleae

Resistance to pyrethroid insecticides has evolved in Bactrocera oleae populations in Greece, threatening the efficacy of control interventions based on this insecticide class. Here we report the collection of populations from Crete, with resistance levels reaching up to 132-folds, compared to susceptible laboratory strains and show that pyrethroid resistance is substantially suppressed by the PBO synergist, suggesting the involvement of detoxification enzymes. To identify specific candidate genes implicated in resistance, we performed comparative transcriptomic analysis, between the pyrethroid resistant populations from Crete and the susceptible laboratory strains, using both whole bodies and Malpighian tubules. Several genes were found differentially transcribed between resistant and susceptible flies in each comparison, with P450s being among the most highly over-expressed detoxification genes in pyrethroid resistant populations. Four of the over-expressed P450s (Cyp6A61, Cyp6G6, Cyp4P6 and Cyp6G28) were recombinantly expressed in Escherichia coli and in vitro metabolism assays revealed that CYP6A61 is capable of metabolizing alpha-cypermethrin, while CYP6G6, CYP4P6 and CYP6G28 are capable of metabolizing deltamethrin. No metabolism of neonicotinoid insecticides was recorded. We further silenced CYP6G6 in vivo, via RNAi, which led to a small, but significant increase in deltamethrin toxicity. The study provides valuable information towards the development of molecular diagnostics and evidence-based insecticide resistance management strategies.

The variation of a cytochrome P450 gene, CYP6G4, drives the evolution of Musca domestica L. (Diptera: Muscidae) resistance to insecticides in China

Long term and excessive insecticide use has resulted in some environmental problems and especially, insecticide resistance evolution in insect pests. The variation of cytochrome P450 monooxygenases (P450s), associated with the metabolic detoxification of toxic xenobiotics, is often involved in insecticide resistance. Here, we found that the variation in a P450 gene, CYP6G4, is the most important driver of carbamates resistance in the house fly (Musca domestica). Deciphering the detailed molecular mechanisms of the insecticide resistance is critical for performing suitable insecticide resistance management strategies. Our research results revealed that the combination of amino acid mutations (110C-330E-360N/S, 110C-330E-360S) of CYP6G4 could improve the resistance to propoxur. The nucleotide variations in the promoter region of CYP6G4 significantly increased the luciferase activity by the reporter gene assays. Additionally, miR-281-1-5p was confirmed to post-transcriptionally down-regulate the expression of CYP6G4. These findings suggest that three independent mechanisms; amino acid mutations of the P450 protein, mutations in the promoter region and low expression of post-trans-regulatory factors, as the powerful strategies for the insect resistance to toxic compounds, play a crucial role in the evolutionary processes of insecticide resistance.

Insecticide resistance management of Bemisia tabaci (Hemiptera: Aleyrodidae) in Australian cotton - pyriproxyfen, spirotetramat and buprofezin.

Bemisia tabaci is a globally significant agricultural pest including in Australia, where it exhibits resistance to numerous insecticides. With a recent label change, buprofezin (group 16), is now used for whitefly management in Australia. This study investigated resistance to pyriproxyfen (group 7C), spirotetramat (group 23) and buprofezin using bioassays and available molecular markers. Bioassay and selection testing of B.tabaci populations detected resistance to pyriproxyfen with resistance ratios ranging from 4.1 to 56. Resistance to spirotetramat was detected using bioassay, selection testing and sequencing techniques. In populations collected from cotton, the A2083V mutation was detected in three populations of 85 tested, at frequencies ≤4.1%, whereas in limited surveillance of populations from an intensive horticultural region the frequency was ≥75.8%. The baseline susceptibility of B.tabaci to buprofezin was determined from populations tested from 2019 to 2020, in which LC50 values ranged from 0.61 to 10.75 mg L-1 . From the bioassay data, a discriminating dose of 200 mg L-1 was developed. Recent surveillance of 16 populations detected no evidence of resistance with 100% mortality recorded at doses ≤32 mg L-1 . A cross-resistance study found no conclusive evidence of resistance to buprofezin in populations with high resistance to pyriproxyfen or spirotetramat. In Australian cotton, B.tabaci pest management is challenged by ongoing resistance to pyriproxyfen, while resistance to spirotetramat is an emerging issue. The addition of buprofezin provides a new mode-of-action for whitefly pest management, which will strengthen the existing insecticide resistance management strategy. © 2023 Commonwealth of Australia. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Molecular targets of insecticides and herbicides – Are there useful overlaps?

New insecticide modes of action are needed for insecticide resistance management strategies. The number of molecular targets of commercial herbicides and insecticides are fewer than 35 for both. Few commercial insecticide targets are found in plants, but ten targets of commercial herbicides are found in insects. For several of these commonly held targets, some compounds kill both plants and insects. For example, herbicidal inhibitors of p-hydroxyphenylpyruvate dioxygenase are effective insecticides on blood-fed insects. The glutamine synthetase-inhibiting herbicide glufosinate is insecticidal by the same mechanism of action, inhibition of glutamine synthetase. These and other examples of shared activities of commercial herbicides with insecticides through the same target site are discussed. Compounds with novel herbicide targets shared by insects that are not commercialized as pesticides (such as statins) are also discussed. Compounds that are both herbicidal and insecticidal can be used for insect pests not associated with crops or with crops made resistant to the compounds.

Molecular diagnostics for monitoring insecticide resistance in the western flower thrips Frankliniella occidentalis.

Insecticide resistance has emerged in various western flower thrips (WFT) populations across the world, threatening the efficiency of chemical control applications. Elucidation of insecticide resistance mechanisms at the molecular level provides markers for the development of diagnostics to monitor the trait and support evidence-based resistance management. TaqMan and Droplet Digital polymerase chain reaction (ddPCR) diagnostics were developed and validated, against Sanger sequencing, in individual and pooled WFT samples respectively, for the G275E mutation (nicotinic acetylcholine receptor α6 gene, nAChR α6) associated with resistance to nAChR allosteric modulators, site I (spinosyns); L1014F, T929I, T929C and T292V mutations (voltage-gated sodium channel gene, vgsc) linked with pyrethroid resistance; and I1017M (chitin synthase 1 gene, chs1) conferring resistance to growth inhibitors affecting CHS1 (benzoylureas). The detection limits of ddPCR assays for mutant allelic frequencies (MAF) were in the range of 0.1%-0.2%. The assays were applied in nine WFT field populations from Crete, Greece. The G275E (MAF=29.66%-100.0%), T929I and T929V (combined MAF=100%), L1014F (MAF=11.01%-37.29%), and I1017M (MAF=17.74%-51.07%) mutations were present in all populations. The molecular diagnostics panel that was developed in this study can facilitate the quick and sensitive resistance monitoring of WFT populations at the molecular level, to support evidence-based insecticide resistance management strategies. © 2022 Society of Chemical Industry.

Western flower thrips (Frankliniella occidentalis) field resistance to spinetoram in North Carolina

The western flower thrips (Frankliniella occidentalis (Pergande), “WFT”) is an invasive pest of fruit and vegetable crops throughout the southeastern United States. The spinosyn insecticides spinetoram (Radiant®) and spinosad (SpintTor®) have been used to manage WFT in NC tomatoes for >20 years. Control failures with spinetoram were reported by growers in the Piedmont of NC beginning in the mid-2010s. The goal of this study was to investigate the development of WFT resistance to Radiant in tomato fields in Piedmont and mountain production regions of NC. In 2019 and 2020, WFT populations were collected from staked-tomato fields and subjected to dose-response bioassays to estimate lethal concentration values (LC50) for comparison with a susceptible laboratory colony. In 2021, additional populations were collected from each region and evaluated using diagnostic doses of Radiant (100 and 1000 PPM v/v). Results from dose-response bioassays revealed resistance ratios (RR50) as high as 1487.7 in populations from Rowan County in the Piedmont. Additional diagnostic dose bioassays conducted in 2021 further supported reduced susceptibility to Radiant in all five tested populations. Populations from Henderson County in the mountains were much more susceptible than those in the Piedmont, with resistance rations of only 1.18 and 26.15. Bioassays with a single highly resistant colony over 17 generations found survival to remain mostly constant. These results provide evidence supporting the development of practical, field-evolved resistance to spinetoram in WFT in NC, and the need for improved insecticide resistance management strategies.

First detection of resistance to deltamethrin in Spanish populations of the Mediterranean fruit fly, Ceratitis capitata

The control of the Mediterranean fruit fly (Medfly), Ceratitis capitata, in citrus orchards in Spain is mainly based in three insecticides (spinosad, lambda-cyhalothrin and deltamethrin) and the liberation of sterile males. However, Medfly control is compromised by the development of lambda-cyhalothrin resistance and the detection of spinosad-resistant alleles in field populations. We report here, for the first time, resistance to deltamethrin in populations collected in fields under different management strategies, including MagnetMed™ traps coated with this insecticide and/or spinosad and lambda-cyhalothrin used as bait sprays, and even in populations obtained from non-treated fields. Two deltamethrin-resistant strains (BP-delta and Rfg-delta) were generated from the descendants of some of the field populations that showed lower susceptibility to deltamethrin. Both strains showed low susceptibility to MagnetMed™ traps, moderate susceptibility to Ceratipack traps, and lacked cross-resistance to spinosad and lambda cyhalothrin. Our data suggest that deltamethrin resistance was mediated by P450 enzymes, since bioassays with synergists showed that PBO reverted resistance in a field population and the laboratory strains, whereas the effect of DEF and DEM was minor and no mutations were found in the VGSC gene. The inheritance of resistance for both strains was completely recessive, autosomic and did not fit the mortality expected for a recessive character under a monogenic or digenic model. We also found that deltamethrin resistance presented a fitness cost in terms of males’ weight, males’ and females’ longevity and lifetime fecundity, with a more pronounced effect in the BP-strain than in the Rfg-delta strain. Our results highlight the need to implement insecticide resistance management strategies to prevent control failures.

Insecticide resistance in malaria and arbovirus vectors in Papua New Guinea, 2017–2022

BackgroundInsecticide resistance (IR) monitoring is essential for evidence-based control of mosquito-borne diseases. While widespread pyrethroid resistance in Anopheles and Aedes species has been described in many countries, data for Papua New Guinea (PNG) are limited. Available data indicate that the local Anopheles populations in PNG remain pyrethroid-susceptible, making regular IR monitoring even more important. In addition, Aedes aegypti pyrethroid resistance has been described in PNG. Here, Anopheles and Aedes IR monitoring data generated from across PNG between 2017 and 2022 are presented.MethodsMosquito larvae were collected in larval habitat surveys and through ovitraps. Mosquitoes were reared to adults and tested using standard WHO susceptibility bioassays. DNA from a subset of Aedes mosquitoes was sequenced to analyse the voltage-sensitive sodium channel (Vssc) region for any resistance-related mutations.ResultsApproximately 20,000 adult female mosquitoes from nine PNG provinces were tested. Anopheles punctulatus sensu lato mosquitoes were susceptible to pyrethroids but there were signs of reduced mortality in some areas. Some Anopheles populations were also resistant to DDT. Tests also showed that Aedes. aegypti in PNG are resistant to pyrethroids and DDT and that there was also likelihood of bendiocarb resistance. A range of Vssc resistance mutations were identified. Aedesalbopictus were DDT resistant and were likely developing pyrethroid resistance, given a low frequency of Vssc mutations was observed.ConclusionsAedes aegypti is highly pyrethroid resistant and also shows signs of resistance against carbamates in PNG. Anopheles punctulatus s.l. and Ae. albopictus populations exhibit low levels of resistance against pyrethroids and DDT in some areas. Pyrethroid-only bed nets are currently the only programmatic vector control tool used in PNG. It is important to continue to monitor IR in PNG and develop proactive insecticide resistance management strategies in primary disease vectors to retain pyrethroid susceptibility especially in the malaria vectors for as long as possible.Graphic abstract

Flubendiamide Resistance and Its Mode of Inheritance in Tomato Pinworm Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae).

Tomato pinworm, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) is the major pest of tomato crops in Pakistan. Insecticides are commonly used for the management of this insect-pest. To develop a better insecticide resistance management strategy and evaluate the risk of resistance evolution, a field collected population of the tomato pinworm was selected with flubendiamide in the laboratory. We investigated the genetics of flubendiamide resistance and concentration-mortality response to other insecticides by selecting a field strain of tomato pinworm with commercial flubendiamide formulation. Tuta absoluta was reciprocally crossed with resistant strain (Fluben-R) and was selected up to 13 generations, while F1 progeny was back-crossed with resistant parent (Fluben-R). The results of LC50 and Resistance Ratio (RR) demonstrated a higher resistance developed in field and laboratory-selected strains (G2 and G13, respectively). Field-collected and laboratory-selected (Fluben-R) strains demonstrated higher intensity of concentration-mortality response against chlorantraniliprole, thiamethoxam, permethrin, abamectin and tebufenozide compared to susceptible ones. Based on the overlapping of 95% FL, it demonstrated significant differences, revealing that it was not sex linked (autosomal) with no maternal effects. The backcross analysis of the F1´ resistant parent resulting in significant differences at all concentrations suggests that resistance is controlled by more than one factor; the null hypothesis was rejected and inheritance was under polygenic control. Resistance progression from 38 to 550 folds demonstrated that T. absoluta can develop a higher level of resistance to flubendiamide. Concentration-mortality response experiments demonstrated that the LC50 of some tested insecticides was higher for field-collected and laboratory-selected strains, suggesting that resistance mechanisms should be studied at a molecular level for better understanding. These results could be helpful to design resistance management strategies against the tomato pinworm.

Resistance to Beta-cypermethrin, Azadirachtin, and Matrine, and Biochemical Characterization of Field Populations of Oedaleus asiaticus (Bey-Bienko) in Inner Mongolia, Northern China.

Oedaleus asiaticus (Bey-Bienko) is an economically devastating locust species found in grassland and pastoral areas of the Inner Mongolia region of northern China. In this study, resistance to three frequently used insecticides (beta-cypermethrin, matrine, and azadirachtin) was investigated in six field populations of O. asiaticus using the leaf-dip bioassay method. The inhibitory effects of synergists and the activities of detoxification enzyme activities in the different populations were determined to explore potential biochemical resistance mechanisms. The results showed that the field populations SB (resistance ratio [RR] = 7.85), ZB (RR = 5.64), and DB (RR = 6.75) had developed low levels of resistance to beta-cypermethrin compared with a susceptible control strain. Both the SB (RR = 5.92) and XC (RR = 6.38) populations had also developed low levels of resistance against matrine, with the other populations remaining susceptible to both beta-cypermethrin and matrine. All field populations were susceptible to azadirachtin. Synergism analysis showed that triphenyl phosphate (TPP) and diethyl-maleate (DEM) increased the toxicity of beta-cypermethrin significantly in the SB population, while the synergistic effects of TPP, piperonyl butoxide (PBO), and DEM on the toxicity of matrine were higher in SB (SR 3.86, 4.18, and 3.07, respectively) than in SS (SR 2.24, 2.86, and 2.29, respectively), but no synergistic effects of TPP, PBO, and DEM on azadirachtin were found. Biochemical assays showed that the activities of carboxylesterases (CarEs) and glutathione-S-transferases (GSTs) were significantly raised in all field populations of O. asiaticus, with a significant positive correlation observed between beta-cypermethrin resistance and CarE activity. The activities of cytochrome P450 monooxygenases (P450) and multi-function oxidases (MFO) were elevated in all six field populations, and P450 activity displayed strong positive correlations with the three insecticides. Our findings suggest that resistance to beta-cypermethrin in O. asiaticus may be mainly attributed to elevated CarE and GST activities, while P450 plays an important role in metabolizing matrine and azadirachtin. Our study provides insights that will help improve insecticide resistance management strategies.