Resistance Management Strategies Research Articles

First Report of Helicoverpa armigera (Lepidoptera: Noctuidae) Resistance to Flubendiamide in Brazil: Genetic Basis and Mechanisms of the Resistance

The cotton bollworm Helicoverpa armigera (Lepidoptera: Noctuidae) is a significant pest in the world and it was identified in Brazil in 2013, causing severe economic losses. Recent studies showed a significant decrease in the susceptibility of H. armigera to diamide insecticides in Brazil. Understanding the genetic basis and mechanisms of the resistance are essential to develop proactive resistance management strategies. A laboratory strain of H. armigera resistant to the phthalic acid diamide flubendiamide (Flub-R) was selected from a field-collected population to characterize the resistance. The resistance ratio of the Flub-R strain was >50,000-fold. The inheritance pattern of the resistance was characterized as an autosomal dominant trait. Flub-R showed no cross-resistance to the anthranilic diamides chlorantraniliprole, cyantraniliprole or cyclaniliprole. Susceptible strain larvae that fed on flubendiamide-treated soybean leaves at field-recommended rates were killed while heterozygotes and Flub-R larvae showed a high survival and no reduction in the leaf consumption, confirming the functional dominance of the resistance. No indication of metabolic resistance was detected. The partial sequencing of ryanodine receptor (RyR) genes covering the transmembrane II to VI did not show any amino acid mutations, indicating the presence of a non-common resistance mechanism to diamide insecticides in the Flub-R strain.

Large-Scale Monitoring of the Frequency of Ryanodine Receptor Target-Site Mutations Conferring Diamide Resistance in Brazilian Field Populations of Fall Armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae).

Simple SummaryFall armyworm (FAW), Spodoptera frugiperda, is a destructive moth pest species on various crops, particularly corn. It is native to the tropical regions of the Western Hemisphere such as Brazil, but recently invaded Africa, India, China, and Australia. Its larval stages damage crops by feeding, and to keep them under damage thresholds, insecticide applications are common. Due to frequent insecticide applications, FAW evolved resistance to different chemical classes of insecticides, including diamides. Field relevant levels of diamide resistance are usually conferred by ryanodine receptor (RyR) mutations and compromising recommended label rates. Diamide resistance in FAW so far remained restricted to laboratory-selected strains. Here, we investigated the frequency of specific resistance mutations in field-collected Brazilian populations of FAW by an F2 screen, selected two populations (BA-R and TF-R) for high levels of diamide resistance, deciphered the genetics of resistance, and employed a molecular genotyping assay to correlate resistance levels with the presence of RyR mutations. Crossin studies indicated that resistance is autosomal and (incompletely) recessive in both strains. F1 backcrosses suggested monogenic resistance, supported by the identification of an I4734M/K target-site mutation in the RyR. Our results will help to sustainably manage diamide resistance in FAW in Brazil.Fall armyworm (FAW), Spodoptera frugiperda, is an important lepidopteran pest in the Americas, and recently invaded the Eastern Hemisphere. In Brazil, FAW is considered the most destructive pest of corn and cotton. FAW has evolved resistance to many insecticides and Bacillus thuringiensis (Bt) proteins. Here, a large-scale monitoring was performed between 2019 and 2021 to assess diamide insecticide susceptibility in more than 65 FAW populations sampled in corn and cotton. We did not detect a significant shift in FAW susceptibility to flubendiamide, but a few populations were less affected by a discriminating rate. F2 screen results of 31 selected FAW populations across regions confirmed that the frequency of diamide resistance alleles remained rather stable. Two laboratory-selected strains exhibited high resistance ratios against flubendiamide, and cross-resistance to anthranilic diamides. Reciprocal crosses indicated that resistance is autosomal and (incompletely) recessive in both strains. F1 backcrosses suggested monogenic resistance, supported by the identification of an I4734M/K target-site mutation in the ryanodine receptor (RyR). Subsequent genotyping of field-collected samples employing a TaqMan-based allelic discrimination assay, revealed a low frequency of RyR I4790M/K mutations significantly correlated with phenotypic diamide resistance. Our findings will help to sustainably employ diamides in FAW resistance management strategies across crops.

Geographic distribution of deltamethrin resistance in malaria vectors from 2010 to 2020 in Republic of Benin, West Africa

The current study aims to establish the cartography of deltamethrin resistance in malaria vectors from 2010 to 2020 in Republic of Benin. An. gambiae s.l. populations were collected from March to July during the great rainy season in Ouémé in 2010, Littoral in 2012, Atlantic in 2012, Couffo in 2020 and Collines in 2012. An. gambiae s.l. populations were also collected from May to October during the rainy season in Alibori in 2012 and in 2015. Susceptibility tests were done following WHO protocol on unfed females’ mosquitoes aged 2-5 days old reared from larval and pupal collections with papers impregnated with deltamethrin (0.05%). The results showed that the populations of Anopheles gambiae s.l. from Adjara, Dangbo and Missérété were resistant to deltamethrin in 2010 whereas the populations of Anopheles gambiae s.l. from Kandi, Malanville, Cotonou, Allada and Dassa-Zoumè were resistant to this product in 2012. The populations of Anopheles gambiae s.l. from Parakou were resistant to deltamethrin in 2015 whereas the populations of Anopheles gambiae s.l. from Dogbo were resistant to the same product in 2020. The establishment of mapping or geographic distribution of deltamethrin resistance in malaria vectors from 2010 to 2020 in Republic of Benin is useful as this will properly inform control programs of the most suitable insecticides to use and facilitate the design of appropriate future resistance management strategies.

Inheritance and Fitness Costs of Vip3Aa19 Resistance in Mythimna separata.

The “high-dose/refuge” strategy is expected to work most effectively when resistance is inherited as a functionally recessive trait and the fitness costs associated with resistance are present. In the present study, a laboratory selected Mythimna separata strain that have evolved >634.5-fold resistance to Vip3Aa19 was used to determine the mode of inheritance. To determine if fitness costs were associated with the resistance, life history parameters (larva stage, pupa stage, pupal weight, adult longevity and fecundity) of resistant (RR), -susceptible (SS) and heterozygous (R♂S♀ and R♀S♂) strains on nontoxic diet were assayed. The LC50 values of R♀S♂ were significantly higher than that of R♂S♀ (254.58 μg/g vs. 14.75 μg/g), suggesting that maternal effects or sex linkage were present. The effective dominance h of F1 offspring decreased as concentration increased, suggesting the resistance was functionally dominant at low concentration and recessive at high concentration. The analysis of observed and expected mortality of the progeny from a backcross suggested that more than one locus is involved in conferring Vip3Aa19 resistance. The results showed that significant differences in many life history traits were observed among the four insect genotypes. In short, resistance to Vip3Aa19 in M. separata was inherited as maternal and multigene and the resistance in the strain was associated with significant fitness costs. The results described here provide useful information for understanding resistance evolution and for developing resistance management strategies.

Characterizing the sublethal effects of SmartStax PRO dietary exposure on life history traits of the western corn rootworm, Diabrotica virgifera virgifera LeConte.

The western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte, is an economically important pest of field corn (Zea mays L.) across the United States (U.S.) Corn Belt. Repeated use of transgenic hybrids expressing Bacillus thuringiensis (Bt) proteins has selected for field-evolved resistance to all current rootworm-active Bt proteins. The newest product available for WCR management is SmartStax® PRO, a rootworm-active pyramid containing Cry3Bb1, Cry34/35Ab1 [now reclassified as Gpp34Ab1/Tpp35Ab1] and a new mode of action, DvSnf7 dsRNA. Understanding the fitness of adult WCR after dietary exposure to SmartStax® PRO will identify potential impacts on WCR population dynamics and inform efforts to optimize resistance management strategies. Therefore, the objective of the present study was to characterize the effect of SmartStax® PRO dietary exposure on WCR life history traits. Adult WCR were collected during 2018 and 2019 from emergence tents placed over replicated field plots of SmartStax® PRO or non-rootworm Bt corn at a site with a history of rootworm-Bt trait use and suspected resistance to Cry3Bb1 and Cry34/35Ab1. Adult survival was reduced by 97.1–99.7% in SmartStax® PRO plots relative to the non-rootworm Bt corn plots during the study. Individual male/female pairs were fed different diets of ear tissue to simulate lifetime or adult exposure. Life history parameters measured included adult longevity, adult head capsule width, lifetime female egg production, and egg viability. Results indicate that lifetime or adult exposure to SmartStax® PRO significantly reduced adult longevity and lifetime egg production. Larval exposure to SmartStax® PRO significantly reduced WCR adult size. Results from this study collectively suggest that SmartStax® PRO may negatively impact WCR life history traits, which may lead to reduced population growth when deployed in an area with WCR resistance to Bt traits.

Mistranslating refuge crops: analyzing policy mobilities in the context of Indian Bt cotton production

Abstract. In light of recent pink bollworm (PBW) pest infestations in several cotton-producing states in India, farmers of genetically engineered Bt cotton (Bt for Bacillus thuringiensis) have faced fierce criticism for their noncompliance with the national insect resistance management (IRM) strategy. We argue that this criticism is short-sighted and one-dimensional. Building upon the literature on policy assemblages we show that the implementation of the IRM strategy in India was seriously flawed due to government-induced mistranslations of foreign strategies in the form of policy-diluting alterations. We first show that India's IRM strategy differs substantially from successful strategies pursued in the USA or China. Second, we present results from a representative survey in the state of Telangana (n= 457) and show that India's IRM strategy neglects moral economic considerations and entrepreneurial agricultural logic that Indian cotton farmers strive for. We conclude that pink bollworm pest infestations in India are not the fault of farmers but rather the result of a mismanaged biotechnology project undertaken by the Indian government and its associated responsible ministries.

Insecticide Resistance in the Disease Vector Culex pipiens in Morocco: Intensity, Mechanisms, and Contribution in Insecticide Resistance Management

West Nile (WN) virus has been detected in Morocco in 1996, 2003, and 2010. One WN human case and 94 equine cases with 42 deaths were reported in the first outbreak. The second and the last epizootics were in Kénitra and Mohammedia regions, respectively. Culex pipiens mosquitoes were strongly suspected as WN vectors during these epizootics in Morocco. To help propose the first insecticide resistance management strategy in Morocco, we provide baseline data on the resistance status of C. pipiens mosquitoes to insecticides most used in public health in Morocco. We investigated the resistance intensity of C. pipiens and the role of monooxygenases in pyrethroids resistance using the synergist piperonyl butoxide (PBO) in three prefectures of central Morocco: Mohammedia, Benslimane, and Skhirate. Bioassays were carried out using WHO (World Health Organization) diagnostic test kits for adult mosquitoes, with DDT 4%; deltamethrin 0.05%, 0.25%, and 0.5%; bendiocarb 0.1%, 0.5%, and 1%; and malathion 5%. The synergist PBO 4% was used to check for the involvement of detoxification enzymes in pyrethroids resistant populations. Mosquito populations tested displayed high resistance intensity to pyrethroids and carbamates in Mohammedia and moderate resistance intensity in Skhirate. In Benslimane, the resistance intensity of C. pipiens was high to carbamate and moderate to pyrethroids. The pre-exposure to PBO restored full or partial susceptibility to pyrethroids in the different regions. According to our finding, Mohammedia and Benslimane are at risk level 3 of control failure, while Skhirate is at risk level 2 of it. The employment of IRM is therefore imperative in all study sites.

Functional analysis of cyantraniliprole tolerance ability mediated by ATP-binding cassette transporters in Aphis gossypii glover

Cyantraniliprole, a second-generation anthranilic diamide insecticide, is widely used to control chewing and sucking pests. ATP-binding cassette transporters (ABCs) are a ubiquitous family of membrane proteins that play important roles in insect detoxification mechanisms. However, the potential effects of ABCs on cyantraniliprole-resistance remain unclear. In the present study, synergism bioassays revealed that verapamil, an ABC inhibitor, increased the toxicity of cyantraniliprole by 2.00- and 12.25-fold in the susceptible and cyantraniliprole-resistant strains of Aphis gossypii. Based on transcriptome data, the expression levels of ABCB4, ABCB5, ABCD1, ABCG4, ABCG7, ABCG13, ABCG16, ABCG17, ABCG26 and MRP12 were upregulated 1.56-, 1.32-, 1.51-, 2.03-, 1.65-, 1.50-, 4.18-, 6.07-, 4.68- and 4.69-fold, respectively, in the cyantraniliprole-resistant strain (CyR) compared to the susceptible strain (SS), as determined using RT-qPCR. Drosophila melanogaster ectopically overexpressing ABCB5, ABCG4, ABCG7, ABCG16, ABCG17, ABCG26 and MRP12 exhibited significantly increased tolerance to cyantraniliprole by 11.71-, 2.39-, 4.85-, 2.06-, 3.75-, 4.20- and 3.50-fold, respectively, with ABCB5 and ABCG family members being the most effective. Furthermore, the suppression of ABCB5, ABCG4, ABCG7, ABCG16, ABCG17, ABCG26 and MRP12 significantly increased the sensitivity of the CyR strain to cyantraniliprole. These results indicate that ABCs may play crucial roles in cyantraniliprole resistance and may provide information for shaping resistance management strategies.

Reduction in malaria burden following the introduction of indoor residual spraying in areas protected by long-lasting insecticidal nets in Western Kenya, 2016-2018.

Long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS) are the main malaria vector control measures deployed in Kenya. Widespread pyrethroid resistance among the primary vectors in Western Kenya has necessitated the re-introduction of IRS using an organophosphate insecticide, pirimiphos-methyl (Actellic® 300CS), as a pyrethroid resistance management strategy. Evaluation of the effectiveness of the combined use of non-pyrethroid IRS and LLINs has yielded varied results. We aimed to evaluate the effect of non-pyrethroid IRS and LLINs on malaria indicators in a high malaria transmission area. We reviewed records and tallied monthly aggregate of outpatient department (OPD) attendance, suspected malaria cases, those tested for malaria and those testing positive for malaria at two health facilities, one from Nyatike, an intervention sub-county, and one from Suba, a comparison sub-county, both located in Western Kenya, from February 1, 2016, through March 31, 2018. The first round of IRS was conducted in February-March 2017 in Nyatike sub-county and the second round one year later in both Nyatike and Suba sub-counties. The mass distribution of LLINs has been conducted in both locations. We performed descriptive analysis and estimated the effect of the interventions and temporal changes of malaria indicators using Poisson regression for a period before and after the first round of IRS. A higher reduction in the intervention area in total OPD, the proportion of OPD visits due to suspected malaria, testing positivity rate and annual malaria incidences were observed except for the total OPD visits among the under 5 children (59% decrease observed in the comparison area vs 33% decrease in the intervention area, net change -27%, P <0.001). The percentage decline in annual malaria incidence observed in the intervention area was more than twice the observed percentage decline in the comparison area across all the age groups. A marked decline in the monthly testing positivity rate (TPR) was noticed in the intervention area, while no major changes were observed in the comparison area. The monthly TPR reduced from 46% in February 2016 to 11% in February 2018, representing a 76% absolute decrease in TPR among all ages (RR = 0.24, 95% CI 0.12-0.46). In the comparison area, TPR was 16% in both February 2016 and February 2018 (RR = 1.0, 95% CI 0.52-2.09). A month-by-month comparison revealed lower TPR in Year 2 compared to Year 1 in the intervention area for most of the one year after the introduction of the IRS. Our findings demonstrated a reduced malaria burden among populations protected by both non-pyrethroid IRS and LLINs implying a possible additional benefit afforded by the combined intervention in the malaria-endemic zone.

Multiple resistance to imazethapyr, atrazine, and glyphosate in a recently introduced Palmer amaranth (Amaranthus palmeri) accession in Wisconsin

AbstractThe continued dispersal of Palmer amaranth can impose detrimental impacts on cropping systems in Wisconsin. Our objective was to characterize the response of a recently introduced Palmer amaranth accession in southern Wisconsin to postemergence (POST) and preemergence (PRE) herbicides commonly used in corn and soybean. Greenhouse experiments were conducted with the Wisconsin putative herbicide-resistant accession (BRO) and two additional control accessions from Nebraska, a glyphosate-resistant (KEI2) and a glyphosate-susceptible (KEI3) accession. POST treatments were 2,4-D, atrazine, dicamba, glufosinate, glyphosate, imazethapyr, lactofen, and mesotrione at 1X and 3X label rates. PRE treatments were atrazine, mesotrione, metribuzin, S-metolachlor, and sulfentrazone at 0.5X, 1X, and 3X label rates. Plant survival of each accession was ≥63% after exposure to imazethapyr POST 3X rate. Survival of BRO and KEI2 was 44% (±13) and 50% (±13), respectively, after exposure to atrazine POST 3X rate. Survival of BRO was 69% (±12) after exposure to glyphosate POST 1X rate, whereas survival of KEI2 was 44% (±13) after exposure to glyphosate POST 3X rate. After exposure to 2,4-D POST 1X rate, KEI2 and KEI3 survival was 38% (±13) and 50% (±13), respectively. Survival of all accessions was ≤31% after exposure to 2,4-D POST 3X rate or dicamba, glufosinate, lactofen, and mesotrione POST at either rate. Plant density reduction of KEI2 was 77% (±13) after exposure to atrazine PRE 1X rate, whereas density reduction of BRO was 56% (±13) after exposure to atrazine PRE 3X rate. Plant density reduction of all accessions was ≥94% after exposure to mesotrione PRE 1X and 3X rates or metribuzin, S-metolachlor, and sulfentrazone PRE at either rate. Our results suggest that each accession is resistant (≥50% survival) to imazethapyr POST, that BRO and KEI2 are resistant to atrazine and glyphosate POST, and that KEI2 and KEI3 are resistant to 2,4-D POST. The recently introduced BRO accession exhibited multiple resistance to imazethapyr, atrazine, and glyphosate POST. In addition, atrazine PRE was ineffective for BRO control, suggesting that diversified resistance management strategies will be critical for its effective management.

Baseline susceptibility of Australian Myzus persicae (Hemiptera: Aphididae) to novel insecticides flonicamid and afidopyropen

The green peach aphid, Myzus persicae (Sulzer) is a significant global pest of a broad range of horticultural and grain crops. Control of M. persicae is primarily dependent on insecticides, however, this species has a high propensity to evolve insecticide resistance and has evolved resistance to over 80 insecticides from various chemical groups worldwide. In Australia, widespread resistance to carbamates, organophosphates, pyrethroids and neonicotinoids in M. persicae populations is commonplace. Given the ability of M. persicae to establish resistance to new chemistries quickly, programs are needed to monitor susceptibility to new insecticides before their widespread use. In this study, we used leaf-dip bioassays to generate sensitivity data and investigate potential cross-resistance in multiple field-collected populations of Australian M. persicae to two recently registered insecticides, flonicamid and afidopyropen. After 144 and 168 h exposure, we found little variation in the susceptibility of M. persicae populations to either flonicamid or afidopyropen, and no evidence of sensitivity shifts in the field. Additionally, there was no evidence of cross-resistance between flonicamid or afidopyropen and multiple known resistance mechanisms for carbamate, pyrethroid, organophosphate and neonicotinoid insecticides. The sensitivity data generated in this study prior to the evolution of field resistance provides a useful starting point for future resistance monitoring, and allows for the development and implementation of insecticide resistance management strategies which should prolong the long-term efficacy of flonicamid and afidopyropen against M. persicae.

Bisexual Attract-and-Kill: A Novel Component of Resistance Management for Transgenic Cotton in Australia.

In Australia, destruction of overwintering pupae of Helicoverpa armigera (Hübner) and Helicoverpa punctigera (Wallengren) (Lepidoptera: Noctuidae) has been a key component of mandatory resistance management schemes to constrain development of resistance to Bt toxins in transgenic cotton. This has been accomplished by tillage (‘pupae busting’), but it is expensive and can interfere with farming operations. Bisexual attract-and-kill technology based on plant volatile formulations offers a potential alternative in some circumstances. We discuss strategies for using such products and describe two trials in which three applications of an attract-and-kill formulation substantially reduced the numbers of Helicoverpa spp. moths and the numbers of potentially overwintering eggs they laid. One trial tested a curative strategy in which the last generation of moths emerging from transgenic cotton was targeted. The other tested a preventive strategy which aimed to reduce the numbers of eggs in the last generation. The preventive strategy reduced egg numbers by about 90% and is now included as an optional alternative to pupae busting in resistance management strategies for Australian cotton. It is limited to fields which have not been defoliated prior to 31 March and was developed to be used primarily in southern New South Wales. In the 2020–2021 cotton season, it was adopted on approximately 60% of the eligible cotton area. We describe the process whereby the strategy was developed in collaboration with the transgenic technology provider, supported by the cotton industry, and approved by the regulatory authority.

Resistance Allele Frequency to Cry1Ab and Vip3Aa20 in Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae) in Louisiana and Three Other Southeastern U.S. States.

The corn earworm/bollworm, Helicoverpa zea (Boddie), is a pest species that is targeted by both Bacillus thuringiensis (Bt) maize and cotton in the United States. Cry1Ab and Vip3Aa20 are two common Bt toxins that are expressed in transgenic maize. The objective of this study was to determine the resistance allele frequency (RAF) to Cry1Ab and Vip3Aa20 in H. zea populations that were collected during 2018 and 2019 from four southeastern U.S. states: Louisiana, Mississippi, Georgia, and South Carolina. By using a group-mating approach, 104 F2 iso-lines of H. zea were established from field collections with most iso-lines (85) from Louisiana. These F2 iso-lines were screened for resistance alleles to Cry1Ab and Vip3Aa20, respectively. There was no correlation in larval survivorship between Cry1Ab and Vip3Aa20 when the iso-lines were exposed to these two toxins. RAF to Cry1Ab maize was high (0.256) and the RAFs were similar between Louisiana and the other three states and between the two sampling years. In contrast, no functional major resistance allele (RA) that allowed resistant insects to survive on Vip3Aa20 maize was detected and the expected RAF of major RAs with 95% probability was estimated to 0 to 0.0073. However, functional minor RAs to Vip3Aa20 maize were not uncommon; the estimated RAF for minor alleles was 0.028. The results provide further evidence that field resistance to Cry1Ab maize in H. zea has widely occurred, while major RAs to Vip3Aa20 maize are uncommon in the southeastern U.S. region. Information that was generated from this study should be useful in resistance monitoring and refinement of resistance management strategies to preserve Vip3A susceptibility in H. zea.

Baseline Susceptibility and Resistance Allele Frequency in Ostrinia furnacalis in Relation to Cry1Ab Toxins in China.

Asian corn borer (ACB), Ostrinia furnacalis (Guenée) is a destructive pest of corn and major target of transgenic corn expressing Bt (Bacillus thuringiensis) toxins in China. It is necessary to establish the baseline susceptibility of geographically distinct ACB populations to Cry1Ab protein and estimate the resistance alleles frequency. The median lethal concentration (LC50) and LC95 values of Bt toxin Cry1Ab for 25 geographically distinct populations collected in 2018–2019 ranged from 0.86 to 71.33, 18.58 to 5752.34 ng/cm2, respectively. The median effective concentration (EC50) and EC95 values ranged from 0.03 to 10.40 ng/cm2 and 3.75 to 172.86 ng/cm2, respectively. We used the F2 screening method for estimating the expected frequency of resistance alleles of the 13 ACB populations, to Bt corn (Bt11 × GA21) expressing the Cry1Ab toxin. The neonates could not survive on the leaves of transgenic maize Bt11 × GA21 with cry1Ab gene, the Cry1Ab resistance allele frequency was still low in each geographic population in the field, ranging from 0.0032–0.0048, indicating that the sensitivity of ACB to Cry1Ab was still at a high level, and there were no viable resistant individuals in the field at present. The susceptibility of 25 populations of ACB collected in China showed regional differences, although the Cry1Ab resistance allele frequency in these ACB populations is still at a low level. This provides essential knowledge for making the decision to commercialize Bt maize, and monitoring resistance development and evaluating resistance management strategies in the future in China.

Insect resistance management facing African smallholder farmers under climate change.

Changes in climatic conditions affect pest populations and ultimately result in increased pest status and yield losses. While pesticide application is usually the first defensive tool used to control pest species that threaten crop production, genetically modified (GM) crops with insecticidal traits (Bt crops) are becoming more common. The indiscriminate and over use of insecticides, and absence of insect resistance management (IRM) strategies ultimately lead to evolution of resistance against these technologies. IRM faces significant challenges in the African context. In this paper we use examples of cotton, maize, cowpea and tomato pests to illustrate their potential to evolve resistance to insecticides and also highlight the importance of IRM strategies, both with regard to the use of pesticides and the cultivation of Bt cotton, Bt maize and Bt cowpea.

Changes in Dicamba Use are Ahead

The first steps in the development of dicamba tolerant transgenic plants were conducted by Sandoz Crop Protection in Palo Alto, CA and then contractually followed up at the University of Nebraska. The subsequent development by Monsanto of soybean and cotton varieties that would tolerate post-emergent application of dicamba substantially changed the use patterns of dicamba in the United States. Transgenic dicamba-tolerant (DT) seeds were first approved in 2016 in the United States, although the post-emergent use of dicamba was not legal that year. In 2017 and 2018, there was substantial market penetration of DT soybean and cotton seeds into the market and the occurrence of dicamba off-target movement (OTM) was highly variable across the United States. The driving force behind these new seed traits was the widespread failure of glyphosate to control broadleaf weeds effectively, especially those from the Conyza and Amaranthus genera. Herbicide research and development in the United States has historically involved both industry and academic weed scientists usually operating in a symbiotic and mutually respectful relationship, although there may have been disagreements at times about some aspects of herbicides and their development. The relatively recent introduction of DT varieties and legal post-emergent dicamba in the United States was a dynamic time for weed control, and adoption of DT crops and subsequent OTM of dicamba greatly changed the working relationships between academic scientists and representatives from Monsanto and some other private companies. Perhaps the greatest change was the lack of access of research materials that would be available to academic scientists for evaluation prior to the retail sale of those materials. Historically, academic scientists would have the ability to evaluate various new technologies and provide objective, independent comments on their potential utility prior to commercialisation. Monsanto largely restricted access to the DT seeds or new herbicide formulations. There are some states that have long-established policies that they will not recommend a new herbicide technology unless they have examined it under their specific field conditions. For example, University of Arkansas researchers would not recommend the use of post-emergent dicamba on DT crops when it first became legal to use. Monsanto responded by filing legal challenges of various types against the University of Arkansas faculty, including 64 exhibits of various legal aspects. Many other states had varying degrees of restrictions placed upon their research efforts, and most scientists had to sign various forms of confidentiality agreements to obtain access to the research material from Monsanto. There were two major differences in the dicamba labels when first introduced in 2017 and then again two years later. The first major difference was an entire section on herbicide resistance confirmation validation and management that was clearly stated on the label. The authors of this paper remind the readers that the reason we have dicamba being used is because of the wholesale failure of glyphosate resistance management systems. The golden era of weed control, essentially 100% weed control with no crop injury, was lost due to the complete lack of any resistance management strategies. The US EPA added label language hopefully to avoid evolution of resistance in weeds from happening again with essentially any new herbicide. Many herbicide users expect all new labels to include resistance management language. The second obvious change to the label was the duration of validity, which was normally many years in previous pesticide registrations. The first dicamba label, which came out in 2017, was valid for only two years. The next label which came out in 2019, was only valid for five years, although there is widespread speculation on the future of that label.

Magnitude of Resistance and Metabolism of Acaricides in Two-spotted Spider Mite, Tetranychus urticae Koch on Vegetables in Southern Districts of Tamil Nadu

Background: Two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae) is a destructive, polyphagous and cosmopolitan pest infesting a wide range of vegetables. Farmers frequently use acaricides in the vegetable ecosystem for mite management leading to increased probability for the development of resistance against acaricides in mite species. Literature about resistance in T. urticae to novel acaricides is scanty from this region. Hence, this study was aimed to evaluate the magnitude of acaricide resistance in T. urticae populations on vegetable crops from Southern districts of Tamil Nadu against seven acaricides. The role of detoxification enzymes in conferring bio-chemical resistance in the mite species was also studied. Methods: The laboratory experiments were conducted at completely randomized design (CRD) during 2019-2021 in central instrumentation laboratory, Department of Agricultural Entomology, Agricultural College and Research Institute, Tamil Nadu Agricultural University, Madurai. The level of resistance in T. urticae populations to fenazaquin, propargite, spiromesifen, buprofezin, fenpropathrin, diafenthiuron and chlorfenapyr was evaluated following the leaf dip bioassay technique. The activity of the detoxifying enzymes viz., Glutathione S Transferase (GST), Mixed Function Oxidase (MFO) and Carboxylesterase (CarE) were estimated. Result: Fenazaquin was highly toxic to T. urticae, which recorded a low level of resistance (2.00 to 8.62-fold). T. urticae exhibited a low to moderate level of resistance to fenpropathrin (1.86 to 37.28-fold), moderate to a high level of resistance to diafenthiuron (15.81 to 50.53-fold), high level of resistance to propargite (45.16 to 65.10-fold) and chlorfenapyr (54.67 to 100.14-fold) and extremely high level of resistance to spiromesifen (193.04 to 452.61-fold) and buprofezin (377.97 to 514.44-fold). Among all the test populations, the highly resistant DAmRg population exhibited the highest specific activity of the detoxifying enzymes, viz., GST (26.98 nmoles ml-1 min-1 mg of protein-1), MFO (5.07 nmoles ml-1 min-1 mg of protein-1) and CarE (827.90 nmoles ml-1 min-1 mg of protein-1). The CarE activity was found to be positively correlated with highly resistant acaricide, propargite (r = 0.995) and MFO activity with buprofezin having an extremely high level of resistance (r = 0.997). This preliminary knowledge would be instrumental in framing the acaricide resistant management (ARM) strategies.

Inheritance mode and fitness costs of acetamiprid resistance in brown planthopper, Nilaparvata lugens (Stål)

The brown planthopper, Nilaparvata lugens (Stål), is a major rice pest in Asia. Acetamiprid is a widely used neonicotinoid insecticide for N. lugens control. Because of the frequent and excessive applications of chemical insecticides, moderate levels of resistance against acetamiprid have been found in field populations of N. lugens in China. To study the inheritance mode and fitness costs of acetamiprid resistance in N. lugens, an acetamiprid-resistant strain (AC-R) was selected from a susceptible strain (AC-S) in the laboratory. After 28 generations of selection, AC-R showed 26.15-fold resistance compared to AC-S. The LC50 and degree of dominance (D) values of the F1RS and F1SR (progenies of reciprocal crosses) indicated that the acetamiprid resistance in N. lugens was inherited as autosomal and incompletely dominant. Significant differences between the expected and observed mortalities of the F2 individuals suggested that acetamiprid resistance is controlled by multiple genes. The AC-R strain showed a relative fitness of 0.71 with a significantly decreased male adult longevity, fecundity, net reproductive rate (R0), and finite rate of increase (λ), and a prolonged adult preoviposition period (APOP). However, the durations of the 1st, 2nd, and 4th instar nymphs of AC-R were significantly shorter than those of AC-S. The current study provides valuable information for understanding acetamiprid resistance and optimizing insecticide resistance management strategies of N. lugens in the field.

Effectiveness and cost-effectiveness against malaria of three types of dual-active-ingredient long-lasting insecticidal nets (LLINs) compared with pyrethroid-only LLINs in Tanzania: a four-arm, cluster-randomised trial

SummaryBackgroundLong-lasting insecticidal nets (LLINs) have successfully reduced malaria in sub-Saharan Africa, but their effectiveness is now partly compromised by widespread resistance to insecticides among vectors. We evaluated new classes of LLINs with two active ingredients with differing modes of action against resistant malaria vectors.MethodsWe did a four-arm, cluster-randomised trial in Misungwi, Tanzania. Clusters were villages, or groups of hamlets, with at least 119 households containing children aged 6 months to 14 years living in the cluster's core area. Constrained randomisation was used to allocate clusters (1:1:1:1) to receive one of four types of LLIN treated with the following: α-cypermethrin only (pyrethroid-only [reference] group); pyriproxyfen and α-cypermethrin (pyriproxyfen group); chlorfenapyr and α-cypermethrin (chlorfenapyr group); or the synergist piperonyl butoxide and permethrin (piperonyl butoxide group). At least one LLIN was distributed for every two people. Community members and the field team were masked to group allocation. Malaria prevalence data were collected through cross-sectional surveys of randomly selected households from each cluster, in which children aged 6 months to 14 years were assessed for Plasmodium falciparum malaria infection by rapid diagnostic tests. The primary outcome was malaria infection prevalence at 24 months after LLIN distribution, comparing each of the dual-active-ingredient LLINs to the standard pyrethroid-only LLINs in the intention-to-treat population. The primary economic outcome was cost-effectiveness of dual-active-ingredient LLINs, based on incremental cost per disability-adjusted life-year (DALY) averted compared with pyrethroid-only LLINs, modelled over a 2-year period; we included costs of net procurement and malaria diagnosis and treatment, and estimated DALYs in all age groups. This study is registered with ClinicalTrials.gov (NCT03554616), and is ongoing but no longer recruiting.Findings84 clusters comprising 39 307 households were included in the study between May 11 and July 2, 2018. 147 230 LLINs were distributed among households between Jan 26 and Jan 28, 2019. Use of study LLINs was reported in 3155 (72·1%) of 4378 participants surveyed at 3 months post-distribution and decreased to 8694 (40·9%) of 21 246 at 24 months, with varying rates of decline between groups. Malaria infection prevalence at 24 months was 549 (45·8%) of 1199 children in the pyrethroid-only reference group, 472 (37·5%) of 1258 in the pyriproxyfen group (adjusted odds ratio 0·79 [95% CI 0·54–1·17], p=0·2354), 512 (40·7%) of 1259 in the piperonyl butoxide group (0·99 [0·67–1·45], p=0·9607), and 326 [25·6%] of 1272 in the chlorfenapyr group (0·45 [0·30–0·67], p=0·0001). Skin irritation or paraesthesia was the most commonly reported side-effect in all groups. Chlorfenapyr LLINs were the most cost-effective LLINs, costing only US$19 (95% uncertainty interval 1–105) more to public providers or $28 (11–120) more to donors per DALY averted over a 2-year period compared with pyrethroid-only LLINs, and saving costs from societal and household perspectives.InterpretationAfter 2 years, chlorfenapyr LLINs provided significantly better protection than pyrethroid-only LLINs against malaria in an area with pyrethroid-resistant mosquitoes, and the additional cost of these nets would be considerably below plausible cost-effectiveness thresholds ($292–393 per DALY averted). Before scale-up of chlorfenapyr LLINs, resistance management strategies are needed to preserve their effectiveness. Poor textile and active ingredient durability in the piperonyl butoxide and pyriproxyfen LLINs might have contributed to their relative lack of effectiveness compared with standard LLINs.FundingJoint Global Health Trials scheme (UK Foreign, Commonwealth and Development Office; UK Medical Research Council; Wellcome; UK Department of Health and Social Care), US Agency for International Development, President's Malaria Initiative.

A new generation of long-lasting insecticidal nets

The scale-up of malaria interventions over the past two decades has resulted in substantial reductions in malaria burden, especially in sub-Saharan Africa, which accounts for 95% of the global malaria burden. 1 Bhatt S Weiss DJ Cameron E et al. The effect of malaria control on Plasmodium falciparum in Africa between 2000 and 2015. Nature. 2015; 526: 207-211 Crossref PubMed Scopus (1439) Google Scholar , 2 WHOWorld malaria report 2020: 20 years of global progress and challenges. https://www.who.int/publications/i/item/9789240015791Date: Nov 30, 2020 Date accessed: December 5, 2021 Google Scholar Between 2000 and 2019, an estimated 1·5 billion malaria cases and 7·6 million malaria deaths were averted, with many of the early gains attributed to widescale deployment of insecticide-treated nets and availability of effective drugs. 1 Bhatt S Weiss DJ Cameron E et al. The effect of malaria control on Plasmodium falciparum in Africa between 2000 and 2015. Nature. 2015; 526: 207-211 Crossref PubMed Scopus (1439) Google Scholar However, progress in global malaria control and elimination efforts have stagnated in recent years, the reasons for which are multifactorial and include the development and spread of insecticide resistance in malaria vectors. The massive scale-up of insecticide-treated nets and, later, long-lasting insecticidal nets (LLINs), which have an insecticide incorporated into the net fibre and can last longer under typical use, was accompanied by the emergence of vector resistance to pyrethroids. 3 Hancock PA Hendriks CJM Tangena JA et al. Mapping trends in insecticide resistance phenotypes in African malaria vectors. PLoS Biol. 2020; 18e3000633 Crossref PubMed Scopus (37) Google Scholar This resistance is now present in all primary vectors throughout much of sub-Saharan Africa. 3 Hancock PA Hendriks CJM Tangena JA et al. Mapping trends in insecticide resistance phenotypes in African malaria vectors. PLoS Biol. 2020; 18e3000633 Crossref PubMed Scopus (37) Google Scholar , 4 Knox TB Juma EO Ochomo EO et al. An online tool for mapping insecticide resistance in major Anopheles vectors of human malaria parasites and review of resistance status for the Afrotropical region. Parasit Vectors. 2014; 7: 76 Crossref PubMed Scopus (86) Google Scholar , 5 Moyes CL Athinya DK Seethaler T et al. Evaluating insecticide resistance across African districts to aid malaria control decisions. Proc Natl Acad Sci USA. 2020; 117: 22042-22050 Crossref PubMed Scopus (17) Google Scholar Studies have shown that a new generation of LLINs that include the synergist piperonyl butoxide have improved efficacy compared with pyrethroid-only nets. 6 WHOGlobal plan for insecticide resistance management in malaria vectors. https://apps.who.int/iris/handle/10665/44846Date: 2012 Date accessed: December 5, 2021 Google Scholar , 7 Mosha JF Kulkarni MA Lukole E et al. Effectiveness and cost-effectiveness against malaria of three types of dual-active-ingredient long-lasting insecticidal nets compared with pyrethroid-only long-lasting insecticidal nets in an area with pyrethroid-resistant mosquitoes in Tanzania: a four-arm, cluster-randomised trial. Lancet. 2022; 399: 1227-1241 Summary Full Text Full Text PDF PubMed Scopus (3) Google Scholar However, although piperonyl butoxide can restore susceptibility in pyrethroid-resistant mosquito populations wherein the primary resistance mechanism is metabolic detoxification by oxidase enzymes, it has minimal impact on other mechanisms of pyrethroid resistance. Insecticide-treated nets with novel active ingredients and different modes of action are needed. The WHO Global Plan for Insecticide Resistance Management recommends the use of two or more compounds of different insecticide classes to make a single product or formulation as an approach to combating resistance. 6 WHOGlobal plan for insecticide resistance management in malaria vectors. https://apps.who.int/iris/handle/10665/44846Date: 2012 Date accessed: December 5, 2021 Google Scholar The challenge is developing products that are not only effective against pyrethroid-resistant mosquitoes but are also safe to humans and are amenable to incorporation into the net fibres. Effectiveness and cost-effectiveness against malaria of three types of dual-active-ingredient long-lasting insecticidal nets (LLINs) compared with pyrethroid-only LLINs in Tanzania: a four-arm, cluster-randomised trialAfter 2 years, chlorfenapyr LLINs provided significantly better protection than pyrethroid-only LLINs against malaria in an area with pyrethroid-resistant mosquitoes, and the additional cost of these nets would be considerably below plausible cost-effectiveness thresholds ($292–393 per DALY averted). Before scale-up of chlorfenapyr LLINs, resistance management strategies are needed to preserve their effectiveness. Poor textile and active ingredient durability in the piperonyl butoxide and pyriproxyfen LLINs might have contributed to their relative lack of effectiveness compared with standard LLINs. Full-Text PDF Open Access