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The production of almonds and pistachios in California's Central Valley employs insecticides for the management of their primary pest, navel orangeworm.The pyrethroid Bifenthrin is commonly used, and now a strain of Amyelois transitella Walker (Lepidoptera: Pyralidae) (R347) obtained from Kern County almond orchards with a history of Bifenthrin use has acquired >110-fold resistance toward pyrethroids. One method to improve control is to use additives and spray adjuvants, which are applied simultaneously with an insecticide to increase coverage and/or duration of control. We tested 2 levels of the naturally occurring clay Kaolin as an additive, alone and in combination with either Bifenthrin or the diamide Chlorantraniliprole, to determine if it could reduce feeding damage and decrease survival of pyrethroid-resistant A. transitella on almonds in the laboratory and improve the efficacy of Chlorantraniliprole in the field. Larval performance was measured for the strains R347 and ALM (34.7-fold resistance compared to susceptible lab strain) reared on treated almonds. Strain R347 had 1.9-fold greater survival and caused 1.3-fold more feeding damage than strain ALM across all treatments, although both strains were susceptible to the combination of Kaolin + insecticide. Kaolin synergized Bifenthrin for R347, decreasing survival by 10.0%. Kaolin did not reduce feeding damage for either strain. When combined with insecticide, feeding damage was similar to insecticide alone, but the addition of Kaolin to the insecticide generally decreased survival more than the insecticide alone. In the field, the addition of Kaolin to Chlorantraniprole during application helped retain activity against this challenging pest.

Management of the common bed bug (Cimex lectularius L.) necessitates the use of multiple control techniques. In addition to synthetic pesticides and mechanical interventions, plant-derived essential oils represent one of the control options. Mixtures of two or more essential oil components (monoterpenoids) exhibit synergistic toxicity effects against insects due to increased cuticular penetration. Monoterpenoids, such as carvacrol, eugenol and thymol, are neurologically active and inhibit the nerve firing activity of C. lectularius. However, the effects of mixtures of these monoterpenoids on their toxicity and neuroinhibitory potential against C. lectularius are not known. In this study, the toxicity levels of a tertiary mixture of carvacrol, eugenol and thymol (1:1:1 ratio) and a binary mixture of synthetic insecticides, bifenthrin and imidacloprid (1:1 ratio) were evaluated against C. lectularius through topical bioassays and electrophysiology experiments. Both a mixture of monoterpenoids and the mixture of synthetic insecticides exhibited synergistic effects in topical bioassays. In electrophysiology experiments, the monoterpenoid mixture led to greater neuroinhibitory effects, whereas a mixture of synthetic insecticides caused higher neuroexcitatory effects in comparison to single compounds. This study shows evidence for neurological mechanisms of synergistic interactions between monoterpenoids and provides information regarding the utilization of natural compound mixtures for C. lectularius management.

The efficacy of aerial application and chemigation of insecticides is not well explored for western bean cutworm, Striacosta albicosta (Smith), management in corn. In the short term, inadequate application of insecticides can lead to control failures when insect pests are not effectively targeted. In the longer term, exposure to sublethal insecticide concentrations can contribute to the evolution of insecticide resistance.The goal of this study was to compare aerial application and chemigation under simulated conditions to determine the most effective insecticide application method for managing S. albicosta.Three larval stages were exposed to the highest and lowest label rates of commercial formulations of bifenthrin (36.8 and 112.1 g a.i. ha–1) and chlorantraniliprole (52.7 and 75.1 g a.i. ha–1). Experiments were conducted in spray chambers, utilizing a carrier volume of 18.7 L ha–1 for aerial application and 1.57 cm ha–1 for chemigation. Mortality was recorded at 16, 24, and 41 h after infestation. The simulated aerial application was more effective than simulated chemigation in controlling S. albicosta, resulting in 100% mortality 24 h after infestation. Within the chemigation applications, chlorantraniliprole treatments were effective at both rates for all instars, while the high rate of bifenthrin exhibited greater efficacy than the lower rate. In conclusion, it was evidenced that the same insecticide active ingredients do not yield equivalent efficacy when applied via aerial application compared to chemigation.The present study highlights the importance of selecting appropriate insecticide application methods in controlling S. albicosta larvae.

Rhopalosiphum padi is an important global wheat pest. The pyrethroid insecticide bifenthrin is widely used in the control R. padi. We explored the resistance potential, cross-resistance, adaptive costs, and resistance mechanism of R. padi to bifenthrin using a bifenthrin-resistant strain (Rp-BIF) established in laboratory. The Rp-BIF strain developed extremely high resistance against bifenthrin (1033.036-fold). Cross-resistance analyses showed that the Rp-BIF strain had an extremely high level of cross-resistance to deltamethrin (974.483-fold), moderate levels of cross-resistance to chlorfenapyr (34.051-fold), isoprocarb (27.415-fold), imidacloprid (14.819-fold), and thiamethoxam (11.228-fold), whereas negative cross-resistance was observed to chlorpyrifos (0.379-fold). The enzymatic activity results suggested that P450 played an important role in bifenthrin resistance. A super-kdr mutation (M918L) of voltage-gated sodium channel (VGSC) was found in the bifenthrin-resistant individuals. When compared with the susceptible strain (Rp-SS), the Rp-BIF strain was significantly inferior in multiple life table parameters, exhibiting a relative fitness of 0.69. Our toxicological and biochemical studies indicated that multiple mechanisms of resistance might be involved in the resistance trait. Our results provide insight into the bifenthrin resistance of R. padi and can contribute to improve management of bifenthrin-resistant R. padi in the field. Graphical Abstract

The spotted-wing drosophila, Drosophila suzukii (Matsumura), is a global economic pest of berry crops and stone fruit. Since management of this pest primarily relies on calendar insecticide applications, and field-derived resistance to spinosad has already been documented in California caneberry production, there is significant concern for development of resistance to other insecticides. In this study, susceptibility of D. suzukii populations collected from caneberry and strawberry fields to two pyrethroids, zeta-cypermethrin, and bifenthrin, was assessed in 2019 and 2020. Resistance to both pyrethroids were observed in flies from all sampling sites. For flies collected from caneberries in 2019, the LC50 values ranged from 4.5 to 5.2 mg liter–1 with RR50s ranging from 7.5- to 8.7-fold. Our 2020 assays showed that susceptibility of flies to the discriminating dose of zeta-cypermethrin decreased significantly as the season progressed. For flies collected from strawberries in 2020, the LC50s ranged from 19.0 to 36.1 mg liter–1 and from 30.3 to 90.7 mg liter–1 for zeta-cypermethrin and bifenthrin, respectively. The RR50 values varied from 19.0- to 36.1-fold for zeta-cypermethrin and from 15.9- to 47.7-fold for bifenthrin. This study is the first report of field-derived pyrethroid resistance in D. suzukii from two major California berry production areas. Adoption of informed insecticide resistance management practices would be essential to prolong the efficacy of products available to control D. suzukii. Future molecular work is needed to unravel the underlying genetic mechanisms conferring the observed pyrethroid resistance and to develop robust diagnostics that can inform integrated pest management of this pest.

The granulate ambrosia beetle, (Motschulsky), and the black stem borer, (Blandford) (Coleoptera: Curculionidae: Scolytinae), are important pests of ornamental, fruit and nut trees in the eastern USA. A commonly employed method of evaluating insecticide efficacy against ambrosia beetles relies on treating tree bolts infused with ≥50 % ethanol, which are highly attractive to ambrosia beetles. We conducted experiments at three locations to test the hypothesis that the efficacy of marginally effective insecticides may be better demonstrated using bolts infused with 10 % ethanol than ≥50 % ethanol, where the latter may be so attractive that the ambrosia beetles overcome the effects of the insecticides. The insecticides tested in this study were half and fully labeled application rates of bifenthrin, which are highly effective in reducing ambrosia beetle attacks, and the full rate of indoxacarb, which was reported to have marginal efficacy. On bolts infused with 50 % ethanol, attacks (i.e. numbers of entry holes) were lower on those treated with the full and half-rate of bifenthrin than the untreated ones. Attacks on bolts infused with 10 % ethanol were too low to allow for the detection of statistical differences among the insecticide treatments. We confirmed that indoxacarb was ineffective in reducing attacks regardless of the ethanol concentration. We conclude that the current evaluation system should continue to employ ≥50 % ethanol.

Pyrethroid insecticides are critical for malaria control in Africa. However, resistance to this insecticide class in the malaria vector Anopheles funestus is spreading rapidly across Africa, threatening the success of ongoing and future malaria control programs. The underlying resistance mechanisms driving the spread of this resistance in wild populations remain largely unknown. Here, we show that increased expression of two tandemly duplicated P450 genes, CYP6P9a and CYP6P9b , is the main mechanism driving pyrethroid resistance in Malawi and Mozambique, two southern African countries where this insecticide class forms the mainstay of malaria control. Genome-wide transcription analysis using microarray and quantitative RT-PCR consistently revealed that CYP6P9a and CYP6P9b are the two genes most highly overexpressed (>50-fold; q < 0.01) in permethrin-resistant mosquitoes. Transgenic expression of CYP6P9a and CYP6P9b in Drosophila melanogaster demonstrated that elevated expression of either of these genes confers resistance to both type I (permethrin) and type II (deltamethrin) pyrethroids. Functional characterization of recombinant CYP6P9b confirmed that this protein metabolized both type I (permethrin and bifenthrin) and type II (deltamethrin and Lambda-cyhalothrin) pyrethroids but not DDT. Variability analysis identified that a single allele of each of these genes is predominantly associated with pyrethroid resistance in field populations from both countries, which is suggestive of a single origin of this resistance that has since spread across the region. Urgent resistance management strategies should be implemented in this region to limit a further spread of this resistance and minimize its impact on the success of ongoing malaria control programs.

The QuEChERS method was adjusted to determine bifenthrin residues in grapes and grape leaves. Extraction and cleanup procedures were optimized to decrease co-extracted materials and enhance the detection of bifenthrin. The method was validated per the European Union (EU) Guidelines criteria. Accuracy ranged from 98.8% to 93.5% for grapes and grape leaves, respectively. Precision values were 5.5 and 6.4 (RSDr) and 7.4 and 6.7 (RSDR) for grapes and grape leaves, respectively. LOQs (the lowest spiking level) were 2 and 20 µg/kg for grapes and grape leaves, respectively. Linearity as determination coefficient (R2) values were 0.9997 and 0.9964 for grapes and grape leaves, respectively, in a matrix over 1–100 µg/L range of analyte concentration. This was very close to the value in the pure solvent (0.9999), showing the efficiency of the cleanup in removing the co-extracted and co-injected materials; the matrix effect was close to zero in both sample matrices. Dissipation of bifenthrin was studied in a supervised trial conducted in a grapevine field during the summer of 2023 at the recommended dose and double the dose. Dissipation factor k values were 0.1549 and 0.1672 (recommended dose) and 0.235 and 0.208 (double dose) for grapes and grape leaves, respectively. Pre-harvest interval (PHI) was calculated for the Maximum Residue Limit (MRL) values of the EU database. Residues of bifenthrin were removed effectively from grapes using simple washing with tap water in a laboratory study. Residues reached the MRL level of 0.3 mg/kg in both washing treatments, running or soaking in tap water treatments for 5 min. Removal from leaves did not decrease residue levels to the MRL in grape leaves.

Persistent use of the insecticide D-cyphenothrin has resulted in heavy environmental contamination and public concern. However, microbial degradation of D-cyphenothrin has never been investigated and the mechanism remains unknown. During this study, for the first time, an efficient D-cyphenothrin-degrading bacterial strain Staphylococcus succinus HLJ-10 was identified. Response surface methodology was successfully employed by using Box-Behnken design to optimize the culture conditions. At optimized conditions, over 90% degradation of D-cyphenothrin (50 mg·L−1) was achieved in a mineral salt medium within 7 d. Kinetics analysis revealed that its half-life was reduced by 61.2 d, in comparison with the uninoculated control. Eight intermediate metabolites were detected in the biodegradation pathway of D-cyphenothrin including cis-D-cyphenothrin, trans-D-cyphenothrin, 3-phenoxybenzaldehyde, α-hydroxy-3-phenoxy-benzeneacetonitrile, trans-2,2-dimethyl-3-propenyl-cyclopropanol, 2,2-dimethyl-3-propenyl-cyclopropionic acid, trans-2,2-dimethyl-3-propenyl-cyclopropionaldehyde, and 1,2-benzenedicarboxylic acid, dipropyl ester. This is the first report about the degradation of D-cyphenothrin through cleavage of carboxylester linkage and diaryl bond. In addition to degradation of D-cyphenothrin, strain HLJ-10 effectively degraded a wide range of synthetic pyrethroids including permethrin, tetramethrin, bifenthrin, allethrin, and chlorempenthrin, which are also widely used insecticides with environmental contamination problems. Bioaugmentation of D-cyphenothrin-contaminated soils with strain HLJ-10 substantially enhanced its degradation and over 72% of D-cyphenothrin was removed from soils within 40 d. These findings unveil the biochemical basis of a highly efficient D-cyphenothrin-degrading bacterial isolate and provide potent agents for eliminating environmental residues of pyrethroids.

Soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is a damaging invasive pest of soybean in the upper Midwest. Threshold-based insecticide applications are the primary control method for soybean aphid, but few insecticide groups are available (i.e., pyrethroids, organophosphates, and neonicotinoids). To quantify current levels of soybean aphid susceptibility to pyrethroids in the upper Midwest and monitor for insecticide resistance, leaf-dip bioassays were performed with λ-cyhalothrin in 2013–2015, and glass-vial bioassays were performed with λ-cyhalothrin and bifenthrin in 2015 and 2016. Soybean aphids were collected from 27 population-years in Minnesota and northern Iowa, and were compared with a susceptible laboratory colony with no known insecticide exposure since discovery of soybean aphid in North America in 2000. Field-collected aphids from some locations in leaf-dip and glass-vial bioassays had significantly lower rates of insecticide-induced mortality compared with the laboratory population, although field population susceptibility varied by year. In response to sublethal concentrations of λ-cyhalothrin, adult aphids from some locations required higher concentrations of insecticide to reduce nymph production compared with the laboratory population. The most resistant field population demonstrated 39-fold decreased mortality compared with the laboratory population. The resistance documented in this study, although relatively low for most field populations, indicates that there has been repeated selection pressure for pyrethroid resistance in some soybean aphid populations. Integrated pest management and insecticide resistance management should be practiced to slow further development of soybean aphid resistance to pyrethroids.