Updating integrated mite management 50 years later: comparing laboratory pesticide susceptibility of a 'new' generalist predatory mite to a cornerstone specialist predator.

BACKGROUND: Historically, integrated mite management in Washington apple orchards has focused on conservation of the predatory mite Galendromus occidentalis (Nesbitt) to reduce secondary pest mite pressure. However, pesticide use has changed to include more selective products, coinciding with a shift in the predatory mite community composition to include a new major predator, Amblydromella caudiglans (Schuster). There is evidence that A. caudiglans is more pesticide sensitive than G. occidentalis. Therefore, updates to pesticide selectivity recommendations are needed to conserve this 'new' key predator. Using bioassays, we examined the lethal (female mortality) and sublethal effects (fecundity, egg hatch, larval survival) of 4 fungicides and 11 insecticides on A. caudiglans, to determine whether existing conservation recommendations can be applied to this predatory mite. Susceptibility was compared with prior research on G. occidentalis. RESULTS: Mancozeb was the least selective fungicide tested on A. caudiglans; it caused high acute toxicity and sublethal effects. Carbaryl was the least selective insecticide and caused 100% mortality. Captan was the most selective fungicide. Chlorantraniliprole and cyantraniliprole were the most selective insecticides and therefore least likely to disrupt biological control by A. caudiglans. Non-target effects on A. caudiglans and G. occidentalis were similar, but A. caudiglans experienced higher mortality to some broad-spectrum insecticides. CONCLUSIONS: All the products tested had some non-target effects on A. caudiglans. However, A. caudiglans sensitivity to most tested pesticides was similar to that of G. occidentalis. In general, existing spray recommendations for conserving G. occidentalis can be adjusted slightly and applied to A. caudiglans conservation. © 2023 Society of Chemical Industry. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Seed treatment with chlorantraniliprole and carbaryl mixture for managing fall armyworm on maize: systemic synergism, control efficiency and synergistic mechanism.

BACKGROUND: Fall armyworm (Spodoptera frugiperda) is one of the major invasive pests in China, and has been widely controlled by labor-intensive foliar sprays of agrochemicals in maize (Zea mays L.). RESULTS: Systemic bioassay showed that mixtures of chlorantraniliprole (Chlor) and carbaryl (Carb) had dramatically synergistic effect on toxicity to S. frugiperda. Particularly, a mixture of Chlor with Carb at a mass ratio of 2:1 (MCC) exhibited the highest toxicity to S. frugiperda. Therefore, seed treatment of Chlor mixed with Carb was studied as a simple, accurate, efficient and low-cost control technology. Our results showed that MCC treatment shortened the median lethal time and 90% lethal time to S. frugiperda compared to Chlor- and Carb-alone treatments. Meanwhile, smaller leaf consumption by S. frugiperda was recorded under MCC treatment compared to Chlor- and Carb-alone treatments. In field trial, maize-seed treatment with MCC showed efficacy up to 39 days post-emergence in preventing S. frugiperda foliar damage at a low infestation pressure. Moreover, chemical quantification by ultrahigh-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) showed that Chlor residues were more absorbed and concentrated in maize leaves of MCC treatment, compared to that of Chlor-alone treatment. CONCLUSION: These results suggested that seed treatment with MCC can be applied to increase the control efficacy and reduce the cost of Chlor-alone treatment for controlling S. frugiperda. The present study provided evidence of an enhanced translocation and accumulation of Chlor residues in maize leaves under MCC treatment, which likely contributed to a synergistic effect against S. frugiperda. © 2022 Society of Chemical Industry.

Rim101-upregulated Fets contribute to dark pigment formation in gray cells of Candida albicans.

Candida albicans has long been known to switch between white and opaque phases; however, a third cell type, referred to as the 'gray' phenotype, was recently characterized. The three phenotypes have different colonial morphologies, with white cells forming white-colored colonies and opaque and gray cells forming dark-colored colonies. We previously showed that Wor1-upregulated ferroxidases (Fets) function as pigment multicopper oxidases that regulate the production of dark-pigmented melanin in opaque cells. In this study, we demonstrated that Fets also contributed to dark pigment formation in gray colonies but in a Wor1-independent manner. Deletion of both WOR1 and EFG1 locked cells in the gray phenotype in some rich media. However, the efg1/efg1 wor1/wor1 mutant could switch between white and gray in minimal media depending on the ambient pH. Specifically, mutant cells exhibited the white phenotype at pH 4.5 but switched to gray at pH 7.5. Consistent with phenotype switching, Fets expressions and melanin production were also regulated by ambient pH. Ectopic expression of the Rim101-405 allele in the mutant enabled the pH restriction to be bypassed and promoted gray cell formation in acidic media. Our data suggest that Rim101-upregulated Fets contribute to dark pigment formation in the gray cells.

Genetically engineered zebrafish liver (ZF-L) cells as an in vitro source for zebrafish acetylcholinesterase (zfAChE) for the use in AChE inhibition assays.

Zebrafish acetylcholinesterase (zfAChE) preparations employed for the evaluation of acetylcholinesterase inhibition are usually extracted from animal tissues, a procedure suffering from both technical and ethical limitations, which may be alleviated using an in vitro expression system for enzyme generation. For this end, a protocol for stable transfection and selection of zebrafish liver (ZF-L) cells using an adapted expression plasmid "ZF-L Exp" was developed. After insertion of zfAChE cDNA, the enzyme was efficiently expressed in transgenic ZF-L cell lines, which were then used as a high yield source of zfAChE activity for acetylcholinesterase (AChE) inhibition assays. An adapted assay protocol was used to demonstrate the effects of carbaryl, dichlorvos and caffeine as model AChE inhibitors towards zfAChE. Dimethyl sulfoxide (DMSO) was also strongly inhibitory towards zfAChE. Finally, we provide data on the stability of zfAChE enzyme preparations. The novel test system provides a promising in vitro test system for the assessment of zfAChE inhibition.

Knockdown of NADPH-cytochrome P450 reductase increases the susceptibility to carbaryl in the migratory locust, Locusta migratoria.

BACKGROUND: NADPH-cytochrome P450 reductase (CPR) plays important roles in cytochrome P450-mediated metabolism of endogenous and exogenous compounds, and participates in cytochrome P450-related detoxification of insecticides. However, the CPR from Locusta migratoria has not been well characterized and its function is still undescribed. RESULTS: The full-length of CPR gene from Locusta migratoria (LmCPR) was cloned by RT-PCR based on transcriptome information. The membrane anchor region, and 3 conserved domains (FMN binding domain, connecting domain, FAD/NADPH binding domain) were analyzed by bioinformatics analysis. Phylogenetic analysis showed that LmCPR was grouped in the Orthoptera branch and was more closely related to the CPRs from hemimetabolous insects. The LmCPR gene was ubiquitously expressed at all developmental stages and was the most abundant in the fourth-instar nymphs and the lowest in the egg stage. Tissue-specific expression analysis showed that LmCPR was higher expressed in ovary, hindgut, and integument. The CPR activity was relatively higher in Malpighian tubules and integument. Silencing of LmCPR obviously reduced the enzymatic activity of LmCPR, and enhanced the susceptibility of Locusta migratoria to carbaryl. CONCLUSION: These results suggest that LmCPR contributes to the susceptibility of L. migratoria to carbaryl and could be considered as a novel target for pest control.

Characterization of the Fifth Putative Acetylcholinesterase in the Wolf Spider, Pardosa pseudoannulata.

Background: Acetylcholinesterase (AChE) is an important neurotransmitter hydrolase in invertebrate and vertebrate nervous systems. The number of AChEs is various among invertebrate species, with different functions including the 'classical' role in terminating synaptic transmission and other 'non-classical' roles. Methods: Using rapid amplification of cDNA ends (RACE) technology, a new putative AChE-encoding gene was cloned from Pardosa pseudoannulata, an important predatory natural enemy. Sequence analysis and in vitro expression were employed to determine the structural features and biochemical properties of this putative AChE. Results: The cloned AChE contained the most conserved motifs of AChEs family and was clearly clustered with Arachnida AChEs. Determination of biochemical properties revealed that the recombinant enzyme had the obvious preference for the substrate ATC (acetylthiocholine iodide) versus BTC (butyrylthiocholine iodide). The AChE was highly sensitive to AChE-specific inhibitor BW284C51, but not butyrylcholinesterase-specific inhibitor tetraisopropyl pyrophosphoramide (ISO-OMPA). Based on these results, we concluded that a new AChE was identified from P. pseudoannulata and denoted as PpAChE5. Conclusion: Here we report the identification of a new AChE from P. pseudoannulata and increased the AChE number to five in this species. Although PpAChE5 had the biggest Vmax value among five identified AChEs, it showed relatively low affinity with ATC. Similar sensitivity to test insecticides indicated that this AChE might serve as the target for both organophosphorus and carbamate insecticides.

Reduced expression of exocytotic proteins caused by anti-cholinesterase pesticides in Brachionus calyciflorus (Rotifera: Monogononta).

The organophosphate and carbamate pesticides methyl-parathion and carbaryl have a common action mechanism: they inhibit acetylcholinesterase enzyme by blocking the transmission of nerve impulses. However, they can alter the expression of exocytotic membrane proteins (SNARE), by modifying release of neurotransmitters and other substances. This study evaluated the adverse effects of the pesticides methyl-parathion and carbaryl on expression of SNARE proteins: Syntaxin-1, Syntaxin-4 and SNAP-23 in freshwater rotifer Brachionus calyciflorus. Protein expression of these three proteins was analyzed before and after exposure to these two pesticides by Western Blot. The expression of Syntaxin-1, Syntaxin-4 and SNAP-23 proteins in B. calyciflorussignificantly decreases with increasing concentration of either pesticides. This suggests that organophosphates and carbamates have adverse effects on expression of membrane proteins of exocytosis by altering the recognition, docking and fusion of presynaptic and vesicular membranes involved in exocytosis of neurotransmitters. Our results demonstrate that the neurotoxic effect of anticholinesterase pesticides influences the interaction of syntaxins and SNAP-25 and the proper assembly of the SNARE complex.

Reduced expression of exocytotic proteins caused by anti-cholinesterase pesticides in Brachionus calyciflorus (Rotifera: Monogononta) / Redução da expressão de proteínas de exocitose causados por pesticidas anti-colinesterase em Brachionus calyciflorus (Rotifera: Monogononta)

AbstractThe organophosphate and carbamate pesticides methyl-parathion and carbaryl have a common action mechanism: they inhibit acetylcholinesterase enzyme by blocking the transmission of nerve impulses. However, they can alter the expression of exocytotic membrane proteins (SNARE), by modifying release of neurotransmitters and other substances. This study evaluated the adverse effects of the pesticides methyl-parathion and carbaryl on expression of SNARE proteins: Syntaxin-1, Syntaxin-4 and SNAP-23 in freshwater rotifer Brachionus calyciflorus. Protein expression of these three proteins was analyzed before and after exposure to these two pesticides by Western Blot. The expression of Syntaxin-1, Syntaxin-4 and SNAP-23 proteins in B. calyciflorussignificantly decreases with increasing concentration of either pesticides. This suggests that organophosphates and carbamates have adverse effects on expression of membrane proteins of exocytosis by altering the recognition, docking and fusion of presynaptic and vesicular membranes involved in exocytosis of neurotransmitters. Our results demonstrate that the neurotoxic effect of anticholinesterase pesticides influences the interaction of syntaxins and SNAP-25 and the proper assembly of the SNARE complex.

ResumoOs pesticidas organofosforados e carbamatos metil- paration e carbaril tem um mecanismo de ação comum: eles inibem a enzima acetilcolinesterase, bloqueando a transmissão dos impulsos nervosos. No entanto, eles podem alterar a expressão de proteínas de membrana de exocitose (SNARE), através da modificação da libertação de neurotransmissores e outras substâncias. Este estudo avaliou os efeitos adversos dos pesticidas metil- paration e carbaril sobre a expressão de proteínas SNARE: Sintaxina -1, Sintaxina-4 e SNAP-23 em rotíferos de água doce Brachionus calyciflorus. A expressão destas três proteínas foi analisada antes e depois da exposição a estes dois pesticidas por Western Blot. A expressão das proteínas Sintaxina-1, Sintaxina-4 e SNAP-23 em B. calyciflorus diminui significativamente com o aumento da concentração de ambos os pesticidas. Isto sugere que os organofosfatos e carbamatos têm efeitos adversos sobre a expressão de proteínas de membrana de exocitose, alterando o reconhecimento, de encaixe e fusão de membranas pré-sinápticas e vesiculares envolvidas na exocitose de neurotransmissores. Nossos resultados demonstram que o efeito neurotóxico de pesticidas anticolinesterásicos influencia a interação de sintaxinas e SNAP-25 e a montagem correta do complexo SNARE.

Effects of Pesticide Mixtures on Host-Pathogen Dynamics of the Amphibian Chytrid Fungus.

Anthropogenic and natural stressors often interact to affect organisms. Amphibian populations are undergoing unprecedented declines and extinctions with pesticides and emerging infectious diseases implicated as causal factors. Although these factors often co-occur, their effects on amphibians are usually examined in isolation. We hypothesized that exposure of larval and metamorphic amphibians to ecologically relevant concentrations of pesticide mixtures would increase their post-metamorphic susceptibility to the fungus Batrachochytrium dendrobatidis (Bd), a pathogen that has contributed to amphibian population declines worldwide. We exposed five anuran species (Pacific treefrog, Pseudacris regilla; spring peeper, Pseudacris crucifer; Cascades frog, Rana cascadae; northern leopard frog, Lithobates pipiens; and western toad, Anaxyrus boreas) from three families to mixtures of four common insecticides (chlorpyrifos, carbaryl, permethrin, and endosulfan) or herbicides (glyphosate, acetochlor, atrazine, and 2,4-D) or a control treatment, either as tadpoles or as newly metamorphic individuals (metamorphs). Subsequently, we exposed animals to Bd or a control inoculate after metamorphosis and compared survival and Bd load. Bd exposure significantly increased mortality in Pacific treefrogs, spring peepers, and western toads, but not in Cascades frogs or northern leopard frogs. However, the effects of pesticide exposure on mortality were negligible, regardless of the timing of exposure. Bd load varied considerably across species; Pacific treefrogs, spring peepers, and western toads had the highest loads, whereas Cascades frogs and northern leopard frogs had the lowest loads. The influence of pesticide exposure on Bd load depended on the amphibian species, timing of pesticide exposure, and the particular pesticide treatment. Our results suggest that exposure to realistic pesticide concentrations has minimal effects on Bd-induced mortality, but can alter Bd load. This result could have broad implications for risk assessment of amphibians; the outcome of exposure to multiple stressors may be unpredictable and can differ between species and life stages.

Evolved pesticide tolerance in amphibians: Predicting mechanisms based on pesticide novelty and mode of action.

We examined 10 wood frog populations distributed along an agricultural gradient for their tolerance to six pesticides (carbaryl, malathion, cypermethrin, permethrin, imidacloprid, and thiamethoxam) that differed in date of first registration (pesticide novelty) and mode-of-action (MOA). Our goals were to assess whether: 1) tolerance was correlated with distance to agriculture for each pesticide, 2) pesticide novelty predicted the likelihood of evolved tolerance, and 3) populations display cross-tolerance between pesticides that share and differ in MOA. Wood frog populations located close to agriculture were more tolerant to carbaryl and malathion than populations far from agriculture. Moreover, the strength of the relationship between distance to agriculture and tolerance was stronger for older pesticides compared to newer pesticides. Finally, we found evidence for cross-tolerance between carbaryl and malathion (two pesticides that share MOA). This study provides one of the most comprehensive approaches for understanding patterns of evolved tolerance in non-pest species.

Enhancement of insecticides against codling moth (Lepidoptera: Tortricidae) with L-aspartate in laboratory and field experiments.

The idea of enhancing insecticide efficacy against phytophagous insects with feeding stimulators was proposed as early as the 1960s, and a number of insect feeding stimulators based on sugars, molasses, and cottonseed extracts, biologically active at relatively high (5% and higher) concentrations, have been advocated. Here, we show that an acidic amino acid, L-aspartate, stimulates feeding in codling moth neonates at much lower concentrations and acts as an effective tank-mixed additive for increasing efficacy of insecticides, reducing fruit damage, and increasing yield of the fruit. In laboratory experiments, 1 mg/ml L-aspartate increased foliage consumption by 40-60% and, when added to Assail 30 SG, Baythroid XL, Delegate WG, or Carbaryl 80S, maintained its feeding stimulatory properties and reduced LD50(s) by approximately 10 times. In a 3-yr field trial, addition of L-aspartate to the aforementioned insecticides at 395 g/ha reduced fruit damage from approximately 6%, on average to < 1% for first-generation codling moth, and from approximately 20 to approximately 5% for the second generation. Interestingly, addition of L-aspartate also increased the average weight of apples by 11-27%, as measured at the time of harvest.

Efficacy of herbal shampoo base on native plant against head lice (Pediculus humanus capitis De Geer, Pediculidae: Phthiraptera) in vitro and in vivo in Thailand.

Head lice infestation (or pediculosis) is an important public health problem in Thailand, especially in children between the ages 5 and 11 years. Head lice resistance is increasing, chemical pediculicides have lost their efficacy, and, therefore, alternative pediculicides such as herbal shampoos have been proposed to treat head lice infestation. Thus, the present study investigated the efficacy of three herbal shampoos based on native plants in Thailand (Acorus calamus Linn., Phyllanthus emblica Linn., and Zanthoxylum limonella Alston) against head lice and compared them with carbaryl shampoo (Hafif shampoo, 0.6% w/v carbaryl), malathion shampoo (A-Lice shampoo, 1.0% w/v malathion), and commercial shampoos (Babi Mild Natural' N Mild and Johnson's baby shampoo) in order to assess their in vitro and in vivo efficacy. For in vitro study, doses of 0.12 and 0.25 ml/cm(2) of each herbal shampoo were applied to filter paper, then 10 head lice were place on the filter paper. The mortalities of head lice were recorded at 5, 15, 30, and 60 min. The results revealed that all herbal shampoo were more effective on pediculicidal activity than chemical and commercial shampoos with 100% mortality at 15 min; LT50 values ranged from 0.25 to 1.90 min. Meanwhile, chemical shampoos caused 20-80% mortality, and LT50 values ranged from 6.50 to 85.43 min. On the other side, commercial shampoos showed 4.0% mortality. The most effective pediculicide was Z. limonella shampoo, followed by A. calamus shampoo, P. emblica shampoo, carbaryl shampoo, malathion shampoo, and commercial shampoo, respectively. In vivo results showed that all herbal shampoos were also more effective for head lice treatment than chemical and commercial shampoos with 94.67-97.68% of cure rate after the first treatment; the second treatment, 7 days later, revealed that the cure rate was 100%. Meanwhile, chemical shampoo showed 71.67-93.0% of cure rate and, unfortunately, commercial shampoos were nontoxic to head lice and showed 0% of cure rate after the first and the second treatments. Our data showed that three herbal shampoos of native plants in Thailand in this study are suitable to be used as pediculicides for Thai children since it is safe for children and there is no side-effect after application.

Molecular and functional characterization of cDNAs putatively encoding carboxylesterases from the migratory locust, Locusta migratoria.

Carboxylesterases (CarEs) belong to a superfamily of metabolic enzymes encoded by a number of genes and are widely distributed in microbes, plants and animals including insects. These enzymes play important roles in detoxification of insecticides and other xenobiotics, degradation of pheromones, regulation of neurodevelopment, and control of animal development. In this study, we characterized a total of 39 full-length cDNAs putatively encoding different CarEs from the migratory locust, Locusta migratoria, one of the most severe insect pests in many regions of the world, and evaluated the role of four CarE genes in insecticide detoxification. Our phylogenetic analysis grouped the 39 CarEs into five different clades including 20 CarEs in clade A, 3 in D, 13 in E, 1 in F and 2 in I. Four CarE genes (LmCesA3, LmCesA20, LmCesD1, LmCesE1), representing three different clades (A, D and E), were selected for further analyses. The transcripts of the four genes were detectable in all the developmental stages and tissues examined. LmCesA3 and LmCesE1 were mainly expressed in the fat bodies and Malpighian tubules, whereas LmCesA20 and LmCesD1 were predominately expressed in the muscles and hemolymph, respectively. The injection of double-stranded RNA (dsRNA) synthesized from each of the four CarE genes followed by the bioassay with each of four insecticides (chlorpyrifos, malathion, carbaryl and deltamethrin) increased the nymphal mortalities by 37.2 and 28.4% in response to malathion after LmCesA20 and LmCesE1 were silenced, respectively. Thus, we proposed that both LmCesA20 and LmCesE1 played an important role in detoxification of malathion in the locust. These results are expected to help researchers reveal the characteristics of diverse CarEs and assess the risk of insecticide resistance conferred by CarEs in the locust and other insect species.

Investigation of gastrointestinal effects of organophosphate and carbamate pesticide residues on young children.

This prospective study was designed to investigate whether there is any association between gastrointestinal effects and pesticide residue exposure (as measured by metabolite levels in urine and faecal samples) in young children and to describe background levels of pesticide residues in samples from healthy children in the UK. Children (N=136) between the ages of 1.0 and 4.2 years were recruited. Of these, 107 provided background baseline samples and 26 provided samples when suffering from gastrointestinal symptoms. Urine samples (from all populations) were positive for (non-specific) carbaryl metabolite (urine 19/78, faeces 9/99), organophosphate metabolites (urine 103/135, faeces 47/111) and pirimicarb metabolite (urine 72/175, faeces 45/135). There were no statistically significant differences between samples from children when healthy or unwell. The urinary 95th percentile values for the healthy population of young children in this study were 31 nmol/l (carbaryl metabolite), 2156 nmol/l (total organophosphate metabolites) and 139 nmol/l (pirimicarb metabolite). In this study, samples from children suffering gastrointestinal symptoms were no more associated with anti-cholinergic pesticide metabolite levels or rotaviral infection than samples from healthy children. Background levels of anti-cholinergic pesticide metabolites in healthy UK children were in agreement with previously reported levels from the US and Germany.

Life history, natural enemies, and management of Disholcaspis quercusvirens (Hymenoptera: Cynipidae) on live oak trees.

Live oak (Quercus virginiana Mill.) trees are hosts to a complex of gall making arthropods. However, the bullet galls produced by the asexual generation of the cynipid Disholcaspis quercuscirens (Ashmead) can esthetically and physically damage nursery and street trees, and thus reduce tree value. We sought to describe the unknown sexual generation of D. quercusvirens, describe the development of galls from both generations, record adult cynipid and parasitoid activity periods, and evaluate the efficacy of several insecticides to suppress the gall makers and prevent additional gall formation. The oviposition period for asexual females occurred from late November to January in both years of the caging study. Eggs laid into dormant buds resulted in small bud galls in which the sexual generation developed for 4-5 mo. Sexual adults emerged and laid eggs in young elongating shoots in April. Bullet galls began protruding from branches in June, and asexual wasps emerged 5-7 mo later. Cynipids that emerged from the bullet (asexual generation) and bud (sexual generation) galls were genetically identical. Both generations were heavily parasitized. Targeting asexual females with an early December treatment of bifenthrin or acephate significantly reduced the number of bud galls, but control did not extend to the next generation of bullet galls, possibly because of reinvasion from neighboring infested trees.

Insect herbivores change the outcome of plant competition through both inter- and intraspecific processes.

Insect herbivores can affect plant abundance and community composition, and theory suggests that herbivores influence plant communities by altering interspecific interactions among plants. Because the outcome of interspecific interactions is influenced by the per capita competitive ability of plants, density dependence, and intrinsic rates of increase, measuring herbivore effects on all these processes is necessary to understand the mechanisms by which herbivores influence plant communities. We fit alternative competition models to data from a response surface experiment conducted over four years to examine how herbivores affected the outcome of competition between two perennial plants, Solidago altissima and Solanum carolinense. Within a growing season, herbivores reduced S. carolinense plant size but did not affect the size of S. altissima, which exhibited compensatory growth. Across seasons, herbivores did not affect S. carolinense density or biomass but reduced both the density and population growth of S. altissima. The best-fit models indicated that the effects of herbivores varied with year. In some years, herbivores increased the per capita competitive effect of S. altissima on S. carolinense; in other years, herbivores influenced the intrinsic rate of increase of S. altissima. We examined possible herbivore effects on the longer-term outcome of competition (over the time scale of a typical old-field habitat), using simulations based on the best-fit models. In the absence of herbivores, plant coexistence was observed. In the presence of herbivores, S. carolinense was excluded by S. altissima in 72.3% of the simulations. We demonstrate that herbivores can influence the outcome of competition through changes in both per capita competitive effects and intrinsic rates of increase. We discuss the implications of these results for ecological succession and biocontrol.

Plant essential oils affect the toxicities of carbaryl and permethrin against Aedes aegypti (Diptera: Culicidae).

ABSTRACT Phytochemicals have been considered as alternatives for conventional pesticides because of their low mammalian toxicity and environmental safety. They usually display less potent insecticidal effects than synthetic compounds, but may express as yet unknown modes of action. In the current study, we evaluated 14 plant essential oils for their toxicities and synergistic effects with carbaryl and permethrin against fourth instars of Aedes aegypti (L.) as well as 5-7-d-old adults. Six essential oils showed significant synergistic effects with carbaryl at 10-50 mg/liter, but paradoxically all of them decreased the toxicity of permethrin against Ae. aegypti larvae. None showed toxicity or synergistic effects on Ae. aegypti adults, at doses up to 2,000 ng/ insect. The six essential oils displaying synergistic effects in Ae. aegypti larvae inhibited the in vitro activities of cytochrome P450 monooxygenases and carboxylesterases in the low milligram per liter range. The data indicated that cytochrome P450 monooxygenases and carboxylesterase were probably targets for these natural synergists. Thus, the mechanism of synergism was most likely inhibition of metabolism and not interacting target site effects.

Effects of carbaryl-bran bait on trap catch and seed predation by ground beetles (Coleoptera: Carabidae).

Carbaryl-bran bait is effective against grasshoppers without many impacts on nontarget organisms, but ground beetles (Coleoptera: Carabidae) may be susceptible to these baits. Carabids are beneficial in agricultural settings as predators of insect pests and weed seeds. Carabid species and their consumption of weed seeds have not been previously studied in agricultural settings in Alaska. This study examined the effect of grasshopper bran bait on carabid activity-density, as measured by pitfall trap catches, and subsequent predation by invertebrates of seeds of three species of weed. Data were collected in fallow fields in agricultural landscape in the interior of Alaska, near Delta Junction, in 2008 and 2010. Bait applications reduced ground beetle activity-density by over half in each of 2 yr of bait applications. Seed predation was generally low overall (1-10%/wk) and not strongly affected by the bait application, but predation of lambsquarters (Chenopodium album L.) seed was lower on treated plots in 1 yr (340 seeds recovered versus 317 seeds, on treated versus untreated plots, respectively). Predation of dandelion (Taraxacum officinale G. H. Weber ex Wiggers) seeds was correlated with ground beetle activity-density in 1 yr, and predation of dragonhead mint (Dracocephalum parvifolium Nutt.) seed in the other year. We conclude that applications of carbaryl-bran bait for control of grasshoppers will have only a small, temporary effect on weed seed populations in high-latitude agricultural ecosystems.

Insecticide resistance in head lice: clinical, parasitological and genetic aspects.

Insecticide treatment resistance is considered to be a major factor in the increasing number of infestations by head lice. The large insecticide selection pressure induced by conventional topical pediculicides has led to the emergence and spread of resistance in many parts of the world. Possible mechanisms of resistance include accelerated detoxification of insecticides by enzyme-mediated reduction, esterification, oxidation that may be overcome by synergistic agents such as piperonyl butoxide, alteration of the binding site, e.g. altered acetylcholinesterase or altered nerve voltage-gated sodium channel, and knockdown resistance (kdr). Clinical, parasitological and molecular data on resistance to conventional topical pediculicides show that treatments with neurotoxic insecticides have suffered considerable loss of activity worldwide. In particular, resistance to synthetic pyrethroids has become prominent, probably because of their extensive use. As other treatment options, including non-insecticidal pediculicides such as dimeticone, are now available, the use of older insecticides, such as lindane and carbaryl, should be minimized, owing to their loss of efficacy and safety concerns. The organophosphorus insecticide malathion remains effective, except in the UK, mostly in formulations that include terpineol.

Effects of dichlorvos and carbaryl on the activity of free and immobilized acetylcholinesterase.

Acetylcholinesterase (AChE) is responsible for the rapid hydrolytic degradation of the neurotransmitter acetylcholine into inactive products choline and acetic acid. The purpose of this study was to examine the effect of carbaryl and dichlorvos on the activity of AChE. In this experimental study, 60 samples of free and immobilized form of AChE were prepared. Determination of AChE activity followed the Ellman's method with modifications. Briefly, 200 µl of the enzyme solution was combined with 400 µl of 25 mM phosphate-buffered saline, 200 µl of DTNB [5,5'-dithio-bis(2-nitrobenzoic acid)], and 200 µl of 300 µM acetylthiocholine iodide. Triplicate (1000 µl) samples were transferred to clean 1.5-ml centrifuge tubes, mixed, and held on ice until analysed and the change in absorbance was measured. For inhibition studies, substrate solutions were pre-incubated with dichlorvos and/or carbaryl. Dichlorvos and carbaryl were used at the concentrations of 100 and 500 µM. The activity was evaluated at 412 nm using Ceceil, CE 1020 spectrophotometer. Phosphate buffer (pH 7.35) was used for blanks. AChE activity was quantified as mM/ml/min. AChE activity of free form is more affected by Dichlorvos (0.09 ± 0.03 mM/ml/min) than immobilized form (0.19 ± 0.02 mM/ml/min). AChE activity of free form is more affected by carbaryl (0.11 ± 0.01 mM/ml/min) than immobilized form (0.1 ± 0.04 mM/ml/min). Comparison of mean AChE activity showed that the activity of the enzyme in presence of dichlorvos and carbaryl was significantly lower compared to controls. To calculate the significance of the difference, the t-test for paired values was applied. The results of our study indicate that dichlorvos and carbaryl cause decrease in AChE activity for both free and immobilization form of enzyme. It is therefore concluded that measuring AChE activity is a way to evaluate poisoning with carbaryl and dichlorvos.