Carbamate Insecticide Methomyl Research Articles

EPA targets methomyl insecticide

The US Environmental Protection Agency is proposing measures to reduce runoff and drift of the carbamate insecticide methomyl to protect vulnerable endangered species. The changes would amend the agency’s registration review decision made in October 2020 under the administration of former president Donald J. Trump. Methomyl is used on field crops, vegetables, and orchards. It is also approved for use in a fly-bait product. The EPA is evaluating the risks of methomyl to human health and the environment as part of a registration review process that happens every 15 years. The agency completed an evaluation of the effects of methomyl on threatened and endangered species in March 2021, finding that the insecticide is likely to adversely affect more than 1,000 species. It is now consulting with the Fish and Wildlife Service and the National Marine Fisheries Service to determine what mitigation measures are needed to protect affected species. In the

The endocrine-disrupting potential of a generic carbamate insecticide methomyl, as explored in a 90-day study in vivo

The endocrine-disrupting potential of a generic carbamate insecticide methomyl, as explored in a 90-day study in vivo

Ambient moisture causes methomyl residues on corn plants to rapidly lose toxicity to the pest slug, Arion subfuscus, Müller (Gastropoda, Stylommatophora)

The carbamate insecticide methomyl is sometimes used to control slugs in field corn and soybean by foliar applications, but control outcomes in research trials and commercial operations have been mixed. In this study, laboratory bioassays were conducted on dusky slug, Arion subfuscus Müller, a common pest of corn and soybean in the Mid-Atlantic United States, to evaluate residual toxicity of Lannate LV (methomyl) at low and high concentrations corresponding to label recommended field rates, and if toxicity may be affected by ambient moisture or repellency to treated plants. Without wetting events, methomyl residues on corn plants caused 90–100% mortality of A. subfuscus for two days and 70–90% mortality for six days. When corn plants were briefly misted with ca. 0.3 cm of water 6 h after methomyl application, mortality was 36% 12 h after treatment, and 0 to 5% 24 h after treatment for both low and high rates. Repellency of A. subfuscus to corn plants treated with the high rate of methomyl was narrowly significant (P = 0.04) and low rate was not significant. These results suggest that high ambient moisture needed to elicit slug activity in the field also abates toxicity of methomyl residues, explaining why field control is usually poor despite high mortality in the lab.

Exposure of Helicoverpa armigera Larvae to Plant Volatile Organic Compounds Induces Cytochrome P450 Monooxygenases and Enhances Larval Tolerance to the Insecticide Methomyl.

Simple SummaryUpon insect herbivory plants release herbivore-induced plant volatiles (HIPVs) to elicit either direct antiherbivore defenses by intoxicating the herbivore or indirect defenses by attracting natural enemies. Insect herbivores use sophisticated detoxification systems, including cytochrome P450 monooxygenases (P450s), to cope with plant defensive chemicals and insecticides. Many behaviors of insects are manipulated to a large extent by olfaction. However, few studies concern the role of olfaction in insect adaptation to xenobiotics. In this study we show that olfactory exposure of Helicoverpa armigera, a devastating pest of many important crop plants that has developed high levels of resistance to various insecticides, to four plant volatile compounds limonene, nerolidol, 2-heptanone and cis-3-hexenyl acetate dramatically increases larval tolerance to carbamate insecticide methomyl. Inhibition of P450s by piperonyl butoxide (PBO), a well-known P450 inhibitor, compromises the effects of volatile exposure. Exposure to the four volatiles upregulates multiple detoxification systems, including cytochrome P450s. Our findings indicate that induction of insecticide-detoxifying P450s by plant volatiles prior to actually inflicting plant damage may confer insect larvae more time to pre-activate insect detoxification systems prior to the ingestion or contact of insecticides, leading to increased larval tolerance to insecticides.Plants release an array of volatile chemicals into the air to communicate with other organisms in the environment. Insect attack triggers emission of herbivore-induced plant volatiles (HIPVs). How insect herbivores use these odors to plan their detoxification systems is vital for insect adaptation to environmental xenobiotics. Here we show that the larvae of Helicoverpa armigera (Hübner), a broadly polyphagous lepidopteran herbivore, have the capacity to use plant volatiles as cues to upregulate multiple detoxification systems, including cytochrome P450 monooxygenases (P450s), for detoxification of insecticides. Olfactory exposure of the fifth instars to two terpene volatiles limonene and nerolidol, and two green-leaf volatiles 2-heptanone and cis-3-hexenyl acetate significantly reduced larval susceptibility to the insecticide methomyl. However, larval pretreatment with piperonyl butoxide (PBO), a known P450 inhibitor, neutralized the effects of volatile exposure. Furthermore, larval exposure to the four plant volatiles enhanced activities of P450 enzymes in midguts and fatbodies, and upregulated expression of CYP6B2, CYP6B6 and CYP6B7, P450s involved in detoxification of the insecticide. Larval exposure to 2-heptanone and limonene volatiles also enhanced activities of glutathione-s-transferase and carboxylesterase. Our findings suggest that olfactory exposure to HIPVs enhances larval insecticide tolerance via induction of detoxification P450s.

A study of photocatalytic degradation of methomyl and its commercial product Lannate-90

Photocatalytic degradation of the carbamate insecticide methomyl and its commercial product Lannate-90 in aqueous suspension of TiO2 and ZnO using an Osram ultra-vitalux' lamp (315-400 nm) was investigated. The objective of the investigation was to study and compare the rates of photochemical degradation of the pure active compound and its formulated product in order to find out the impact of inert ingredients on degradation processes. The photochemical degradation of pure methomyl was found to be slower than the degradation of its commercial product Lannate-90. Photodegradation was investigated by UV-Vis spectrometry and HPLC, while mineralization was monitored using IC and TOC analyses. Light absorption capabilities of catalysts were characterized by ultraviolet-visible diffuse reflectance spectroscopy method, while the stability of catalysts was studied by infrared analyses. Degradation products of methomyl and its formulated product were identified by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) results and tentative photodegradation pathways were proposed.

Phenolic and flavonoid compounds in aqueous extracts of thunbergia laurifolia leaves and their effect on the toxicity of the carbamate insecticide methomyl to murine macrophage cells

Background: Thunbergia laurifolia is a Thai herb and has been used in Thai folklore medicine for centuries. Generally, Thais consume T. laurifolia as a herbal tea because of its beneficial properties as an antidote for chemical toxins, drug-, arsenic-, strychnine-, alcohol- and food-poisoning. However, its effectively against some insecticide compounds, e.g. methomyl, has not yet been determined.Objective: To examine the protective effect of aqueous extract from leaves of T. laurifolia on methomyl (MT) poisoning of murine macrophage cells (anti-MT effect) and to identify phenolic and flavonoid compounds in the extract. Methods: T. laurifolia was extracted with water and stored in freeze-dried form. The extract was investigated for its antioxidant activity and some phenolic and flavonoid compounds were identified using liquid chromatography–mass spectrometry (LC-MS). To study anti-MT effects in RAW264.7 murine macrophage cells, these were treated with leaf extract either before (pre-treatment), concomitantly (combined) or after (post-treatment) exposure to MT and cell viability determined in an MTT test (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide).Results: The extract exhibited strong antioxidant properties based on total extractable phenolic content (TPC), total extractable flavonoid content (TFC), 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) radical scavenging, 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging and Ferric ion reducing antioxidant power (FRAP) activity. The LC-MS analyses of phenolic compounds indicated the presence of caffeic acid, rosmarinic acid, catechin, rutin, isoquercetin, quercetin and apigenin as bioactive compounds. Viability of RAW 264.7 murine macrophage cells treated with MT was increased significantly by post-treatment with leaf extract but not by combined or pre-treatments. Conclusion: The aqueous extract of T. laurifolia leaves contained abundant antioxidant activity. Flavonoids present were catechin, rutin, isoquercetin, quercetin and apigenin. The aqueous leaf extract was able to help cells recover from the effects of exposure to MT.Keywords: Thunbergia laurifolia, phenolics, flavonoids, methomyl, RAW264.7 murine macrophages, insecticide

ABCs of Insect Resistance to Bt.

ABCs of Insect Resistance to Bt.

Carbamate insecticide methomyl confers cytotoxicity through DNA damage induction

Carbamate insecticide methomyl could induce genotoxic effects, including micronuclei, chromosome aberrations and sister-chromatid exchanges. However, methomyl induction of cytotoxicity through DNA damage is largely unknown. Here we identify cytotoxicity and potential genotoxicity of methomyl in vitro. We have employed alkaline comet assay, γH2AX foci formation and DNA ladder assay to detected DNA damage and apoptosis of Drosophila S2, HeLa and HEK293 cells. The alkaline comet assay was used to evaluate total DNA single strand breaks (SSBs) in the target cells exposed in vitro to sublethal concentrations of methomyl. As expected, methomyl induced significant concentration-dependent increases in DNA damage of target cells compared with the negative control, as measured by increases in tail length (μm), tail DNA (percentage of the comet tail) and tail moment (arbitrary units). In agreement with the comet assay data, the percentage of γH2AX positive reaction in HeLa cells also revealed methomyl caused DNA double strand breaks (DSBs) in a time-dependent manner. Moreover, methomyl induced a significant increase of apoptosis in Drosophila S2, HeLa and HEK293 cells in a concentration- and time-dependent manner, as determined by Urea PAGE DNA fragmentation analysis. In conclusion, methomyl is a strongly genotoxic agent that induces cell DNA damage and apoptosis in vitro at these sublethal concentrations.

Avoidance behavior of earthworms under exposure to pesticides: Is it always chemosensorial?

Soil avoidance by earthworms has been generally considered a relevant and sensitive endpoint for assessing soil contamination by xenobiotics. However, when pesticide ecotoxicological assessment is concerned, the sensitivity of the recently standardized avoidance assay has been questioned. We hypothesized that this controversy may be due to the specific pesticide mode of action of the chemicals used rather than reveal inconsistencies in the test feasibility, i.e. provided that no pesticides interfering with neuronal pathways are tested, this bioassay should keep expected high levels of sensitivity. In this study, the avoidance behaviour of the earthworm Eisenia andrei under exposure to the carbamate insecticide methomyl [S-methyl N-(methylcarbamoyloxy)thioacetimidate] was linked to the corresponding acetylcholinesterase (AChE) inhibition. Significant AChE inhibition occurred at lower concentrations (from 0.86 mg Kg−1 onwards) than significant avoidance of spiked soil (from 5.62 mg Kg−1 onwards). This indicates that assessments regarding pesticides that have neurotoxic activity may be biased if behavioral endpoints are selected. Despite theoretical hypothesis that have been raised, this should be the first study providing preliminary experimental evidence on such a link between avoidance behavior and neuronal impairment levels in earthworms. Further studies are ongoing that should refine conclusions of this study.

Plasma and Brain Cholinesterase in Methomyl-Intoxicated Free-Ranging Pigeons (Columba Livia f. Domestica)

A mortality event caused by exposure to the carbamate insecticide methomyl was diagnosed in several hundred pigeons fed treated corn kernels in a city park. A cholinesterase inhibitor insecticide was initially suspected based on clinical signs and a significant inhibition (P < 0.05) of brain cholinesterase (ChE) activity compared with normal values for the species. However, brain ChE activity was within the normal range in birds subsequently submitted in an advanced stage of autolysis. Two groups of 10 healthy pigeons were allocated into a control group and an experimental group, which was offered corn samples retrieved from the incident site. Within minutes of ingesting the contaminated corn, the birds became immobile, had transient wing fluttering, and developed profuse salivation immediately followed by death. Plasma ChE activity at death had declined by more than 95% of preexposure levels (0.04 +/- 0.02 vs. 1.56 +/- 0.23 micromol/min per milliliter). Brain activity in the sagittal brain sections that were immediately frozen after death was inhibited by > or =50% of control birds (13.5 +/- 2.2 vs. 27.5 +/- 1.8 micromol/min per gram). However, the sagittal sections left for 1.5 days at ambient temperature of 25 degrees C had normal or higher activity, an effect that was attributed to a combination of spontaneous reactivation and dehydration. After incubation of both plasma and brain homogenates for 1 hr at 37 degrees C, ChE activity recovered by 2- and 1.46-fold, respectively. An organophosphorus and carbamate screen conducted by 2 independent laboratories identified and quantified methomyl in treated kernels at 400 ppm. These results indicate that spontaneous reactivation and dehydration can mask previous reductions in ChE activity.

Thin-layer chromatography for selective detection of methomyl in forensic casework

The carbamate insecticides baygon (propoxur), carbaryl (sevin), carbofuran (furadon), methomyl (Dunet), and bendiocarb, etc., are widely used for crop protection. Because of their ready availability they are often misused for homicidal and suicidal purposes in India. During the years 2000 to 2004 Pune Regional Forensic Science Laboratory detected 23 cases of human poisoning involving use of methomyl.

Thiodicarb

Dimethyl N,N'-[thiobis(methyliminocarbonyloxy)] bis-(ethanimidothiolate), C10H18N4O4S3, is an example of a sulfenylated biscarbamate insecticide. The molecule has an approximate twofold axis through the central S atom which joins the two methyliminocarbonyloxyethanimidothiolate units. One of the two arms is planar in the crystal. Semi-empirical geometry optimization for an isolated molecule favors a model with both arms planar and, thus, crystal packing may be responsible for the observed non-planarity in one arm. Bond lengths and angles have similar values to those of the 'monomeric' carbamate insecticide methomyl.

Genotoxic effects of the carbamate insecticide methomyl. I. In vitro studies with pure compound and the technical formulation "Lannate 25".

The carbamate insecticide methomyl and the methomyl-containing technical formulation "Lannate 25" were tested on whole blood human lymphocyte cultures. Both products induced dose-dependent increases in chromosome aberrations and micronuclei. Lannate 25 induced DNA damage as measured by the alkaline elution assay and hydroxylation of guanine at the C8 position. Sister chromatid exchanges were not increased significantly with either product. Overall, the technical formulation was more active than the pure compound, when compared at similar concentrations of active principle. Moreover, a different ratio of CREST-positive/CREST-negative micronuclei was observed with the two products, pure methomyl being relatively more active than Lannate 25 in the induction of CREST-positive micronuclei. On the basis of these results, previous evaluations of methomyl as a nongenotoxic compound should be reconsidered.

Serum esterase inhibition in birds: a nondestructive biomarker to assess organophosphorus and carbamate contamination.

With the aim of proposing a nondestructive biomarker for monitoring the toxicological risk to birds of exposure to the organophosphorus insecticide azamethiphos and the carbamate insecticide methomyl, laboratory studies were performed on serum "B" esterases in Japanese quail (Coturnix coturnix japonica). The birds received two single dose treatments of each compound (azamethiphos and methomyl), i.e., 50 mg/kg and 250 mg/kg respectively. In the first treatment, serum butyrylcholinesterase (BChE) and carboxylesterase (CbE) were drastically inhibited in the azamethiphos-treated group, 24 h after the dose. No inhibition was detected for BChE and CbE activities in the methomyl-treated group, 24 h after the dose. In the second treatment, the birds died or were sacrificed 3 h after the dose. Serum BChE and brain acetylcholinesterase (AChE) were strongly inhibited after treatment with both insecticides. Serum CbE, hepatic microsomal CbE and 7-ethoxyresorufin dealkylation activities were also inhibited. A statistically significant correlation between serum BChE and brain AChE was found at lethal and sublethal doses of these xenobiotics. The experimental results indicate that the nondestructive biomarker BChE can give an early qualitative and semi-quantitative warning of the toxic effects of organophosphate and carbamate insecticides in birds.

Laboratory evaluation of the toxicity of 1,3-di(methoxycarbonyl)prop-l-en-2-yl dimethyl phosphate (‘Bomyl’) and methomyl to susceptible and multi-resistant strains of houseflies (musca domesticaL.)

The toxicity of 1,3-di(methoxycarbonyl)prop-l -en-2-yl dimethyl phosphate (‘Bomyl’) to female houseflies (Musca domestica L.) was compared with that of the carbamate insecticide methomyl. Insecticide-susceptible (Cooper) and multi-insecticide-resistant (G and GIV) strains of flies were tested by exposure to granular bait and by topical application of technical formulations. Females from G and GIV strains were shown to be resistant to bomyl and methomyl, and resistance levels were related to the insecticide and test method used. Resistance ratios for bomyl and methomyl were low for the GIV strain when the toxicants were applied topically, being x6.1 and x 9.3 respectively at the LD95 level, but when sugar granules were coated with the insecticides and fed to flies, the resistance ratios were higher at x 43.0 and x 15.6. Flies from the resistant G strain were also shown to be resistant to the granular bait formulations of bomyl and methomyl when the granules were scattered or suspended from treated bait targets. A small proportion of flies from the resistant G and susceptible strains recovered from knockdown after feeding on methomyl granules, but most of these had lost their ability to fly. There was no significant recovery of flies in any of the bomyl tests. The feeding responses of individual female flies to scattered bomyl granules was also studied. Flies from the resistant G strain took significantly longer than susceptible flies to initiate a feeding response (P<0.001). Once feeding had commenced there was no difference between the strains in the time spent.

Response of insecticide‐resistant and susceptible houseflies (Musca domestica) to a commercial granular bait formulation containing methomyl

Female houseflies (Musca domestica L.) from a susceptible and a multi-insecticide-resistant strain were used to evaluate the relative toxicity of an insecticide bait formulation of the carbamate insecticide methomyl. Individual flies were allowed to feed on bait granules for an unrestricted period or for 5 s. Resistant flies took longer than susceptible flies to initiate a feeding response. When allowed to feed continuously, those from the resistant strain spent longer feeding than susceptible ones. The time taken to knock-down (KD), including feeding times, was significantly greater for resistant than susceptible flies (P less than 0.001), but once the proboscis was withdrawn from the granule there was no difference in KD times between the strains. All flies from both strains were knocked down, and only a very small number of resistant and susceptible flies recovered. The toxic effects of methomyl on flies which were restricted to a 5 s feed ranged from no observed effect to KD in less than 1 min. After feeding for 5 s, 81% of resistant and 98% of susceptible flies developed signs of methomyl poisoning. More resistant than susceptible flies recovered from KD, giving final mortalities of 46% and 88% respectively. With both feeding regimes, some flies of both strains which had apparently recovered from KD had lost their ability to fly. Observations have also shown that 8% of resistant flies may have been repelled by methomyl granules. The implication of these results on the survival of M. domestica in intensive animal units following exposure to methomyl bait is also discussed.

A 13-Kilodalton Maize Mitochondrial Protein inE. coliConfers Sensitivity toBipolaris maydisToxin

The Texas male-sterile cytoplasm (cms-T) of maize carries the cytoplasmically inherited trait of male sterility. Mitochondria isolated from cms-T maize are specifically sensitive to a toxin (BmT-toxin) produced by the fungal pathogen Bipolaris maydis, race T, and the carbamate insecticide methomyl. A mitochondrial gene unique to cms-T maize, which produces a 13-kilodalton polypeptide associated with cytoplasmic male sterility, was expressed in Escherichia coli. After addition of BmT-toxin or methomyl, inhibition of whole cell respiration and swelling of spheroplasts were observed in Escherichia coli cultures producing the novel mitochondrial protein; these effects are similar to those observed with isolated cms-T mitochondria. The amino-terminal region of the 13-kilodalton polypeptide appears to be essential for proper interaction with the BmT-toxin and methomyl. These results implicate the 13-kilodalton polypeptide in conferring toxin sensitivity to mitochondria of cms-T maize.

Insecticide-insensitive acetylcholinesterase from a laboratory selected and a field strain of housefly ( Musca domestica) (L.)

1. 1. Acetylcholinesterase from the heads of a strain of houseflies selected for resistance to the carbamate insecticide methomyl, and from a methomyl-resistant field strain was found to be less sensitive to inhibition by methoml than that from a susceptible strain. 2. 2. The enzyme from resistant insects was also more tolerant to malaoxon, dichlorvos and bomyl but not to azamethiphos. 3. 3. The decrease in sensitivity to inhibition appeared to be due to an increase in affinity for substrate.

RELATIVE TOXICITY OF SIX INSECTICIDES TO MALE AND FEMALE PHOLETESOR ORNIGIS (WEED) (HYMENOPTERA: BRACONIDAE), A PARASITE OF THE SPOTTED TENTIFORM LEAFMINER, PHYLLONORYCTER BLANCARDELLA (FABR.) (LEPIDOPTERA: GRACILLARIIDAE)

AbstractThe susceptibility of male and female Pholetesor ornigis (Weed) to the pyrethroid insecticides permethrin, fenvalerate, and deltamethrin, the organophosphorous insecticides azinphosmethyl and phosmet, and the carbamate insecticide methomyl, was compared in the laboratory using two populations from Norfolk County, Ontario. Female P. ornigis were more susceptible than males to permethrin. There was no sexual difference in the susceptibility of P. ornigis to the other five insecticides tested. The implications of these results for the biological control potential of P. ornigis in commercial apple orchards are discussed. The results obtained for permethrin, fenvalerate, azinphosmethyl, and methomyl were compared with those obtained in a study completed 6 years earlier using P. ornigis from another location in Ontario; the results suggest that P. ornigis from Norfolk County have low levels of resistance to permethrin (3.3-fold), fenvalerate (2.2-fold), and methomyl (4.1-fold).

Laboratory assessment of different methods of applying a commercial granular bait formulation of methomyl to control adult houseflies (Musca domestica l.) in intensive animal units

AbstractFemale houseflies (Musca dornestica L.) from a susceptible and a multiinsecticide‐resistant strain were used to evaluate the toxicity of a granular insecticide bait formulation of the carbamate insecticide methomyl. The bait was either applied to a polystyrene bait target, or scattered over the floor of the fly treatment cages. Targets were treated with methomyl granules dissolved in water with and without apaste carrier or the granules were applied directly to the target using an adhesive. Scattered methomyl granules proved the most effective of the various treatments assessed. Based on the KT90 values, the most effective suspended bait treatments against susceptible or resistant flies were water as a carrier, and egg or ‘Lap’ wallpaper paste as adhesives; the least effective were ‘Polycell’ regular wallpaper paste as an adhesive and carboxymethylcellulose as a carrier. A proportion of flies from both the susceptible and the resistant strain recovered from knockdown; most of these lost their ability to fly (‘hoppers’) and subsequently survived the treatments. When bait targets treated with methomyl granules were fixed at right angles to the wall/floor junction of the treatment cages most of the recovered flies fed again on the bait and received a lethal dose. The mortality of flies exposed to suspended bait targets was influenced by the level of light. For both strains of fly, mortality decreased as the light intensity was lowered; this effect was more pronounced with the resistant strain. The implication of these results for the application of methomyl bait is discussed.