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Vegetable crops, more than other agricultural crops, are exposed to great damages caused by slugs. Current control methods rely on chemical molluscicides that are often ineffective and harmful to non - target organisms, specially Carabids. Parasitic nematode Phasmarhabditis hermaphrodita (Schneider) parasites many slugs and snails and has been formulated as biological molluscicide. In this investigation, effectiveness of P. hermaphrodita applied in recommended and half the recommended dose in slug control in greenhouse lettuce and cabbage was evaluated and compared with metaldehyde and methiocarb pellets. Tested mollusicides did not stop feeding of Arion lusitanicus Mabille and did not achieve long term protection from slug damage. The use of standard dose of P. hermaphrodita in lettuce and cabbage provided satisfactory protection from slugs to harvest. Half recommended dose of P. hermaphrodita showed lower level of protection compared with recommended dose. Repeated applications of half recommended dose of P. hermaphrodita could boost molluscicidal effect to the level of the efficacy reached by standard dose, so it could find their place in practice. Effective control of A. lusitanicus using parasitic nematodes provides great opportunity to replace chemical molluscicides in organic production and to reduce their negative side effect to non - target organisms and the environment.

Following the limitations regarding the use of the neonicotinoids: clothianidin, thiamethoxam and imidacloprid there are no currently available insecticide seed dressings for oilseed rape in Poland. For maize here is only one seed dressing containing methiocarb available with a very narrow registered scope of use. The impact of limitations on protection possibilities of other major Polish agricultural crops is either negligible or non-existent. In consequence a group of economically important insect pests of maize [dungbeetles (Melolonthidae); click beetles (Elateridae); noctuid moths (Agrotinae)] and oilseed rape [leaf miners (Agromyzidae), turnip sawfly (Athalia colibri Christ.), cabbage weevils (Curculionidae), cabbage root fly (Hylemyia brassicae Bche.), diamond-back moth (Plutella maculipennis Curt.)] is left without any legal possibility of chemical control. For the other important pests of the early growth stage of oilseed rape development, there are only pyrethroids available together with one product containing chloropiryfos that can be applied once per vegetation season. Since both maize and oilseed rape are grown in Poland on the area of approximately 1 million ha (each crop), this situation raises concerns about production possibilities as well as development of pest resistance.

Initial Evaluation of the Effectiveness of Selected Active Substances in Reducing Damage To Rape Plants Caused By Arion Lusitanicus (Gastropoda, Pulmonata, Arionidae) Spray forms of various chemical compounds including compounds of plant origin, molluscicides, and insecticides were tested in order to investigate their possibilities for reducing damage to young rape plants caused by the slug Arion lusitanicus Mabille, 1868. Among them, abamectin (0.2%), methiocarb (0.5%) and metaldehyde (1.0%) reduced damage to the plants, although metaldehyde remained active for only nine days. These three chemical compounds were not phytotoxic to rape plants, and none of them proved lethal to the slugs at the concentration used. The reduction in rape plant damage was obtained as a result of their deterrent and/or antifeedant action. The results indicate that abamectin has high potential usefulness in protecting winter rape seedlings from slugs.

The matrix effects in HPLC/electrospray ionization (ESI)-MS analysis are difficult to compensate for because of their large variability. It is, therefore, often more practical to include uncertainty due to the matrix effect into the uncertainty budget rather than try to compensate. This work presents an empirical approachthe matrix effect graph approachfor estimating the uncertainty due to the matrix effect in HPLC/ESI-MS analysis of pesticide residues in fruits and vegetables. At certain time intervals (1 month), a calibration graph using extracts of different fruits/vegetables as calibration solutions is prepared, and a regression line is fitted through these data. These fruits/vegetables may be either from the commodity group of the samples or from different commodity groups. The relative residuals of the calibration point peak areas are calculated and plotted against the measurement time. We term the resulting graph the matrix effect graph. The root mean square of the relative residuals is calculated and used as the estimate of relative uncertainty of the sample peak areas caused by the matrix effect. The matrix effect graph obtained over fruits/vegetables from different commodity groups can also be used to identify fruits/vegetables with extreme matrix effects. The matrix effect graph approach was used for determination of thiabendazole, aldicarb, imazalil, and methiocarb and was validated with tomato, cucumber, and sweet corn matrixes at the 0.5 mg/kg concentration level. When different commodity groups were used to compile the matrix effect graph, results of analysis of all samples agreed with the spiked concentrations within the expanded uncertainties (at k = 2 level). When the matrix effect graph was compiled using fruits from the same commodity group as the analyzed samples (fruiting vegetables in this case), agreement was found in 98 of the cases.

1 The stability of the resistance in the Western Flower Thrips, Frankliniella occidentalis (Pergande) to selective insecticides (acrinathrin, formetanate and methiocarb) was studied in both laboratory and field conditions. 2 In laboratory strains reared over a sufficient number of generations in insecticide free-conditions, levels of resistance were stable. 3 Laboratory strains selected for resistance showed moderate to very high levels of resistance. In the strain ACR9, very highly resistant to acrinathrin [resistance factor (RF) > 1000-fold], resistance was maintained with little change after 5 and 8 months without acrinathrin exposure. In the MET9 strain, resistance to methiocarb (RF = 40) was maintained after 5 months without selection pressure (RF = 33). However, 3 months later, there was a significant increase in the susceptibility to this insecticide (RF = 10). The formetanate resistance in the FOR7 strain showed a no significant decline during the 8 months without selection (from RF = 31 to RF = 17). 4 The field-collected strains from sweet pepper greenhouses (PTF4, PP2 and PM5) showed a marked fall in the LC50 to acrinathrin and methiocarb, and a slight decrease to formetanate, after being reared in the laboratory in the absence of selection pressure for 8 months. 5 In greenhouses, a significant fall in resistance to the selected insecticides was produced when insecticide pressure was withdrawn, at the end of the season, probably caused by the immigration of thrips from nearby crops or weeds, and the dilution of resistance through interbreeding with susceptible individuals. 6 Factors influencing stability or reversion of insecticide resistance are discussed.

In this study the land snail (Eobania vermiculata), one of the most abundant gastropod of Egyptian farms, was investigated to determine the lethal toxic action of methomyl and methiocarb and to identify the biochemical and histochemical changes as a function of sublethal dose or concentration on the digestive gland of this snail under laboratory conditions, using topical application and baiting techniques. The results showed that methomyl exhibited greater efficacy than did methiocarb against the snails in both techniques. However, higher mortality rates were obtained in the topical application technique than in the poison bait experiments. Biochemical and histochemical examinations revealed that treatment of the snails with methomyl and methiocarb either by topical application or toxic baits caused significant decrease in carbohydrate, lipid and protein contents. This decrease was also more obvious after topical application than after baiting technique, and methomyl was found to be more toxic than methiocarb.

Neozygites floridana is an important natural enemy of the two-spotted spider mite, Tetranychus urticae . Pesticides used in strawberries that might affect the conservation and enhancement of this beneficial fungus were therefore studied. This was done in a laboratory study by letting non-inoculated (healthy) mites and mites inoculated with N. floridana feed on strawberry leaf disks treated with one of the following pesticides: the fungicides tolylfluanid, fenhexamid or cyprodinil + fludioxonil or the acaricide/insecticide/molluscicide methiocarb. The effect of these pesticides on mortality and egg production of T. urticae and on the killing capacity and sporulation of N. floridana were determined. Tolylfluanid increased the mortality of non-inoculated mites (75.3%) compared to the non-inoculated control (27.5%). Methiocarb also killed non-inoculated mites. Fenhexamid did not have any effect on the mortality of non-inoculated mites (19.2%), neither had cyprodinil + fludioxonil (19.1%). Tolylfluanid did not reduce the mortality of mites inoculated with N. floridana (89.3%) compared to the inoculated control (80.0%). Neither did methiocarb, it rather increased the mortality of inoculated mites (93.2%). Fenhexamid did, however, reduce the mortality of inoculated mites (66.7%). The same was true for cyprodinil + fludioxonil (48.7%). In addition, cyprodinil + fludioxonil increased the time to death of inoculated mites (6.69 days) compared to the control (6.10 days), and inhibited sporulation of N. floridana (7.9% sporulation) compared to the control (42.4% sporulation). Tolylfluanid also reduced sporulation of N. floridana (15.5% sporulation). Results from this study indicate that the use of the fungicides tested will potentially reduce the survival and efficacy of the natural enemy N. floridana in the field.

Susceptibility to spinosad of western flower thrips (WFT), Frankliniella occidentalis (Pergande), from south-eastern Spain was determined. LC(50) values of the field populations without previous exposure to spinosad collected in Murcia in 2001 and 2002 ranged from 0.005 to 0.077 mg L(-1). The populations collected in Almeria in 2003 in greenhouses were resistant to spinosad (LC(50) > 54 mg L(-1)) compared with the authors' highly susceptible laboratory strain. The highly sensitive laboratory strain leads to very high resistance ratios for the field populations (>13 500), but these ratios do not necessarily mean resistance problems and control failures (spinosad field rate 90-120 mg L(-1)). The populations collected in Murcia from some greenhouses in 2004 were also resistant to spinosad (RF > 3682). Spinosad overuse, with more than ten applications per crop, produced these resistant populations in some greenhouses. Spinosad showed no cross-resistance to acrinathrin, formetanate or methiocarb in laboratory strains selected for resistance towards each insecticide. Correlation analysis indicated no cross-resistance among spinosad and the other three insecticides in 13 field populations and in nine laboratory strains. The synergists piperonyl butoxide (PBO), S,S,S-tributyl phosphorotrithioate (DEF) and diethyl maleate (DEM) did not enhance the toxicity of spinosad to the resistant strains, indicating that metabolic-mediated detoxification was not responsible for the spinosad resistance. These findings suggest that rotation with spinosad may be an effective resistance management strategy.

Predation of slugs by Carabidae may contribute significantly to slug control in an integrated approach in pasture and arable crops Carabidae are susceptible to many insecticides used in field crops and to the molluscicide methiocarb but populations tend to recover within 1 month through migration from adjacent areas However in the longterm repeated insecticide and molluscicide treatments may affect carabid numbers and diversity in agricultural habitats The effect of pesticides on carabid populations can be reduced in soils rich in organic matter and recovery enhanced by establishment of beetle refugia in conservation headlands and winter cover crops and by avoiding deep and frequent soil cultivation

The major mechanism of resistance to most insecticides in Frankliniella occidentalis (Pergande) is metabolic, piperonyl butoxide (PBO) suppressible, mediated by cytochrome-P450 monooxygenases and conferring cross-resistance among insecticide classes. The efficacy of insecticide mixtures of acrinathrin, methiocarb, formetanate and chlorpyrifos was studied by topical exposure in strains of F. occidentalis selected for resistance to each insecticide. The method consisted in combining increasing concentrations of one insecticide with a constant low rate of the second one as synergist. Acrinathrin activity against F. occidentalis was enhanced by carbamate insecticides, methiocarb being a much better synergist than formetanate. Monooxygenase action on the carbamates would prevent degradation of the pyrethroid, hence providing a level of synergism by competitive substrate inhibition. However, the number of insecticides registered for control of F. occidentalis is very limited, and they are needed for antiresistance strategies such as mosaics and rotations. Therefore, a study was made of the synergist effect of other carbamates not used against thrips, such as carbofuran and carbosulfan, against a susceptible strain and a field strain. Neither carbamate showed synergism to acrinathrin in the susceptible strain, but both did in the field strain, carbosulfan being a better synergist than carbofuran. The data obtained indicate that low rates of carbamates could be used as synergists to restore some pyrethroid susceptibility in F. occidentalis. Copyright © 2007 Society of Chemical Industry

A sensitive method using liquid chromatography with electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) was developed and validated to quantify and confirm 13 pesticides, including aldicarb sulfoxide, aldicarb sulfone, oxamyl, methomyl, formetanate, 3-hydroxycarbofuran, carbendazim, thiabendazole, aldicarb, propoxur, carbofuran, carbaryl, and methiocarb, in soy-based infant formula. Data acquisition under MS/MS was achieved by applying multiple reaction monitoring of 2 fragment ion transitions to provide a high degree of sensitivity and selectivity for both quantitation and confirmation. Different approaches to constructing calibration curves were compared and discussed to address issues of the extraction efficiency or recovery, and matrix effects. Matrix-matched standard calibration curves with the use of isoprocarb as an internal standard were finally used to achieve the best accuracy of the method. Under most circumstances, recoveries of 13 pesticides, spiked at 5.0, 25.0, and 45.0 g/kg, were close to 100%. The method detection limits (signal-to-noise ratio 3:1; g/kg) of 13 pesticides were 0.2 for thiabendazole and methiocarb, 0.6 for aldicarb, and 0.1 for the others.

Insecticide resistance monitoring using a Potter precision spray tower with discriminating concentration and log dose probability techniques underpins the Australian insecticide management strategy for Frankliniella occidentalis Pergande. Abamectin, acephate, chlorpyrifos, dichlorvos, dimethoate, endosulfan, fipronil, malathion, methamidophos methidathion, methiocarb, methomyl, pyrazophos and spinosad are recommended for use against F. occidentalis but abamectin, methiocarb and pyrazophos are the only chemicals where insecticide resistance has not been detected. Although not registered, chlorfenapyr was effective against F. occidentalis and should be pursued for that purpose. In contrast, chlorpyrifos, dichlorvos and malathion resistance were detected at low to moderate levels throughout the study period putting their sustainable use for F. occidentalis control in doubt. Although it appears that acephate, dimethoate, endosulfan, fipronil, methamidophos, methidathion and spinosad remain effective, some populations contained a small percentage of thrips that survived exposure to a concentration that killed 100% of the susceptible strain. Subsequent laboratory selection of one such population separately with fipronil and spinosad caused an increase in resistance to these insecticides. These products must now be considered at risk. This is the first report of fipronil or spinosad resistance in populations of F. occidentalis.

The interactions between six insecticides (methiocarb, formetanate, acrinathrin, deltamethrin, methamidophos and endosulfan) and three potential synergists (piperonyl butoxide (PBO), S,S,S-tributyl phosphorotrithioate (DEF) and diethyl maleate (DEM)) were studied by topical exposure in strains selected for resistance to each insecticide, and in a susceptible strain of Frankliniella occidentalis (Pergande). In the susceptible strain PBO produced appreciable synergism only of formetanate, methiocarb and methamidophos. Except for endosulfan, PBO synergized all the insecticides to varying degrees in the resistant strains. A very high level of synergism by PBO was found with acrinathrin, which reduced the resistance level from 3344- to 36-fold. PBO slightly synergized the carbamates formetanate (4.6-fold) and methiocarb (3.3-fold). PBO also produced a high synergism of deltamethrin (12.5-fold) and methamidophos (14.3-fold) and completely restored susceptibility to both insecticides. DEF did not produce synergism with any insecticide in the resistant strains and DEM was slightly synergistic to endosulfan (3-fold). These studies indicate that an enhanced detoxification, mediated by cytochrome P-450 monooxygenases, is the major mechanism imparting resistance to different insecticides in F occidentalis. Implications of different mechanisms in insecticide resistance in F occidentalis are discussed.

The potential for reducing slug populations in crops through predation by generalist carabid beetles is well documented. However, few studies have considered interactions between biological and chemical control agents of slugs. Laboratory assays supported previous findings that the consumption of metaldehyde by slugs (Deroceras reticulatum) leads to increased duration of feeding bouts by carabid beetles (such as Pterostichini) on sub-lethally affected individuals. However, a similar effect was not found for Pterostichus melanarius exposed to slugs fed on the other widely applied pelleted molluscicide formulation (methiocarb). Examination of beetle survival after consumption of slugs containing molluscicides demonstrated the strong biocidal properties of methiocarb, whereas metaldehyde consumption (ingested through slug predation) did not differ from control slugs killed by freezing. Beetle avoidance of slugs containing a more toxic molluscicide compound and the interaction between slug mucus production and beetle attack rates are discussed.

The population response of western flower thrips, Frankliniella occidentalis (Pergande) to triflumuron, growth regulator of the benzoyl-phenyl-urea group which performs a chitin-inhibiting action, was the subject of an experimental field test. The characteristics of the active ingredient (knock-down effect, temporal persistence and overall effect of the substance) were assessed in comparison with the responses of two synthetic insecticides (methiocarb, chlorpyrifos-methyl) and in relation to the different treatment strategies (number and dates of treatments). The results of the experimental tests were analysed using a specially developed innovative method, which allows to evaluate precisely and in quantitative terms the response of the system (modification in the population dynamics of thrips) to the treatment carried out. The observations performed highlight that, at the considered doses, triflumuron is characterized by a weak knock-down effect but by good temporal persistence which makes it a product endowed with a distinct larvicidal activity. Furthermore, its action is better overall than that of chlorpyrifos-methyl and is comparable with that of methiocarb.

In Hawaii, Zonitoides arboreus (Say) is a serious pest of potted orchids, particularly those grown in bark- or coir-based media. This snail, which feeds preferentially on roots at or near the surface, causes the plant to become unstable within the pot which makes it unmarketable. Affected plants cannot be sold until roots have regrown. There is little published information about the control of this important pest. Our primary objective was to test commercially available and experimental molluscicides for control of Z. arboreus in laboratory and greenhouse trials. Molluscicides were first tested within Petri dishes to facilitate behavioural observations related to attraction or repellency of food baits and other products added to filter paper, and mortality of snails exposed to chemicals in this manner. Promising chemicals were then tested in greenhouse trials. Chemicals tested included a wide variety of commercial products containing metaldehyde; methiocarb (a carbamate); a bait product containing iron ph...

Summary The effect on slugs of spinosad, grapefruit extract, copper hydroxide, and extracts of eight species of herbal plants was tested in laboratory conditions. Cabbage leaf circles and winter rape plants were treated with these substances at various concentrations and exposed to slug feeding. The influence of applied substances on the condition and vitality of the slugs and the quantity of plant damage caused by them were evaluated. A strong deterrent effect was found in the case of copper hydroxide and methiocarb, and a short-lasting deterrent effect in the case of grapefruit extract. Of the tested herbal plant extracts, Calendula officinalis extract was found to have a weak deterrent effect, while Polygonum hydropiper extract stimulated slug feeding and increased the amount of plant damage. The selected substances may be of potential use in protecting plants against slugs.

Thrips are reported as important pests on table grapes in United States and several countries of Europe. Damage caused by thrips, particulary Frankliniella occidentalis, was observed on niagara table grape crop in Limeira-SP, Brazil. During the blooming period, high thrips densities were observed feeding on pollen and small berries. The symptoms left were more visible after the development of the berries and were characterized by dark scars and suberized surface on berries, sometimes causing the berry to crack, and the seed to prolapse. The effect of insecticides thiacloprid or methiocarb, associated or not with the entomopathogenic fungus Metarhizium anisopliae were evaluated during the blooming period. For evaluation of thrips damage on fruits, the treatments were applied three additional times, 7, 14 and 21 days after the first application. The treatments were: a) M. anisopliae (strain 1037) 1x10(7) conidia/mL; b) thiacloprid 20mL/100L; c-d) methiocarb 100 and 150mL/100L; e) methiocarb 100mL/100L + M. anisopliae 1x10(7) conidia/mL. Only methiocarb, associated or not with the fungus, was effective in reducing thrips infestation, and no phytotoxic damage was observed. The efficiency of methiocarb 150mL/100L and the insecticide associated with the fungus for the control of the thrips population was 84.2 and 95.5%, respectively. In both cases, there was a reduction of approximately 70% in the number of berries with scars symptoms. For control of thrips on table grapes, chemical insecticides associated or not with M. anisopliae should be applied during the blooming period of the crop. Os tripes são mencionados como importantes pragas da cultura da uva de mesa em diversos países da Europa e Estados Unidos. Em área de cultivo da uva Niagara localizada na região de Limeira-SP verificou-se a ocorrência de danos provocados por Frankliniella occidentalis. Essa praga foi observada, principalmente, durante a fase de florescimento, alimentando-se de pólen e bagas em início de formação. Os sintomas do ataque são mais visíveis com o desenvolvimento dos frutos e caracterizam-se por cicatrizes escuras e suberizadas nas bagas, provocando em alguns casos a rachadura das mesmas com prolapso das sementes. Avaliou-se o efeito de uma única aplicação dos inseticidas Calypso 480SC (thiacloprid) e Mesurol (methiocarb) associados ou não ao fungo entomopatogênico Metarhizium anisopliae, sobre a população da praga durante o período de florescimento. Para a avaliação do dano nos frutos foram realizadas mais três aplicações 7, 14 e 21 dias após a primeira. Os tratamentos foram: a) M. anisopliae (isolado 1037) 1x10(7) conídios/ml; b) Calypso 20ml/100L; c-d) Mesurol 100 e 150ml/100 L; e) Mesurol 100ml/100L + M. anisopliae 1x10(7) conídios/ml. Apenas o produto Mesurol associado ou não ao entomopatógeno apresentou efeito de controle sobre a praga, não sendo observados danos fitotóxicos. Nos tratamentos Mesurol 150ml/100L e do produto associado com o fungo a eficiência de controle da população do tripes foi de 84,2 e 95,5%, respectivamente, nos dois casos com redução de aproximadamente 70% no número de bagas com sintomas de ataque da praga. Para o controle de tripes em uva as aplicações de inseticidas químicos combinados ou não com M. anisopliae devem ser realizadas na época de florescimento da cultura.

Response of western flower thrips, Frankliniella occidentalis (Pergande), to selection for resistance to insecticides commonly used to control this pest in Murcia (south-east Spain) was studied under field and laboratory conditions. In the field, plots within sweet pepper crops in commercial and experimental greenhouses were treated under different selection strategies: insecticide rotation versus formetanate reiteration, formetanate reiteration versus acrinathrin reiteration, and formetanate reiteration versus methiocarb reiteration. Thrips populations were sampled monthly and bioassayed against methiocarb, methamidophos, acrinathrin, endosulfan, deltamethrin and formetanate. In the laboratory, F occidentalis strains were selected against each insecticide for several generations. To evaluate cross-resistance, each selected strain was bioassayed with the other insecticides. Frankliniella occidentalis populations showed a rapid development of acrinathrin resistance, reaching high levels in field and laboratory conditions. Formetanate and methiocarb resistance were also observed, although development was slower and at moderate levels. Cross-resistances between acrinathrin/ deltamethrin and acrinathrin/formetanate were detected under field and laboratory conditions. Formetanate/methiocarb cross-resistance was suspected in laboratory selections, but not in field assays. Simultaneous moderate resistance levels to the three specific insecticides against thrips (formetanate, methiocarb and acrinathrin) were shown in laboratory selection strains, indicating a general mechanism of resistance, probably metabolic.

Thirty-nine field populations of Frankliniella occidentalis (Pergande) were collected from different crops (sweet pepper, tomato, lettuce, artichoke, melon, cucumber, carnation, broad bean, peach and plum) in Murcia (south-east Spain). All populations were reared separately in the laboratory to obtain enough individuals for bioassays. Female thrips were bioassayed, using a standard topical application method, against methiocarb, methamidophos, acrinathrin, endosulfan, deltamethrin and formetanate. Methiocarb was the only insecticide that showed a high efficacy against F occidentalis at field dose rates. Acrinathrin and methamidophos were moderately effective, while endosulfan and deltamethrin were ineffective. Only moderate levels of resistance (Resistance Ratios at LC 50 of 10-30) were detected for the selective insecticides methiocarb, formetanate and acrinathrin used against F occidentalis in crops where these insecticides are used intensively. This generalized and low level of resistance to these insecticides, coupled with a lack of efficacy for the three broad-spectrum insecticides, was observed even in intensively managed vegetable crops. Implementation of IPM strategies in Murcia has contributed to more successful insecticide anti-resistance management.

Laboratory experiments were done to test the efficacy of a number of pesticides against the eggs of the field slug, Deroceras reticulatum (Muller). Research was based on paper-contact toxicity tests in which the eggs were continuously exposed to the compounds and the mortality rate assessed each day. The compounds tested included molluscicides (metaldehyde and methiocarb), herbicides (ioxynil, bromoxynil, pyridate), insecticides (thiocyclam hydrogen oxalate, imidacloprid, diflubenzuron, teflubenzuron, azadirachtin), and other compounds such as saponin, carvone and Pongamia pinnata (L.) extract. The herbicides ionynil and bromoxinyl, and the active ingredient of neem ( Azadirachta indica A. Juss) oil, azadirachtin, killed all the eggs of D. reticulatum at doses

Slugs are major pests of oilseed rape that are poorly controlled by conventional bait pellets. A series of laboratory experiments investigated the potential of seed-dressings to control slug damage in this crop. Four compounds: metaldehyde, methiocarb, cinnamamide and 3,5-dimethoxycinnamic acid (DMCA) were tested at a range of doses for phytotoxicity and ability to reduce damage by Deroceras reticulatum (Müller). Metaldehyde and methiocarb were not phytotoxic at any doses, whereas all doses of cinnamamide and DMCA were. All compounds reduced slug damage, but metaldehyde and methiocarb consistently performed better than cinnamamide and DMCA. Metaldehyde and methiocarb seed-dressings were compared with baited pellets containing the same active ingredients at recommended field doses. The seed-dressings protected plants from damage by D reticulatum and Arion subfuscus (Draparnaud) as well as, or better than, baited pellets. We therefore recommend that metaldehyde and methiocarb should be field-tested as seed dressings to control slugs in oilseed rape.

In Venezuela, lethal control of wintering Dickcissels (Spiza americana) is considered a threat to the species survival. To help farmers protect their rice and sorghum crops from depredations by Dickcissels and to minimize the killing of large numbers of these birds, alternative non-lethal crop protection measures are needed. To that end, the responses of captive Dickcissels to three bird-repellent chemicals applied to rice seed were evaluated. In one-cupfeedingtrials, treatments ® of methiocarb (0.05% g g-1, applied as Mesurol 75% wettable ® powder) and anthraquinone (0.5%, applied as Flight Control) reduced consumption of rice by 70% relative to pretreatment consumption. Other anthraquinone treatments (0.05, 0.1%) and methyl anthranilate (0.05%) were ineffective. In two-cup trials, with untreated millet as the alternative food, consumption of rice treated with0.05 and 0.1% anthraquinone was reduced by 90% relative to pretreatment levels. Overall, Dickcissels responded to the repellents similarly to the r...

Pesticides with N,N-dimethyl and thiomethyl moieties (aminocarb, methiocarb and fenthion) were irradiated under artificial light (λ > 290 nm) in an amorphous wax phase from Persica laevis DC. The effect of the presence of the wax on the photolysis rate differed in the three pesticides, increasing it in aminocarb, having little effect in methiocarb and slowing it down in fenthion. The presence of the wax affected the qualitative photodegradation behaviour of all the pesticides. The data obtained were compared with those for pirimicarb, which had been studied earlier. © 2001 Society of Chemical Industry

Two trials were carried out to test the effects of field applications of snail baits on populations of house mice (Mus domesticus) inhabiting cereal-cropping fields during a mouse plague in South Australia. In the first trial, grain based pellets containing 2% w/w active ingredient methiocarb, were laid in trails across fields before crops were sown. The second tested the effect of whole wheat grains treated with 1% w/w methiocarb when broadcast across maturing barley crops. Treatment effects were estimated by comparison with untreated control plots. In the methiocarb-treated wheat trial, comparison was also made with 0.3% w/w strychnine-treated wheat treatments. Methiocarb baiting reduced estimated mouse numbers by 0–46%. Surviving mice did not accept the excess bait material available. In contrast, strychnine-treated wheat reduced estimated mouse numbers by 86–94%. These trials indicate that methiocarb is not likely to be a useful field rodenticide. Furthermore, the consumption of bait by mice is not likely to jeopardise snail control operations. However, methiocarb baits could cause sufficient mortality to pose a threat to rare or endangered granivorous rodents inhabiting agricultural fields.

In two concurrent field experiments, the effects of three types of soil cultivation and two patterns of nematode application were studied in order to investigate their effects on damage to winter wheat by slugs (assessed at Zadoks Growth Stage 12). In experiment 1, infective juveniles (IJs) of the nematode Phasmarhabditis hermaphrodita were applied to soil as an overall spray or as a band spray (8-cm wide), centred on the drill rows (16.7-cm apart). Nematodes were either left undisturbed on the soil surface or harrowed into the soil immediately after application. The control provided by nematodes was compared with that provided by metaldehyde and methiocarb pellets broadcast at the recommended rate immediately after drilling. In this experiment, winter wheat on plots treated with IJs showed significantly less slug damage than on wheat plots treated with metaldehyde or methiocarb pellets or untreated plots. There was no significant difference in plant damage between plots treated with band and overall spra...

A flow-injection (FI) spectrophotometric system is proposed for the determination of phenols and carbamates. In the FI manifolds, the solutions of phenols or carbamates (the latter after hydrolysis with NaOH) were injected into a diazonium ion carrier stream at pH 9.5 (buffered with tetrahydroborate), which was formed by mixing 2,4,6-trimethylaniline (TMA) with nitrate in a sodium dodecyl sulfate aqueous micellar medium. Absorbance was measured at 550 nm. The system combines the advantages derived from the use of TMA for the coupling of phenols in basic micellar media, because of the inhibition of the self-coupling reaction of the reagent, with the precision and speed of the FI procedures. Other diazotized reagents produced excessive blank signals. The procedures were successfully applied to the determination of phenolic drugs (epinephrine, acetaminophen, and guaiacol) in pharmaceuticals and carbamates (bendiocarb, benfuracarb, carbaryl, carbofuran, methiocarb, promecarb, and propoxur) in pesticide products and water samples.

A strain of western flower thrips ( Frankliniella occidentalis ) with resistance to methiocarb was collected from a Danish greenhouse for investigation of possible resistance mechanisms. Bioassays with methiocarb showed moderate (10-fold) resistance at LC 50 in the greenhouse-collected strain compared to a susceptible laboratory strain. Piperonyl butoxide, a cytochrome P450 monooxygenase inhibitor, showed no synergistic effect on the tolerance level to methiocarb. In vitro assays of enzyme activities showed significantly increased activity of acetylcholinesterase (2.6-fold), general esterases (1.3-fold), and glutathione S -transferases (1.2-fold) in the resistant strain. Assays of acetylcholinesterase sensitivity to inhibition by methiocarb, dichlorvos, and eserine showed no indications of insensitive acetylcholinesterase in the resistant strain. These results indicated that increased activity of acetylcholinesterase contributed to methiocarb resistance in the resistant strain. The slightly increased activity of general esterases and glutathione S -transferases may also have contributed to methiocarb resistance.

Summary Daily activity of slugs, Deroceras reticulatum and Arion distinctus, was studied in the laboratory in relation to the presence of shelters so as to define optimal conditions for using traps to forecast crop damage. Under constant temperature and humidity, activity of slugs began with the lights off. Its arrest occurred after a period of activity with the lights on. Slugs rested most frequently under a shelter on bare earth and rarely used the same shelter for more than two consecutive days. When food was placed under the shelter, the number of slugs found under the shelter was more constant throughout the 24 h period, but lower during diurnal rest. The presence of 4% methiocarb pellets under the shelter led to an increased occupation by slugs, due to the poisoning of some of them. Acts of aggression were more numerous in A. distinctus than in D. reticulatum. In D. reticulatum the smallest slug was the least aggressive and suffered more attacks from the other slugs. In A. distinctus the numbers of attacks suffered or provoked varied little with the size of the slug, but the smallest slug showed less interactions with other slugs.

Previous studies have shown that seed dressing with methiocarb or metaldehyde can protect newly emerged oilseed rape seedlings from slug damage. Here, we document two mini-plot field experiments testing these seed dressings. Both metaldehyde and methiocarb significantly reduced slug damage compared with untreated control seeds, but both seed dressings performed less well to the metaldehyde bait pellets. Protection offered by metaldehyde seed dressing was short-lived, whereas methiocarb seed dressings gave protection throughout the 4 weeks duration of both experiments.

From 1993 to 1995 the effectiveness of various insecticides applied as a seed-coating to control Thrips tabaci in winter leeks ( Allium porrum L.) was investigated in the field. Seed-coatings with fipronil and imidacloprid gave a good control, hut carhofuran, diflubenzuron, methiocarh, tefluhenzuron and vamidothion were not effective. The most effective insecticide, fipronil, did not cause phytotoxicity, whereas imidacloprid reduced and slowed germination.

Thirteen molluscicides containing metaldehyde, three molluscicides containing metaldehyde plus carbaryl, one molluscicide containing metaldehyde plus methiocarb and one molluscicide containing methiocarb alone were tested for efficacy against the brown slug, Vaginula plebeia Fischer, and the two-striped slug, Veronicella cubensis (Pfeiffer). With the exception of Corry's Liquid Slug, Snail and Insect Killer against V. plebeia, all tested molluscicides caused significant mortalities against both species. Selected molluscicides were further evaluated for persistence under simulated rainfall; Deadline One Last Meal for Slugs and Snails, Deadline 40, Deadline Bullets and Slug and Snail AG Pelleted Bait, all of which contain metaldehyde as the active ingredient, consistently produced high mean percentage mortalities against both species. Efficacy of certain molluscicides decreased steadily with time, whereas efficacy of other molluscicides increased initially before declining. Mold grew on the majority of molluscicides after application. Liquid paste and liquid formulations were more resistant to mold development than pelleted, granule or coated granule formulations. In a separate study, physical barriers composed of copper or fiberglass screens repelled both slug species.

Methiocarb is a carbamate molluscicide widely used in pelleted form. Wood mice Apodemus sylvaticus are commonly found in arable fields and will eat methiocarb pellets. Two previous field studies on the impacts on arable wood mice of broadcasting methiocarb pellets produced contrasting results, the number of mice being temporarily reduced in one but not the other. The season of application is also likely to influence the degree of impact on populations but the previous trials were both in autumn. The aim of the present study was to determine the effects on wood mice of broadcast applications of methiocarb in both autumn and spring and to determine whether depression of brain and serum cholinesterase (ChE) activity, a biomarker of exposure, could be detected in mice alive on treated fields after application. In trials carried out in October 1994 and April 1995, there were decreases in the number of wood mice on arable fields following pesticide application. The October decline (78%) was greater than that in April (33%), even though the activity of the mice appeared to be more heavily centred on the hedgerows, where pellets were not applied, in the autumn. Despite the reductions in numbers, no depression of ChE activity was detected in mice captured alive after application, suggesting that either exposed animals were not captured or that reactivation of ChE activity was rapid. This study confirmed that broadcast application of methiocarb can reduce wood mouse populations on arable fields. It also demonstrated that such effects can occur irrespective of season and that measurement of ChE activity in mice trapped after application may fail to indicate that exposure of the population has occurred.

Red-winged Blackbirds ( Agelaius phoeniceus ) cause substantial damage to a variety of crops throughout North America. Nonlethal methods for controlling damage are generally ineffective, and environmental and cost concerns have limited the availability of chemical repellents such as methiocarb. One means of potentially lowering the effective application rate of methiocarb and similar aversive compounds is by combining the treatment with sensory cues. We tested groups ( n = 4) of male Red-winged Blackbirds in a series of 4-day feeding trials using brown rice treated with 0.025% (g/g) methiocarb, five times less than the previously established effective bird repellent rate. Each methiocarb treatment suppressed rice consumption, whether the repellent was alone or combined with a visual (red dye) and/or volatile (methylpyrazine) cue. When rice treated with just the sensory cues was subsequently presented, the red dye, but not the methylpyrazine, continued to deter feeding on rice. These results show that post...

Two field collected strains of western flower thrips, Frankliniella occidentalis, were tested against proprietary and experimental formulations of insecticide. Thrips were tested using a novel method whereby thrips were confined in testing units throughout all stages of the bioassay procedure. The bioassay technique proved to be quick and robust. Of the chemicals tested, the two non-registered compounds chlorfenopyr and fipronil were most active against field-collected F. occidentalis. The field-collected strains were tolerant to a range of organophosphate, carbamate and pyrethroid chemicals. Comparisons of dose-response curves with established field-use-rates indicate that only methiocarb and methamidophos are likely to be completely effective in the field. The theoretical implications of the data for management of F. occidentalis in Australia is discussed.

A laboratory test was developed as a quick screening method for investigating the effectiveness of different pesticides as seed treatments against the slug Deroceras reticulatum in winter wheat. Seed treatments were applied with and without a coating agent. The most effective treatments in preventing damage by slugs to the seeds were: bromoyxnil, carvone, ioxynil, thiocyclam hydrogen oxalate and methiocarb. Anthraquinone, thiodicarb, isazofos and Bacillus thuringiensis were less effective. The coating agent had some influence on the effectiveness of these treatments, but was not significant. Among the most effective pesticides, only methiocarb did not demonstrate any phytotoxic effects. Isazofos showed moderate phytotoxicity. Coating significantly improved germination of seeds treated with carvone and thiocyclam hydrogen oxalate. Other treatments did not react to coating.

Loading of active ingredient between individual pellets varied significantly. The coefficients of variation (CV) for thiram ranged from 25 to 77% and for hymexazol, methiocarb, furathiocarb and imidacloprid between 12 and 34%. With carbofuran the CV ranged from 14 to 62% depending on pelleting process and applied dose. Stability of applied pesticide after storage depended on pellet type and applied fungicide/insecticide combination. Decrease of thiram during storage was related to the pellet type, but hymexazol decreased in all pellet types, especially in combination with furathiocarb, benfuracarb and carbosulfan. Carbofuran, methiocarb, tefluthrin and imidacloprid individually were stable during storage. The conversion rate of furathiocarb, benfuracarb and carbosulfan to carbofuran during storage was related to the pellet type and was enhanced by the presence of hymexazol. Analysis of the active ingredients in pellets periodically after sowing showed the percentage of the initial thiram concentrations present 4 weeks after sowing varied 0–75%. Hymexazol decreased quickly in the pellets and after 4 weeks no active ingredient could be detected, in most pellet types, even with slow release products. Thirteen to 71% of furathiocarb, benfuracarb, carbosulfan, carbofuran and tefluthrin was still present in the pellets after 8 weeks, depending on pellet type and insecticide/fungicide combination in the pellets.

In two experiments, the rhabditid nematode Phasmarhabditis hermaphrodita, a parasite of slugs, was cultured in vitro and applied as a drench to soil at four dose rates (3 108, 1 109, 3 109 and 1 1010 ha-1) 1 or 4 days before planting lettuce seedlings in a polythene tunnel. The effects of the four nematode doses on slug damage during the first 3 weeks after planting and on the numbers of slugs found within and below lettuce plants at harvest were measured. Results were then compared with untreated plots and with plots where methiocarb pellets were applied at the recommended field rate. In the first experiment, methiocarb pellets significantly reduced the percentage of plants damaged by slugs, but the nematode did not. In the second experiment, methiocarb pellets and the second highest dose of nematodes significantly reduced the percentage of plants damaged by slugs. The different effect of the nematode in the two experiments may have resulted from differences in the timing of nematode application and/or d...

Some of the possible reasons for the failure of white clover ( Trifolium repens ) seedlings to establish and develop were investigated. Experimental plots were sown with 3 kg white clover seed ha −1 and either 12 or 24 kg perennial ryegrass ( Lolium perenne ) seed ha −1 and given no treatment, herbicide (bentazone), insecticide (triazophos), molluscicide (methiocarb) or all possible combinations of these treatments. Using the higher rate of ryegrass seed led to a greater proportion of this forage in the swards that developed. Use of the herbicide led to higher yields at one site in the second year, with fewer weeds and a greater proportion of ryegrass than clover in the swards. Insecticide and molluscicide generally had little or no effect, although molluscicide increased clover content and decreased ryegrass content at one site in the first harvest year.

The nematode Phasmarhabditis hermaphrodita, a parasite of slugs, was cultured in vitro and applied as a drench in two outdoor mini‐plot field experiments to test the capacity of the nematode to protect Chinese cabbage seedlings and wheat seeds from damage by the field slug Deroceras reticulatum. The first experiment compared a single dose of nematodes (2 X 1010 ha‐1) with methiocarb pellets added at the recommended field rate (5.5 kg.product ha‐1 ) and untreated plots. Plots treated with either nematodes or methiocarb pellets had significantly less slug damage than untreated plots and, from the third week onwards, there was significantly less slug damage on plots treated with nematodes than on methiocarb‐treated plots. At the end of the experiment, 6 weeks after treatment, both slug numbers and biomass were significantly higher in untreated plots than in either methiocarb‐treated or nematode‐treated plots. In the second experiment, six nematode doses ranging from 1 X 10 8 to 2 X 1010 ha‐1 were compared wi...

Two field experiments were carried out at North Wyke, Devon in 1985 (Experiment A) and 1986 (Experiment B) to investigate the effectiveness of either cutting or rotational sheep-grazing managements for raising the clover content of clover-depleted swards. Subplots were pretreated in March with (a) propyzamide at 0·4kg a.i. ha-1, (b) chlorpyrifos at 0·72 kg a.i. ha-1 and methiocarb at 0·22 kg a.i. ha-1, (c) carbofuran at 1·3 kg a.i. ha-1, or (d) not so treated, in order to reduce grass tiller density, control insect and mollusk pests, or control all invertebrate pests respectively (a-c), Carbofuran was not applied to swards that were to be grazed subsequently. The propyzamide pretreatment (a) significantly reduced the quantity of herbage dry matter (DM) grazed and the silage DM yields in both years, but raised the numbers of active clover buds, and clover stolon density and its weight in 1986, though not in 1985, The pesticide package (b) raised the quantity of herbage DM grazed in both years, and the silage DM yield in 1986, Carbofuran (c) raised silage yields in 1985. Neither pretreatment (b) nor (c) significantly affected clover performance. In comparison with sheep grazing, cutting showed a trend to higher DM yields, and significantly raised clover stolon density and weight in both years, and active bud numbers in 1986. The periodic sheep grazing management included recovery intervals of 14 d and 35 d. In 1986 (but not 1985) the longer recovery interval raised herbage DM consumption, but had no effect on clover development. The cutting management included nitrogen inputs of either 100 kg ha-1 in March, or none. N input raised annual DM yields in 1986 (but not 1985) but did not affect clover DM yields or performance in either year. The experiments at North Wyke were supported by on-farm experiments using exclosure cages at ten sites in 1985 and nine in 1986, in Yorkshire, Wales, the Midlands and Devon. In both years, application of propyzamide as in treatment (a) reduced DM yields (P

In the United States, Mesurol 75% wettable powder (active ingredient methiocarb) was formerly registered as a bird repellent on blueberries and cherries. In part because of concerns over residue levels, this chemical is no longer registered for use on fruit. One approach to reducing residues is to lower the application rate. Methiocarb was evaluated on blueberries in an aviary trial at application rates of 0.6, 1.1 and 1.6 kg ha−1 and in the field at 1.1 and 1.6 kg ha−1. Inthe aviary trial, individually caged cedar waxwings (Bombycilla cedrorum) were not repelled by the application at 0.6 kg ha−1, but consumption of blueberries was reduced by 60% with the treatments at 1.1 and 1.6 kg ha−1. In the field trial at 1.1 kg ha−1, bird damage to blueberries in the treated plot was 57%, compared with 29.5% on the untreated plot. In the field trial at 1.6 kg ha−1, blueberry loss at 7 and 14 days post-treatment was 59% and 85% on the treated unit and 65% and 85% on the control, respectively. Methiocarb residues on blueberries decreased from 8.56 p.p.m. at 1 day post-treatment to 1.28 p.p.m. at 14 days post-treatment. The results of these trials (a) suggest that reduced methiocarb applications do not effectively control bird damage to blueberries and (b) do not support further pursuit of a new Mesurol registration for this use.

BACKGROUND: Western flower thrips (WFT), Frankliniella occidentalis (Pergande), is among the most important crop pests in the south-eastern region of Spain. Its increasing resistance to insecticides constitutes a serious problem, and understanding the mechanisms involved is therefore of great interest. Use of synergists to inhibit the enzymes involved in insecticide detoxification is widely used to determine their responsibility for insecticide resistance. However, they do not always act as intended or expected, and caution must be exercised when interpreting synergist results. RESULTS: Laboratory-selected strains of WFT were used to analyse the effects of the synergists piperonyl butoxide (PBO), S,S,S-tributyl phosphorotrithioate (DEF) and methiocarb on total esterase activity. Significant differences were found, indicating esterase activity inhibition by DEF, a lower effect for methiocarb and a small inhibition of the activity by PBO. Esterase isoenzyme inhibition by these compounds showed a similar result; this assay revealed an extreme sensitivity of Triplet A (resistance-associated esterases) to DEF. In an in vivo assay carried out with these compounds at different incubation times, only DEF caused posterior in vitro esterase activity inhibition, with a maximum effect 1 h after treatment. CONCLUSION: In this work, only DEF shows true synergistic inhibition of WFT esterases. Copyright © 2011 Society of Chemical Industry

In a laboratory experiment, grey field slugs ( Deroceras reticulatum ) were introduced to trays of clay soil drilled with wheat seeds at 10 or 25 mm depth. Trays were left without molluscicide, or methiocarb pellets were drilled with the seeds or placed on the surface of the soil immediately after drilling. In the absence of molluscicide, there was less damage to seeds drilled at 25 mm than at 10 mm. Methiocarb pellets drilled with seeds at 10 mm depth killed slugs and reduced damage to seeds and seedlings, but the percentage of seeds killed was similar to the percentage of deeper-drilled seeds killed where no molluscicide had been applied. Pellets drilled with deeper-sown seeds did not kill slugs, or reduce damage to seeds and seedlings, whereas pellets placed on the soil surface immediately after sowing were effective in killing slugs and reducing plant damage irrespective of drilling depth. The best protection from slug damage was provided by deeper drilling combined with pellets broadcast on the soil surface. In a field experiment, methiocarb pellets broadcast immediately after drilling at two depths killed slugs and protected seedlings from damage, whereas pellets drilled with seeds were ineffective because seed-bed conditions prevented slugs from reaching seeds and pellets (only 4% of seeds were killed by slugs in the absence of molluscicide treatment). The implications of these results for slug control and for non-target fauna (wood mice and ground beetles) are discussed.

Summary The effects of repeated annual application of methiocarb-based slug pellets, broadcast on the soil surface and drilled into the seed bed, on carabid beetle activity were investigated over a four year period on a winter-sown cereal field using pitfall traps in barriered plots. Following applications in late autumn all winter-active carabid populations were severely depressed; total carabid activity falling to less than 5% and 10–15% following broadcast and drilled applications, respectively, compared with untreated plots. Spring and summer-active species, not active at the time of application, were largely unaffected by applications and were responsible for a gradual recovery of total activity from early spring onwards. Activity of all affected winter species remained demonstrably depressed on treated areas for the remainder of their seasonal incidence. However, all except one species, Bembidion obtusum, recovered to normal activity levels in the following season prior to reapplication. Recovery patterns are discussed in terms of the known biology of the species involved. Evidence that a minority of summer-active species were also affected by treatments, sometimes positively and sometimes negatively, were attributed to indirect effects possibly involving prey availability and foraging behaviour. The long-term ecological and short-term agronomic implications of methiocarb effects on carabid populations in winter-sown cereals are discussed.

We conducted enclosure trials near Huron, CA in the San Joaquin Valley from 12 to 23 January 1999 to determine the efficacy of Flight Control™ (50% anthraquinone) and Mesurol ® (75% methiocarb) in preventing horned lark damage to lettuce seedlings. Flight Control™ (FC) and Mesurol ® were evaluated as foliar sprays at application rates of 2.79 and 2.27 kg ha −1 , respectively. Horned lark damage to lettuce seedlings treated with antraquinone was greater ( p =0.015) than for methiocarb ® , 60 versus 20%, respectively, and seedlings in control plots were 100% destroyed. While this level of damage is probably unacceptable to lettuce growers, it should be remembered that the enclosure situation caused an artificially high bird pressure on the crop. Further studies in open fields under a more normal bird pressure are warranted.

Summary The effects of adding the molluscicides methiocarb and metaldehyde to pelleted foods on the encounter, acceptance, feeding and post-meal stages of the foraging sequence of the slugs Deroceras reticulatum and Arion distinctus have been studied using two complementary laboratory techniques - video and acoustic recordings. Whereas non-feeding slugs encountered wheat grains at random, slugs which fed on wheat grains or pellets encountered them more frequently because of changes in locomotor pattern and olfactory attraction. Slugs would almost always feed on the first pellet they found, regardless of the presence or absence of molluscicide: thereafter they fed on only one pellet in every four encountered. Far fewer slugs accepted wheat grains. Slugs ate much less from pellets containing molluscicide, and meals were more irregular. The relative amounts of non-toxic pellets of various types which were eaten gave no indication of the relative amounts eaten when molluscicide was added. Meal length did not correlate well with meal size on different pellet types because softer pellets were eaten faster. Most Deroceras fed several times on non-toxic pellets or pellets containing methiocarb, although subsequent meals were shorter than the first meal. Most returned to shelters by dawn. In contrast, metaldehydefed slugs were rapidly immobilised; they seldom fed again, moved little, and few regained shelter. Arion were also inhibited after methiocarb meals but Deroceras were not. Arion distinctus moved less, ate less during a meal, and had fewer meals on nontoxic baits than Deroceras reticulatum.

Summary Slug foraging paths recorded using time lapse video techniques under infra-red light were fitted to a correlated random walk model. Analyses were carried out on slugs in arenas where no food was present, as well as those containing commercial molluscicides at two rates of application. Slugs were found to search randomly in empty arenas and those containing commercial metaldehyde baits, but deviated from random search patterns when in the presence of commercial methiocarb bait. Differential attraction from a distance is suggested as a cause of these differences.