Abamectin Residues Research Articles

Sub-lethal effects of abamectin suppressing colonies of the leaf-cutting antAcromyrmex subterraneus subterraneus

An assessment of the sub-lethal effects of abamectin on queens of the leaf-cutting ant Acromyrmex subterraneus subterraneus (Hymenoptera: Formicidae) was carried out. A concentration-response bioassay was conducted by exposing media workers (head capsule width ranging from 1.69 to 1.83 mm) to filter paper impregnated with abamectin residue. This bioassay allowed selection of the abamectin concentrations (0, 10, 50 and 100 mg AI ml−1) to be used in the experiment in which eight queens were exposed to the insecticide. The highest concentration killed queens, but those exposed to lower concentrations survived and were placed back in their nests. Reductions in leaf consumption, fungus garden volume, and foraging activity were observed in colonies whose queens were exposed to higher abamectin concentration (50 mg AI ml−1). Colonies with queens exposed to 50 mg AI ml−1 were suppressed after 11 weeks. The dissection of queen ovaries revealed a marked decrease in the number of ovarioles per ovary and oocytes per ovariole with increased insecticide concentration. It would appear that, as abamectin-exposed queens became reproductively impaired, producing little or no progeny, colony members were not replaced and this led to colony suppression. © 2000 Society of Chemical Industry

Monitoring the susceptibility of citrus rust mite (Acari: Eriophyidae) populations to abamectin.

A citrus leaf disk bioassay was developed to monitor the susceptibility of citrus rust mite, Phyllocoptruta oleivora (Ashmead), populations to abamectin. Disks from leaves of several citrus cultivars were equally suitable bioassay substrates, and there was no difference in mortality when mites were sprayed directly or exposed to dry abamectin residue. The concentration-response relationship was determined at intervals over 2 yr for a reference population of citrus rust mites that had been maintained in culture and never exposed to acaricides. Three diagnostic concentrations of abamectin were selected based on the response of the reference population and were used to test the susceptibility of 15 populations of mites from commercial citrus groves. Comparisons with the reference population showed reduced levels of susceptibility in some populations. Populations of citrus rust mites from 6 commercial groves were sprayed twice in 1997 with combinations of acaricides designed to exert different intensities of selection pressure from abamectin. None of these populations showed a change in their response to abamectin in pre- and postspray bioassays, although their susceptibility was usually less than that of mites from the susceptible reference population. Biweekly counts of rust mites on fruit in these 6 groves suggested that, relative to groves which received no abamectin or 1 abamectin spray, mite control was not adversely affected in the groves sprayed twice with abamectin. The bioassay method is discussed in relation to factors that affect the interpretation of results from its use, and factors that may affect the development of resistance to abamectin in citrus rust mite populations are presented. This study has provided baseline data with which the results of ongoing tests of the response of citrus rust mite populations to abamectin can be compared.

Determination of abamectin residues in fruits and vegetables by high-performance liquid chromatography

A rapid and sensitive HPLC method has been developed and validated for the determination of abamectin residues (avermectin B 1a and B 1b, as well as the metabolite 8,9- Z-avermectin B 1) in apples, pears and tomatoes. Residues are extracted with acetonitrile. The diluted extract is cleaned up on a C 18 solid-phase extraction cartridge. Abamectin residues are derivatised with trifluoroacetic acid and 1-methylimidazole and determined by reversed-phase liquid chromatography with fluorescence detection (excitation: 365 nm and emission: 470 nm). High and consistent recoveries, ranging from 88 to 106%, were obtained, at spiking levels of 10, 20 and 50 μg/kg, when analysing apples, pears and tomatoes.

Photostability of Abamectin/Zein Microspheres

Abamectin, a natural product pesticide that degrades rapidly in air and sunlight, has been encapsulated with the protein zein. The result was a mineral oil suspension that included a photostabilized abamectin. After exposure to simulated sunlight, the microsphere suspension provided a several-fold increase in recoverable abamectin residue. The enhanced photostability of the microspheres is due to retarded reaction between oxygen and the diene chromophore of abamectin, in the presence of light. The zein could function as a quencher of singlet oxygen and/or a physical oxygen barrier.

Potential for Integration of Biological and Chemical Control of Greenhouse Whitefly (Homoptera: Aleyrodidae) Using Encarsia formosa (Hymenoptera: Aphelinidae) and Abamectin

The compatibility of abamectin with Encarsia formosa Gahan (Hymenoptera: Aphelinidae) as a part of integrated pest management of the greenhouse whitefly, Trialeurodes vaporariorum Westwood (Homoptera: Aleyrodidae), was assessed in a series of laboratory and greenhouse experiments. In laboratory experiments using commercially formulated abamectin at the concentration recommended for greenhouse use, mortality of the adult parasitoids ranged from 100%, when exposed to 2-h-old abamectin residues on bean plants (Phaseolus vulgaris) in the presence of whitefly larvae, to 0% when exposed to 24-h-old residues without whitefly larvae. More than 50% of the E. formosa successfully eclosed from parasitized whitefly pupae on bean leaves dipped in formulated abamectin. In the greenhouse experiment, the combined treatment of abamectin and E. formosa maintained significantly lower densities of whiteflies on poinsettia, Euphorbia pulcherrima (Willdenow), throughout the season with fewer abamectin applications than did abamectin alone. Moreover, the percentage of parasitism did not differ significantly among plants treated with and without abamectin. Abamectin might be used to reduce whitefly numbers on poinsettia without eliminating the parasitoid population when releases of E. formosa are not satisfactory. A possible explanation for the partial selectivity of abamectin to E. formosa is discussed.

High-Performance Liquid Chromatographic Method for the Determination of Occupational Exposure to the Pesticide Abamectin

As part of a survey of occupational exposure to pesticides in greenhouses for growing ornamentals, analytical methods were developed and validated for the measurement of exposure of workers to the pesticide abamectin. Abamectin consists of a mixture of avermectin-Bla and avermectin-Blb, which are numbers of a class of fermentation products of the soil microorganism Streptomyces Avermitilis. Because of the high molecular weight of the avermectins (>800 daltons), high-performance liquid chromatography (HPLC) was the analytical method of choice. Previously described HPLC methods that used fluorescence detection were adapted and validated for the determination of dermal exposure by the analysis of cotton gloves and foliar dislodgeable residue. IOM samplers (developed at the Institute of Occupational Medicine, Edinburgh, U.K.) for collecting the inspirable fraction of dust or aerosols were tested for the determination of airborne abamectin concentrations in greenhouses. An analytical procedure considerably simpler than published methods appeared suitable for the determination of abamectin residues on cotton gloves and on greenhouse foliage. Analytical recovery from cotton gloves, solutions offoliar dislodgeable residues, and air-sampling filters was essentially complete. However, air concentrations of abamectin could not be reliably Measured by using the IOM sampling device because of breakdown during sampling. Between-day coefficients of variation for solutions of dislodgeable residue and cotton glove extracts were between 3% and 6% for abamectin concentrations between 5 and 140 µg/L.

HIGH-PERFORMANCE LIQUID CHROMATOGRAPHIC METHOD FOR THE DETERMINATION OF OCCUPATIONAL EXPOSURE TO THE PESTICIDE ABAMECTIN

As part of a survey of occupational exposure to pesticides in greenhouses for growing ornamentals, analytical methods were developed and validated for the measurement of exposure of workers to the pesticide abamectin. Abamectin consists of a mixture of avermectin-B1a and avermectin-B1b, which are members of a class of fermentation products of the soil microorganism Streptomyces Avermitilis. Because of the high molecular weight of the avermectins (greater than 800 daltons), high-performance liquid chromatography (HPLC) was the analytical method of choice. Previously described HPLC methods that used fluorescence detection were adapted and validated for the determination of dermal exposure by the analysis of cotton gloves and foliar dislodgeable residue. IOM samplers (developed at the Institute of Occupational Medicine, Edinburgh, U.K.) for collecting the inspirable fraction of dust or aerosols were tested for the determination of airborne abamectin concentrations in greenhouses. An analytical procedure considerably simpler than published methods appeared suitable for the determination of abamectin residues on cotton gloves and on greenhouse foliage. Analytical recovery from cotton gloves, solutions of foliar dislodgeable residues, and air-sampling filters was essentially complete. However, air concentrations of abamectin could not be reliably measured by using the IOM sampling device because of breakdown during sampling. Between-day coefficients of variation for solutions of dislodgeable residue and cotton glove extracts were between 3% and 6% for abamectin concentrations between 5 and 140 micrograms/L.

Longevity and Oviposition of Adult Liriomyza trifolii (Diptera: Agromyzidae) Exposed to Abamectin in the Laboratory

The impact of abamectin residues on Liriomyza trifolii (Burgess) adults was studied in the laboratory. Residues induced mortality of L. trifolii females through ingestion and contact; mortality of males appeared to be related only to contact. Stippling (leaf puncturing) and oviposition by females were inhibited. These effects were not readily reversed when females were no longer exposed to abamectin residues. Abamectin was not repellent to L. trifolii females.

MORTALITY OF TETRANYCHUS URTICAE KOCH (ACARI: TETRANYCHIDAE) FROM ABAMECTIN RESIDUES: EFFECTS OF HOST PLANT, LIGHT, AND SURFACTANTS

Residues of abamectin (avermectin, Avid), 15 ppm; abamectin + Leaf Act 80, 15 + 25 ppm; abamectin + Sunspray oil, 15 + 25 ppm, and a water control were evaluated for length of control of twospotted spider mite, Tetranychus urticae Koch, on 3 host species: azalea, Rhododendron × ‘Red Ruffle’; lima bean, Phaseolus limensis var. limenus L. H. Bailey cv. ‘Henderson’ bush; and peach, Prunus persica L. Batsch cv. ‘Nemaguard’; and under sunlight and fluorescent light regimes. Abamectin alone or in combination with the surfactants, 21 days post treatment, resulted in 42.6 – 91.8% and 88 – 93% mite mortality under sunlight and fluorescent light, respectively. No treatments on azalea or peach under sunlight caused > 37% mortality. Treatments caused similar mite mortality 1 day posttreatment under fluorescent light, but after day 1 treatments on peach caused < 62 % mortality while treatments on azalea caused < 46% mortality. The addition of oil increased mite mortality significantly on beans under sunlight at 14 days. At 21 days both Leaf Act 80 and oil increased mite mortality on bean compared to abamectin alone.