Rainfastness and residual activity of insecticides to control Japanese beetle (Coleoptera: scarabaeidae) in Grapes

Does commercial indoxacarb pose ecotoxicological consequences? Employing a multi-marker approach in the model species Theba pisana

Indoxacarb is one of the most extensively used oxadiazine insecticides worldwide, but it may exert detrimental effects on ecosystems, population dynamics, and health. Due to the lack of knowledge on the ecotoxicity of indoxacarb, it is still challenging to assess whether this insecticide poses an ecotoxicological impact on terrestrial environments. Therefore, our study aims to provide novel data on the toxic effects of 28-day dietary exposure to commercial grade indoxacarb at two environmentally relevant concentrations, 0.02 µg/mL and tenfold (0.2 µg/mL) on the model species, Theba pisana. Their effects were studied using a multiple biomarker approach by evaluating physiological, biochemical, and histopathological responses. After 28 days of treatment, indoxacarb at both concentrations significantly reduced the food intake and growth of the treated snails. Also, it caused decreases in lipid peroxidation (LPO)  levels after 7 and 14 days of exposure, whereas an opposite effect occurred after 21 and 28 days. All treated snails were found to exhibit a lower content of glutathione (GSH) after all times of exposure. Moreover, catalase (CAT), glutathione-S-transferase (GST), and glutathione peroxidase (GPx) activities, as well as protein content (PC), were elevated in the treated snails after all time intervals. Post exposure to both realistic indoxacarb concentrations, changes in acetylcholinesterase (AChE) activity between a decrease and an increase were observed. Furthermore, indoxacarb caused histo-architectural changes in the hepatopancreas of T. pisana. Our results demonstrate that, at environmentally relevant concentrations, indoxacarb poses negative consequences for T. pisana, indicating its ecotoxicological impacts.

Dissipation and Residue Pattern of Dinotefuran, Fluazinam, Indoxacarb, and Thiacloprid in Fresh and Processed Persimmon Using LC-MS/MS

Pesticides which are diluted and sprayed according to the pre-harvest interval (PHI) are generally decomposed and lost through various factors and pathways, and the leftover pesticides are known as residual pesticides. This study aims to determine the dissipation of residual amounts of dinotefuran, fluazinam, indoxacarb, and thiacloprid in persimmon and the changes in the concentration of various processing products. Pesticide spraying is performed in accordance with the GAP (good agricultue practice) of Korea, and the processed products are manufactured using a conventional method after removing the skin of persimmons. The modified QuEchERS (Quick, Easy, Cheap, Effective, Rugged, and Safe) method and an optimized method using LC-MS/MS (liquid chromatography mass spectrometry) is implemented to analyze the residual pesticides. The linearity, recovery, and LOQ (limit of quantitation) are presented to verify the analysis method. The amount of residual pesticides tested decreases significantly in a time-dependent manner, regardless of the minimal dilution effect present due to growth. The residual concentration does not vary significantly during the processing stage despite the removal of the systemic pesticides, dinotefuran and thiacloprid. The residues of non-systemic pesticides, fluazinam and indoxacarb, are typically removed by the peeling removal and processing methods. The reduction factor of dinotefuran, whose residual concentration is increased, is less than 1, and the absolute amount of pesticides is decreased through processing. The results of this study can be used as the scientific basis data to ensure the safety of residual pesticides in processed products in the future.

Permethrin Residual Activity Against Ambrosia Beetle (Coleoptera: Curculionidae: Scolytinae) Attacks Following Field Aging and Simulated Rainfall Weathering

Adult ambrosia beetles (Coleoptera: Curculionidae: Scolytinae) bore into ornamental nursery trees resulting in trunk vascular tissue damage, which can potentially kill trees. Ambrosia beetle exposure to surface-applied insecticides is minimal after internal trunk galleries are formed, so effective management requires insecticide treatments to be applied near the time of infestation or to have residual activity on the bark. Tree trunk sections (bolts) were used to determine the effect of field aging or irrigation (i.e., simulated rainfall weathering) on permethrin residual activity against ambrosia beetles. In all experiments, 30-cm-long bolts from Liriodendron tulipifera L. (Magnoliales: Magnoliaceae) were hollowed and filled with 70% ethanol at field deployment to induce ambrosia beetle attacks over a 2-wk period. To evaluate insecticide residual activity, permethrin was sprayed onto tree bolts at 0, 8, 17, or 24 d before ethanol addition, and then bolts were deployed along a wooded border in fall 2017 and spring 2018. Tree bolts with permethrin residues ≤17 d old had significantly fewer ambrosia beetle attacks than bolts with 24-d-old residues or the non-permethrin-treated control bolts. To evaluate simulated rainfall weathering, permethrin was applied to tree bolts 8 or 22 d before ethanol (spring 2018) or 10 or 24 d before ethanol (fall 2018) with half of the bolts receiving regular irrigation events. Irrigation had no significant effect on permethrin residual activity against ambrosia beetles during either test. This study determined ambrosia beetle control was affected by permethrin residue age more than simulated rainfall weathering, and a reapplication interval of ≤17 d maximized beetle control.

Curative Activity of Insecticides Used to Control Spotted-Wing Drosophila (Diptera: Drosophilidae) in Tart Cherry Productions

Spotted-wing drosophila (Drosophila suzukii Matsumura) is a major pest of soft-skinned fruit and due to the low infestation tolerance for marketable fruit, growers take preventive actions to hinder spotted-wing drosophila damages. Insecticides application is one of the measures taken by growers. Although intensive spraying programs have been used to manage spotted-wing drosophila, its early infestation, rapid reproduction, and vast range of host have caused damage to still occur in fruit, including tart cherries, Prunus ceraus (Linnaeus). Therefore, there is a merit for information on insecticide's curative activity to understand whether sprays manage spotted-wing drosophila individuals within infested fruit. Tart cherry fruit were exposed to spotted-wing drosophila adults for 3 d. After this infestation period, insecticides were applied 1 and 3 d later. Small larvae, large larvae, and pupae were counted 9 d after initial infestation. A parallel set of insecticide-treated tart cherries were subjected to residue analysis. Phosmet and spinetoram were able to reduced live spotted-wing drosophila counts compared with the control at all life stages and insecticide application times, whereas zeta-cypermethrin, acetamiprid, and cyantraniliprole were less consistent in reducing spotted-wing drosophila numbers. Chromobacterium subtsugae demonstrated no curative action. Residue analysis demonstrated that zeta-cypermethrin residues mostly remained on fruit surface. Small portions of phosmet, spinetoram, and cyantraniliprole were able to penetrate fruit surfaces and move into subsurface tissues. Acetamiprid was the only compound which >47% penetrated into the fruit subsurface consistently across both years. Curative activity demonstrated in this study can provide additional tactics for spotted-wing drosophila management in tart cherry Integrated Pest Management (IPM) programs.

Insecticide residue longevity for on-site screening of Drosophila suzukii (Matsumura) resistance

BACKGROUND

Preventative application of insecticides reduces marketable yield losses caused by Drosophila suzukii females that selectively lay eggs into ripe and ripening fruits. However, repeated applications of insecticides increase the risk of resistance development. It is therefore critical to test field-collected flies on-site to assess the level of sensitivity of D. suzukii to insecticides to monitor resistance, before it becomes a widespread issue. This requires that insecticide-treated vials be readily available to conduct bioassays. Thus, bioassays were conducted using malathion-, methomyl-, zeta-cypermethrin-, phosmet-, spinetoram- and spinosad-treated scintillation vials at 1 to 28 days after treatment to assess how residue age affects insecticide toxicity in scintillation vials. The impact of temperature on residue longevity was also assessed.

RESULTS

Insecticide-treated vials stored for 28 days provided reliable estimates of susceptibility of D. suzukii to some of the tested insecticides. The toxicity of malathion remained consistently high throughout the experiment followed by methomyl. However, toxicities of zeta-cypermethrin, phosmet were variable whereas those of the spinosyns declined relatively quickly. Overall, storage temperature did not affect the residual toxicity of most of the tested insecticides except zeta-cypermethrin.

CONCLUSION

These findings suggest that the toxicity of insecticide residues in treated vials remains active for ≤28 d for malathion and ≤21 and 28 days in methomyl-treated vials stored at 4 °C in Georgia and Michigan, respectively. However, the toxicities of spinosad, zeta-cypermethrin and phosmet were less consistent. Hence, vials treated with these insecticides should be freshly made to be effective for screening D. suzukii field populations for resistance. © 2020 Society of Chemical Industry.

Rainfastness of Insecticides Used to Control Spotted-Wing Drosophila in Tart Cherry Production

Tart cherry production is challenged by precipitation events that may reduce crop protection against spotted-wing drosophila (Drosophila suzukii) (SWD). Due to SWD's devastating impacts on yield, growers are often faced with the option of insecticide reapplication. Semi-field bioassays were used to assess simulated rainfall effects towards adult mortality, immature survival, and residue wash-off from different plant tissues for several compounds. Tart cherry shoots were treated with 0, 12.7 or 25.4 mm of simulated rainfall and infested with SWD for 5 days. Adult mortality was recorded 1, 3, and 5 days after shoots were infested, while immature stage individuals were counted 9 days after the first infestation day. All insecticides demonstrated higher adult mortality and lower immature survival compared with the untreated control at 0 mm of rainfall. Adult mortality and immature survival caused by phosmet, zeta-cypermethrin, and spinetoram were adversely affected by simulated rainfall. In all bioassays, acetamiprid was the least affected by simulated rainfall. Residue analysis demonstrated phosmet and spinetoram residues to be the most sensitive to wash-off. This study demonstrates different rainfall effects on SWD control for several compounds. This information may provide a basis for making an informed decision on whether reapplication is required.

Dissipation of neonicotinoid insecticides imidacloprid, indoxacarb and thiamethoxam on pomegranate (Punica granatum L.)

Neonicotinoid insecticides such as imidacloprid, indoxacarb and thiamethoxam are widely used for control of a large number of insect pests of pomegranate crop. Their residue levels were evaluated on pomegranate fruits over 2 years during the same cropping season. The QuEChERS analytical method in conjunction with LC-MS/MS was validated to analyse the insecticides on pomegranate fruits with peel (whole fruit), without peel (aril) and in the field soil. The method performance was satisfactory with the limit of quantification (LOQ) of 0.005 mg/kg which was below the maximum residue limits (MRLs) in pomegranate for the 3 compounds. A first order reaction kinetics was observed for the three insecticides with the half -life of degradation of 8-11.1 days for imidacloprid; 7.4-8.4 days for indoxacarb and 9.8-14.2 days for thiamethoxam. Though the insecticides are systemic in nature, the residues in the edible pomegranate aril were always < LOQ. The maximum residue levels of imidacloprid on pomegranate was less than its MRL of 1 mg/kg, so the pre-harvest interval (PHI) required was 1 day only. For indoxacarb, 31-42 days PHI was needed for the residues to reduce to its MRL of 0.02 mg/kg. The PHI of thiamethoxam was 46-77 days, the time required for its residues to reduce to its MRL of 0.01 mg/kg. Higher rainfall possibly facilitated faster dissipation of imidacloprid residues from pomegranate whereas indoxacarb and thiamethoxam remained unaffected. The results of the study can be utilized to incorporate these three chemicals in the plant protection program of pomegranate and fixation of MRL in India.

Susceptibility of Euseius concordis (Mesostigmata: Phytoseiidae) to pesticides used in citrus production systems

Euseius concordis (Chant) is an important predatory mite found in citrus orchards. The toxicity of 19 pesticides used in citrus orchards on biological and population parameters of this mite was assessed. Our results indicated that formetanate hydrochloride, dimethoate and phosmet were highly harmful (100% mortality) to E. concordis. Carbosulfan, diflubenzuron, fenpropathrin, gamma-cyhalothrin, imidacloprid, lambda-cyhalothrin, lambda-cyhalothrin + thiamethoxam, mineral and vegetable oils, spinosad and thiamethoxam reduced the female's survival and/or fecundity, and were moderately harmful to E. concordis. Besides the acute toxicity, carbosulfan and formetanate hydrochloride were highly persistent [>30 days after spraying (DAS)]; dimethoate was moderately persistent (16-30 DAS); spinosad, gamma-cyhalothrin, lambda-cyhalothrin and lambda-cyhalothrin + thiamethoxam were slightly persistent (5-15 DAS); and the other pesticides were considered to be short-lived (<5 DAS). All compounds except lambda-cyhalothrin and thiamethoxam increased the pre-oviposition period in the female offspring. Carbosulfan, deltamethrin, diflubenzuron, etofenprox, fenpropathrin, gamma-cyhalothrin, mineral and vegetable oils, pyriproxyfen and tebufenozide reduced offspring fecundity, whereas thiamethoxam increased the fecundity. Mineral and vegetable oils reduced female longevity of the predator mite. Regarding population effects, imidacloprid, lambda-cyhalothrin, lambda-cyhalothrin + thiamethoxam and thiamethoxam led to an increase in net reproductive rate (R _o ), intrinsic rate of increase (r), and finite rate of increase (λ) of E. concordis. Diflubenzuron, etofenprox, and mineral and vegetable oils reduced R _o , r and λ. All pesticides except beta-cypermethrin, fenpropathrin and imidacloprid reduced the mean generation time (T) of the predator. Therefore, semi-field and field studies are needed to assess the compatibility of these compounds with E. concordis before adoption in IPM programs.

Susceptibility of Ceraeochrysa cubana larvae and adults to six insect growth-regulator insecticides

The impacts of six insect growth-regulators were assessed on the predator Ceraeochrysa cubana (Hagen) larvae and adults. Our results showed that diflubenzuron, lufenuron and pyriproxyfen caused 100% larva mortality, whereas buprofezin, methoxyfenozide and tebufenozide were similar to control treatment. In comparison to the control, buprofezin prolonged the duration of larval stage, while methoxyfenozide and tebufenozide reduced the predator larva development time. Buprofezin, methoxyfenozide and tebufenozide did not affect the C. cubana duration and survival of pupal stage, fecundity and fertility. However, methoxyfenozide and tebufenozide reduced predator female and male longevities. Based on a reduction coefficient, diflubenzuron, lufenuron and pyriproxyfen were highly harmful to first instar larvae, while buprofezin, methoxyfenozide and tebufenozide were considered slightly harmful to the predator. Estimating the life table parameters, our results showed that buprofezin, methoxyfenozide and tebufenozide reduced the C. cubana R_o, r and λ. In comparison to the control, buprofezin prolonged the T and methoxyfenozide and tebufenozide shortened the predator T. In adults, our results showed that the insecticides did not cause significant mortality, but diflubenzuron, lufenuron and pyriproxyfen reduced the C. cubana fecundity and longevity. Diflubenzuron and lufenuron also reduced the C. cubana fertility. Based on a reduction coefficient, diflubenzuron and lufenuron were highly harmful to C. cubana adults, while pyriproxyfen was slightly harmful and buprofezin, methoxyfenozide and tebufenozide were considered harmless to the predator. Therefore, insect growth-regulators affect the C. cubana biological or populational parameters, and they can harm the integrated pest management programs that aim the predator conservation and/or augmentation in agroecosystems.

Lethal and sublethal effects of pesticides on Chrysoperla carnea larvae (Neuroptera: Chrysopidae) and the influence of rainfastness in their degradation pattern over time

The predator Chrysoperla carnea is a model species for the study of non-target effects of pesticides under different scenarios: registration of plant protection products under the European Union and effects of the Bt toxin. Laboratory and persistence studies were carried out with six pesticides currently used in corn crops in Spain that were applied at their maximum field recommended concentrations. The assessed end-points were larval mortality, survivorship until adult stage, duration of the larval and pupal periods, fecundity, fertility and sex ratio of the emerged adults. Based on the total effect (lethal and sublethal) caused to L3 larvae in contact with fresh residues in the laboratory, pendimethalin was harmless (IOBC 1), lambda-cyhalothrin, abamectin, and hexythiazox were slightly harmful (IOBC 2), deltamethrin was moderately harmful (IOBC 3) and chlorpyrifos was harmful (IOBC 4). Afterwards, the residues of the two most toxic pesticides in the lab (deltamethrin and chlorpyrifos) were aged under greenhouse conditions (22 ± 2 °C, 40 ± 10 % R.H., 16.9 μmol m(-2) s(-1) UV radiation) in the presence and absence of artificial rainfall (10 l m(-2) h(-1), applied 24 h after pesticide application). Deltamethrin was classified as short lived (IOBC A) in both cases. However, degradation of chlorpyrifos residues was accelerated in the presence of rainfall, leading to the classification as slightly persistent (IOBC B), while in absence of rainfall it behaved as persistent (IOBC D). Every pesticide can be recommended for inclusion in corn IPM programs where the predator is present except chlorpyrifos that exhibited high direct toxicity in the lab and prolonged residual action even in the presence of rainfall.

Rainfastness of insecticides used to control Japanese beetle in blueberries

Field-based bioassays were used to determine the relative impact of rainfall on the relative toxicity of four insecticides, phosmet, carbaryl, zeta-cypermethrin, or imidacloprid, from different chemical classes on adult Japanese beetles, Popillia japonica Newman, in highbush blueberries, Vaccinium corymbosum L. Bioassays were set up 24 h after spraying occurred and Japanese beetle condition was scored as alive, knockdown or immobile 1, 24, and 48 h after bioassay setup. All insecticides were significantly more toxic than the untreated control and zeta-cypermethrin consistently had the greatest toxic effect against the Japanese beetles. All insecticides experienced a decrease in efficacy after simulated rainfall onto treated blueberry shoots, although the efficacy of zeta-cypermethrin was the least affected by rainfall. This study will help blueberry growers make informed decisions on when reapplications of insecticides are needed in the field with the aim of improving integrated pest management (IPM).