Toxicity of thiamethoxam to Tetranychus urticae Koch and Phytoseiulus persimilis Athias-Henriot (Acari Tetranychidae, Phytoseiidae) through different routes of exposure

BACKGROUND: Knowledge of the impact of insecticides on Tetranychus urticae Koch and its predator Phytoseiulus persimilis Athias‐Henriot is crucial for IPM. This study evaluates the effect of thiamethoxam on T. urticae and its predator by considering different routes of exposure (topical, residual and contaminated food exposures) and their combinations. RESULTS: Thiamethoxam effects on T. urticae were higher when residual and contaminated food exposures were considered. The total effect was higher than 90% where contaminated food exposure was involved. On P. persimilis, the total effect was higher in residual and contaminated prey exposures compared with topical exposure, and all combinations of routes of exposure attained a total effect higher than 90%. CONCLUSION: Thiamethoxam was found to be toxic to T. urticae and P. persimilis; however, the impact of the insecticide depended on the routes of exposure and their combinations. Lethal and sublethal effects occurred in residual and contaminated food exposures, while only sublethal effects occurred in topical exposure of predators and prey. The toxicity of thiamethoxam on prey and predator increased with the number of exposure routes involved. By limiting exposure to thiamethoxam to ingestion of contaminated food only, the impact of the pesticide was more favourable to P. persimilis than to its prey. Copyright © 2010 Society of Chemical Industry     

The effect of the weaver ant,Oecophylla smaragdina (Hymenoptera: Formicidae), on the mango seed weevil,Sternochetus mangiferae (Coleoptera: Curculionidae), in mango orchards in the Northern Territory of Australia

Abstract

The mango seed weevil, Sternochetus mangiferae (Fabricius), is one of the major mango insect pests in northern Australia. A reasonable level of control can be obtained with insecticide sprays together with orchard sanitation, but the only option available for organic growers is the latter. Weaver ants, Oecophylla smaragdina (Fabricius), are effective in controlling the main insect pests in citrus, cashew and mango orchards. To determine whether weaver ants, which are usually abundant in non-sprayed mango orchards, have the potential to control the mango seed weevil, field experiments together with regular monitoring programmes at six orchards in the Northern Territory of Australia were conducted from 2001 to 2003. Data from two conventional orchards showed that the treatment with weaver ants plus soft chemicals produced lower levels of downgraded fruits (<0.5%) compared to the treatment with chemical insecticides (1.4 – 2.1%). In three organic or insecticide-free orchards, fruits were much less damaged on trees with weaver ants (<1%) than on trees without the ants (2.5 – 15.7%). In the sixth orchard, that had much higher mango seed weevil populations than the others, levels of downgraded fruits were lower on trees with abundant weaver ants than on trees with fewer weaver ants. We conclude that weaver ants are efficient biocontrol agents of the mango seed weevil, and that for successful control of the pest it is important both to maintain the ants at high levels and to destroy excess fruits.     

Effect of potential bioinoculants and organic manures on root‐rot and wilt,growth, yield and quality of organically grown Coleus forskohlii in a semiarid tropical region of Bangalore (India)

Based on earlier results obtained in pot experiments, 2‐year field experiments were conducted with five bioinoculants and neem cake under organic field conditions (with vermicompost as a nutritional supplement) to evaluate their potential to control root‐rot and wilt (a complex problem involving Fusarium chlamydosporum and Ralstonia solanacearum) of the medicinal plant Coleus forskohlii. Plants treated with arbuscular mycorrhizal fungus (Glomus fasciculatum), neem cake or Pseudomonas fluorescens showed significantly increased plant height (15–31%), plant spread (25–33%), number of branches (63–67%) and dry root (129–200%) yields, and reduced disease incidence (47–50%) compared to controls. Increases in yields were reflected by increases in N (51–81%), P (17–76%) and K (44–74%) uptake. The forskolin content of the roots was found not to be affected by any of the bioinoculants, but forskolin yield (calculated) was increased significantly by treatment with G. fasciculatum (227%), neem cake (222%) or P. fluorescens (159%).     

The efficacy of spinosad against the western flower thrips, Frankliniella occidentalis, and its impact on associated biological control agents on greenhouse cucumbers in southern Ontario

Insecticides are the most commonly used tactic to control western flower thrips (WFT), Frankliniella occidentalis Pergande (Thysanoptera: Thripidae), on greenhouse cucumber. However, WFT has developed resistance to several of the insecticides presently in use. In addition, some of these insecticides adversely affect greenhouse biological control agents used to control WFT, resulting in subsequent pest resurgence. Therefore, there is a need to identify novel insecticides with unique modes of action for use in integrated pest management (IPM) programs to effectively control WFT with minimal impact on associated biological control agents. In laboratory bioassays conducted in 2001, immature and adult WFT and three associated greenhouse biological control agents: Amblyseius cucumeris Oudemans (Acarina: Phytoseiidae), Orius insidiosus Say (Hemiptera: Anthocoridae) and Encarsia formosa Gahan (Hymenoptera: Aphelinidae) were exposed to direct, direct/residual, and residual contact applications of the novel biopesticide, spinosad (Conserve 120 SC), and the industry standard for whitefly control, endosulfan (Thiodan 50 WP). In all three types of assay, spinosad was effective against immature and adult WFT life stages. It showed low toxicity to A. cucumeris, moderate toxicity to O. insidiosus and high toxicity to E formosa. Greenhouse studies involving exposure of immature and adult WFT and adult biological control agents to cucumber leaves sprayed previously with spinosad supported the laboratory data. Spinosad showed low toxicity to A. cucumeris exposed to leaves 1 day after treatment (DAT), moderate toxicity to O. insidiosus 1 and 8 DAT, and high toxicity to E. formosa up to 28 DAT. These data, along with spinosad's unique mode of action, suggest it would be a valuable reduced-risk control agent for greenhouse cucumber IPM programs.     

The effects of repeated applications of the molluscicide metaldehyde and the biocontrol nematode Phasmarhabditis hermaphrodita on molluscs, earthworms, nematodes, acarids and collembolans: a two-year study in north-west Spain

Over two years, six consecutive field experiments were done in which the chemical molluscicide metaldehyde and the nematode biocontrol agent Phasmarhabditis hermaphrodita (Schneider) were applied at the standard field rates to replicated mini-plots successively planted with lettuce, Brussels sprouts, leaf beet and cabbage, to compare the effectiveness of different treatments in reducing slug damage to the crops. Soil samples from each plot were taken prior to the start of the experiments, and then monthly, to assess the populations of slugs, snails, earthworms, nematodes, acarids and collembolans. The experiments were done on the same site and each plot received the same treatment in the six experiments. The six treatments were: (1) untreated controls, (2) metaldehyde pellets, (3 and 4) nematodes applied to the planted area 3 days prior to planting without or with previous application of cow manure slurry, (5) nematodes applied to the area surrounding the planted area 3 days prior to planting, and (6) nematodes applied to the planted area once (only in the first of the six consecutive experiments). Only the metaldehyde treatment and the nematodes applied to the planted area at the beginning of each experiment without previous application of manure significantly reduced slug damage to the plants, and only metaldehyde reduced the number of slugs contaminating the harvested plants. The numbers of slugs, snails and earthworms in soil samples were compared among the six treatments tested: with respect to the untreated controls, the numbers of Deroceras reticulatum (Müller) were significantly affected only in the metaldehyde plots, and the numbers of Arion ater L only in the plots treated with nematodes applied to the planted area 3 days prior to planting without previous application of manure; numbers of snails (Ponentina ponentina (Morelet) and Oxychilus helveticus (Blum)) were not affected by the treatment. The total numbers of all earthworm species and of Lumbricus spp were unaffected by the treatment, but Dendrobaena spp increased significantly in the plots treated with manure. The numbers of nematodes, acarids and collembolans in soil samples were compared between the untreated controls and the treatments with nematodes applied 3 days prior to planting to the planted area or to the surrounding area, without previous application of manure: the treatment had a significant effect on the number of nematodes in soil samples, but acarids and collembolans were unaffected.