The effects of insecticide dose and herbivore density on tri-trophic effects of thiamethoxam in a system involving wheat, aphids, and ladybeetles

Abstract

a b s t r a c tWe assess how herbivore density and insecticide dose affects the tri-trophic interactions among thiamethoxam-treated wheat (Triticum sp.), Rhophalosiphum padi and the predatory Coleomegilla maculata DeGeer. In the first experiment 2nd and 4th instar C. maculata were fed aphids reared for 24 h on wheat plants treated with sub-lethal thiamethoxam soil drenches to assess the effect of insecticidal dose on the predator. In the second experiment a constant, sub-lethal thiamethoxam soil drench was used on wheat plants, but the plants were infested with different densities of aphids. Aphids from each density treatment were then fed to C. maculata 2nd instars. Insecticide levels within wheat and aphid tissues were quantified using a competitive ELISA. In experiment one, 4th instars of C. maculata displayed no negative effects after consuming aphids from treated plants. However, 2nd instars of C. maculata ate more treated aphids than untreated aphids and larval development times varied between the untreated larvae and those receiving the low dose of the insecticide. In experiment two, the 2nd instar C. maculata displayed slower walking speeds after consuming aphids from low aphid density plants. Thiamethoxam within wheat tissue was found at higher levels with increasing dose. This insecticide was also found at higher levels in wheat plants with the lowest aphid density. Clothianidin, a toxic metabolite of thiamethoxam, was found in aphids that had fed on thiamethoxam-treated wheat, but no differences between treatments were observed. The neonicotinoid treatment altered the quality of R. padi as prey for 2nd instar C. maculata, but this depended on the aphid infestation level on the plants. In addition to revealing a potential deleterious effect of thiamethoxam systemic insecticides in wheat, our assays provide insight into the design and interpretation of toxicity assays involving systemic neonicotinoids and herbivores.Published by Elsevier Ltd.

Nanostructural and mechanical property changes to spider silk as a consequence of insecticide exposure

“…The control spiders received 1.0 ml of the acetone daily. We considered the insecticide concentration used to be sublethal to the spiders on the basis that it is sub-lethal to its target insects (Bredeson et al, 2015) and P. audax is many orders of magnitude larger. Moreover, we did not find the exposed spiders to experience any more mortality, tremors, paralysis or uncoordinated movements than the control spiders (see below for details of the procedures).…”

Impact of fungicide and insecticide use on non-target aquatic organisms in rice paddy fields

“…The authors emphasized that aquatic animals, including mollusks, are in direct contact with the contaminants present in the aquatic environment, and they can thus be a suitable model for future studies on the neuronal and behavioral consequences of neonicotinoid poisoning. In a recent study, BREDESON et al (2015) found clothianidin, a toxic metabolite of thiamethoxam, in aphids that were fed with wheat plants treated with thiamethoxam. This suggested that studies on the effects in herbivores of thiamethoxam residues and its metabolites are important.…”

Invertebrate communities in spring wheat and the identification of cereal aphid predators through molecular gut content analysis

“…Populations of polyphagous predators vary by year (Chambers et al, 1983), tillage treatments (Rice and Wilde, 1991), and seed treatment prevalence (Seagraves and Lundgren, 2012). Additionally, the ability of species to control aphid populations may be negatively impacted by seed treatments (Bredeson et al, 2015). Direct observations, ELISA (enzyme-linked immunosorbent assay), gut dissections and PCR-based gut-content analysis have been employed to understand cereal aphid consumption by generalist predators.…”