Leaf surfaces and the bioavailability of pesticide residues

Laboratory bioassays were carried out to determine the toxicity to Folsomia candida Willem (Collembola: Isotomidae) of residues of a pyrethroid insect icide, deltamethrin, and an organophosphorus insecticide, dimethoate, on di fferent leaf surfaces. The test leaves included a range of species and leav es of different ages. Dose-response relationships were estimated for F cand ida walking over the various treated leaf substrates, Probit analysis was u sed to estimate the means and standard deviations of the associated toleran ce distributions expressed as gAI ha(-1). Parallelism tests were undertaken to compare the susceptibilities of F candida to the two compounds applied to the different leaf surfaces. On deltamethrin-treated leaf surfaces, the LD50 values for F candida varied from 6.36 to 77.14 g AI ha(-1). F candida was least susceptible to deltamethrin residues when applied to leaves of dw arf bean (Phaseolus vulgarus L) and the highest susceptibility was observed following application to leaves of seedlings of barley (Hordeum vulgare L) , In contrast, the LD,, values observed for dimethoate treatments did not d iffer significantly between leaf types, ranging from 1.35 to 8.69 gAI ha(-1 ). The laboratory data on susceptibility of F candida on different leaf typ es for different pesticides can be used to investigate the role of leaf sur face properties in modifying the toxicity of applied pesticides to exposed invertebrates. (C) 2001 Society of Chemical Industry.