Pesticide exposure patterns and avoidance behaviour in non-target arthropods

For a pesticide to be registered for use, the risk to non-target arthropods must first be assessed. Standardised laboratory tests are conducted to evaluate lethal and sublethal effects on these species, with sublethal assessments focusing on reproductive effects. One other sublethal effect reported in the scientific literature is behavioural changes – such as hyperactivity or arrested movement – in non-target arthropods exposed to pesticide residues. Avoidance behaviour is also of interest in this context, where individuals display signs of irritation or repellence, thus showing a preference for untreated surfaces. Behavioural changes can be a precursor to more deleterious effects of pesticides, while avoidance behaviour is seen as both positive and negative, depending on the context. Regulatory studies expose individuals to homogeneous residues, even though pesticide spray within crop systems is often heterogeneous. Regulatory studies thus consider the worst case scenario yet this leaves no consideration of effects arising from realistic exposure in the environment, in particular effects of avoidance behaviour. Additionally, little is known of pesticide exposure patterns at spatial scales relevant to non-target arthropods. This thesis documents studies of movement behaviour and avoidance behaviour in a predatory mite (Typhlodromus pyri) when exposed to three insecticides. Irritation, reduced activity and avoidance behaviour were observed in mites exposed to residues in arenas with residues covering half and the whole surface. The thesis also documents the quantification of pesticide residues and spray patterns at small spatial scales, and these results were combined with movement data to investigate how populations are impacted by heterogeneous residues and pesticide avoidance behaviour through individual-based modelling. The simple model showed that both heterogeneous pesticide residues and avoidance behaviour lead to increased longevity and reproduction in individuals. Additionally, novel methods for quantifying spray residues, spray patterns, and behavioural bioassays are presented.