Pesticide uptake and locomotor behaviour in the woodlouse: an experimental study employing video tracking and ¹⁴C-labelling

The toxicity of soil pesticide residues to target and non-target organisms depends on the amount of chemical absorbed by the organism. One of the principle factors governing chemical uptake is the amount of chemical encountered by the animal and, hence, the area of soil contacted. This in turn, depends on the locomotor behaviour of the animal. In the present study, the relationship between the uptake of soil residues of an organophosphate insecticide and locomotor behaviour was examined, employing ¹⁴C-labelled dimethoate and computer-aided video tracking. Groups of male woodlice, Porcellio scaber (Isopoda), walked freely for 22 h on a soil substrate treated with three application rates of the pesticide. A strong correlation was found between pesticide uptake and path length, mean velocity and time spent in locomotor acivity, which is consistent with previously reported modelling studies. Our data suggest a linear relationship for all locomotor parameters except for path length at the highest application rate, where uptake was best described by an inverse exponential relationship. All doses induced hyperactivity in terms of time spent in locomotor activity. However, when compared with a untreated control group, the most pronounced effects were displayed at the lowest dose where path length, mean velocity and turning rate were also significantly different. The number of shifts between locomotor active and inactive periods in the experimental period increased with increasing application rate.