Behavioural response of terrestrial isopods (Crustacea: Isopoda) to pyrethrins in soil or food

Pyrethrins are natural insecticides that have been on the market for decades. In spite of that only limited data are available on the toxicity of pyrethrins to non-target animals. In our study we hypothesized that a pyrethrin-containing insecticide affects terrestrial isopods but they can decrease the toxic effects by avoidance behaviour. Animals were exposed to the insecticide in its manufactured form either via soil or food at doses normally used. The results revealed that 24 h exposure to 20 μl or more of freshly applied insecticide per gram dry soil, which corresponds to 5.2 μg of pyrethrins per cm2 of soil, causes paralysis or death of the test animals. The level of regeneration in the next 48 h was negligible. Upon four-week exposure to food containing the insecticide the quantity of consumed food and the faeces produced decreased. When animals were offered a choice between clean and contaminated soil or food they preferred uncontaminated soil or food. We conclude that isopods are sensitive to pyrethrins. By avoiding contaminated food or soil they can mitigate but probably not entirely prevent the toxic effects of pyrethrins. The behavioural response was found to be of comparable sensitivity with other parameters measured in long-term toxicity tests.

► Isopods are sensitive to pyrethrins and could be affected by their frequent use.
► Woodlice exhibit avoidance behaviour when exposed to pyrethrins in soil or food.
► By avoiding contaminated food or soil woodlice can mitigate the toxic effects.
► Avoidance behaviour test is of comparable sensitivity to long-term toxicity tests.