Neonicotinoids and non-target species: effects of tanned with clothianidin seeds on soil bioindicators

Neonicotinoids, a recently-introduced insecticide class that acts on nicotinic acetylcholine receptors, are often used in seed tanning. They not only successfully control soil insects, but also systemically protect plants from other pests. In the last few years, however, they have come to be considered among the agents responsible for mass bee death in the United States (CCD) and Europe. While neonicotinoid toxicity data concern mainly bees, they are limited on non-target species. In particular, there is little research on their effect on soil invertebrate species that play important roles in ecosystem homeostasis (organic matter degradation and humification processes). Neonicotinoids are systemic products that circulate within the plant, which makes it possible that edaphic species may have contact with these products via tanned seeds rather than through direct plant feeding. With a nod to European Directive 2009/128/EC, aimed at sustainable pesticide use, we analyzed the action of clothianidin, a neonicotinoid used primarily in corn seed tanning, on two edaphic non-target species, rough woodlouse Porcellio scaber and earthworm Eisenia fetida. Both species were evaluated for several lethal and sub-lethal effects: mortality, weight changes, and behavioural responses. The behavioural responses of P. scaber were explored according to the methods used on Santagostino (Longhi, 1995), while avoidance tests were used on E. fetida for the same purpose. Sexually mature individuals of both species were selected from breeding containers and set up in transparent polyethylene trays partially filled with two soil types, natural and standard (OECD artificial soil used in Earthworm, Acute Toxicity tests, 1984). In each soil tray was placed one of three types of corn seed: (i) seed α, tanned with Maxim-XL ® (fungicide), Mesurol ® (repellent for birds), Poncho ® (insecticide clothianidin-based); (ii) seed β, tanned with Maxim-XL ®; (iii) seed γ, without tanning. P. scaber showed a significant difference in mortality between the two soil types; OECD showed itself to be unsuitable for the terrestrial crustacean. In natural soil tests, seed α showed greater survival among the larger individuals and a lower percentage of neonicotinoidi relative to body mass. Seeds β and γ showed a similar limited mortality. For E. fetida, a significant difference was found in the mortality of thesis α seed compared to β and γ seeds in natural soil, but no significant differences were detected among the seed types in OECD soil, which were clearly more suitable for earthworms.