Distinct changes in the life-history strategies of Folsomia candida Willem (Collembola: Isotomidae) due to multi- and transgenerational treatments with an insecticide

Abstract Chronic exposure of soil animals with insecticides over multiple generations can induce modifications to their life-history. Moreover, insecticide effects over generations may be substantially different if subsequent generations get direct exposure repeatedly (multigenerational effect), or direct exposure affects only the parent generation, but the subsequent ones not (transgenerational effect). These are essential but understudied aspects of the environmental risk assessment. The present study assessed the multi- and transgenerational effects of the insecticide Trebon® 30 EC (active ingredient etofenprox) on 15 life-history traits (initial length, final length, absolute growth, total number of eggs, number of clutches, time of maturation, ratio of egg diameters, egg volume, unhatched ratio, reproduction investment, mortality, food consumption, velocity, movement energy, growth-reproduction trade-off) of the collembolan Folsomia candida Willem, 1902 in a four-generation long laboratory study. In the multigenerational treatment, all four generations were treated by the insecticide, while in the transgenerational one, only the parent generation was treated, but the consecutive three generations were not. When a generation was treated with the insecticide, six sublethal concentrations of the Trebon® 30 EC (0, 0.766, 1.303, 2.215, 3.765, and 6.4 ml insecticide L−1 water) were applied to see dose-response effects. In the multigenerational treatment, dose-dependent effects of the insecticide were pronounced from the parent to the F2 generation, with high mortality, especially in the highest concentration. Conversely, in the transgenerational treatment the most effects on life-history traits were found in the F3 generation. The results show that in the multigenerational treatment, either the population becomes resistant, or it could compensate for the effects of the insecticide in the long term. In the F1 generation, the number of eggs and clutches decreased, the mortality increased, and the growth-reproduction trade-off shifted in the direction of growth. Rather similar results were found in the F2 generation, with the difference that all animals died in that case if the insecticide was applied for consecutive generations repeatedly, and five to eight times higher than the recommended field concentration (0.766–1.303 ml L−1). Furthermore, our experiment detected evidence of an apparent transgenerational effect. While in the F1 and F2 generation of the transgenerational treatment, few effects were found, in the F3 generation, 10 out of the 15 traits showed a dose-response relationship. This finding indicates the long-term transgenerational effects of the Trebon® 30 EC insecticide on several F. candida life-history traits. We concluded that the influence of both treatment methods on life-history traits is strong but appreciably distinct. Our results support the view that transgenerational epigenetic heritability should be taken into account in environmental risk assessment.