Evolution of pesticide resistance in seed beetles: transgenerational effects of sub-lethal pyrethroid concentration on morphology and development

Abstract

Insecticide resistance is an example of rapid evolution under strong selection pressure and, is therefore of great importance for human and environmental health and economy. Acanthoscelides obtectus is a globally distributed Coleoptera pest that attacks bean seeds and degrades their quality. One method of protecting against seed beetles is the application of a widely used group of pesticides- pyrethroids. Insecticides, as xenobiotics, can induce stress in pests, leading to destabilization of their development and changes in their morphology. Fluctuating asymmetry (FA), small random deviations between right and left sides of bilateral symmetrical traits, is considered as a result of developmental instability and is thus a measurable indicator of phenotypic response to stress during morphogenesis in insects. In this work, we exposed four populations of A. obtectus to sub-lethal doses (LD20) of pyrethroid insecticide for five generations in a laboratory evolution experiment. To estimate the level of stress, we monitored the effects of the pesticide on shape changes and the level of FA using a geometric morphometric approach. Our results showed that beetles treated with LD20 significantly changed their morphology in the thorax region, while the effect on the level of FA was minor. This work uses experimental evolution as a powerful tool to study pesticide resistance and paves the way for further studies on morphological adaptations, modularity and developmental stability under stress conditions.