Lethal and sublethal effects of five common herbicides on the wolf spider, Pardosa milvina (Araneae: Lycosidae)

We tested lethal and sublethal effects of five commonly applied herbicides on the agrobiont wolf spider Pardosa milvina. Pardosa were collected from two agricultural fields; one kept under continuous crop rotation and sprayed for over twenty years, the other had no pesticide application for the last twelve years. Male and female Pardosa from each site were exposed to one of seven herbicide treatments (atrazine, glyphosate, mesotrione, S-metolachlor, rimsulfuron, a combination of all five herbicides, or a distilled water control; N = 1201) and maintained for 52 days on the treated soil substrate. We recorded mortality, prey capture behavior, weight change, courtship behavior, and egg sac production across treatments. Mesotrione and the five-herbicide combination showed significantly higher mortality than control substrates while atrazine, glyphosate and S-metolachlor showed significantly higher survival than the control. Both male spiders and spiders collected from the conventional field had reduced survival under some herbicide treatments. Prey capture behavior varied significantly by herbicide treatment, sex, and site. We observed significant weight change differences in males and differences in egg sac production in females, with, compared to the control, significant male weight loss in the rimsulfuron treatment collected from the no herbicide field, and a decrease in egg sac production in rimsulfuron and S-metolachlor treatments among females collected from the no herbicide field. Our results show some herbicides may have modest but significant fitness benefits (atrazine, glyphosate, and S-metolachlor) while others strongly increase the mortality of a generalist predator (mesotrione and the combination herbicide treatment).