Field evidence of an airborne enemy-avoidance kairomone in wolf spiders

Hogna helluo, Pardosa milvina, and Trochosa ruricola are co-occurring species of wolf spiders within agricultural fields in the eastern USA. The largest species, H. helluo, is a common predator of the two smaller species, P. milvina and T. ruricola. H. helluo frequently resides within soil fissures where P. milvina and T. ruricola may be attacked when they enter or walk near these fissures. We tested the ability of P. milvina and T. ruricola to avoid H. helluo-containing burrows by detecting airborne enemy-avoidance kairomones associated with H. helluo. To simulate soil fissures and control for visual and vibratory means of predator detection, we baited funneled pitfall traps with one of the following (N = 20 traps/treatment): (1) blank (empty trap); (2) one house cricket (Acheta domesticus); (3) one adult female H. helluo; and (4) one adult male H. helluo. Over two separate 3-d periods, we measured pitfall capture rates of P. milvina and T. ruricola as well as other incidentally captured ground-dwelling arthropods. During the day, male P. milvina showed significant avoidance of pitfall traps baited with H. helluo of either sex but showed no avoidance of empty traps or those containing crickets. At night, male T. ruricola showed a qualitatively similar pattern of avoiding H. helluo-baited traps, but the differences were not statistically significant. We found no evidence that other ground-dwelling arthropods either avoided or were attracted to H. helluo-baited traps. This study suggests that an airborne enemy-avoidance kairomone may mediate behavior among male P. milvina in the field.