Functional Responses and Switching of Tetragnatha laboriosa Hentz (Araneae: Tetragnathidae) and Clubiona pikei Gertsh (Araneae: Clubionidae) for the Aphids Rhopalosiphum maidis (Fitch) and Rhopalosiphum padi (L.) (Homoptera: Aphididae)

Abstract

Laboratory experiments were performed to determine the functional responses and switching behavior of the two dominant spider species of southern Quebec (Canada) corn crops, Tetragnatha laboriosa Hentz and Clubiona pikei Gertsh, and for the two dominant aphid species, Rhopalosiphum maidis (Fitch) and Rhopalosiphum padi (L.). Each spider species was tested with one, and then with the two aphid species at increasing prey density. Switching tests were done by offering the spiders two different ratios of aphid species (4:1 and 1:4). Both spider species showed sigmoid, complex, domed-shaped and, sometimes, linear functional responses in both the monospecific and bispecific tests. Complex functional responses were observed only with C. pikei . Hence, the capture rates were often density-dependent, although inverse density-dependent capture rates were obtained at high prey densities. Both spider species consumed disproportionally more R. maidis than R. padi , whatever the ratio. A greater exploration rate of the experimental spaces by R. maidis could explain the predators' preference. These results suggest that these spiders have some potential for being effective biological control agents.