Effects of intraguild predation and cannibalism in two generalist phytoseiid species on prey density of the pink citrus rust mite in the presence of high-quality food

Intraguild predation (IGP) and cannibalism influence the effectiveness of biological control with generalist predators. In Japanese citrus orchards, two generalist phytoseiid species, Euseius sojaensis (Ehara) and Amblyseius eharai Amitai et Swirski, occur simultaneously, but only the former can control Aculops pelekassi (Keifer). First, we investigated the intensity of IGP and cannibalism in E. sojaensis and A. eharai in the presence and absence of pine pollen, which is a high-quality alternative food for these predatory mites. Amblyseius eharai was a stronger intraguild predator and cannibalistic predator than E. sojaensis with or without pollen. In the presence of pollen, although IGP and cannibalism were relaxed in both species, they were not dramatically reduced in A. eharai. Next, we investigated the effects of IGP and cannibalism on A. pelekassi control by changing the release ratio of E. sojaensis and A. eharai in the presence of pollen. With release of E. sojaensis alone, the E. sojaensis population increased and thus A. pelekassi was controlled. With release of A. eharai alone, however, the A. eharai population did not increase and thus A. pelekassi was not controlled. Simultaneous release of E. sojaensis and A. eharai reduced the rate of E. sojaensis population increase. Moreover, A. pelekassi densities were higher with a higher release ratio of A. eharai. These results suggest that A. eharai diminishes the biological control efficiency of the phytoseiid complex owing to IGP and cannibalism, even in the presence of high-quality food, and thus could indirectly increase pest populations.