We sampled the predator communities of large (100+ acre) commercial potato fields in Washington State that were treated with “hard” (broad-spectrum) or “soft” (selective) pesticides, and also fields under organic pest management. Our goal was to determine the impact of these different pest management regimes on the community structure and density of generalist predators. In 2001 we collected natural enemies from 8 hard, 3 soft, and 3 organic fields; in 2002 we sampled 5 hard, 5 soft, and 5 organic fields. Foliage predators were collected using a D-vac suction sampler, while ground-dwelling predators were collected using pitfall traps. Soft and organic fields had a greater abundance of Geocoris spp., Nabis spp., and spiders in the foliage, and carabid and staphylinid beetles on the ground, than fields treated with hard chemicals. Geocoris spp., Nabis spp., and spiders composed approximately 75% of the foliage predators, while carabid and staphylinid beetles, and linyphiid spiders, composed the majority of ground predators. Densities of these predator taxa were statistically indistinguishable between soft and organic fields. Linyphiid spider densities were not significantly affected by treatment regime. Concurrently with predator sampling we also monitored the major economic pests – green peach aphids, Myzus persicae (Sulzer), and Colorado potato beetles, Leptinotarsa decemlineata (Say), – by visually searching plant foliage. Pest densities were higher in organic fields than in soft and hard fields. It appears that the soft pesticides we examined may allow the integration of chemical and biological control in potato fields, controlling pests while also conserving generalist predators.
Species 1: Heteroptera Nabidae Nabis (Damsel bug)
Species 2: Heteroptera Geocorinae Geocoris (Big-eyed bugs)
Species 3: Homoptera Aphididae Myzus persicae (Green peach aphid)
Keywords: conservation biological control, generalist predator
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