A field experiment was conducted to examine the impact of bird and spider predation on lepidopteran caterpillar densities and broccoli productivity. Densities of Pieris rapae and Trichoplusia ni large caterpillars and their post-caterpillar stages were reduced significantly by bird predation. The abundance of large caterpillars was also reduced on plants where spiders were allowed to forage freely. Further, plants foraged by birds, spiders, or birds plus spiders sustained less feeding damage attributable to leaf-chewing caterpillars than plants without birds or spiders (the check). Plants foraged by bird and/or spiders were also larger than check plants.
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