Both insectivorous birds and spiders have been observed preying on caterpillar pests inhabiting Brassica plants in Hawaii, but no studies have tested their predatory impact on caterpillar pest densities. A field experiment was conducted at the Poamoho Experiment Station on the island of Oahu, Hawaii, to determine the impact of birds and spiders on caterpillar pest densities, marketable crop yield, and growth performance of broccoli. Plants were randomly assigned to one of four treatments: 1) predator exclusion (prevented birds access and reduced spiders), 2) spider access (excluded birds), 3) bird access (spider reduction), and 4) check (plants accessible to birds and spiders). Two cage types were used to prevent bird access and reduce spider densities on selected broccoli plants. Plants accessible by birds supported fewer mid and late Lepidoptera instars and incurred less leaf damage than other treatments. Despite lower numbers of these caterpillar stages on bird accessible plants, there were no differences in the number of heads infested by larvae. This suggests that forming heads provide an enemy free space from bird predation. The experiment also showed that birds may interfere with mortality imposed by other natural enemies (i.e., pathogens, parasitoids) of caterpillar pests.
Species 1: Lepidoptera Pieridae Artogeia rapae (imported cabbageworm)
Species 2: Lepidoptera Noctuidae Trichoplusia ni (cabbage looper)
Keywords: generalist predator, Araneae
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