The diamondback moth, Plutella xylostella (L.), is the primary pest of brassicas in many areas of the world. Insecticide resistance in diamondback moth populations limits brassica production in these areas. Biological control offers an alternative to insecticides, but little is known of whether multiple natural enemies have additive, antagonistic, or synergistic effects on pest populations. I am testing if Podisus maculiventris (Say) (Heteroptera: Pentatomidae) and Cotesia plutellae Kurdj. (Hymenoptera: Ichneumonidae) have antagonistic, synergistic, or additive effects on diamondback moth populations in cabbage (Brassica oleracea var. capitata) by comparing diamondback moth populations and plant damage in replicated field cages containing 1) diamondback moth, 2) diamondback moth with P. maculiventris, 3) diamondback moth with C. plutellae, and 4) diamondback moth with P. maculiventris and C. plutellae. Podisus maculiventris is an effective predator of moth larvae, and C. plutellae is regarded as one of the most important parasitoids of the diamondback moth. Additive effects would be present if the observed diamondback moth abundance and plant damage in the combined natural enemy treatment are not significantly different than expected, based on the single natural enemy treatments. Synergistic effects would be present if the observed values in the combined natural enemy treatment are significantly less than expected. Antagonistic effects would be present if the values in the combined natural enemy treatment are significantly greater than expected. These results will provide information on alternative methods for suppression of diamondback moth populations, and will also provide empirical evidence towards understanding ecological interactions between multiple natural enemies.
Keywords: Biological Control, Population Dynamics
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