ARTHROPOD PREDATORS IN CABBAGE (CRUCIFERAE) AND THEIR POTENTIAL AS NATURALLY OCCURRING BIOLOGICAL CONTROL AGENTS FORPIERIS RAPAE(LEPIDOPTERA: PIERIDAE)

Abstract

AbstractWe used three sampling methods to identify the arthropod predators most abundant and active in fields of cabbage,Brassica oleraceaL. var.capitata, and determined those most likely to be important predators of the imported cabbageworm,Pieris rapaeL., by testing the predators’ abilities to forage on cabbage plants and to feed onPieris rapaein small arenas in the laboratory. Abundance and activity in the field were monitored with pitfall traps, sticky traps applied directly to leaves, and plant samples. Four criteria were used to assess the species’ potential value as a predator ofPieris rapaein cabbage: relatively high overall abundance in trap catches and plant samples, occurrence on plant foliage in the field, a high propensity to feed onPieris rapaeeggs and first instars, and the ability to search for larvalPieris rapaeon cabbage plants. Four species, the wolf spiderPardosa milvina(Hentz) (Araneae: Lycosidae), the harvestmanPhalangium opilioL. (Opiliones: Phalangiidae), and the lady beetlesColeomegilla maculata lengiTimberlake andHippodamia variegata(Goeze) (Coleoptera: Coccinellidae), demonstrated these attributes, although all four species appeared unable to search for prey on some parts of the cabbage plants, owing to unsure footing on the plants’ slippery cuticular wax. Linyphiids (Araneae) and syrphids (Diptera), the most abundant taxa in the plant samples, may prove better at thoroughly searching cabbage plants, but remain to be tested in future laboratory trials. Our results show that only a small portion of the predatory arthropod species that occur in cabbage fields is likely to prey onPieris rapaeon the plants, although important questions remain about the roles of some taxa. Future efforts to enhance biological control ofPieris rapaeby naturally occurring predators can now focus on further elucidating and finding ways to enhance the roles of those predators that are effective.