Enhancement of Biological Control with Insectary Plantings

Beneficial insectary planting is a form of conservation biological control that involves introducing flowering plants into agricultural and horticultural systems to increase nectar and pollen resources required by some natural enemies of insect pests (Landis et al. 2000). Many predatory and parasitic insects rely on pollen and nectar for their survival and reproductive success. Two examples of such insect groups are hoverflies (Diptera: Syrphidae) and several species of predatory and parasitic wasps (Hymenoptera). Agroecosystems with florally abundant non-crop habitat have been associated with significantly higher numbers of pollen and nectar feeding natural enemies in and around farm fields (Cowgill 1989, Cowgill et al. 1993) and orchards (Leius 1967). Many farmscapes however are florally impoverished and in such conditions the benefit of these insects may be of limited value. Some research has demonstrated the potential of planting flowers in and around farm fields to increase local numbers of pollen and nectar feeding natural enemies and lead to reduced pest populations (Kloen and Altieri 1990, White et al. 1995, Hickman and Wratten 1996). Research is still needed to identify which plants have the greatest potential as beneficial insectary plants. Pollen and nectar-feeding insects are not attracted to all flowers equally. Rather they exhibit selectivity for the flowers from which they feed (Cowgill et al. 1993, Lunau and Wacht 1994). An understanding of the seasonal phenology of the pest we wish to target is crucial and whether the critical period of control synchronizes with the blooming time of the insectary flower and the phenology of natural enemy species. Evidence in the literature suggests that provisions of floral resources will attract hoverfly adults resulting in increased oviposition rates within fields and therefore decreases in aphid population numbers. Examples of such an approach have been demonstrated in California by Kloen and Altieri (1990), in New Zealand by White et al. (1995), and in the United Kingdom by Hickman and Wratten (1996). Colley and Luna (2000) have reported the relative attractiveness of selected insectary flowers to hoverflies, showing preferential attraction of hoverfly adults to some flower species.