Evaluation of supplemental flowering plant strips for sustainable enhancement of beneficial insects

View the project final report

• 2008 annual report

Commodities

• Fruits: berries (blueberries)

Practices

• Natural Resources/Environment: biodiversity, habitat enhancement
• Production Systems: permaculture

We compared blueberry fields with native perennial flower plantings on their perimeters to fields without flower perimeters in order to determine the impact of this conservation strategy on beneficial insects in crop fields. We found significantly more pollinators and natural enemies of crop pests in the fields adjacent to wildflower plantings. Natural enemies (mostly parasitoid wasps) were especially impacted by the presence of flowers, and were found in greater abundance in fields with flower plantings even 40 meters inside fields. Also, a late-season recovery of natural enemies following pre-harvest insecticide applications was seen only in fields adjacent to wildflower plantings.

Introduction:

Stands of flowering plants can provide many resources for beneficial insects, including nectar, pollen, alternate prey, and a complex architecture that provides shelter from the elements. However, many agricultural landscapes in the North Central Region lack the flowers that would have historically provided these resources, and this has compromised the ability of farmers to rely on natural enemies for pest control or on native pollinators for crop pollination. In this two-year project we tested the hypothesis that supplemental native flower strips sown in the border of blueberry fields would provide a benefit to growers by increasing local populations of beneficial insects.

There has been a growing interest in recent years about the economic and ecological benefits of re-incorporating natural habitats into agricultural systems (Bianchi et al. 2006, Kleijn and Sutherland 2003, Landis et al. 2000), in part because of the documented declines in populations of beneficial insects (e.g. Biesmeijer et al. 2006). The suspected reasons for these declines include pesticide use, loss of habitat, and a paucity of flowering plants within agricultural landscapes (Carvell et al. 2006, Landis et al. 2000).

Natural habitat outside the cropped area has consistently been shown to support beneficial insects (Bianchi et al. 2006, Kremen et al. 2002, Kremen et al. 2004, Steffan-Dewenter 2003), but this is something that most growers cannot manipulate easily. Lands adjacent to fields are often not owned by the grower, may be managed for wood production rather than to support natural enemies, and may be urbanized. Also, farms are increasingly situated adjacent to human development, and setting aside land for supporting beneficial insects is not always economically feasible. For these farms, providing resources directly into the field border is more likely to be adopted as a strategy to create habitat for beneficial insects.

Crop fields in the North Central Region used for fruit and vegetable production have strips of land around them that are typically mown. These headlands are potential areas for integration of flowering plants once the benefit of these practices is demonstrated to growers.

Manipulation of the environment around cropped areas by establishing flowering plants can increase natural enemy populations (Long et al. 1998, Rebek et al. 2005) and provide forage for wild bees that can increase their abundance (Buchi 2002, Kells et al. 2001). Provision of nectar and pollen by these plants can lead to greater parasitoid survival and fecundity (Jervis et al. 1993, Wackers 2004). This approach has also been demonstrated to reduce pest populations in Brassica (White et al. 1995) and cereal fields (Hickman and Wratten 1996), although adjacent flowering plants had no consistent effect in broccoli (Zhao et al. 1992).

Cover crops can be a useful tactic to support natural enemies in crop fields (Nicholls et al. 2000, Kinkorová and Kocourek 2000, Bugg and Waddington 1994). Unfortunately placement of the resource plants inside conventional crop fields inevitably creates potential for disturbance or death of beneficial insects when the crop is cultivated or treated with insecticide(Lee et al. 2001). Placement of these resources outside the crop area provides a more benign environment for beneficial insects where they can feed on nectar and pollen, utilize alternate hosts, and find refuge in an area not impacted by harmful disturbances (Sotherton 1984, Thomas et al. 1991).

This project is of particular relevance to specialty crop farmers that are under pressure to reduce pesticide inputs while also producing the highest quality food. These crops are becoming more important in our region as commercial farms diversify, small farms are established to supply fresh food to local markets, and the public increasingly values fresh produce grown near to the point of sale. We tested whether sown native flower strips can support beneficial insects and thereby provide greater pest control and pollination in specialty crop landscapes, with the aim of building a foundation for more effective conservation of natural enemies and pollinators in the region.

1. 1. Determine the impact of a flowering perennial strip on the abundance of natural enemies and pests in the adjacent blueberry field.

   2. Determine the effect of a perennial strip on abundance and diversity of native bees in the adjacent blueberry field.

   3. Determine the effect of native bees on blueberry pollination.

   4. Determine effect of the flower strips on the nesting activity of native cavity-nesting bees.