BIODIVERSITY AND CONSERVATION BIOLOGICAL CONTROL: DO BUFFER STRIPS WITH WILDFLOWERS ENHANCE NATURAL ENEMIES IN NEIGHBORING CROP HABITATS?

Abstract

Grass buffer strips are commonly deployed along crop borders in North American agricultural landscapes. Such borders filter nutrient and pesticide runoff to neighboring habitats and foster biodiversity. The addition of wildflowers in these strips to provide nectar and pollen resources can positively impact natural enemies of crop pests, particularly hymenopteran parasitoids. I investigated the presence/absence of wildflowers on natural enemy abundance in buffer strips and in neighboring soybean fields in 2005 and 2006. I predicted that wildflowers would attract and act as a source of natural enemies which would then disperse into neighboring crop fields.

In both years, sticky cards were used to measure the abundance of aerial arthropods in pure stands of wildflowers and in neighboring soybean plots. Pitfall traps were also used in 2006 to measure abundance of epigeal taxa. In the 2005 experiment, sticky card captures of hymenopteran and dipteran parasitoids were 72.7% higher in buffers containing partridge pea compared to the other buffer types. Similarly, communities of all beneficial arthropods captured by sticky card and pitfall traps in 2006 were significantly 79.8% to 72.3 % higher, respectively, in the partridge pea buffers compared to communities in the soybean crop. However, buffer effects on populations of parasitoids and predators in the neighboring crop were mixed in both experiments depending on the particular functional group and specific family of arthropods. Results suggest that partridge pea was a source for canopy-dwelling dipteran parasitoids and saprovores, but acted as a sink for canopy-dwelling mymarids, canopy-dwelling predators and ground-dwelling ants, and had a neutral effect on all others. However, these effects did not extend far into the soybean crop and were generally not discernible beyond 6m.

This study provides evidence that a pure stand of an attractive source of floral resources in a bordering non-crop area may not be desirable for enhancing conservation biological control. The species of flower and desired natural enemy should be taken into consideration before determining the mix of plant species to include in a buffer strip.