Intercropping to Create Local Refugia for Natural Enemies of Arthropod Pests: Flowers and Birds in Organic Agroecosystems

Farmer surveys conducted during the first year of a multi-year research program investigating the diversity and utilization of North-central Florida farmlands by birds demonstrated a great interest by organic producers in the potential impact birds have on insect populations in their cropping systems (Jacobson at al. 2003). They expressed interest in management recommendations designed to enhance the presence and foraging activities of insectivorous birds on their farms. Therefore based upon this interest we developed the following objectives for this study:

1. Analysis of census data collected in 2000 & 2001 indicated that the occurrence, densities, and foraging activities of birds in cropped fields are significantly higher in those having the greatest diversity of vegetation (polycultures vs. monocultures). These within cropped field density differences occurred even though the densities of birds in the non-cropped landscape surrounding these fields did not differ significantly (Jones et al. ms). Additionally, the occurrence, densities, and especially foraging activity of birds in polycultures were highest in those having sunflowers (Helianthus annuus) and other decorative flowers intercropped between vegetable rows. Analysis of birds by feeding guilds indicated that insectivorous bird densities were significantly higher in these polyculture systems (Jones et al. unpublished data). In this study we tested the hypothesis that sunflower rows included in a polyculture system increases the occurrence, densities, and foraging activities of insectivorous birds in cropped fields. Additionally, we attempted to determine the density of sunflower rows per acre needed to maximize bird presence and foraging activities while having the least impact upon yield per acre of other marketable crop production.

2. Foraging patterns, behavioral patterns / activity budgets of insectivorous bird species utilizing cropped treatment and control plots was documented to determine their actual use of these cropped areas. We also documented which insects were preyed upon by birds within the experimental plots via visual observation. We verified that birds were consuming economically important pest insects by capturing a sample of birds directly after foraging within cropped areas and administering an emetic to these individuals. Insects found within regurgitate samples were identified to order and family and compared to our insect surveys.

3. As a secondary objective, Helianthus spp. are listed in many extension fact sheets (Univ. of Florida Extension Circular 563, Univ. of Rhode Island Landscape Horticulture Factsheet, Univ. of Maine Coop Extension Bulletin # 7150) and other such publications (Long 1993, Starcher 1995, Turton 1998) as an excellent plant to attract beneficial insects (those known to be pollinators, to prey upon or parasitize agricultural insect pests) such as lacewings and ladybird beetles. Therefore we also performed a limited survey of the insect fauna found in our test plots to establish a partial listing and the relative occurrences of such beneficial arthropods in the test systems.