Working towards a sustainable agriculture: Landscape diversity, beneficial insects and pest suppression
A comparison of ground beetle (Coleoptera: Carabidae) populations in potato fields and adjacent natural areas determined that a greater diversity of carabid species exist in natural areas than within crops. Predation on Colorado potato beetle eggs was also greater in natural areas than within crops. At broader scales, the composition of the landscape within 1.5 km of crops influenced within-crop carabid community composition. Furthermore, predation on Colorado potato beetle eggs and green peach aphid increased as the amount of natural area surrounding fields increased. These results suggest that restoration of natural areas within farmscapes may benefit biological control.
Objective 1: To determine if and at what scale the amount/diversity of natural habitat surrounding Wisconsin potato fields influences arthropod natural enemy diversity and abundance within fields. We hypothesize that arthropod natural enemy diversity and abundance will be greatest in fields surrounded by large amounts of diverse natural habitat.
Objective 2: To determine if and at what scale the amount/diversity of natural habitat surrounding Wisconsin potato fields influences suppression of pests by natural enemies within fields. We hypothesize that a greater abundance and diversity of natural enemies in fields surrounded by extensive natural habitat will result in increased pest suppression within these fields.
Objective 1: Currently, we have completed analysis of a season-long study (conducted end of summer 2004 through summer 2005) of ground beetle (Coleoptera: Carabidae) community composition in potato fields and adjacent grassy habitats set in landscapes with varying amounts and diversities of natural habitat. We collected and identified over 80 species of carabids, many of which are important predators, within potatoes and adjacent grassy habitats (the most common natural area found bordering potato fields). To complete our analysis, we are currently compiling and analyzing GIS data to accurately quantify the amount and diversity of natural habitat present within different distances of the sampled potato fields. Preliminary analyses suggest that increasing the amount of non-crop areas within the broader landscape does not have a significant effect on beetle diversity or abundance. Rather, there are large differences in the species richness and community composition between potato and adjacent grassy habitats.
We are also continuing to count and identify natural enemies collected in sweep net samples from these same fields. This latter data will allow us to examine if natural areas are important sources of ladybird beetles (Coleoptera: Coccinellidae), lacewings (Neuroptera: Chrysopidae), damselbugs (Hemiptera: Nabidae) and anthocorids (Hemiptera: Anthocoridae); all of these are important natural enemies of the two main pests of Wisconsin potatoes, Colorado potato beetle Leptinotarsa decemlineata and green peach aphid Myzus persicae.
Objective 2: Currently, we have completed analysis of early-season predation on Colorado potato beetle eggs and late season predation on green peach aphid (June and August 2005). To complete our analysis, we are currently compiling and analyzing GIS data to accurately quantify the amount and diversity of natural habitat present within different distances of the sampled fields. Preliminary results suggest that surrounding landscape does influence predation rates. Potato fields with a high proportion of non-agricultural lands in the vicinity have higher rates of predation pf key potato pests than areas that are mostly within an agricultural matrix. These studies will be repeated in summer 2006 to confirm the results of this past summer’s study.
Impacts and Contributions/Outcomes
Research has been presented at numerous meetings of the Wisconsin Potato Vegetable Growers Association and subgroups (2004-2; 2005-2), raising grower awareness of the beneficial role natural areas can play in improving biological control of pests. This research occurred on cooperator’s farms and provided a hand-on demonstration to growers of how principles of landscape ecology are applied to agricultural problems.
This research has helped lay the foundation for future research that will provide knowledge needed to “ecologically engineer” Wisconsin farmcapes for environmental goods such as natural pest control and conservation of biodiversity. Our findings suggest that both within-farm and broader landscape variation influences native biodiversity and the ecosystem services provided by natural enemies. Yet, our research only demonstrates a potential for enhancing pest control through incorporating natural areas into farmscapes; further research must refine our knowledge of the costs and benefits of this approach so growers can make informed decisions. Ongoing work will be needed to determine if these ecological concepts can be applied to working farms as a way to reduce reliance on insecticides in pest management.