Sustainable Landscapes: Investigating the Landscape Scale Effects of Riparian Habitat on Natural Pest Control

• 2007 annual report

This project comprises a large-scale investigation of the distribution and density patterns of agricultural pests and pest enemies in walnut orchards in relation to the distance to and area of riparian forest and restored riparian forest. The project includes an assessment of spatial distribution and density of insectivorous birds, agricultural pest birds, and two lepidopteran walnut pest species. The project also includes an analysis of foraging behavior of insectivorous birds on walnut orchards in relation to the proximity to and area of restored and remnant riparian forest. The density and successful foraging of insectivorous birds increases significantly with the area of restored and remnant riparian forest surrounding the walnut orchard. The density of agricultural pest bird species decreases with increasing area of riparian habitat. Abundance of two major walnut pests, codling moth and navel orange worm, have no significant relationship to area of riparian habitat, although abundance of navel orange worm trended toward lower abundance with increased area of riparian habitat.

Introduction

Research on sustainable agriculture has emphasized the biogeographic region as the most appropriate unit for pest-management research (Altieri 1994). However, there is little understanding of the effects of natural areas and landscape diversity on pests and pest predators. Some studies suggest that proximity to natural habitat could increase the numbers of generalist natural enemies of pest species through increased access to food and nesting resources, refugia, and winter habitat (Altieri 1994, Marino and Landis 1996). Movements of species between natural and agricultural areas could have cascading effects on all levels of the food webs in both habitats (Polis et al. 1997). These effects could include changes in the populations of natural enemies or pests of agriculture that could then have cascading effects on other trophic levels and thus on crop success. In order to support a diverse landscape and economic viability of producers, it is essential to understand how areas surrounding the farm affect the dynamics of natural biological control. Integrated pest management usually focuses on natural enemies found on the farm. However, it is increasingly clear that assemblages or guilds of highly mobile predators found in adjacent habitat, such as generalist insectivorous birds, can also effectively suppress populations of pest species in agricultural settings (Symondon et al. 2002). For example, birds are mobile links between natural habitat and agricultural areas (Lundberg and Moberg 2003). Due to their mobility, they can move to high-density food patches, and are capable of complex prey-switching and specialization behaviors (McFarlane 1976, Kirk et al. 1996). Research has demonstrated that birds can suppress insect populations (Holmes et al. 1979), have top-down effects on pests in agricultural systems, and consequently increase plant growth (Marquis and Whelan 1994, Hooks et al. 2003). Research has also demonstrated that birds can suppress insect pests that are not affected by other natural enemies, such as parasitoids (Jones et al. 2005). A better understanding of the dynamics of generalist bird natural enemies will help producers understand some of the services from natural areas in order to make informed habitat management decisions on a landscape scale LITERATURE CITED Altieri, M.A. 1994. Biodiversity and Pest Management in Agroecosystems. Food Products Press, New York. Holmes, R.T., J.C. Schultz, P. Nothnagle. 1979. Bird predation on forest insects: an exclosure experiment. Science 206:462-463. Hooks, C.R., R.R. Pandey, and M. W. Johnson. 2003. Impact of avian and arthropod predation on lepidopteran caterpillar densities and plant productivity in an ephemeral agroecosystem. Ecological Entomology 28:522-532. Jones, G. A., K. E. Sieving, M. L. Avery, R. L. Meagher. 2005. Parasitized and non-parasitized prey selectivity by an insectivorous bird. Crop Protection 24: 185-189. Kirk, D.A., M.D. Evenden, et al. 1996. Past and current attempts to evaluate the role of birds as predators of insect pests in temperate agriculture. Current Ornithology 13:175-269. Lundberg, J. and F. Moberg. 2003. Mobile link organisms and ecosystem functioning: implications for ecosystem resilience and management. Ecosystems 6:87-98. Marino, P.C., and D.A. Landis. 1996. Effect of landscape structure on parasitoid diversity and parasitism in agroecosystems. Ecological Applications 6:276-284. Marquis, R.J. and Whelan, C.J. 1994. Insectivorous birds increase growth of white oaks through consumption of leaf-chewing insects. Ecology 75:2007-2014. McFarlane,R.W. 1976. Birds as agents of biological control. Biologist 58,123 –140. Polis, GA, WB Anderson, RD Holt. 1997. Toward an integration of landscape and food web ecology: The dynamics of spatially subsidized food webs. Ann Review of Ecology and Systematics 28: 289-316. Symondson, W.O.C., K.D. Sunderland, and M.H. Greenstone. 2002. Can generalist predators be effective biocontrol agents? Annual Review of Entomology 47:561-594.

My objectives are to answer the following questions concerning the interactions between riparian areas and adjacent farmlands:
1) What are the quantities and distribution patterns of serious agricultural arthropod pests from natural areas into farmlands?
2) Does crop production benefit from elevated densities of pest enemies, including both insect and avian predators, that move from natural areas into nearby farmlands? If so, how far does this beneficial effect of natural habitat extend into farmlands?