Natural vegetation and conservation of ichneumonid wasp diversity in agricultural landscapes

Conversion of natural systems to managed systems and from extensively to intensively managed systems is the most serious threat to biodiversity conservation worldwide. Landuse conversion and intensification may also reduce ecosystem services relied upon by land managers. In particular, natural biological control of agricultural pests can be elusive in intensively farmed, annual crop systems. In such highly disturbed systems, extra-farm vegetation may be critical habitat for maintaining local natural enemy populations and the biological control services they provide to growers. We investigated the importance of natural vegetation in maintaining ichneumonid wasp diversity, an indicator taxon for biodiversity and biological control services, at 35 commercial farm sites in the Central Coast region of California. Wasps were sampled in May, July, and September in 2004, 2005, and 2006. Landuse and vegetation classes were characterized by aerial photo interpretation at two landscape scales (0.5km and 1.5km radii from farm centers). Landcover proportions for each class were quantified to determine landscape complexity. Research landscapes ranged from primarily agricultural to complex vegetation-landuse mosaics. Initial analyses, for 12 research landscapes and combing vegetation classes, showed a positive correlation between ichneumonid diversity and percent of landscape under unmanaged vegetation cover in mid-season (July 2005, r²=0.47, p=0.0194) but not in early or late season comparisons (May and September 2005). Separate analyses on single and combined vegetation classes will be reported to determine if specific types of natural vegetation are strongly associated with ichneumonid diversity. Opportunities and constraints for enhancing biodiversity and biological control in agricultural landscapes will be addressed.