Density estimation for invertebrate predators in agroecosystems.

Abstract

A review of the principal methods available for the estimation of predator density or abundance (suction apparatus, habitat search, mark-release-recapture, fenced pitfall traps, ground photoeclectors, soil flooding, micro habitat removal, catch per unit effort, distance method, trap stones and unfenced pitfall traps) indicated that good data on the efficiency of these methods, and the causes of variation in efficiency, are generally lacking. The relative advantages, disadvantages and limitations of each of these methods are discussed. Since no single sampling method is appropriate for all circumstances, methods appropriate for specific requirements are recommended here, taking account of the type of predator (aphid-specific predators, spiders, carabid and staphylinid beetle adults and larvae) and crop involved and the scale of the investigation. Gaps in our ability to assess the abundance of some species reliably are revealed, especially in extensive sampling programmes, where effort per sample must be limited.