The assessment of potential attractants to beetle pests: Improvements to laboratory pitfall bioassay methods

A single pitfall bioassay has been used as a standard method for testing the response of small beetle pests to potential attractants. However, previous studies have suggested that there may be some potential for improvement and the need for a better understanding of the methodology. In this study, eight species of stored product insects were tested against known attractants to investigate certain aspects of the bioassay procedure likely to influence the sensitivity of the test. The insects tested were Ahasverus advenu, Oryzaephilus surinamensis, Rhyzopertha dominica, Prostephanus truncatus, Sitophilus granarius, S. oryzae, S. zeamais and Stegobium paniceum. The factors investigated were the test duration, pitfall lip size and arena size. For the majority of species tested, either the differentiation between control and attractant results was good, irrespective of the bioassay design, or changes to the bioassay design markedly improved the catch. However, this bioassay method may not be suitable for S. zeamais. Of the assessment periods tested, it was generally found that l h was optimal, or at least as good as the longer alternatives. Although 100 mm arena sizes generally trapped larger numbers of insects, the differentiation between treatment and control samples was optimal with differing arena sizes for the different insect species. Pitfall lip size appears to be the least important factor in increasing the differentiation between treatment and control samples. Although these findings go some way towards improving the methodology of the single pitfall bioassay, there remain some questions on the variability of the insect response under the test conditions. However, on the basis of previous experience and the studies reported here, we are able to suggest the most effective design of the single pitfall bioassay for the species tested. Recommendations for particular aspects of the bioassay design have been chosen to achieve maximum differentiation between control and attractant.