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 testi ng the response of small beetle pests to potential attractants. Howeve r, previous studies have suggested that there may be some potential fo r improvement and the need for a better understanding of the methodolo gy. In this study, eight species of stored product insects were tested against known attractants to investigate certain aspects of the bioas say procedure likely to influence the sensitivity of the test. The ins ects tested were Ahasverus advena, Oryzaephilus surinamensis, Rhyzoper tha 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 sp ecies tested, either the differentiation between control and attractan t results was good, irrespective of the bioassay design, or changes to the bioassay design markedly improved the catch. However, this bioass ay method may not be suitable for S. zeamais. Of the assessment period s tested, it was generally found that 1 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 treatm ent and control samples was optimal with differing arena sizes for the different insect species. Pitfall lip size appears to be the least im portant factor in increasing the differentiation between treatment and control samples. Although these findings go some way towards improvin g the methodology of the single pitfall bioassay, there remain some qu estions on the variability of the insect response under the test condi tions. However, on the basis of previous experience and the studies re ported here, we are able to suggest the most effective design of the s ingle pitfall bioassay for the species tested. Recommendations for par ticular aspects of the bioassay design have been chosen to achieve max imum differentiation between control and attractant. (C) 1998 Elsevier Science Ltd. All rights reserved.