An assessment of re-randomization methods in bark beetle (Scolytidae) trapping bioassays

Abstract

Numerous studies have explored the role of semiochemicals in the behavior of bark beetles (Scolytidae). Multiple funnel traps are often used to elucidate these behavioral responses. Sufficient sample sizes are obtained by using large numbers of traps to which treatments are randomly assigned once, or by frequent collection of trap catches and subsequent re-randomization of treatments. Recently, there has been some debate about the potential for trap contamination to occur when semiochemical treatments (i.e., baits), and not trap-treatment units (i.e., traps and baits), are re-randomized among existing traps. Due to the volatility of many semiochemicals, small levels of contamination could potentially confound results. We conducted a literature survey to determine the frequency of re-randomizing semiochemical treatments (baits) versus trap-treatment units (traps and baits) in scolytid trapping bioassays. We then conducted an experiment to determine if differences in the response of Dendroctonus brevicomis LeConte to attractant-baited traps exist between the two methods. The majority of papers examined reported use of a large number of fixed replicates (traps) rather than re-randomization of treatments at frequent intervals. Seventy-five percent of papers for which re-randomization methods could be determined reported relocation of semiochemical treatments (baits) only. No significant differences in trap catch were observed among multiple funnel traps aged with D. brevcomis baits (Phero Tech Inc., Delta, BC) for 0 d, 30 d and 90 d, suggesting that sufficient levels of contamination did not exist to influence results. We conclude that re-randomizing baits is a viable option to re-randomizing trap and bait units, and could result in a considerable time and cost savings.

Citation

Fettig, C.J.; Dabney, C.P.; McKelvey, S.R.; Borys, R.R. 2006. An assessment of re-randomization methods in bark beetle (Scolytidae) trapping bioassays. Agricultural and Forest Entomology. 8: 267-271.