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

Abstract

1 Numerous studies have explored the role of semiochemicals in the behaviour of bark beetles (Scolytidae). 2 Multiple-funnel traps are often used to elucidate these behavioural 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. 3 Recently, there has been some debate about the potential for trap contamination to occur when semiochemical treatments (baits), and not trap-treatment units (traps and baits), are re-randomized among existing traps. Due to the volatility of many semiochemicals, small levels of contamination could potentially confound results. 4 A literature survey was conducted to determine the frequency of re-randomizing semiochemical treatments (baits) vs. trap-treatment units (traps and baits) in scolytid trapping bioassays. An experiment was then conducted to determine whether differences in the response of Dendroctonus brevicomis LeConte to attractant-baited traps exist between the two methods. 5 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. 6 No significant differences in trap catch were observed among multiple-funnel traps aged with D. brevcomis baits (Phero Tech Inc., Canada) for 0, 30 and 90 days, suggesting that contamination did not influence the results. 7 It is concluded that re-randomizing baits is a viable cost-effective option to re-randomizing trap and bait units. A trapping bioassay was conducted at McCloud Flats, Shasta-Trinity National Forest, Siskiyou Co., California (41.35°N, 121.95°W; 1150 m elevation) during 10 -21 JuneRe-randomizing treatments in bark beetle trapping bioassays 269

Field response of the six‐toothed pine bark beetle, Ips sexdentatus (Col.: Curculionidae, Scolytinae), to pheromonal blend candidates

“…Although the ternary blend described earlier yielded highest catches and a very large positive effect size ( d unbiased = 1.20) comparable to those in the previous trials, the good results of treatment Id + Ie could not be confirmed. Although one of the experimental blocks was removed because of obvious internal exposure heterogeneity, there was a high chance that randomization procedures did not minimize positional effects, as experimental units were not equally represented (Fettig et al. 2006).…”

“…A total of five treatments were thus evaluated within a complete randomized block design. Besides the initial random position assignment, re-randomization of treatment allocation to experimental units within experimental blocks was undertaken on 31 May and 10 August (Fettig et al 2006). Baits were replaced after 6 weeks, well before to the expected duration (SEDQ LLC, Barcelona, Spain).…”

Spatial Displacement of Release Point can Enhance Activity of an Attractant Pheromone Synergist of a Bark Beetle

“…Bark beetle semiochemicals have been classified as either synergists or inhibitors typically with "attractant-challenge"-type experiments in which a bait of undetermined activity is attached to a randomly-selected, attractant-baited trap, and catch is compared to a simultaneously-operated, attractantonly control trap (Reeve and Strom 2004;Fettig et al 2006). If catch in the challenged trap is significantly lower than the control, the test bait is concluded to be inhibitory; if catch is significantly higher than the control, the test bait is concluded to be a synergist or attraction enhancer (Payne et al 1978a;Bedard et al 1980;Bakke 1981;Pureswaran and Borden 2004;Sullivan 2005).…”

“…In studies used to identify pheromone synergists and inhibitors for bark beetles (Coleoptera: Scolytidae), candidate behavioral chemicals are typically released from the same location as an attractant, and the ability of the compounds to modify insect flight to the attractant is then measured, usually with a trap (Reeve and Strom 2004;Fettig et al 2006). However, in natural bark beetle attacks, release points of pheromones (i.e., the individual beetle gallery entrances) are dispersed in space and time.…”

Responses of Dendroctonus brevicomis (Coleoptera: Curculionidae) in Behavioral Assays: Implications to Development of a Semiochemical-Based Tool for Tree Protection

“…All experiments were conducted using similar protocols and a completely randomized design (Fettig et al 2006b). Sixteen-unit multiple funnel traps (Lindgren 1983) were deployed along forest roads.…”