No abstract

Pitfall traps baited with cattle dung are commonly used to characterize local assemblages of coprophilous insects. Baits can be made fresh or be prepared in advance and kept frozen until needed. Insect recoveries are expected to decline with the age of the bait and may be affected by the use of fresh vs. frozen baits. To assess the effect of these two factors on insect recoveries, we performed a pitfall trap experiment that was repeated in four trials spanning 2 years and two locations in southern Alberta, Canada. The experimental design allowed us to minimize the potential confounding effect of short-term weather events. For results combined across trials, baits aged >3 days were largely ineffective for attracting coprophilous species. Frozen baits attracted significantly more insects than did fresh dung for the first 3 days after placement in the field with no difference thereafter. Our findings suggest that insect recoveries in dung-baited pitfall traps can be maximized with the use of frozen baits with replacement every 3–4 days.

We examined the use of bulk mass to predict the number of individuals in samples of the dung beetle Chilothorax distinctus (Müller) (Coleoptera: Scarabaeidae: Aphodiinae: Aphodiini). We first developed linear regression equations to characterise the relationship between the number of beetles in a sample and sample wet mass, air-dried mass, or oven-dried mass. We then applied these equations to samples containing unknown numbers of beetles to obtain a predicted number. The predicted number was subsequently compared to the number obtained by counting each beetle by hand. Wet mass was as suitable as air-dried or oven-dried mass to estimate beetle numbers and was quicker to obtain. The predicted number of beetles in individual samples based on wet mass deviated from the actual number by 0.6–19.9%. For results combined across samples, the discrepancy was 2.2%. We conclude that quantifying C. distinctus by bulk wet mass rather than by hand count provides a reasonable alternative that accelerates the pace of sample processing while providing substantial cost savings. These results add to the small body of literature assessing the accuracy of bulk insect mass as a predictor for the actual number of individuals in large samples of conspecifics.