A comparison of live versus kill pitfall trapping techniques using various killing agents

We compared the efficacies of two arthropod pitfall trapping techniques: live (dry) trapping and kill trapping with three killing agents (water, ethylene glycol, and the recently developed propylene glycol, whose efficacy has not been previously assessed). Kill pitfall traps caught more species than did live pitfalls. Forty-one species were collected only from kill traps (3 being unique to water, II to ethylene glycol, and 8 to propylene glycol), 12 were collected only from live traps, and 32 were collected from both kill and live traps. The same average number of individuals per species was caught for most of those taxa that were collected in both trap types, indicating that better retention of captured arthropods by the killing agent was not responsible for the differences observed in the two pitfall trapping methods. There were no significant differences in captures between propylene and ethylene glycol traps or between water and live traps. Because of species-specific differences in the efficiencies of live and kill pitfall trapping, cross-study entomological comparisons made using kill pitfall trapping and live pitfalling may be confounded. Introduction studies. Water is one of the most commonly used killing agents because of its low cost and high availability, although it may repel certain species (Southwood, 1966). Ethylene glycol is also an inexpensive and effective killing agent, although it may promote capture bias for certain species through differential attractancy (Adis, 1979) and is highly toxic to wildlife (Hall, 1991 ). Propylene glycol is a relatively benign new killing agent that is becoming increasingly recommended for collecting specimens for entomological research but whose efficacy compared to other killing agents is unknown (Hall, 1991 ). Because of this variety of potential pitfall trapping methods, we compared four arthropod procurement techniques-Iive pitfall trapping and kill pitfalling with three current killing agents (water, ethylene glycol, and the recently developed propylene glycol)-to determine whether the methods were equally effective in the collection of terrestrial arthropods. As the effectiveness of propylene glycol as a killing agent has not been previously estabPitfall trapping is one of the most widely used methods of collecting arthropods for entomological research (Adis, 1979). The technique is inexpensive, easy to use, and capable of collecting an array of arthropods belonging to various trophic levels and occupying diverse habitats. To date, most studies that have used pitfall traps have used killing agents to obtain specimens for identification or collection (Adis, 1979). The decision to use kill pitfall traps and the choice of killing agent have important ramifications on the data collected and results inferred, as killing agents may have different efficacies from attractant or repellant properties when compared to dry (non-killing or 'live') traps (Greenslade & Greenslade, 1971; Curtis, 1980). Some once-popular killing agents (such as formalin and picric acid) are now used infrequently because of associated health hazards; relatively less toxic substances have been used as killing agents in more recent