Differential effects of formaldehyde concentration and detergent on the catching efficiency of surface active arthropods by pitfall traps

摘要

Although pitfall traps do not provide absolute density estimation they are effective in collecting mobile arthropods. In order to find out optimal capture efficiency for Araneae, Opiliones, Carabidae and Staphylinidae, five different concentrations of formaldehyde (1, 2, 4, 10, and 20 %) each with or without the addition of the detergent were tested. The traps, plastic cups sheltered by a metal plate, were set out four times a year in a homogenous crop field. The number of Araneae was similar for all formaldehyde concentrations but there were more spiders in traps with the addition of the detergent. This was particularly true for tiny linyphiid species. Number of Opiliones decreased as the concentration increased presumably due to repellency of formaldehyde. Addition of the detergent did not influence the catch of Opiliones. On the other hand, number of Carabidae was positively correlated with the increasing concentration of the formaldehyde fluid. There was no effect of the addition of the detergent. The number of Staphylinidae was greater for higher concentrations but there was a negative effect of the addition of the detergent, i.e. significantly more staphylinids were caught into traps without the detergent. Obtained results show that for the capture of large and mobile arthropods, such as lycosid spiders and carabid beetles, at least 4 % concentration without the addition of the detergent should be used.