Attraction of Aedes triseriatus to carbon dioxide.

Aedes triseriattn (Say) is a low-density, diurnal species that does not readily enter animalbaited traps and is not attracted to light traps (Craig 1983). A variety of other methods have been used to monitor populations. The ovitrap (Loor and DeFoliart 1970) is a useful detection tool, although results are influenced by rainfall and the availability of competing oviposition sites (Berry et al., 1980) and it provides only a qualitative measure of population. Suction devices have proven effective in some situat ions (Nasci 1981, Beier et al. 1982), but their use is relatively laborious and time-consuming for routine monitoring. Human-biting counts also can be quite time-consuming for routine monitoring, and they are subject to extensive variation depending on environmental conditions and the differential attractiveness of collectors (Service 1976). In addition, biting counts may be ill advised in La Crosse encephalitis endemic areas. A standardized method of measuring relative biting activity of this species would be useful in research and, potentially, for routine monitoring by mosquito abatement districts and health departments in areas where the human population is at risk of La Crosse encephalitis. As large catches of Ae. triseriatus have been occasionally observed in CO2-baited CDC miniature light traps operated near tire dumps in Ohio (R. L. Berry, personal communication), we focused on CO2 as an attractant. To determine whether movement, as provided by the presence of a small animal, might enhance the attractivity of CO2, we tested the following in a trap adapted from the design of Pfunter (1979): l) CO2 alone, from sublimating dry ice (1.0-1.4 kgl24 hr), 2) a female white mouse, and 3) CO2 from dry ice plus a female white mouse. A trap with neither dry ice nor a mouse was used as a control. The 3 attractants and the control were randomly assigned to traps at 4 sites in areas of known Aa. triseriatus oviposition activity on the R. P. and M. G. Hanson farm in Iowa County, Wisconsin (Hanson and Hanson 1970). The traps were emptied and the attractant changed daily. The attractivity of CO2 released from a pressurized cylinder was also tested, but only during the last 45 days of the season and not as part of the experimental rotation described above. The Pfunter trap, as modified, is shown in Fig. 1. A polyvinyl chloride (PVC) coupling for 10.2 cm diam sewage pipe was used as the trap body (A). An 8 cm length of sewage pipe (B) was inserted into the upper part of the coupling. The motor mount (C) was constructed from a piece of PVC (3.8 x 5 x 1.9 cm); a semi-circular notch was cut in one end to accommodate the motor (D), and the other end was rounded to the inner contour of the trap body, to which it was attached by metal screws. A vertical hole, 3.2 cm in diameter, was cut in the middle of the mount to increase air flow. The motor was held in place by a spring (E). A circular cover (F) from an old CDC light. trap was fastened 22 cm above the trap body using