Larval behaviour of the winter tick, Dermacentor albipictus (Acari:Ixodidae): evaluation of CO2 (dry ice), and short- and long-range attractants by bioassay

Abstract

ABSTRACTWe report that larvae of Dermacentor albipictus can detect CO2 from a dry ice source at distances up to 3.0 m and initiate increased activation, movement and questing behaviour. The maximum distance that larvae spread was ~0.5 m after 24 h, compared to <0.1 m without CO2 as an excitant. In Petri dish bioassays, 2,6-dichlorophenol, methyl salicylate and o-nitrophenol acted as attractants, albeit with mixed results at 1.0 m, 2.0 m and 3.0 m, respectively. The 2,6-dichlorophenol target was the most effective, although few larvae crawled >1.0 m and CO2 was required as a carrier. In Petri dish bioassays, larvae arrested into dense aggregations on eggshells collected after hatching. This arrestment was associated with the eggshell lipids cholesteryl oleate and cholesteryl palmitate, implying that cholesteryl esters act as assembly pheromones for larvae. Faster response was evident at 65% relative humidity (RH) versus 95% RH. Larvae were not arrested by tick excreta, guanine or related purines. Although larvae can be activated from long distances, in the field they remain fairly localized around the egg mass (hatching location), have limited dispersal and are more responsive in drier conditions. Given their arrestant properties, cholesteryl oleate and cholesteryl palmitate may prove useful in pheromone-assisted control methods because D. albipictus larvae are the single stage of infestation to the host.