Experimental and field evaluations of two acaracides for control of I-pacificus (Acari : Ixodidae) in northern California

Use of acaricides for the control of bodes pacificus (Cooley & Kohls), the vector of Lyme borreliosis in the western United States, can be a beneficia l component in a program to reduce the morbidity of Lyme borreliosis in Cal ifornia. Three commercially available acaricides, carbaryl, chlorpyrifos. a nd diazinon, were evaluated in laboratory bioassays for their effetiveness against I. pacificus adults. Based on bioassay results, chlorpyrifos and ca rbaryl were selected for field evaluations. Chlorpyrifos demonstrated the l owest LD50 in the laboratory and the best overall control in the field tria ls. Chlorpyrifos and carbaryl provided effective control with a residual ef fect on adult ticks up to 7 wk after a single treatment. A field applicatio n timed to coincide with the highest period of adult questing activity prov ed effective in the control of I. pacifcus in a Sierran foothill habitat. J udicious use of either of the acaricides evaluated may help to reduce adult tick densities in a peridomestic environment and thereby reduce the risk o f human exposure to Lyme borreliosis and other tick-tome agents.