Effect of age, application date, and life stage on the susceptibility of free-living lone star ticks (Acari: Ixodidae) to acaricides.

Abstract

Laboratory and field assays in Oklahoma during 1980 to 1983 showed clearly that all free-living stages of the lone star tick, Amblyomma americanum (L.), increased in susceptibility to acaricides with age. The order of rate of increase in susceptibility was adults > nymphs > larvae. However, laboratory assays revealed that overwintered populations of nymphs and adults increased in susceptibility to acaricides at a somewhat slower rate than when these stages were maintained at a constant temperature of ca. 27°C in the laboratory. The inherent order of susceptibility was larvae > nymphs > adult males > adult females; however, large differences in the susceptibility of life stages of equal age in laboratory assays were apparently reduced by the order of age of life stages when exposed to acaricides in field assays. Acaricides applied in mid-May were more effective against nymphs and adults than applications in mid-March, while applications in late August were intermediate in effectiveness against nymphs. Applications of acaricides were less effective against larvae in late July and early August than in late August and early September.