Density effects in larval and nymphal stages of the blacklegged tick (Ixodes scapularis) life cycle:: Experiments and mathematical models

We have used a combination of experiments and mathematical models to investigate possible regulatory factors of immature stage density in the life cycle of the blacklegged tick Ixodes scapularis. Laboratory experiments in which naive whitefooted mice (Peromyscus leucopus) were repeatedly anesthetized and infested, at two week intervals, with various numbers of unfed larvae revealed density dependence in the fraction completing engorgement,but only after repeated infestation of the same host with sequential cohorts of larvae. Experiments exposing unanesthetized, unrestrained P: leucopus to various densities of unfed larvae in small laboratory arenas detected density dependence in the amount of grooming behavior by P. leucopus and in the number of larvae that successfully became engorged. Similar experiments with unfed nymphs revealed no density-dependent effects in any of several stages, despite heavy mortality associated with host grooming. A mathematical model of host finding and engorgement, using differential equations, was fitted to the experimental data and represents a first step toward filling an important gap in comprehensive models of the tide life cycle.