Similarity in Responses of Laboratory-Reared and Field-Collected Lone Star Tick (Acari: Ixodidae) Nymphs to Repellents

Ticks and tick-borne diseases that affect humans are a growing source of concern in the U.S. and elsewhere in the world (Gratz 1999, Annu. Rev. Entomol. 44: 51-75). The lone star tick, Amblyomma americanum (L.), is increasingly a problem in the southeastern, south-central and mid-Atlantic states because it readily bites humans, is expanding its range, and has been implicated in the transmission of ehrlichial pathogens (Childs and Paddock 2003, Annu. Rev. Entomol. 48: 307-337). Although progress has been made recently in the development of area-wide tick control technologies (Pound et al. 2000, J. Med. Entomol. 37: 588-594), repellents remain the primary method of personal protection against tick bites (CDC 2002 Lyme disease. Department of Health and Human Services, Centers for Disease Control and Prevention, Ft. Collins, CO, 12 p). The ultimate test of a repellent is its efficacy in the field. However, in conducting a successful field test using multiple concentrations of multiple repellents intended for use on human skin, one is faced with several challenges. It is difficult to recruit sufficient volunteers, who may be required to walk through tick habitats and expose their skin to thorns, poisonous plants, and biting arthropods to contact ticks. On a local scale, ticks tend to follow a clumped distribution (overdispersed data) that complicates data analysis and may result in some repellent-concentration combinations being exposed to few ticks. Wet vegetation hampers host acquisition by ticks, so weather postponements requiring volunteer rescheduling are a potential complication. Not surprisingly, much of the efficacy data for tick repellents have been generated in the laboratory. The reluctance to extrapolate from these laboratory efficacy data to the field stems from valid concerns, not the least of which involves a lack of