[1] USDA ARS, Beltsville Agr Res Ctr, Epidemiol & Syst Lab, Biosyst Unit Parasite Biol, Beltsville, MD 20705 USA
[2] Univ Colorado, Dept Environm Populat & Organism Biol, Boulder, CO 80309 USA
[3] Nat Hist Museum, Dept Zool, London SW7 5BD, England
[4] Univ Colorado Museum, Boulder, CO 80309 USA