Reduced longevity of Dermacentor variabilis and Ixodes scapularis (Acari: Ixodidae) molting from immatures fed on Rattus norvegicus.

Nymphal and adult Dermacentor variabilis (Say) molting from larvae and nymphs, respectively, that fed on a Holtzman strain of Rattus norvegicus demonstrated reduced longevity compared with those from immature stages that fed on albino laboratory mice, Mus musculus. The decrease in survivorship did not appear to be caused by host-acquired resistance; lower feeding weights, longer feeding times, and reduced molting were not observed. In addition, reduced survivorship was not limited to ticks fed on Holtzman rats. It was also demonstrated in adult D. variabilis molting from nymphs that fed on Wistar strain rats, but the effect was not as severe as with Holtzman rats. Moreover, reduced survivorship occurred in Ixodes scapularis Say that fed on rats, but, again, the effect as less severe than on D. variabilis. Nymphal feeding on mice appeared to counteract the negative effect of larval feeding on rats in both adult D. variabilis and I. scapularis.