Submitted to: Journal of Medical Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 18, 1997
Publication Date: N/A
Interpretive Summary: A rhythmic pattern of detaching and dropping from a host would be advantageous to engorged ticks if this behavior increased the probability of an individual falling into a habitat favorable for oviposition and egg incubation or development to the next life stage. A detachment rhythm would also increase the chance a tick would survive if it resulted in an increased probability of unfed ticks encountering a host by concentrating them into areas most often frequented by potential hosts. Experiments showed that when engorged female cattle ticks detach from calves, most of the detachment activity occurs during the morning near the time of sunrise and in the afternoon just before sunset. The time at which sunrise occurs along with the time animals feed appear to be important in the synchronization of the detachment rhythm. Generally, cattle are grazing during the times of day when most engorged cattle ticks detach. If cattle are in pastures with a mixed cover of trees, brushy vegetation, and grasses, conditions for survival of engorged females, eggs and larvae will be more favorable, but in improved pastures with few trees and minimal brushy vegetation conditions for survival of ticks would be greatly reduced. This information on the biology of the cattle tick is useful in creating tick control programs that use schemes for vegetative management, pasture vacation, or pasture rotation as part of an integrated pest management approach for tick control or eradication.
A bimodal, diurnal rhythm of detachment was observed for engorged female Boophilus annulatus fed on Hereford heifers confined in individual stalls in an open-sided barn and exposed to ambient climate and light. In experiments during which hosts were fed each morning or both morning and evening, a morning period of increased detachment activity occurred during a six-hour period centered around the 2 h collecting interval in which sunrise occurred. A second peak of activity occurred during a six-hour interval that included a two-hour activity peak that began from six to 10 h later than the morning peak period. Three-fourths or more of the ticks detached during these 12 h. In some cases the largest percentage of the ticks detached during the morning period of peak activity, but sometimes the peak period of detachment activity occurred during the afternoon. In contrast, an eight-h morning period of increased detachment activity, during which 43.6 % of the total number of the engorged ticks from heifers fed only in the evening detached, began in the interval between 0200 and 0400 h. About the same percentage of ticks (38.5) detached during a six-h period that began at 1400 h. The experiments demonstrated the general nature of the pattern of detachment of B. annulatus from cattle. Further experiments to determine the factors that synchronize or influence the timing of detachment would be useful to explain the basis for the rhythm. The less precisely delimited pattern of detachment of engorged females from cattle fed only in the evening, as contrasted with the rhythm observed for ticks that detached from heifers fed in the morning or both morning and evening, indicates that the nutritional or physiological state of the host may influence the rhythm exogenously.