Light and Temperature Sensitivity of Feeding-related and Reproductive Processes in Amblyomma americanum (Acari: Ixodidae) on Cattle

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Abstract
Photoperiod and temperature significantly influenced the proportion of nymphal Amblyomma americanum (L.) that attached, fed, and detached from cattle, whereas photoperiod, temperature, and the interaction of photoperiod and temperature influenced the number of females that fed. The highest proportion of nymphs and females fed in a photoperiod of LD 12:12 (nymphs, 98%; females, 100%), the fewest in a photoperiod of LD 8:16 (nymphs, 62%; females, 51%). The weight of engorged nymphs was influenced by photoperiod and temperature (maximum, 10.2 mg in LD 16:8 at 25°C; minimum, 5.6 mg in LD 8:16 at 30°C), and the weight of engorged females by photoperiod, temperature, and photoperiod–temperature interaction (maximum, 674.6 mg in LD 16:8 at 25°C; minimum, 160.5 mg in LD 8:16 at 30°C). Feeding time (i.e., attachment to detachment) was shortest (5.3 days) in populations of nymphs in LD 16:8 at 25°C and in populations of females in LD 12:12 at 20°C (13.9 days) but longest for nymphs (9.6 days) in LD 12:12 at 20°C and for females in LD 8:16 at 30°C (20.0 days). In nymphs, photoperiod, temperature, and photoperiod–temperature interaction influenced the time required to attain the 10th and 95th percentiles of the detaching population. These factors also influenced the time required to attain the 10th percentile in populations of detaching females, but only photoperiod and temperature affected the time required to attain the 95th percentile. The proportion of populations of fed female A. americanum that oviposited and the subsequent proportion of eggs eclosing were influenced by photoperiod, temperature, and photoperiod–temperature interaction. In an imaginary cohort of 100 females, adjusted for proportion feeding, oviposition, and eclosion of eggs, a 560-fold difference existed in the potential number of offspring produced under LD 16:8, 25°C versus LD 8:16, 30°C. These data and characteristics of seasonal feeding activity by A. americanum on cattle are discussed in light of existing theories concerning diapause in ticks.