Submitted to: Journal of Medical Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 14, 2009
Publication Date: November 5, 2009
Citation: Lohmeyer, K.H., Pound, J.M., George, J.E. 2009. Effects of photoperiod on reproduction, nymphal development timing and diapause in Amblyomma maculatum (Acari: Ixodidae). Journal of Medical Entomology. 46:1299-1302. Interpretive Summary: Laboratory studies were conducted to better understand the effects of the environment on seasonal activity and development of the Gulf Coast tick, an important parasite of livestock and domestic animals in the gulf region of the United States. Ticks in differing stages of development were held at various light/dark schedules to simulate seasonal differences in daylength: dark, increasing daylength, equal light/dark, and decreasing daylength. Some species of ticks respond to differing light schedules by entering into developmental diapause, a state of inactivity that allows the tick to survive inclement environmental changes. In this study, significant differences in immature tick developmental time due to exposure to differing light schedules were observed. However, this study demonstrates that developmental diapause in the Gulf Coast tick does not appear to be induced by changes in daylength. In comparison, previous research has shown that a closely related species, the Lone Star tick, can be induced into developmental diapause by manipulation of daylength. The inability of the Gulf Coast tick to diapause may explain why its range is more limited to tropical regions than that of the Lone Star tick.
Technical Abstract: Female engorgement weight, oviposition, and molting times of larvae and nymphs of Amblyomma maculatum Koch were studied at various photoperiods under constant humidity and temperature in the laboratory. Ticks were held at 0:24, 10:14, 12:12, or 14:10 (L:D) photoperiods during the egg through unfed nymphal stage, then at either the same or another regime during development from fed nymphs to adults. No significant photoperiodic effects were observed on oviposition, female engorgement weights, survival to unfed nymphs, or molting time to unfed nymphs. Mean nymphal molting times were significantly slower for nymphs held at the short day regime of 10:14 (L:D) during the larval stage and 12:12 (L:D) during the nymphal stage (25.2 d) when compared to those held at either the long-day regime of 14:10 (L:D) during both life periods (21.3 d) or the neutral photoperiod of 0:24 (L:D) during both life periods (22.9 d). Significantly longer mean molting times also were observed in ticks held under regimes of 12:12 (L:D) during the larval phase and then either 10:14, 12:12, or 0:24(L:D) (25 d, 24.8d, and 24.8 respectively) during the nymphal phase when compared to the long-day regime of 14:10 (L:D) during both life periods or the neutral photoperiod of 0:24 (L:D) during both life periods. Ticks held under regimes of 10:14 during the larval phase and then under 0:24 or 10:14 (L:D) ( 25 d and 24.5 respectively) also had significantly longer mean molting times when compared to the long-day regime of 14:10 (L:D) during both life periods or the neutral photoperiod of 0:24 (L:D) during both life periods. No significant differences in survival to either the nymphal or adult stage were observed for any photoperiodic regime, and at day 25 no individuals were observed to be in a state of developmental diapause. Observations from this study demonstrate that developmental diapause does not appear to be photoperiodically induced in fed nymphal A. maculatum in the laboratory.