Effect of short photoperiod on the development of Haemaphysalis longicornis (Ixodida: Ixodidae).

The invasive tick, Haemaphysalis longicornis Neumann, is now present across most of the mid-Atlantic States in the eastern United States. This tick ends its seasonal activity in late October to early November, with larvae being the last life-stage observed questing. Previous research has revealed that the activity of H. longicornis is influenced by photoperiod: short daylight lengths trigger diapause in nymphs, marking it as the primary overwintering stage. However, whether engorged larvae can enter diapause or are affected by short daylight is unclear. In this study, we tested in the laboratory whether the photoperiod Affects the development of H. longicornis engorged larvae and engorged nymphs under constant temperature and humidity. The results showed that engorged larvae molted significantly faster (3 days faster) when the photoperiod was 9 h of light as opposed to 14 h. In contrast, changes in the photoperiod did not affect the molting of engorged nymphs. Our results demonstrate that engorged larvae respond to short daylight length, by molting faster. These results suggest that engorged larvae are unlikely to overwinter under field conditions and support the expectation that nymphs are the primary overwintering stage for H. longicornis in the United States.