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Morphogenetic diapause in Amblyomma variegatum (Acari: Ixodidae)
R G Pegram1, E T Mwase, D Zivkovic
1Economics of Ticks' Project, Food and Agriculture Organization, Lusaka, Zambia.
Medical and Veterinary Entomology
|October 1, 1988
Summary
A diapause mechanism in Amblyomma variegatum females, likely triggered by short days, synchronizes their life cycle. This diapause is broken by chilling, ensuring offspring survival during favorable seasons.
Area of Science:
- Veterinary Entomology
- Insect Physiology
- Ecology
Background:
- Amblyomma variegatum exhibits distinct seasonal activity patterns in southern Africa.
- Understanding the regulatory mechanisms behind this seasonality is crucial for tick control and disease management.
Purpose of the Study:
- To investigate the role of diapause in regulating the seasonal activity of Amblyomma variegatum.
- To identify the environmental cues and physiological stages involved in diapause induction and termination.
Main Methods:
- Engorged Amblyomma variegatum females were subjected to controlled laboratory and natural field conditions throughout the year.
- Photoperiod and temperature variations were manipulated to assess their effects on pre-oviposition periods.
- Chilling treatments were applied to investigate diapause termination.
Main Results:
- Females exposed to short-day conditions (September-October) exhibited significantly longer pre-oviposition periods.
- Artificial photoperiod changes did not significantly affect pre-oviposition periods.
- A short chilling period (18°C for 48 hours) effectively terminated diapause and induced oviposition.
Conclusions:
- A morphogenetic diapause mechanism exists in Amblyomma variegatum, likely induced by photoperiodic cues in unfed females.
- Diapause is terminated by environmental factors such as rainfall and decreased soil temperature, possibly simulated by chilling.
- This diapause synchronizes the tick's life cycle to favorable climatic periods, optimizing egg and larval survival.