Life cycle of Spinose ear tick, Otobius megnini (Acari: Argasidae) infesting the race horses in Nuwara Eliya, Sri Lanka.

This study investigated the life cycle of the Spinose ear tick, Otobius megnini, a parasite found in race horses in Nuwara Eliya, Sri Lanka, with findings to provide insights into the tick’s survival and reproduction processes.

Life Cycle Observations

• The research was carried out to explore the life cycle of Otobius megnini, a tick that infests domestic and wild animals, and occasionally humans. The research focused on ticks found infesting race horses in Nuwara Eliya, Sri Lanka.
• The tick population for the study was collected from fully engorged nymphs found on horses. Nymphal stages are intermediate between the larval and adult forms. They were maintained at temperatures of 10°C, 22°C and 28°C to study the effects of temperature on their lifecycle.
• The immature forms of the ticks were reared on New Zealand rabbits for the study.

Larval Stage Observations

• Only larvae weighing more than 0.9mg, which formed 84.9% of the total population, successfully moulted to the nymphal stage.
• This moulting period took an average of 5.6 (±1.7) days. None of the larvae maintained at a temperature of 10±1°C were able to moult.
• Survival rate of larvae was significantly higher at 28±1°C (44.2±4.3days) as compared to 22±1°C (35.6±9days).

Nymphal Stage Observations

• A majority of nymphs (95.6%) weighing over 10mg moulted into adults within a period of 12.5(±3.1) days when kept at 28±1°C. In lower temperature conditions of 10±1°C, nymphs went into diapause, or a state of suspended development, for 81.1(±72.0) days.

Adult Stage Observations

• Larger female specimens (weighing >13mg; 93%) laid eggs for a period of 44.6(±17.8) days with a mean pre-oviposition period of 10.3(±5.1) days. Here, pre-oviposition period refers to the time between a mature female beginning to feed and her laying the first batch of eggs.
• In terms of lifespans, females survived significantly longer (369.8±128.3days) compared to males (210.4±54.1days).
• Interestingly, some female ticks were observed laying eggs without mating.

Overall Findings and Implications

• Overall, the life cycle of these ticks completed within 123 days. The study confirmed that these ticks go through just one nymphal instar or stage, similar to the Neotropical population of the same species.
• Currently, the infestation by O. megnini is reported to be a serious concern for horses in the Nuwara Eliya racecourse. The study’s findings may have implications for disease management, particularly as there is the possibility of it spreading to nearby dairy farms due to the tick’s dynamic life cycle.