401. Time since blood-feeding (hunger) in Ixodes ricinus ticks : measurement and consequences
- Author
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Udobi, Munachimso I. and Wall, Richard
- Abstract
Developing precise and practicable techniques to determine the feeding history of ticks would be an important advance for tick research. Such information could be used to help interpret studies of questing and feeding behaviour and pathogen transmission. Current approaches to determine tick feeding history involve the quantitative analysis of the tick lipid reserves. Although relatively precise, this technique is labour and time intensive and ultimately leads to destruction of the tick. The work described in Chapter 2 aimed to evaluate a non-destructive index to estimate of time since blood feeding in Ixodes ricinus, using quantitative ratios derived from tick body measurements. Changes in body measurements over time were compared with lipid analysis. This showed that morphological measurements, described as the 'hunger index', appeared to have little predictive value for individual ticks as an index of time-since-feeding in relation to lipid analysis. However, it may be of value at the population level, and was used to compare cohorts of ticks collected in spring and autumn, and to make inferences on the phenology of these ticks. The effect of time since feeding on the relationships between temperature, humidity and saturation deficit, and tick survival was evaluated in Chapter 3. There was a significant decrease in tick survival as saturation deficit increased. Mean tick survival time was 11.6 days at ≥ 3.73mmHg and ticks survived for up to 60 days at lower SD conditions (≤ 2.5mmHg). However, no clear effect of hunger on sensitivity to saturation deficit could be established experimentally, partially because ticks were highly sensitive to saturation deficit with an abrupt transition between the saturation deficits where ticks either all survived, or all died. Nevertheless, some indication of a greater sensitivity of starved ticks to saturation deficit was evident at 2.5mmHg, suggesting that in high saturation deficit conditions mortality was increased even in ticks with high lipid reserves. Conventionally, live animals are used as blood-hosts to rear ticks in vitro, however several ethical and welfare issues have been raised with this practice. A suitable alternative would be to develop an artificial feeding system which excludes the use of live animals for tick rearing for experimental purposes. In Chapter 4, an artificial feeding system was evaluated for feeding I. ricinus ticks. Silicone membranes made using Goldbeater's skin were prepared and used to evaluate the optimum conditions for I. ricinus feeding. The results demonstrate that good levels of probing and attachment to the membrane was achieved and tick mortality significantly decreased at 37 ℃ and 70% RH in the ticks maintained in a climate-controlled incubator. However, s. In Chapter 5, feeding and walking assays were used to assess the changes in tick behaviour as starvation progressed. In the feeding assay, the results showed a significant increase in tick attachment to the feeding membrane with starvation; after 6 weeks of starvation over 70% of the nymphs were probing or attached to the membrane within the first hour. In the walking assay, there was a significant decrease in tick activity with starvation and, as hunger increased, ticks appeared less likely to walk across a filter paper ring, impregnated with an essential oil which was considered likely to act as a repellent. In the final Chapter, the data are discussed generally in the context of climate change, modelling tick populations and the impact of starvation on tick behaviour.
- Published
- 2023