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30 April 2019 Seasonal changes in populations of sheep tick, Ixodes ricinus (L., 1758) (Acari: Ixodinae) in natural biotopes of St. Petersburg and Leningrad province, Russian Federation
L.A. Grigoryeva, N.K. Tokarevich, O.A. Freilikhman, E.P. Samoylova, G.A. Lunina
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Abstract

Changes in the seasonal activity and age composition of adults and nymphs in populations of the Ixodes ricinus in northwestern Russia have been studied. Adult ticks and nymphs were collected on flag twice a month from April to October in 2014–2016. They were investigated for biological age (light-optical preparations of the midgut after staining fat with Sudan III). DNA isolated from ticks was analyzed using real-time PCR (fluorescent probe technology) for the presence of Borrelia burgdorferi s.l. pathogens based on amplification of the 16SrRNA and Hbb gene fragments.

The season of activity of the adults shows one peak, the largest numbers show up in July–August (September). The population of adults is composed of two generations. The first generation is active from the beginning of the season until nearly its end, mid-October. Until the end of June, young individuals with large fat reserves predominate in the population. From July to the end of September, the adult population is formed mainly of mature individuals. Older individuals in the population appear from mid-July, and become dominating only in August and, mainly, in September. Ticks of the second generation, as young individuals, were recorded from the end of August until the end of the season of activity. The active nymphs were captured from late April until late October. The season of activity of nymphs begins and ends with a 100% content of young individuals. The spring population (April–May) consists of young nymphs, in June the proportions of young and mature are equalized, in July and August the ratio of mature and old nymphs is balanced, in September old individuals prevail, which were not found in October. The first generation is the nymphs who have hatched from August to October during the previous season, and the second one is the nymphs hatching in August of the current year. The lifespan of adults and nymphs can reach 13–15 months. The proportion of infected ticks in May and June is 24.5% and 25%, with the highest rates of in the young (10–12 months) part of population (70–85% of individuals). In July, the number of mature (12–13 months) individuals increases (up to 75–95%), at the same time the average values of infection fall to 20.8%. In August, the shares of mature (45–55%) and old -13–15 months (45–55%) individuals are approximately balanced. Borrelia contamination is also decreasing (14.3%). In September, the number of mature individuals (29.7%) was about 2 times lower than the old ones (65.3%), and the infection rate decreased to 11.4%.

The population of nymphs and adults is composed of two tick generations in the season of activity. The season of activity of adult ticks is holistic; it is not interrupted during the summer months. Infection of adults with Borrelia decreases simultaneously with the ageing of the population.

© Systematic & Applied Acarology Society
L.A. Grigoryeva, N.K. Tokarevich, O.A. Freilikhman, E.P. Samoylova, and G.A. Lunina "Seasonal changes in populations of sheep tick, Ixodes ricinus (L., 1758) (Acari: Ixodinae) in natural biotopes of St. Petersburg and Leningrad province, Russian Federation," Systematic and Applied Acarology 24(4), 701-710, (30 April 2019). https://doi.org/10.11158/saa.24.4.14
Received: 8 February 2019; Accepted: 11 April 2019; Published: 30 April 2019
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KEYWORDS
age structure
Borrelia burgdorferi s.l.
Ixodes ricinus
PCR
seasonal activity
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