Temperature conditions allowing metamorphosis of Hyalomma marginatum nymphs: insights from laboratory experiments

Authors

STACHURSKI, F., DUHAYON, M., GUIN, A.-S., GIUPPONI, C., BAH, M. T.

Abstract

Since the establishment of the Hyalomma marginatum tick, one of the main vectors of the Crimean-Congo haemorrhagic fever virus, has been recorded in mainland France, populations have only been observed in areas characterized by a Mediterranean climate. During the lifecycle of this two-host species, only two stages, the eggs laid by engorged females and the engorged nymphs, develop in the environment. Studies were carried out to understand the climatic factors, mainly the temperature (T{degrees}), which restrict its spreading. The moulting of the engorged nymphs was thus studied in climatic chambers at different constant T{degrees} (18{degrees}C to 40{degrees}C) and under various daily fluctuating T{degrees} cycles (the coldest was 8-20{degrees}C and the warmest was 16-30{degrees}C). The mortality rate of the engorged nymphs was lower than 4%, except for the lowest tested T{degrees} (18{degrees}C, 8-20{degrees}C and 8-22{degrees}C). Engorged nymphs could survive for a long time at 2{degrees}C (the mortality rate exceeded 10% only after 40 days at that T{degrees}) if the ticks were placed at that cold temperature immediately. On the other hand, they were more sensitive if they had already begun to develop before being placed at 2{degrees}C: when the metamorphosis had already started 8 days ago, the mortality rate reached 96% for the nymphs transferred for 3 weeks at cold T{degrees}. Using different methods, the development threshold was determined to be around 14{degrees}C. The median moulting time depended on the number of degree-days (D{degrees}) accumulated daily over the threshold. It ranged from 10 days (at 40{degrees}C) to 68 days (at 18{degrees}C) and was shorter for the T{degrees} cycles than for the constant T{degrees} equal to the mean T{degrees} of the cycles (68 days at 18{degrees}C but 52 days at 14-22{degrees}C and 37 days at 10-26{degrees}C). Consequently, the mean daily temperature is inadequate to assess the number of D{degrees} experienced by the moulting ticks. Formulas are proposed to determine the number of daily D{degrees}. The moulting required 196 D{degrees} (median time) for nymphs placed at fluctuating T{degrees} and 237 D{degrees} for those exposed to constant T{degrees}. It is suggested that this is due to inertia in nymph development: metamorphosis does not stop immediately when the T{degrees} goes back under the threshold.

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The authors list and abstract were imported from bioRxiv on 24 Oct 2026.

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