The survival of all stages of Haemaphysalis longicornis was investigated at different densities and at 3 levels of relative humidity. Larvae survived longer when the density was higher, or the size of a cluster was larger, or both. However, in nymphs and adults, there was no significant relationship between the density and the survival period. Moreover, in nymphs and adults, there was no positive relationship between the size of the aggregation and tick longevity, except for 2 nymphs/vial in high humidity. These results suggest that the advantage gained from a higher density, or from taking part in a cluster, or both, differed between stages. Furthermore, the fact that the survival period of larvae and nymphs was influenced by cohort suggests that a maternal effect, as well as aggregation, influences the survival of immature ticks.

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