Pardosa species do not overwinter in the adult stage in the Holarctic region, therefore penultimate instars should avoid precocious maturation in autumn. We tested how artificially increased temperature and/or lengthened light regime would affect the pre-overwintering development of two common species with different phenological patterns. Juvenile instars of Pardosa agrestis (Westring 1861) and P. hortensis (Thorell 1872) were collected in autumn from the field. The experimental spiders were held either indoor at 26 °C or outdoors at ambient temperature and were exposed either to short or to long daylength. Molting events were monitored for five months. At outdoor temperatures no spiders reached adulthood and molts of younger instars occurred more frequently at long daylength. In the indoor temperature groups all P. hortensis and the majority of P. agrestis individuals reached adulthood during the experiment. Long daylength treatment enhanced the effect of increased temperature by almost halving the time needed to reach adulthood in both species. Penultimate instars of both species needed at least 17 days to molt, while earlier instars, present only in P. agrestis, responded rapidly to higher temperature by molting. This stage dependent response suggests that earlier instars can use favorable autumnal temperatures to catch up with penultimate instars which leads to higher synchrony of developmental stages in the overwintering and spring populations.
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