Ecology and conservation of the moth Dysauxes ancilla

Abstract: The ecology of the moth Dysauxes ancilla was studied in the only Swedish breeding area at Beijershamn, situated on the Baltic island of Öland. The population is a northern outpost, separated from the species´ continous distribution area in middle- and southeast Europe. There is a general opinion that there has been a reduction of the species distribution during the last decades, but no studies have been performed. The species is red-listed as critically endangered. The results showed that the population is currently restricted to an area of 4 ha, with an estimated population size at 1000-2000 individuals. The habitat consists of dry meadows with a short grass community and stands of Quercus robur and Juniperus communis. Earlier findings of the moth in the area suggest a larger former distribution, which has now contracted to the single extant population because of overgrowth of all other suitable habitat areas. The area where D. ancilla occurred was never grazed regularly, except for a sparse grazing by horses. The decline was therefore mainly caused by natural successsion of the formerly more open landscape. Within the habitat ovipositing females and larvae are restricted to edge zones facing south and to an ancient shore line facing southwest. The dependence of these microhabitats are ascribed to two factors. First, being on the northern edge of the species´ distribution the need for warm microclimatic conditions is strong. Second, larvae occur where there are both a high abundance of food plants and well developed layers of Q. robur. The latter gives enough of humidity for the pre-imaginal stages, but larvae are also concealed from predators and parasitoids in this substrate. Further larvae are polyphagous, and my results suggest performance advantages from food-mixing and posssibly also from food-switching. Adults of D. ancilla are sedentary and all movements occurred within the breeding area. Mean distance between two successive captures was 43 m (males) and 9 m (females), and the longest single move was 144 m. Further the moths showed a behavioural reluctance to enter adjacent areas of other habitat types, e.g. heavily grazed meadows or dense vegetation. Conservation efforts should focus on managing the continuity of the current breeding area. This can be achieved by grazing, or by manually clearings, at suitable intervals. There are currently no other suitable breeding habitats in the surroundings. This means that the borders of the remaining breeding area should be managed to minimize losses of adult moths to the surrounding. A restoration of former breeding areas, suffiently close to the extant population to achieve connectivity, should only be considered if it is possible to create corridors in a way that prevent the moths from leaving a corridor to the surroundings. If a restoration plan is considered the extant population is a good basis for an expansion in the area since there is no genetic deterioration.