is correlated with temperature and hours of sunlight; a certain amount of both is necessary for the butterfly to emerge from hibernation and therefore influences when diapause ends. Males emerge earlier than females, as they are more willing to fly in lower temperatures than females. Since the common brimstone most closely follows monandrous mating patterns, males may emerge earlier to increase the number of mating chances and therefore reproductive success, as older males have had more time to develop and therefore have a greater advantage. In contrast, females emerge late due to the late seasonal development of host plants such as the alder buckthorn, since these plants are necessary for egg-laying. Female emergence is correlated with host plant development. Conservation As of 2010, G. rhamni does not appear to have a threatened conservation status according to IUCN standards. However, the butterfly has experienced significant population and distribution reduction in areas such as the Netherlands, where its numbers have declined to the point that based on IUCN criterion, it has reached endangered species status. The causes of this population decline are not fully determined, but there are several possible factors. Since the common brimstone is univoltine, it may have difficulties adapting to changing environmental conditions compared to species that have multiple generations a year. For example, there has been a decrease in suitable overwintering environments for the butterflies, with open woodland decreasing in favour of more urban areas. Nitrogen pollution, declining nectar supplies, and rapid ecological changes have also been suggested as other hypothetical factors. Concerns have been raised about the possible future increase of this population decline, but the butterfly mostly does not appear to be a conservation concern due to its widespread and common geographic presence. See also List of butterflies of Great Britain Brimstone moth References External links Gonepteryx Butterflies of Asia Butterflies of Europe Butterflies described in 1758 Taxa named by Carl Linnaeus