Aspects of the ecology of the Lepidoptera associated with Calluna vulgaris on managed northern heath
Aspects of the ecology of the Lepidoptera associated with Calluna vulgaris on managed northern heaths were studied between 1991-1993 at five study areas in Durham, Northumberland and southern Scotland. The study areas were northern heaths that were managed by rotational burning and each comprised a mosaic of even-aged Calluna stands. Lepidoptera were studied in the larval stage of development. A range of even-aged Calluna stands, with different ages and vegetation structures were selected as sample sites and the larval assemblages in the different stands were monitored by sweepnet sampling. A total of 29 species of macrolepidoptera and 3 species of microlepidoptera larvae were recorded. Species lists were similar at the five study areas, but the relative abundance of individual species varied between sites. The degree of similarity between communities was not related to the distance between study areas. The densities of many macrolepidoptera species were closely correlated with Calluna height. Intercorrelation between vegetation architecture variables meant that other factors e.g. green shoot density or flower density could also have been responsible. Lepidoptera diversity varied with Calluna height, due to changes in the dominance of common species and the presence of additional rare species at certain heights. However patterns in diversity were not consistent between study areas. The concentrations of total leaf nitrogen, total phenolics and water were significantly higher in current year's Calluna leaves than in the shoots formed in previous years. In same-aged leaves, there was no relationship between plant age and the concentrations of leaf nitrogen or phenolics. The water content of same-aged leaves was negatively correlated with stand age at some sites and at certain sampling times. Larvae offered different choices of ericaceous plants exhibited significant preferences for different plant species and also for the current year's Calluna leaves rather than previous years' growth. Mechanisms that could be responsible for the observed distribution patterns of larvae in different heights of Calluna are discussed. The maintenance of a mosaic of different-aged Calluna stands on northern heath represents the best conservation strategy for Lepidoptera by maintaining species diversity at a site.