The Distribution and Population Dynamics of Neophilaenus lineatus (L.) and N. exclamationis (Thun.) (Homoptera, Cercopidae) on Pennine Moorland

Abstract

Three types of changes in the spatial distribution of N. lineatus numphs near the edge of their range were observed: a) Movement to different feeding positions in different instars on Nardus stricta and Juncus squarrosus, Festuca ovina sites. b) A change of host plants on the Juncus site only, accompanied by: c) An increased tendency for nymphs to aggregate within spittles. N. exclamationis on Festuca, Agrostis grassland showed none of these. Nymphal mortality was highest where considerable movements outside the protective spittle were involved, and lowest in N. exclamationis. Overall nymphal and egg mortality was approximately the same in each year and each species regardless of population density. Adult mortality was greatly influenced by chance occurrences of climatic catastrophes and there was no compensation for this at other stages in the life cycle. Maintenance of the populations studied was thus a chance affair making local extinctions common.