Abstract
The nymphs of spittlebugs (Hemiptera, Cercopidae) are xylem-feeders and live on herbs, grasses or woody plants within their self-produced spittle masses. Nymphs of the spittlebug Neophilaenus albipennis live aggregated in these spittle masses on their host plant Brachypodium pinnatum, a common grass in dry grassland. The objective of this study was to estimate nymphal mortality rates and to examine what role aggregation and vegetation structure play in the mortality of the nymphs. The aggregation and mortality were measured using two different methods, direct monitoring and caging of nymphs. The nymphs passively aggregated with up to 4 nymphs per spittle and aggregation decreased with instar. The aggregation of the nymphs resulted in a reduced mortality in all instars. Although it has already been argued that aggregation may be an advantage, this study is the first direct evidence (i.e. direct measurement of single individuals) for the benefit of aggregation to individual spittlebug nymphs. Despite a clumped distribution of N. albipennis nymphs in tall vegetation, nymphal mortality was not correlated with vegetation height.
Highlights
Aggregation of insects in the immature stage has been frequently documented in various taxonomic groups
The nymphal mortality rates decreased with instar and were similar to mortality rates estimated in other Neophi laenus species (Whittaker, 1965b)
No substantial differ ence in total survival rate was found between the two patches Br2 and Br498, the phenology of the nymphs differed
Summary
Aggregation of insects in the immature stage has been frequently documented in various taxonomic groups. Aggregation may entail costs such as intra-specific com petition (Faeth, 1990) or higher infection rates through, for instance, viruses (Hochberg, 1991). The balance of these advantages or disadvantages of aggregation will affect mortality of the immatures and may have a strong influence on the population dynamics of species. The spittle is thought to give shelter to the nymphs, pro tecting them from predation and providing a suitable microclimate (Whittaker, 1970). Is there reduced mortality in aggre gated spittlebug nymphs? How does the aggregation come about?
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