Intraspecific competition as a selective pressure on the choice of oviposition site in a phytophagous insect

Abstract

Our aim was to clarify the factors providing selective pressures on the choice of oviposition sites in phytophagous insects. To this end, we examined the spatial distribution of eggs of the sawfly leaf miner, Profenusa japonica. The study was conducted over five consecutive years on three subpopulations found in riverbeds in central Japan. Profenusa japonica lays eggs on leaflets of Rosa multiflora, and its larvae mine a single leaflet for the entire larval stage. The egg distribution among leaflets was uniform (regular) at all sites examined in each year. The distribution within leaflets was also uniform, and it appeared that females avoided ovipositing on areas of the leaf that already contained eggs. Few parasitoids were found in eggs or larval stages, despite intensive examination. Larval mortality increased, mainly as a result of exploitative competition, when there were two or three larvae per leaflet. Starvation caused by resource competition for leaflet tissues was an important mortality factor. Therefore, we suggest that P. japonica females avoided ovipositing on areas of the leaflet that already contained eggs to prevent exploitative competition among larvae sharing the same leaflet. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 92, 641–650.