Intraspecific competition as a selective pressure on the choice of oviposition site in a phytophagous insect SHINJI SUGIURA 1,2 *, KAZUO YAMAZAKI 3 and YUICHI YAMAURA 2 1 Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan 2 Department of Forest Entomology, Forestry and Forest Products Research Institute (FFPRI), 1 Matsunosato, Tsukuba, Ibaraki, 305-8687 Japan 3 Osaka City Institute of Public Health and Environmental Sciences, 8-34 Tojo-cho, Tennoji-ku, Osaka 543-0026, Japan Received 30 May 2006; accepted for publication 10 January 2007 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. ADDITIONAL KEYWORDS: enemy free space – preference–performance hypothesis – Profenusa japonica – Rosa multiflora – Tenthredinidae. INTRODUCTION The selection of oviposition sites by phytophagous insects is a critical factor in their survival and fitness (e.g. Schultz, 1983). Because the distribution of food plants is typically spatially heterogeneous, the ovipo- sition sites selected by adult females directly affect the survivorship of offspring (e.g. Thompson, 1988). Because variation in oviposition behaviour can be genetic and heritable (Jaenike, 1990; Jaenike & Holt, 1991; Thompson & Pellmyr, 1991), natural selection may favour the choice of oviposition sites that facili- tate the growth and survival of offspring (Holland, Buchanan & Loubeau, 2004). What factors provide selective pressures on the choice of oviposition sites in phytophagous insects? Factors such as the quality and quantity of host plants, predation, parasitism, fungal infection, and inter- and intraspecific competi- tion may affect the sites chosen by adult females for oviposition (Tuomi, Niemelä & Mannila, 1981; Bultman & Faeth, 1985; Potter, 1985; Faeth, 1990; Price, 1991; Connor & Taverner, 1997). For sedentary insects such as leaf miners that feed on a limited resource for the entire larval stage, the oviposition sites selected by adult females may directly affect the survivorship of offspring. Because leaves are spatially isolated from each other, compe- tition among individuals sharing a particular leaf is likely to occur. Therefore, inter- and intraspecific com- petition may be significant selective pressures for ovipositing site selection by leaf miners. Interspecific *Corresponding author. E-mail: ssugiura@ffpri.affrc.go.jp Biological Journal of the Linnean Society, 2007, 92, 641–650. With 3 figures © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 92, 641–650 641 Downloaded from https://academic.oup.com/biolinnean/article/92/4/641/2701139 by guest on 17 October 2023