RESOURCE QUALITY AND SPATIAL VARIATION IN SEX-RATIOS OF A FREE-LIVINGSOLITARY SAWFLY, DINEURA-VIRIDIDORSATA (HYM, TENTHREDINIDAE)

The sex ratio in final-instar larvae of a birch-feeding, free-living s olitary sawfly, Dineura virididorsata, was investigated in Finnish Lap land. The prepupal proportion of females, pooled over ten sites, was 5 6%, and at four individual sites the sex ratio was significantly femal e-biased. Larval survival from egg to prepupae did not differ between the sexes. This suggests a female-biased primary sex ratio in the fiel d. The sex ratio varied among the sites but not among host trees withi n sites. Contrary to previous results with hymenopterans, we did not f ind that differences in the sex ratio depended on forage quality: site -specific or tree-specific sex ratios did not correlate with the avera ge prepupal weight. A literature search indicated that female-biased s ex ratios are also common in other free-living sawflies. We are unable to explain sex ratios of Dineura virididorsata or other free-living s awflies with existing general models.