Abstract 1. For insect herbivores the quality of the larval host plant is a key determinant of their fitness. Only little attention, however, has been given to the effects of plants on mating success of males and its consequence for the reproductive output of their mates. In addition, almost all the studies that have investigated the influence of host plants on herbivore fitness components have been done in the laboratory, and less is known of these effects in natural conditions.
2. Using the phytophagous European grapevine moth (Lobesia botrana Den. & Schiff., Lepidoptera: Tortricidae), we tested the influence of grape cultivars as larval food on the probability of acquiring a mate for both sexes, and on the reproductive output of females and males.
3. Results from this study stress the importance of larval host plants on the reproductive success of both sexes. Larval diet differentially affected mating success and reproductive output of male and female moths. Fecundity, egg size, and egg hatchability were significantly different when larvae were fed on particular grape cultivars.
4. A given cultivar that is of poor quality for females is generally also of poor quality for males. A cultivar, however, could be suitable for females but not for males and vice-versa. Apparently, the nutrients required for adult reproduction are not necessarily the same for males and females.
5. The important conclusion from this study is that evaluating the differential effect of host-plant species on traits associated with reproductive success of herbivores requires that the effects on both sexes be taken into account.