Larval food source promotes cyclic seasonal variation in polyandry in the moth Lobesia botrana

In Mediterranean vineyards the European grapevine moth, Lobesia botrana, usually completes three non-overlapping larval generations per year. Larvae feed on inflorescences and unripe or ripe grapes. Previous work has shown that the larval food source has a huge effect on adult size and fitness. We investigated if larval food also affects the propensity of females to mate polyandrously. Levels of polyandry were monitored with baited traps in a vineyard for two years and then compared with data from laboratory trials using vine-reared individuals. In the field, polyandry levels followed a cyclic annual pattern associated with the larval food source. Large females that fed on ripe grapes exhibited significantly higher levels of polyandry than smaller females that fed on inflorescences. Females that fed on unripe grapes showed intermediate levels of remating. Polyandry also tended to increase later in each flight. Laboratory trials confirmed a direct effect of larval feeding on levels of polyandry. Overall, these results showed that the seasonal variation in polyandry exhibited by L. botrana in the field occurs, at least in part, because of food-derived changes regulating female size. Results also suggested that larval feeding could shape sexual size dimorphism and polyandry levels. Larval nutrition should therefore be considered as an important ecological factor by those studying the evolutionary significance of polyandry and sperm competition in the Lepidoptera. Copyright 2005.