Interactions between Apion species (Coleoptera: Curculionidae) and Polygonaceae. I. Apion curtirostre Germ, and Rumex acetosa L.

Apion curtirostre is the commonest weevil attacking Rumex acetosa in the Lancaster area. The ovipositional behaviour, larval development, emergence and hibernation of A. curtirostre are described. From dissection of samples of stems of R. acetosa , abundance curves for the stages of A. curtirostre and its chalcid parasitoids were constructed and the between‐stage mortalities determined. There is an exponential relationship between R. acetosa stem height and number of A. curtirostre eggs laid. Male stems of R. acetosa appear earlier and are smaller than female stems. Taller stems, at least in female plants, live longer than shorter ones. Apion survival is lower in male than in female stems. Stem sex is the primary determinant of opposition choice with stem thickness a secondary determinant. A. curtirostre eggs introduced experimentally into stems of four Rumex species survived significiantly better in R. acetosa than in any other species. Survival in R. acetosa female plants was twice that in males. Survival of A. curtirostre eggs at densities of 4, 8 and 16 per R. acetosa stem was twice that at densities of 32 and 64 per stem. The stem size of female R. acetosa was reduced as the number of attacking weevils increased. There was no significant effect in males. No adverse effect on seed production was detected. The nature of the relationship between A. curtirostre and R. acetosa is discussed.