Effect of Scotch broom, Cytisus scoparius, pod size and patch density on Exapion fuscirostre (Coleoptera, Apionidae) seed weevil oviposition

摘要

Cytisus scoparius (L) Link (Fabaceae) is a broom species of European origin introduced both accidentally and as an ornamental plant to Australia, New Zealand and America, where it is classified as a noxious invasive species. One of its main seed predators is Exapion (Exapion) fuscirostre (Fabricius), a weevil with a Palearctic distribution and which has been introduced to United States and New Zealand as a biological control agent. Factors influencing the insect's choice of oviposition location are crucial for the plant's reproductive success. We examined E. fuscirostre oviposition on the host plant, C. scoparius, in the European Mediterranean region. We analysed the effect of pod size, seed abortion rate and host plant patch density on seed infestation rate. Oviposition was greater in patches with low-medium plant densities. Oviposition was also negatively related with seed abortion rate per pod and the rate of infestation by other seed-eating insects. Pod dimensions, particularly width, were positively related with E. fuscirostre oviposition.