Preferential infestation of fruits within theMedicago truncatula — M. littoralis (Leguminosae) complex by the bean weevilBruchidius bimaculatus

Abstract

The bean weevilBruchidius bimaculatus was found in fruits of 68 of 217 populations of theMedicago truncatula — M. littoralis complex of Israel, Greece, Italy and Spain. Infestation was higher in fruits of somewhat larger than mean size, and in the more pubescent and tightly coiled fruits. Bean weevil size proved to be independent of fruit size, so that the “preference” for larger fruits does not seem due to adaptation to a larger food source or a larger domicile. Fruit size has been used to delimit the host “species”M. truncatula andM. littoralis, but the character proved to be unimodal, and it is apparent that the taxonomy of the plant complex requires further clarification. Of the 11 472 fruits examined, less than 4% were infested. Given that the plants have evolved indehiscent legumes in which typically only one of the approximately six seeds survives to reproduce, and that very few seeds of a fruit are destroyed, the bruchid's infestation appears to be non-harmful, and indeed the association may be mutualistic.