TheSitona [Col.: Curculionidae] species occurring onMedicago and their natural enemies in the Mediterranean region

Abstract

TwentySitona species were found in the Mediterranean region during surveys on 17 volunteer and/or cultivated species ofMedicago. The distribution of the weevils was analyzed using the 3 concepts of abundance, constancy and dominance. EightSitona species were consistently recorded on lucerne and medics; of these, 3 were “constants” and only 2,S. humeralis Stephens andS. lineatus Linnaeus, also “dominants” in the sites investigated. Sixteen species of natural enemies were identified (table 4), including 3 egg predators, 3 egg parasitoids, 1 entomogenous fungus, 2 nematodes and 5 parasitoids of adult weevils. The effect of each organism on theSitona population numbers was slight, not exceeding in most cases an average mortality of 15%. At high host densities however, the braconidMicroctonus aethiopoides Loan which is the preponderant parasitoid, caused estimated mortalities up to 80% during a single weevil generation. Noticeable changes in the relative importance of the natural enemies were observed between the areas surveyed, with onlyM. aethiopoides and the mymarid egg parasitoidPatasson lameerei Debauche occurring widely. Moroccan, French and Greek strains of these 2 parasitoids were forwarded to Australia for the biological control ofS. humeralis there.