Pest beetles affecting Acacia tortilis in Tunisia: infestations and control methods

Acacia tortilis subsp. raddiana, a species endemic to the arid region of Tunisia, has been protected since 1980 following the establishment of Bouhedma National Park. Its natural regeneration is limited by predation on its seeds by two species of weevils (Coleoptera: Bruchinae): Bruchidius aurivillii and Bruchidius raddianae. This study has shown that the rate of seed infestation by these two weevils varies from year to year. Thus, the seed infestation rate by B. aurivillii fell from 74.54 per cent to 38.5 per cent between 2008 and 2009, whilst that of B. raddianae rose from 24.53 per cent to 63.27 per cent over the same period. Both are monovoltine species and their emergence is closely linked to the phenology of their host plant. Furthermore, several parasitoid Hymenoptera of these seed borers were identified during this study, including members of the families Pteromalidae, Eulophidae, Eupelmidae and Trichogrammatidae. Finally, two methods of mechanical and chemical control were tested in the park and proved effective, opening up possibilities for controlling these two seed-feeding pests.