Virulence of a New Isolate of Cytoplasmic Polyhedrosis Virus against the Red Palm Weevil, Rhynchophorus ferrugineus (Oliv.) (Order: Coleoptera, Family: Curculionidae)

The red palm weevil (RPW), Rhynchophorus ferrugineus (Oliv.) is a serious pest of date palms and causes substantial losses worldwide. Due to its hidden nature of habitat, managing this pest is extremely difficult. This study reveals a new biological control agent that is beneficial for controlling this pest. In the laboratory, the virus was isolated from a colony of diseased larvae; the median lethal dose (LD50) and median lethal time (LT50) of this virus were determined, and the biological activities of the virus were assessed. Microscopic examination of the diseased larvae provided an evidence of the presence of polyhedral inclusion bodies (PIBs) in all typical tissues where the virus is known to develop. Electron microscopic examination revealed various shapes of polyhedra, most of which were hexagonal and tetragonal. Experiments were conducted to investigate viral propagation and virulence against different larval instars. The results showed that the initial infected dose (5×103 PIB/larva) increased to 600×109 PIB/larva. The LT50values decreased as both viral concentration and larval age increased. Moreover, the percentage of larval mortality significantly increased as larval age increased. It can be concluded that a viral dose of 80×106PIB/ml is sufficient and adequate for suppressing weevil population.