The effect of Caryedon serratus Olivier (Col., Bruchidae) on viability and germination of seeds of Acacia nilotica (L. Willd. ex Del.) in the Sudan

Abstract

Seeds of Acacia nilotica (L. Willd. ex Del.) were sampled from the standing trees, the forest floor and in storage facilities, for infestation by insect-seed borers in the Blue Nile Province in the Sudan. Higher rates of infestation by the larvae of the seed weevil Caryedon serratus Olivier (Col., Bruchidae) were recorded. The larvae of C. serratus bore into the seeds via small holes and feed on the embryo and the endosperm, leaving all infested seeds non-viable. As the seeds are the only means of regenerating A. nilotica forests, infestations by the seed weevils present a serious problem. Generally, the mean infestation rate was extremely high in stored seeds (80–90%), moderate in pods on the forest floor (20%) and least in pods from the standing trees (10%). The results confirmed that C. serratus is a serious pest of stored seeds (Howe, 1952; Amaro, 1958; Green, 1959; Cancella de Fonseca, 1964). The mean infestation rate was significantly ( P = 0.05) higher in pods on the forest floor than in pods from the standing trees. In Wad Dabkara forest, the mean infestation rate was 10.7% and 11.1% in pods from the standing trees in gerf and maya site types, respectively, whereas the mean infestation rate was 17.2% and 16.7% in pods on the forest floor in gerf and maya, respectively. In Wad El Guzuoli forest, the mean infestation rate was 10.8% and 12.5% in pods from the standing trees in gerf and maya, respectively, whereas the mean infestation rate was 16.6% and 17.6% in pods on the forest floor in gerf and maya, respectively. Examination of stored seeds revealed extremely higher infestation rates of 87.8%, 87.6% and 90% of the total number of sampled seeds stored in Sennar, Singa and Wad Medani, respectively. Germination test results have shown that all infested seeds failed to germinate compared with uninfested seeds which gave normal germination. The study suggests collection of good quality insect-free seeds for storage, and treatment of seeds with a suitable contact insecticide or a fumigant to provide further protection during storage. Spraying the seeds or pods in the field is not recommended as the pods are used as a local medicine (probably because of their high tannin content) and they are also an important source of fodder for animals, especially during the very dry and hot summer season.