The biology and ecology of the kola weevil, Sophrorhinus gbanjaensis D. & T. (Coleoptera: Curculionidae)

The biology of the kola weevil S. gbanjaensis were studied under laboratory temperature of 26-28.degree. C and 3 temperature regimes of 25 .+-. 1.degree., 27.5 .+-. 1.degree. and 30 .+-. 1.degree. C. Both mated and unmated females had a pre-oviposition period of 13.3 .+-. 0.5 days. Eggs were laid singly and in special oviposition holes made inside the nut [Cola nitida] by the female. Mated and unmated females oviposited for an average period of 56.0 .+-. 2.2 days and 30.8 .+-. 1.7 days and laid an average of 48.6 .+-. 3.1 eggs and 10.2 .+-. 0.5 eggs, respectively. Under the 3 temperature regimes of 25.degree., 27.5.degree. and 30.degree. C, a significantly higher number of eggs (1304) were laid at 27.5.degree. C when compared with the numbers laid at 25.degree. (686) and 30.degree. C (996). The mean incubation periods of the eggs were 7.9 .+-. 2.3, 5.9 .+-. 1.4 and 5.2 .+-. 0.7 days at 25.degree., 27.5.degree. and 30.degree. C, respectively. There were 5 larval instars. The mean larval periods at 25.degree. and 27.5.degree. C were 29.3 .+-. 4.2 days and 26.5 .+-. 3.3 days, respectively. The mean total periods of development from egg to adult emergence from the nut in S. gbanjaensis at 25.degree. and 27.5.degree. C were 48.4 .+-. 3.5 days and 41.2 .+-. 4.2 days, respectively. Adults of S. gbanjaensis that were allowed to feed and mate freely lived for an average of 71.6 .+-. 3.4 days with a minimum and maximum of 33 and 112 days, respectively. The sex ratios of the laboratory-reared adults of S. gbanjaensis and those that emerged from field-infested nuts were very close to unity. The natural enemies observed were a hymenopterus larval parasite (Ichneumonidae), Phorotrophus mameti; an entomophagous fungus, Botrytis (Beauveria) bassiana and an unidentified mite. Field experiments on the time and sequence of infestation of kola nuts by the kola weevils showed that S.