MOORE, THE SHOOT BORER OF THE MELIACEAE (MAHOGANIES) OF NIGERIA, TOGETHER WITH BRIEF COMMENTS ON TWO STEM BORERS AND ONE OTHER LEPIDOPTERAN FRUIT BORER ALSO FOUND IN NIGERIAN MELIACEAE

SUMMARY The mahogany shoot borer in Nigeria has been found only to attack one subfamily of the Meliaceae, the Swietenoideae. Attack occurs on shoots, fruits and bark in forest and savanna throughout the country, but flowers are only attacked in the rain forest zone. Though determined as H. robusta Moore there are differences in the biology of this insect in Nigeria when compared to that already described for it in India. Control methods are discussed and it is suggested that biological methods offer better possibilities than insecticides. Very little published literature is available on the shoot borer of the Meliaceae in Africa other than brief mention of the occurrence of the pest in the Annual Reports of different Forestry Departments. In West Africa the shoot borer problem has been recognised for many years, but the only biological information to be found is that given by Eidt (1963) which is very brief and does not consider the problem in the savanna. Eidt takes the view that the shoot borer is responsible for the loss of ten years' growth of Meliaceae grown in the high forest in Nigeria. More details on this insect in Nigeria have been published elsewhere by the author (Roberts 1966). During 1965/66 a special study of the shoot borer has been undertaken in Ibadan. This has taken the form of a field study to determine the distribution, hosts and parasites, covering the whole country, together with breeding studies at Ibadan to find out details of the life history. Large numbers of bred adults have been sent to the Commonwealth Institute of Entomology, London, where Mr. D. J. Bradley has determined them all as Hypsipyla robusta Moore. This insect is the same shoot borer found attacking Meliaceae throughout the Old World Tropics and in Africa it has been reported from Ghana, Malawi and Sierra Leone. While accepting the determination it must be noted that there are a number of marked differences in the biology of the Nigerian form when compared with that of the species in India as described by Beeson (1919). For this reason it may be necessary in the future to assign the Nigerian form a sub-specific rank, or even declare it a different species. In Nigeria H. robusta , as in India, appears to pass through four larval instars, the last instar having the same bright blue-green colour just prior to pupation. Typically, eggs are laid on the very young shoots and the young larvae on hatching bore downwards. When mature the larvae pupate in cocoons within the shoots. In the laboratory it has been found that larvae move from shoot to shoot and this undoubtedly happens in the field as shown by the many empty shoots found there. There is usually only one larva per shoot. Symptoms of attack are frass and silk at the tip of the shoot at first, followed by death of the shoot and subsequent die-back.