The biology and ecology of Hypsipyla shoot borers.

Abstract

The Hypsipyla shoot borers are apparently restricted in their feeding to plants belonging to the family Meliaceae, subfamily Swietenioideae, including the high value timber species of Swietenia , Khaya , Toona and Cedrela . The two most important Hypsipyla species with respect to shoot borer activity are H. grandella (Zeller) occurring in the Americas, and H. robusta Moore occurring through areas of Africa and the Asia/Pacific region. Larvae of these species tunnel in the developing shoots of young trees, and in some regions also feed upon the flowers, fruit and occasionally bark of their hosts. Feeding on these non-shoot plant parts may have a significant impact on the population dynamics of the species. A generation usually takes 1 to 2 months, extending to 5 months if larvae enter diapause. Females mate only once and lay between 200 and 450 eggs over 5 to 8 nights. Adults are strong fliers, able to locate host trees over considerable distances. Egg and early instar mortality are high, however even low levels of feeding can significantly impact on tree form. Shoot-feeding larvae pupate within the stem tunnel or amongst soil and plant material at the tree base. The behaviour of larvae and the sites of oviposition and pupation while feeding on fruit, flowers and bark are less well known, and vary according to the host species and the plant part being eaten. Damage to fruit results in their premature shedding, which is circumvented in some areas by webbing produced by the feeding larva. Larval diapause has been reported from areas of low temperature or low rainfall, and occurs immediately following cessation of fruit-feeding despite apparently suitable climatic conditions. D AMAGE from shoot borers of the genus Hypsipyla Ragonot (Lepidoptera: Pyralidae) presents the greatest deterrent to the establishment and cultivation of the high value timber species belonging to the family Meliaceae, including species of Swietenia , Khaya , Toona and Cedrela . The most serious damage to the tree results from the tunnelling of the larva in the developing shoots. This boring leads to the death of the terminal shoot and subsequent production of laterals, eventually resulting in a stunted, continuously branched and crooked tree of greatly diminished value for timber production. Growth rate is reduced and death can result from heavy and repeated attacks. Damage has been recorded on trees from age three months old and 50 cm height (Beeson 1919, 1941; Kalshoven 1926), up to age 14 years and 15 m height (Froggatt 1923; FAO 1958; Streets 1962; Morgan and Suratmo 1976; Suratmo 1977). The borer is thus a problem to both nursery and planted stock. The Hypsipyla species have attracted considerable attention, with mention in over 300 publications. The great majority of these works focus on the shootfeeding habit of the insect and are directed towards management and control. Although causing greatest economic damage during shoot boring, Hypsipyla larvae also feed upon the flowers, fruit and occasionally bark of their hosts. Few studies have been directed at or even mention the biology and population dynamics of the insect when feeding on these alternative plant parts. This review describes the biology and ecology of the main Hypsipyla species and highlights areas warranting further research.