Hypsipyla Shoot Borers of Meliaceae in Sri Lanka - Australian ...

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The life history and phenology of H. robusta varies depending on the host plant and climatic conditions. In temperate and subtropical regions, five generations have been reported with different generations feeding principally on flowers, fruit or shoots (Beeson 1941). In Southern India, the population is more or less continuous with overlapping generations (Mohandas unpublished). Incidence of the pest is confined generally to younger plantations while older trees are almost free from attack. This may be because adult moths are poor fliers and may find it difficult to reach tall trees for oviposition. The difference in the chemical composition of the shoots of mature and young trees may also affect the moths oviposition preference. General observations indicate that borer incidence is greater during the monsoon season. However, data on the incidence of the pest in relation to environmental factors have yet to be generated. Detailed investigation of the population dynamics of H. robusta under different climatic zones is also required. Heavy damage to young saplings of Swietenia spp. in plantations has been caused by larvae of H. robusta boring into the tender shoots. Larvae have also been recorded feeding on the inflorescences and fruits of T. ciliata with distinct shoot, flower and fruit feeding generations. The larvae usually feed under the protection of a loose silken network. It is noted that a single larva can bore into more than one shoot during the course of its development. H. robusta damage is heaviest in young plantations. Older trees are generally free from attack. Although H. robusta attack rarely causes death of saplings, tree growth and form can be severely affected. Repeated attacks on the terminal shoots will cause forking and result in crooked stems. H. robusta can also cause considerable loss of seeds in T. ciliata and X. moluccensis (Sen-Sarma 1981). Reliable, quantitative data on the severity of damage and resulting growth loss are not available. Methods of Control Attempts to control H. robusta using conventional insecticides have been made in the past (Beeson 1941). Screening of new insecticides, especially systemics, is being conducted for short-term control (Mohandas unpublished). The hidden nature of the insect is an obstacle for effective management through chemical means. Although chemical control may become useful in extreme circumstances, its scope for large-scale application under operational conditions is limited. H. robusta has a rich natural enemy complex (Browne 1968; Rao and Bennet 1969; Ramaseshiah and Sankaran 1994). Initial studies were made in 8 India by the Commonwealth Institute of Biological Control (CIBC now IIBC) at Bangalore. Nearly 50 parasite species belonging to the orders Hymenoptera and Diptera have been reported (Rao and Bennet 1969). Some of the most important parasites are Trichogrammatoidea robusta Nagaraja, Aptesis latiannulata (Cam.), Tetrastichus spirabilis Wtstn. and Antrocephalus destructor Wtstn. A survey of H. robusta parasites in southern India revealed Apanteles stennos Nixon and Agathis sp.nr. corphye Nixon to be effective parasites (Ramaseshiah and Sankaran 1994). A nematode parasite of the genus Hexamermis has also been recorded from different locations. The highest level of parasitism was noticed during the monsoon season. It appears that many of the naturally occurring parasites can limit the pest population to some extent. No microbial pathogens have been recorded so far, although, the suitability of Beauveria tenella (Delacroix) as a pathogen of H. robusta has been reported by Kandasamy (1969). A more intensive search for pathogens would be worthwhile. A number of silvicultural control options have been suggested from field observations. It has been found that saplings naturally regenerating under the shade of mother trees incur very little H. robusta damage. Thus, providing overhead and lateral shade has been suggested as a silvicultural method to reduce H. robusta incidence. Pest incidence also appears to be higher in monocultures than in mixed plantings, and higher in open rather than the shaded conditions. These observations and hypotheses need to be tested through field experiments. Research Needs and Future Directions A summary of the research effort into various aspects of the biology and control of H. robusta in India is given in Table 1. Given that H. robusta is a limiting factor for successful establishment of Swietenia spp. plantations, the following research priorities are suggested: • studies on H. robusta incidence and damage in relation to the age of the crop to assess the economic impact; • field trials in different locations to establish the effectiveness of shade and mixed planting as a possible silvicultural management method to reduce pest incidence; • studies on the pheromones of H. robusta for monitoring and mass trapping; • pathogens associated with H. robusta; and • detailed studies on the population dynamics of H. robusta.
Table 1. Summary of current and past research effort on various aspects of Hypsipyla robusta (Moore) biology and control. Area of study Current research – none; * minor; ** major Conclusions Historical research Biology Taxonomy – * Life history * ** Ecology in natural stands – * Ecology in plantations – * Population dynamics – * Natural enemies * ** Other Control – – Biological control – * Chemical control – – Silvicultural control – * Provenance trials – – Pheromone studies – – Genetic engineering – – Other – – Studies of H. robusta in India show that it is a serious pest both on native and exotic Meliaceae. Measurements of the loss of timber production caused by H. robusta and the relative impact of H. robusta on plantations of native and exotic species of 9 Meliaceae are required in order to assess the need for control. The observations that shaded and mixed plantations appear to be less prone to H. robusta attack need to be tested experimentally. References Achan, P.D. 1968. Preliminary observations on the development of an artificial diet for Hypsipyla robusta (Moore). CIBC Technical Bulletin, 10: 23–26. Beeson, C.F.C. 1941. The Ecology and Control of the Forest Insects of India and Neighbouring Countries. Dehra Dun, Vasant Press, 767 p. Browne, F.G. 1968. Pests and diseases of forest plantation trees. Clarendon Press, Oxford, 1330 p. Kandasamy, D. 1969. Hypsipyla robusta (Moore), a new host for Beauveria tenella (Delacroix) Siemazko. Journal Invertebrate Pathology, 13: 149–150. Lal, J.B. 1989. India’s Forests, Myth and Reality. Nataraj Publishers, Dehra Dun, 304 p. Rao, Y.S. 1994. Forestry profiles. Forest News, 7: 1–3. Rao, V.P. and Bennett, F.D. 1969. Possibilities of biological control of the meliaceous shoot borers Hypsipyla spp. (Lepidoptera: Phycitidae). Commonwealth Institute of Biological Control. Technical Bulletin, 12: 61–81. Ramaseshiah, G. and Sankaran, T. 1994. Studies on some parasites of the meliaceous shoot borer Hypsipyla robusta (Moore) in South India. Hexapoda, 6: 39–46. Sen-Sarma, P.K. 1981. Recent advances in forest entomology in India. In: Ananthakrishnan, T.N., ed., Recent advances in entomology in India. Entomology Research Institute, Madras. 65–72.
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