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

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Table 2. Native and exotic tree species of Meliaceae subfamily Swieteniodeae planted in Ghana (Forest Products Research Institute, Ghana, Annual Reports 1969–1979). Tree species Origin Present area planted (ha) excessive shade, while the Taungya system restricted the farmers’ choice of crops and gave the farmers no stake in the trees, as a result of which tending operations were not well executed. Other reasons for plantation failures include fire, poor seed sources, poor species-site matching, inappropriate choice of species, and pests and diseases. The main plantation species that have been grown with some success are exotics such as Tectona grandis L., C. odorata and Gmelina arborea Roxb. (Table 3). Overall establishment success of all species was generally poor, however they were particularly so for native Meliaceae, of which only 9 per cent survived. Table 3. Principal tree species in plantations and survival rate in Ghana (Forestry Department, Planning Branch 1992). Tree species Area planted (ha) Survival (%) Tectona grandis L. 25 800 34 Cedrela odorata L. 7 900 39 Gmelina arborea Roxb. 6 500 58 Mansonia ultissima A. Chev. 3 000 22 Native Meliaceae 2 400 9 Triplochiton scleroxylon K. Schum 100 20 Terminalia ivorensis A. Chev. 150 27 Eucalyptus spp. 2 000 n/a Although the poor establishment of all species in Ghana was largely due to fire, the particularly high failure-rate of plantations of native Meliaceae has been attributed to shoot borer attack (Ofosu-Asiedu, et al. 1991). Shoot borer also resulted in slow growth and poor form (Britwum 1976). Similarly, planting of the exotic Swietenia spp. has been discontinued due to poor fire tolerance and serious shoot borer attack: the trials invariably failed through die-back resulting from shoot borer attack and fire (Ofosu- Asiedu, et al. 1991). Roberts (1966) lists native and exotic Meliaceae that are susceptible to H. robusta in West Africa. The only member of the sub-family Swieteniodeae 60 Present planting rate (ha/Year) of which there is no record of attack by the shoot borer in Ghana is the exotic C. odorata, which is one of the most successful plantation species (Table 3). In Ghana, C. odorata is a fast growing tree and at Pra-Anum, which is in the moist semi-deciduous forest zone with an annual rainfall of 1200–1800 mm, sample plots in a 20-year old plantation had an average height of 39.9 m (Nkansa-Kyere 1974). No pests or diseases of importance have ever been reported on C. odorata although the plant is susceptible to attack by ambrosia beetle Doliopygus condradti Strohm. (Platypodidae), especially during long, dry periods (Wagner et al. 1991). Recently, the Forestry Department has recognised the increasing interest of individual farmers and community associations in plantation establishment and is promoting woodlot establishment on private land and farms through the Collaborative Forest Management Unit. In addition, several private companies have embarked on large-scale, commercial planting of exotic species outside the Forest Reserve. However, efforts by foresters to plant indigenous Meliaceae and Swietenia species in the various countries of West Africa have been frustrated by H. robusta damage and there are currently no plans by the Forestry Department to plant these species in plantations (Table 2). Only one company, the Swiss Lumber Company in the southwest region, has recently invested in planting indigenous Meliaceae. Hypsipyla Research in Ghana Optimal rotation length (yrs) K. ivorensis A. Chev. Native 2400 Planting ceased in forest reserves Not known E. utile (Dawe & Sprague) Sprague Native 2400 Planting ceased in forest reserves Not known E. cylindricum (Sprague) Native 2400 Planting ceased in forest reserves Not known E. angolense (Welw.) DC Native 2400 Planting ceased in forest reserves Not known Cedrela odorata L. Introduced 7900 50 About 40 yrs Swietenia humilis Zucc. Introduced 0 Planting ceased n/a S. macrophylla King Introduced 0 Planting ceased n/a The research into H. robusta in Ghana is summarised in Table 4. The Forestry Research Institute of Ghana (FORIG) have successfully reared H. robusta on an artificial diet and described the stages of the life cycle (Atuahene and Souto 1983). The medium used was the McMorran Grisdale Diet (MGD) generously supplied by Prof. G.I. Gara of the College of Forest Resources, University of Washington, USA. The results revealed differences in the life cycle of H. robusta from those reported in Nigeria (Roberts 1966) and Ivory Coast (Couillard and Guiol 1980).
A number of parasitoids have been bred in the laboratory from field-collected insects (Atuahene and Souto 1983). Parasitoids collected from Hypsipyla spp. in West Africa include Braconids, Eulophids, and Tachinids among others (Roberts 1966, Atuahene and Souto 1983). A parasitic nematode, probably Hexamermis sp., is also common in Ghana. The specific names of most of these parasites have not been determined, and their effects on the pest population are yet to be studied. Table 4. Summary of current and past research effort on various aspects of Hypsipyla spp. biology and control. – none; * minor; ** major. Area of study Current research In the context of developing strategies for integrated pest management of H. robusta in Ghana, FORIG has collaborated with the Dept. of Zoology, University of Oxford on the potential use of insect pathogenic viruses to control mahogany shoot borers (Hauxwell 1997). Larvae were collected from the shoots of K. ivorensis in FORIG’s research nursery at Mesewam in the moist, semi-deciduous forest zone, and from a 5-year-old plantation at the Swiss Lumber Company in Manso Amenfi in the south western moist evergreen forest zone. Larvae were reared on modified tobacco hornworm diet, a general-purpose diet for lepidoptera, emerging adults were preserved for species identification and dead larvae were preserved by freezing and subsequent examination for baculoviruses (Hauxwell 1997). Research Requirements 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 In studies involving the use of artificial diets we have observed high incidence of insect mortality (10–70%) among young instar larvae due to non- 61 feeding, a high incidence of infertile eggs, and low pupal widths and weights (Atuahene and Souto 1983). Future research must look into perfecting a diet for rearing H. robusta. The taxonomy of H. robusta is still not fully understood in West Africa. Entwistle (1968) states that H. robusta probably comprises several races and subspecies. Recent collections from Ashanti and Western Regions of Ghana (Opuni Frimpong and Atuahene, unpublished data) confirmed that the taxonomy of Hypsipyla requires further investigation. While a few natural enemies have been collected, most have not been sufficiently described and their effect on the H. robusta population is not known. The occurrence, impact and possible manipulation of natural enemies should be further investigated. Brunck and Mallet (1993) emphasised the need to bring the experience gained in Latin America and Europe together with work in West Africa, particularly on the selection of resistant or tolerant stock. Recent work in Latin America has identified partial resistance to H. grandella within S. macrophylla and C. odorata (Newton et al. 1993). Although no work has been conducted on resistance in the Meliaceae in Ghana, experience of similar research in other systems support the use of such an approach. Cobbinah (1990) has demonstrated that considerable variability exists in intensity of infestation of seedlings of Milicia spp. by the noxious psyllid, Phytolyma lata (Walker), thus presenting an opportunity for control of the psyllid. Conservation of the germplasm of West African Meliaceae is urgently required before the loss of the natural forests further depletes genetic diversity. FORIG, in collaboration with the Ghana Forestry Department Planning Branch, the Institute of Terrestrial Ecology and Edinburgh University in the UK, have proposed the development of an integrated pest management strategy. The proposed strategy is based on the incorporation of pest resistant planting stock in silvicultural systems to reduce H. robusta impact (Atuahene et al. 1996). This proposal was submitted to the International Tropical Timber Organisation (ITTO). Conclusion Since plant resistance or any other method alone is unlikely to reduce the impact of Hypsipyla spp. to less than economic levels, an integrated pest management strategy is recommended (Newton et al. 1993). In order to implement and effective integrated programme of H. robusta management in West Africa we need to build the capacity to research the critical issues of its biology. Research efforts should then:
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Mayhew and Newton (1998) have revie
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