By
Thomas R. Odhiambo
The International Centre of
Insect Physiology and Ecology (ICIPE)
P.O. Box 30772
Nairobi, Kenya
In January 1968, the pine woolly aphid, Pineus pini (L.), long known as an important pest in the northern temperate zones of North America, as well as central and southern Europe, was reported for the first time in Zambia. It appeared to have been accidentally introduced there, as it had earlier in South America, Australia and Japan. Soon afterwards, in November of the same year, P. pini was discovered in the plant quarantine station at Muguga, Kenya, on scions of Pinus caribea var. hondurensis Loock. obtained from Australia. By January 1969, it was clear that plantations of pines in Muguga and its environs were heavily infested by this exotic aphid pest, and that it was spreading in all directions from Muguga. Two isolated pine woolly aphid outbreaks were soon reported in seed orchards of West Kilimanjaro in Tanzania and in the southern highlands of Sao Hill in Tanzania. These outbreaks were devastating (Odera 1972)
The injury due to the pine woolly aphid consists of a characteristic die-back of the leading shoots, the young needles then turn yellow to red, the older needles drop off prematurely, and the bark tissues deteriorate, resulting in both stunting and slowing down of growth in thickness of the infested trees. In a final scenario, the tree may die. Death of a tree is gradual, usually progressing from the top to the base, and from the outside to the centre of the crown. The aphid pest has the capacity to kill a healthy tree, probably through the toxic effects of its salivary secretion (Odera 1972, 1991). By 1972, the infestation by this aphid pest had covered about 1,400 ha in Kenya, and about 800 ha in Tanzania; and there was the prospect that it would continue its dispersal in all directions, and to colonise all favourable habitats supporting its pine hosts, which number 35 species (Odera 1972). The damage due to P. pini is highly visible and most unsightly, and led to public panic at such devastation, particularly for the plantations of Pinus kesiya and P. patula.
Barely a decade after the very first accidental introduction of the pine woolly aphid with pine scions arriving from extra-continental sources, a second exotic aphid pest was reported in Zambia, Zimbabwe and South Africa in the late 1970's (Odera 1991). The pine needle aphid, Eulachnus rileyi William, is native to European and North American forest pines. It may well be spreading into Eastern Africa, having been reported in Malawi in 1986 in the Dedza forest. By 1991, it was occurring in most forests in that country. In late 1990, it was reported in Kenya for the first time, and may have spread to other eastern African countries by now (Odera 1991).
A very active aphid, E. rileyi feeds on the underside of pine needles, causing yellowish mottling, which eventually leads to the dropping off of the affected pine needle, particularly those of P. patula, P. kesiya and P. oocarpa.
Public alarm in Eastern and Central Africa has recently been further peaked by the accidental introduction of yet another exotic aphid pest, the European cypress aphid, Cinara cupressi (Buckton). The third, and undoubtedly the most devastating of all the exotic aphid pests of softwood plantations in Africa, the European cypress aphid was first discovered in Malawi in 1986, in the Viphya Forest area of northern Malawi. It then spread southwards to reach the Mulanje area in 1988 (Van Rensberg 1989), attacking three main tree species in both forest plantations and urban centres (such as Mzuzu city): cypress, Cupressus lusitanica, Bhutan cypress C. torulosa, and Mulanje cedar, Widdringtonia nodiflora (Odera 1991). The European cypress aphid has quickly spread throughout Southern and Eastern Africa, including Zimbabwe, Tanzania, Burundi, Rwanda, eastern Zaire, Uganda and Kenya. Indeed, while it is not a pest in its native Europe, it has rapidly established itself in Africa (Odera 1991) and Israel (Mendel 1983) as a most devastating cypress pest. Once attacked by this pest, the tree inevitably dies.
The public concern is, first, that the indigenous Mulanje cedar, W. nodiflora, is the national tree of Malawi, while it yields an attractive and valuable timber, and it is termite resistant. Second, that both the Mulanje cedar and the exotic cypress, C. lusitanica, while grown in large plantations and as social forestry stands, are also extensively grown in Eastern Africa as hedges, both in the countryside and in urban centres. Thus, the sudden death of the infested trees of these two species leaves the dead trees as highly conspicuous, and are perceived as grossly unaesthetic to the society because of the patchy, uneven attack and the sooty mould of infested trees. These aesthetic losses, in the words of Rensburg while working in Malawi, are "considered by many officials to be at least as serious as the damage to forest plantations" (Van Rensburg 1988).
In this latter respect, the softwood forests in Malawi, first created in 1930, provide the bulk of the national requirements for wood fuel, support a considerable labour force (directly and indirectly), provide a large proportion of the industrial timber requirements and other forest products, and were created primarily to act as protectors of the water catchment areas (Odera 1991). In the larger African region as a whole, a similar level of importance would be assigned to the forests. In Kenya, 1.5% of the gross domestic product (GDP), or Kshs. 1.3 billion of the value-added, was derived from products from Kenya's own forest products, as compared to 5% of GDP in the value-added derived from Kenya's agricultural sector in the same year. Over 300 licensed sawmills and 4 plywood mills in Kenya supply 30 million cubic metres of roundwood each year for building wood-products, fuel wood, charcoal, and pulp and paper. Over 35,000 people are employed in the forestry sector in Kenya (The World Bank 1990). Kenya's investment in forestry is therefore of direct economic consequence, apart from its other crucial importance in the ecological biosphere of the country, including its vital national importance in the soil management and water conservation strategies. As a consequence, it is not surprising that the Kenya Government is preparing for the launching of a comprehensive, long-term Forestry Master Plan, which will include the improvement of the conservation of indigenous forests, and the promotion of tree-farming by farming households on a pilot basis (The World Bank 1990). Parallel to this effort, is the development of the Strategic Plan for Research and Development, 1989-2000, which the Kenya Forestry Research Institute (KEFRI) launched in 1990 (KEFRI 1990).
The crux of the matter is that, at present, there is no effective control of any of the three exotic aphid pests of softwood forests in Africa (Department of Forestry (1989). The first reaction to the unexpected emergency, that was caused by the outbreak of the pine woolly aphid in 1968, was to call for the extermination of this exotic pest before it spread and became established as an endemic problem. Kenya launched such a scheme in Hay 1969, in spite of entomological advise to the contrary, and without an exact knowledge of the prevailing geographical spread of the woolly aphid (Odera 1972). The programme consisted of the enforced felling of all species of pines in the two administrative divisions (Kikuyu and Limuru Divisions) immediately surrounding the original source areas in Muguga, burning them in toto, and charring of logs prior to transportation to the sawmills. The eradication programme was gazetted in the Legal Notice No. 163 of June 1969, and was intended to create a stop-gap barrier between the Muguga infestation focus, and the pine plantations at the Uplands and all other areas in Kenya (Odera 1972). The eradication schedule was initiated in Nay 1969, and was completed in May 1970, by which time all the pine trees had been completely removed from the declared zone. Nevertheless, it transpired by October 1969 that incipient infestations were already firmly established in the neighbouring areas. In the graphic words of the Chief Forest Entomologist at that time, Jeff Odera (1972), he averred that even with the extension of felling and burning of infested pine stands in these areas outside the declared zone, the results were completely disappointing: "in spite of this heroic work, extermination or even reasonable control has not been secured" (Odera 1972). The practice was abandoned.
The signal failure of this extermination approach to pest control - a scorched earth strategy- is not unlike a similar, simplistic militaristic approach, which had imbued tsetse control for the first half of this century. These classical control methodologies consisted of three main components: bush clearing (in order to destroy the favoured habitats of these disease vectors); the elimination of wildlife as potential disease carriers (by killing the source of blood meal which is the sole source of food for the tsetse); and the application of chemotherapy and chemical insecticidal control (to suppress the vector population, and to therapeutically treat the disease or provide a prophylaxis). None of these technologies have worked for long or in a sustainable manner. For instance, the re-invasion of previously tsetse-cleared areas has occurred repeatedly many times, thus necessitating the spraying of insecticides again and again. As I recently stated (Odhiambo, 1990):
"I believe that the failure (of classic tsetse control) has rested heavily on our almost complete reliance on a militaristic approach to teste vector control. We have been utterly simplistic about the technologies we have constructed to fight tsetse, and we have considered tsetse as an easy target to deal with. Our scorched-earth strategy has simply lacked good intelligence on tsetse."
What we therefore need in our sustainable management strategies for our exotic aphid pests, as has been decisively demonstrated in tsetse control in recent years, is a knowledge-rich management strategy, whose strength is the comprehensive understanding of individual pest species and their holistic world (Odhiambo 1990).
Let us take this knowledge-rich management strategy as our own philosophy for putting together a rational, efficacious system for the control of these three aphid pests, a system which would also be ecologically sustainable, economically feasible, and long term. In this case, therefore, we - the R&D community, the policy- and decision-makers, the donor and financial community, the forestry community, the farming families, and the general public as a whole - need to agree on at least four principles:
First, we need to have the scientific and technological specialists who will mobilize their dedicated efforts in order to garner together a knowledge pool on the critical issues of the life and biology of these exotic aphids in their newly adopted tropical and sub-tropical environments, away from their native temperate habitats. These efforts are in the nature of endeavouring to understand the intimate relationships of these pests with there tree hosts; their relationships with other insects, natural symbionts and enemies; their colonization and dispersal strategies as they lead to their contemporary distribution; their population dynamics; the nature of their virulence, as well as the genetic and biochemical bases for it; and the physiological potentials that each of these species does possess which may regulate the phenomenon of their naturalization to the various genetic variants of the softwood species which each aphid pest species normally colonizes.
Second, we need to lay the scientific foundation for a menu of aphid management technologies that would, in time, build up into an Integrated Pest Management (IPM) system for these aphid pests.
Third, we need to give the prime responsibility for leadership in scientific research, technology development, technology validation and extension, and finally IPM implementation, squarely to the national forestry research and extension service. International institutions, technical assistance agencies, and the donor community have undoubtedly an important role to play, including that concerned with agenda setting; but there should be no doubt where the responsibility for leadership lies. In the case of Kenya, we are most fortunate that we have an R&D institution, KEFRI, which has developed a first-class base for its priority programmes since its founding scarcely four years ago; and it has a strong interactive relationship with its national partner, the Forestry Department. National responsibility for leadership is vital in this case, more even than in the case of agriculture, because of the long time-horizons we have to deal with in any major programme concerning trees.
Fourth, we have realised more than ever before, that all three exotic aphid pests are a continental regional problem, even though each original infestation might have started from a single focus. Our control approaches must therefore consider - as a backdrop to R&D efforts - the regional implementation of the management process, if sustainability of aphid control is to be achieved in a reasonable amount of time. Indeed, the sort of regional approaches that have become accepted for the control of the migrant pests -such a locusts, for the African armyworm and quelea birds - might well be amenable for consideration in respect to the softwood aphid pests.
One of the immediate limitations that are obvious, yet imperative for the long-term, is the dearth of highly trained specialists at the national level. The Kenya Forestry Project (1990) points to the fact that Kenya did not have whatsoever, until recently, the training of specialists in forest protection (The World Bank 1990); and, indeed, the KEFRI Strategic Plan has endeavoured to put some figures for training needs of specialists in the current decade (KEFRI 1990). The International Centre of Insect physiology and Ecology (ICIPE) is well placed to assist in this respect. Together with 18 universities in Africa, including Moi and Kenyatta Universities in Kenya, the ICIPE participates in a highly effective regional training programme for the Ph.D. degree in Insect Science. The African Regional Postgraduate Programme in Insect Science (ARPPIS), established in 1983, admits 10-15 postgraduate scholars each year; and turns out 3-4 years later a cadre of highly motivated, well trained PH.D graduates, who have learned and researched within a relevant environment. Sub-Regional Centres for the Masters Degree in Insect Science are being set up in several regions of Africa. It has been decided that the first three such centres will soon start operating at the University of Zimbabwe, at Harare (for southern Africa); University of Ghana, at Legon, Accra (for West Africa); and the Dschang University Centre in Cameroon (for French-speaking Africa as a whole). The mission to recommend a suitable campus for the Sub-Regional Centre for Eastern and North-Eastern Africa has just completed its work; and a decision on the campus will be made later this year. This graduate training programme, as well as others that could answer to the specific requirements of forest protection, should be supported on a long-term, continuing basis - not simply on a one-time emergency footing.
One should not consider that these forest protection specialists are only needed at KEFRI and the Forest department. They are also needed in the policy arena (in the central planning units of Ministries of the Government), in the forestry plantation sector (to assist in the effective management of healthy, productive plantations), in the industrial sector (as extension agents), and even in the career diplomatic corps (as science attaches among our neighbours, as well as in foreign continents). We need to see the totality of our priority requirements in specialized training sketching over the next 3-4 decades. this strategy requires that our new-style specialists are taught by those who passionately believe in the science of IPM, are relevant to that environment, and are sensitive to the politico-socio-economic climate of the society itself. Page Smith, in his recent book, Killing the Spirit (Smith 1990), has a pertinent message for us:
"There is no decent, adequate, respectable education, in the proper sense of that much abused word, without personal involvement by a teacher with the needs and concerns, academic and personal, of his/her students. All the rest is "instruction' or "information transferral", "communication technique", or some other impersonal and antiseptic phrase, but it is not teaching and the student is not truly learning."
One of the baffling enigmas concerning the three exotic aphid pests is that we have little understanding why that aphids are so devastating to softwood trees when they are in Africa, as contrasted to their behaviour in their native home in the temperate regions, nor do we know what makes them as devastating. There is some speculation that it could be a toxin in the salivary secretion of the aphid, as Mills (1990) speculates in respect to the European cypress aphid.
"Such dramatic responses (dieback in Cupressus as a direct result of aphid feeding) are unusual and probably indicate the involvement of toxic aphid saliva or hypersensitive reactions of the cypress trees"
Furthermore, the devastation resulting from aphid infestation, which often results in the stunting and loss of the thickening of tree stems is yet another enigma, according to the experiment undertaken in Kenya during the early emergency of the pine woolly aphid, the artificial defoliation of pine trees, by amputating the needles near the distal end of the needle sheath using scissors, does not reduce the height or diameter growth rates of the experimental pines in any significant way - unless the defoliation reaches 100% for a whole year (Austara 1970). Consequently, the loss of needles alone os not an adequate factor in mounting intervention measures against aphid pests.
Finally, several observers have noted the fact that there is a tremendous variation in severity of attack within affected stands of almost ant softwood stands attacked by any of the three aphid species. For instance, in the case of P. pini, there is a high tree-to-tree variation among the pine stands: it is common to find a completely healthy tree adjacent to, and with its branches intermingled with, a severely infected neighbour that may even be a dominant in the stand. The observation probably "suggests that resistance to Pineus is subject to genetic control" (Barnes et al. 1976). It seems an invaluable clue to the possibility that one could, in the long run, confirm such variation in resistance, study the genetic basis of such variation, and then develop resistant trees having other desirable silvicultural characteristics. This field of R&D has been greatly exploited in crop production, from time immemorial, and needs to be taken up more systematically in tree production, including that concerning exotic species.
The European cypress aphid demands a decisive riposte. We believe that - the three principal partners in this enterprise in Kenya, the Forestry Department, KEFRI and the ICIPE, together with other institutions that KEFRI will bring in as collaborators in specific areas of priority concern - who are launching a Joint Collaborative Project on "The Sustainable Integrated Pest Management of the Cypress Aphid, Cinara cupressi, in Kenya" have a model mission to perform for Kenya and the larger region as a whole. It is to demonstrate that (a) while spearheading a short-term emergency intervention to attempt to slow down the geographical spread of this aphid pest, it can (b) effectively mount a sharply focused problem-solving long-term R&D programme, a target oriented training programme and a technology development and validation programme that, all in all, will (c) ensure that a productive partnership can be successfully mounted in a vitally important economic area between the national research, development, and extension community, the international R&D community, and the policy- and decision-makers.
If we succeed in this endeavour, we would have laid down a strong foundation for a productive, mission-oriented partnership of the kind that sustainably solves major problems.
Austara, O., 1970. The effects of artificial defoliation on the growth of Pinus patula in East Africa. E. Afr.Agri. For. Journal 36:114-118.
Barnes, R.D., R.F. Jarvis, M.A. Schweppenhauser and L.J. Mullin, 1976. Introduction, spread and control of the pine woolly aphid, Pineus pini (L.) in Rhodesia. S. Afr. For. Journal 96:1-11.
Department of Forestry, Ministry of Natural Resources, 1989. National Progress Report on Forestry, 1985-87, Malawi. Prepared for the Eighth Session of the African Forestry Commission, Blantyre, Malawi, 1-5 May 1989. Lilongwe (Malawi): Department of Forestry, 26 pp.
Kenya Forest research Institute, KEFRI, 1990. A strategic plan for research and development, 1989-2000. Nairobi: KEFRI
Mendel, Z., 1983. Insect pests and diseases of cypress in Israel. La-Yaaran 33:47
Mills, N.J., 1990. Biological control of forest aphid pests in Africa. Bull. Entomol. Res., 80:31-36.
Odera, J.A., 1972. A study of the pine woolly aphid, Pineus pini(L.) (Homoptera:Adelgidae) in East Africa. PhD.Thesis,University of Nairobi.
Odera, J.A., 1991. Some opportunities for managing aphids of softwood plantations in Malawi (FD: MLW/86/20). Rome: Food and Agriculture Organization of the United Nations.
Odhiambo, T.R., 1990. Keynote address. Insect Science Applications, 11:259-263.
Smith, P., 1990. Killing the spirit: Higher education in America. New York: Viking.
The World Bank, 1990. Kenya Forestry Project: Staff Appraisal Report (Report No. 9005-KE). Washington DC. World Bank Agriculture Operations, Eastern Africa Department, Africa Region.
Van Rensburg, N.J., 1989. An investigation of the aphid pests of Forestry Plantations in Malawi, with special reference to the cypress aphid, Cinara cupressi: Report on a visit to Malawi (6-12 August 1989). Mimeo, pp ii-8. Pretoria, South Africa: Plant Protection Research Institute.
