Global information on outbreaks and impact of major forest insect pests and diseases

G.B Allard, S. Fortuna, Lee Su See, J. Novotny, A. Baldini and T. Courtinho 1


Insects and diseases are integral components of forest dynamics, in which they fulfil important roles. However, occasionally the populations grow rapidly to damaging proportions. Such sporadic outbreaks can have catastrophic impacts on forests and trees, in some cases leading to the complete destruction of large areas of natural and/or planted forests, loss or reduction of vital forest ecosystem functions, and considerable economic losses. In developing countries and countries in transition, severe outbreaks may compromise national economies, threatening local economic stability and food security.

Despite the significant adverse impacts and indications that outbreaks of forest insect pests and diseases are on the increase, there has been no attempt to systematically gather and analyse comprehensive information on the type, scale and impact of such outbreaks over time at the global level. Dissemination of information on successful protection and control strategies has also been limited.

A recent initiative by the Food and Agriculture Organization of the United Nations (FAO) aims at facilitating access to such information in order to improve the reliability of risk assessments and the design and application of effective cost-efficient forest protection strategies.

Once completed, the information system will be regularly updated and made widely available by electronic and printed means.

This paper provides a synopsis of the pest situation in some developing countries and countries in transition, describes the development of an information system on forest insects and diseases and presents a summary of the kind of information that will be made available in the form of thematic studies.


Insects and pathogens are integral components of forest ecosystems and normally are present at a relatively low density, causing little damage, and having negligible impact on tree growth and vigour. However, sporadically, in time or space, some species may grow rapidly to damaging numbers, developing outbreaks which may persist for a variable length of time before subsiding. Such large populations may have adverse effects on many aspects of forests such as tree growth and survival, yield and quality of wood and non-wood products, wildlife habitat, recreation, aesthetics, and cultural value. The impact of pests may result in the curtailment of plantation programmes, the abandonment of a given tree species, or the necessity to clearcut large areas dominated by infested trees.

The impact of forest diseases and insect pests has been profound over the centuries. The lack of effective quarantine measures coupled with increases in international trade of agricultural and forest products, exchange of plant materials and long-range air travel has resulted in the introduction of pathogens and insects into new environments. These introductions have led to the destruction of indigenous and introduced tree hosts (Palm, 1999) e.g. the American chestnut Castanea dentata, a dominant tree species in eastern forests of USA was reduced to the status of a threatened species approximately 50 years after the introduction of the chestnut blight disease caused by Cryphonectria parasitica. A newly introduced pest is more likely to continue to increase until food is limiting, and then disperse, extending the outbreak to new areas (FAO 2002).

The growing number of requests from member countries to FAO over the past 14 years, for technical assistance related to forest health problems, indicates that there is an increasing threat to forests by biotic agents. Since 1988, FAO has provided technical assistance for forest health related issues to 20 countries through Technical Cooperation Programmes (TCP).2

Most requests to FAO are related to insect outbreaks which occur in regular cycles over several years and which require emergency intervention to disrupt the insect life cycle, to prevent death of host trees. In any one outbreak more than 100 000 hectares can be affected and more than one country may experience the same outbreak. The causes of such outbreaks are not well known, but may be due to cyclic interactions with natural enemies; temporary reduced resistance of host trees; temporary abundance of development substrate (e.g. bark beetle outbreaks after storms) and/or disruption by external factors (weather, fires, dust, insecticides.) (FAO, 2002).

Experience has shown that pest outbreaks in tropical forest plantations are almost inevitable at some time during the rotation and can cause major economic losses. Countries where a single tree species has been extensively planted are at particular risk. The disease, pitch canker for example is having a detrimental effect on pines worldwide, both in their native and introduced range. This disease caused by Fusarium circinatum (Gibberella circinata) is responsible for the current epidemic affecting native Pinus radiata in California (Correll et al., 1991; Gordon et al., 2001), and is causing severe problems on seedlings in South Africa (Viljoen et al., 1994). Its recent discovery on nursery plants in Chile is also of concern (Wingfield et al., 2002). Countries such as New Zealand, Australia and Chile that have wide scale plantings of P. radiata are particularly at risk from this disease. Because of the large scale losses experienced, there is also concern about the future of another pine, P. patula, the dominant pine species in South Africa.

Little has been done to quantify economic impacts and implications of pests but economic data can be used to secure resources needed to carry out control measures. In east and southern Africa it was estimated that the introduced cypress aphid Cinara cupressivora has killed trees to an estimated value of US$ 41 million and was causing a loss in annual growth increment (including that from dead trees) of a further US$ 14 million per year. In addition, the two pine aphids, Pineus boerneri and Eulachnus rileyi caused a further loss of US$ 2.25 million per year in the region. Information for the analysis included area, growth and monetary values of softwood timber, aphid distribution, feeding ecology, associated tree growth loss and tree mortality. While conservative, these figures secured financing for a biological control programme, which led to substantial reductions of the cypress aphid (Murphy, 1996).

Globally there is limited quantifiable data about pest incidence and their effects on forests and forest products. Insect and disease outbreaks in developing countries are primarily surveyed and reported for plantations and planted trees only, and corresponding surveys of forest declines and diebacks in these countries are rare.

Recent efforts by FAO to develop a global information system (database) on forest pest outbreaks and their impacts are aimed to help remedy the present lack of information and to assist countries through providing a basis for improved planning and decision making in this respect.

This initiative aims at increasing awareness of the severe problems related to forest insect pests and diseases worldwide, providing up-to-date baseline information to support risk assessment and the design and implementation of effective forest protection strategies.

Through further analysis of this information, coupled with further input from countries in the form of thematic case studies, it should be possible to review changes in the geographical distribution of given pests and, based on past impacts (extent of forests affected, documented effects etc.) it may also become possible to project and forecast potential future pest outbreaks. Documentation of control measures can also be used by more than one country as lessons learned principle.

A Global information system on insect pest and disease outbreaks

FAO, with the cooperation of experts from member countries, is compiling data for a global information system on the impact of insect pests and disease outbreaks on natural and planted forests, trees outside forests and other wooded lands. The information system is designed to facilitate documentation on forest health at the country level. Once operational, the information system will be made widely available by both electronic and printed means. The target audience includes national forest services, research and academic institutions, and technical officers dealing with forestry and pest management.

Both qualitative and quantitative information is being assembled on the impact of insect pests and diseases on forest ecosystems (e.g. quantitative losses in forest area and products, economic and environmental damage; and qualitative estimates of damage to trees).

The information system (IS) has been constructed to be fully compatible with FAO's existing forestry databases. Pest descriptors (insects and diseases) are standardised so that they can also be entered into the eco-portal, Ecoport (www.ecoport.org). At this developmental stage all the information is stored in the IS through the application of four input forms 1) information source 2) information on outbreaks/impact/control strategies 3) directory of forest protection experts 4) relevant FAO field activities.

To date the data has been collected mainly through literature and web searches, and this will be verified by country contacts. In order to obtain reliable, comprehensive and updated information on the incidence and extent of forest pests over time, a questionnaire (in English, French and Spanish) has been developed in consultation with national experts from Chile, Malaysia, Slovakia, Thailand, and USA. This questionnaire is intended for distribution to FAO Member countries, using the network of country correspondents nominated within the framework of the FAO Forest Resources Assessment Programme and to identified experts. Countries from all regions will be included in this phase of the work, with special attention given to developing countries and countries with economies in transition. Countries which have recently been seriously affected by pest outbreaks will be among those specifically targeted. Several test questionnaires have been sent to Chile, Lebanon, Malaysia, Morocco, Slovak Republic and Malaysia and responses from technical specialists have been entered into the database.

First Results

Data search

During a preliminary search of 275 documents from FAO supported field activities related to a forest health problems, information covering the impact of insect pests and diseases has been collected for 75 countries (developing and countries in transition). To date more than 300 outbreaks have been recorded in the database, including 113 insect taxa comprising 38 families, 79 genera and 90 species and 28 disease taxa comprising 21 families, 24 genera and 22 species. Between 1980 and 2002, more than 52 million hectares of forests (accumulative figure) in 37 countries were reported to have been damaged by pests.

Of the 75 countries, only 37 have provided quantitative information on impacts of pests and this may only refer to one outbreak year or season. Few countries report any information on economic losses. More information is available for European and Asian countries than from other continents. Thus, at this early stage an analysis of trends at country or regional level is not possible using this information.

Examples of significant recent outbreaks include; Lymantria dispar in the Balkan Peninsular which affected more than 2 million hectares of predominantly Quercus spp. between 1997 and 1999; in Mongolia more than 480 thousand hectares of valuable forest have been damaged by defoliators including Dendrolimus sibiricus, infesting mainly larch; and in Belize, El Salvador, Guatemala, Honduras and Nicaragua, between 2000-2002, a total of more than 150 000 hectares of conifers have been infested by the bark beetle Dendroctonus frontalis .

Case studies

Examples are provided below from three geographic regions which summarise the type and quality of information that is presently available and which emphasise the importance of information on pest impact These studies cover different aspects; the case study from Malaysia provides examples of the curtailment of certain plantation species due to diseases, the South American study summarises the transboundary movement of an introduced insect pest across country borders with associated economic implications while the example from the Slovak Republic analyses cyclic outbreaks of indigenous insects. All attempt to answer some of the following questions: What extraneous factors contribute to the problem? Are pest numbers increasing related to expanding plantation areas? Can pests be controlled and what management options are available and acceptable? Are the pests in fact a problem? Is damage significant when related to the function of the tree host?


Malaysia has approximately 250 000 ha under forest plantations. The main species planted are fast-growing exotics such as Acacia mangium, Falcataria moluccana and Tectona grandis with smaller areas of indigenous species such as Azadirachta excelsa, Dyera costulata and dipterocarp species.

Information on pest outbreaks in Malaysia is based on reports from the field and/or from surveys conducted by researchers from the Forest Research Institute Malaysia (FRIM). To date no pest outbreaks are recorded from natural forests, mainly due to the lack of surveys. This case study discusses two of the most significant disease outbreaks on one of the main plantation species over the last decade.

Heart rot was first found in Acacia mangium in Sabah, Malaysia in 1981 (Gibson 1981) and has since been found in most countries with established A. mangium plantations (Lee 1999). This stem disease is closely associated with fungal invasion of wounds caused by pruning or through mechanical injury. In Malaysia, it was found that although heart rot incidence could be between 50-98%, the volume of wood affected did not exceed 10% (Ivory 1988, Zakaria et al. 1994). This level of degradation is unacceptable in wood intended for construction and appearance grades, but is of little significance for pulp and paper or composites made from plantations grown on a rotation of 7-10 years. Since its discovery there has been no further establishment of large-scale A. mangium plantations on Peninsula Malaysia for production of general use timber. However it is still planted in East Malaysia for the pulp and paper industry.

Root rot, first recorded in 1985, causes between 5-25% mortality of 10-year-old A. mangium. With implementation of the "zero burning" policy by Malaysia and other regional governments, it is anticipated that the disease will have a bigger impact on future A. mangium plantations. This can already be seen in Sumatra, Indonesia, where there has been a significant increase in tree mortality in young second rotation plantations in areas replanted without prior burning.

South America

Chile has 2 100 000 ha of plantations, of which 86% is Pinus radiata. In 1985, the introduction and the establishment of Rhyacionia buoliana seriously threatened this resource. The major symptoms caused by this insect are the destruction of the apical and lateral shoots, causing malformations in the young trees. Studies conducted in the first area of attack indicated that 97% of the trees were damaged with an estimated 38% loss in volume (valuable wood). Integrated pest management (IPM), including improved silvicultural techniques coupled with policy modifications helped resolve the problem. The State discouraged planting Pinus radiata during the first years of infestation, which resulted in a greater diversification of species in the forest plantations (National Forestry Corporation, Programa de Protección Fitosanitaria de la Corporación Nacional Forestal).

Sirex noctilio was first recorded in Uruguay in 1980, in Northern Argentina in 1985 and in Southern Brazil in 1988. In Brazil 300 thousand out of a total 2 million hectares of Pinus ellioti and Pinus taeda plantations were damaged. The estimated mortality reported was 5 trees/ha/year, equal to an economic loss of US$ 7 million/year. For this reason an intensive programme of biological control of the pest was developed, using the nematode Deladenus siricidicola.

The eradication programme in Argentina failed; and coupled with big forestry fires in the Pinus contorta and Pinus ponderosa plantations, caused a dramatic increase in the pest population level.

When the insect reached the areas bordering Chile; a Binational Contingency Plan (Plan de Contingencia Binacional) was implemented in order to control the pest by the introduction of Deladenus siricidicola. After the pest was detected in Chile in 2001 a successful eradication programme was immediately established, at a cost of approximately US$600 000 year.

Losses of US$ 18 to 76 per hectare/ year are predicted if Sirex sp. becomes established in Chile, which would reduce the Gross Domestic Product of the forestry sector by 2%. (Comité de Sanidad Vegetal del Cono Sur - COSAVE and the Pontificia Universidad Católica de Chile).

Slovak Republic

In the Slovak Republic information on pest incidence and impact on forests has long been prioritised by the Ministry of Agriculture and the first information on oak defoliators was published in the 19th Century. Data is collected by the Forest Protection Service through cooperation with the State Forest. Forest owners or users (state and private sector) contribute by providing annual details on volume of wood and area infested.

Forest and other wooded land account for over two fifths of the land area i.e. 2 177 000 hectares. More than half the growing stock consists of broadleaved species, with beech being the most important followed by oak. Norway spruce is the main coniferous species, followed by silver fir, Scots pine and mountain pine.

A graphic example of type of data collected is provided in Figure 1 and represents the damage caused by the bark beetles; Ips typographus, Pityogenes chalcographus and Ips amitinus which are the most serious pests infesting spruce, pine and fir forest stands.

Figure 1: Volume of wood infested by bark beetles on conifers in Slovak Republic

Outbreak periods can be correlated to climatic conditions including severe droughts in the summers of 1991 and 1992, severe winters in 1993 and 1994 with subsequent accumulation of breeding material for first generation bark beetles (spring 1994 and spring 1995) equating to peak outbreak in 1995. Between 1996-98 the population decrease relates to intensive control measures including use of pheromone and tree traps.

Defoliators cause periodic defoliation every 8-10 years, in oak, beech, larch and spruce stands. Important indigenous species include Lymantria dispar and Tortrix viridana, on oak, Dasychira pudibunda on beech, Coleophora laricella on larch and Cephaleia abietis on spruce. Figure 2 presents graphical interpretation of accumulative data for all defoliators on all tree species in the last decade.

During the last outbreak of Lymantria dispar (1992-95), more than 15 000 hectares were infested during the peak year 1993. The oak defoliators from the Families Geometridae and Tortricidae often have concurrent outbreaks. The last significant outbreak occurred in 1996-1999 with peak in 1996,

(20 838 hectares). This outbreak can be correlated to climatic conditions including optimum temperatures for survival of young larvae during spring, coupled with reduced levels of natural enemies.

Figure 2: Area infested by defoliators in Slovak Republic


In the period under review (1980-2002), there have been many environmental and ecological conditions which may have affected forest health and contributed to the decrease in periods between sequential outbreaks. These include climate change with the four warmest years on record since 1860 occurring after 1990 and significant El Nino events. Hurricane Mitch, the deadliest Atlantic hurricane since 1780, which affected Honduras and Nicaragua in 1998, was accompanied by excessive rainfall resulting in flash floods and mud-slides. Complete landscapes and large forest areas were destroyed which contributed to the present serious outbreak of bark beetles.

The adverse impact of forest pests has been further compounded in some countries through inability to carry out sound management practices due to financial constraints.

Preliminary analysis of data available to FAO in the brief period of this study can only provide a synopsis of the global situation noting also that there is generally a lack of reliable data from developing countries. A complete overview can only be achieved with the cooperation of countries by provision of information complemented by thematic studies highlighting critical events over time.

Despite the significant adverse impacts, and indications that outbreaks of forest insect pests and diseases are on the increase, there has been no attempt to systematically gather and analyse comprehensive information on the type, scale and impact of such outbreaks over time at the global level. This is a critical gap which the information will attempt to fill, thus contributing to the control and forecast of future pest outbreaks.


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Zakaria Ibrahim, Wan Razali Wan Mohd., Hashim Md. Nor & Lee, S.S. 1994. The incidence of heart rot in Acacia mangium plantations in Peninsular Malaysia. FRIM Research Pamphlet No. 114.

1 Forestry Officer (Forest Protection), Forestry Department, FAO, Viale delle Terme di Caracalla, 00100 Rome, Italy. Gillian.Allard@fao.org

2 In the following countries: Belize, Bulgaria, China, DPR Korea, El Salvador, Guatemala, Honduras, Kenya, Lebanon, Lithuania, Macedonia, Moldova, Mongolia, Nicaragua, Nigeria, Niger, Romania, Seychelles, Slovakia, and Tanzania.