Forestry & Forest Sciences · Forest Protection, Wildlife & Rangelands · also Forest Protection (insects), Forest Entomology, Tree Pests
Insects that damage trees, seeds, nurseries and timber, how outbreaks develop, and integrated ways to manage them.
In the exams: IFoS Forestry Paper II Section B (forest protection); ICAR AIEEA-PG Group 09 (tree pests, IPM); ICAR AICE-JRF 59 Unit 8; Korea Forestry Engineer written subject Forest Protection
Forest entomology is the study of insects in forests: the species that defoliate, bore into, suck sap from or otherwise damage trees, seeds, nursery stock and timber, the natural enemies that keep most of them in check, and the means by which foresters monitor and manage them. Insects are the most diverse animals on Earth, and the great majority of forest insects are harmless or beneficial, as pollinators, decomposers and food for birds and other wildlife. A small number become pests when their populations rise to levels that cause economic or ecological harm, and a few can kill trees over vast areas, as bark beetles and defoliators have done in North America, Europe and Asia.
This subject covers what a forester needs: the basic morphology and classification of insects relevant to forestry; the major groups of pests by feeding habit, with emphasis on examples from South Asia alongside well-known cases elsewhere (defoliators such as the teak defoliator; bark beetles and wood borers; sap-suckers, gall-formers and shoot borers; seed and cone insects; nursery pests and termites; and insects of stored timber); the population dynamics that cause outbreaks; integrated pest management in forests and plantations; biological control and the use of pheromones; and pest surveillance and quarantine for forest products. Diseases caused by fungi and other pathogens are covered in forest-pathology, and fire in forest-fire-science; wood preservation against insects is treated in wood-seasoning-preservation.
Forest protection is examined in Section B of Paper II of the Indian Forest Service forestry optional, in Unit 8 of the ICAR AICE-JRF forestry syllabus and in the ICAR AIEEA-PG forestry group (tree pests and integrated pest management), and as the Forest Protection written subject of Korea's Forestry Engineer qualification. Questions ask for the scientific names, hosts, damage and management of major pests, the orders to which pests belong and their metamorphosis and mouthparts, the principles of IPM and biological control, the role of pheromones, and quarantine measures such as the international standard for wood packaging.
Pesticide registrations and recommendations differ by country and change often. This manual names classes of control agent and principles, not products or doses; any chemical use must follow the current national registration, the product label and local regulations.
Insects are arthropods with a body divided into three regions: head, thorax and abdomen. The head carries the antennae, compound eyes (and often simple eyes, ocelli) and mouthparts. The thorax has three segments, each bearing a pair of jointed legs, and in most adult insects the second and third segments bear a pair of wings each. The abdomen contains most of the digestive and reproductive organs and, in many females, an ovipositor for laying eggs, which in wood wasps and some parasitoids can drill into wood. The body is covered by a chitinous exoskeleton, which must be shed (moulted) for the insect to grow.
The type of mouthparts determines how an insect feeds and what damage it causes, and therefore how it can be controlled. Chewing (mandibulate) mouthparts, found in beetles, the larvae of moths and butterflies (caterpillars), sawfly larvae, termites and grasshoppers, cut and grind plant tissue: they produce defoliation, boring and gnawing. Piercing-sucking mouthparts, found in bugs (Hemiptera: aphids, scale insects, psyllids, mealybugs, leafhoppers), form a stylet that penetrates tissues to suck sap; they cause wilting, distortion, galls and honeydew, and many transmit plant pathogens such as viruses and phytoplasmas. Rasping-sucking mouthparts are found in thrips. Systemic insecticides act mainly against sucking insects, while stomach poisons and microbial agents such as Bacillus thuringiensis act on chewing insects that eat treated foliage.
Insects develop by metamorphosis. In complete metamorphosis (holometaboly), the life cycle has four stages: egg, larva, pupa and adult; larvae usually differ completely from adults in form and food. Beetles (Coleoptera), moths and butterflies (Lepidoptera), sawflies, wasps and ants (Hymenoptera) and flies (Diptera) undergo complete metamorphosis. In incomplete metamorphosis (hemimetaboly), the stages are egg, nymph and adult, and nymphs resemble small wingless adults with similar feeding habits; bugs (Hemiptera), termites, grasshoppers and crickets (Orthoptera) and thrips develop this way. For pests with complete metamorphosis, the damaging stage is usually the larva (caterpillars, grubs, borers), though adult beetles may also feed; for those with incomplete metamorphosis, nymphs and adults usually feed in the same way.
Most forest pests belong to a few orders. Coleoptera (beetles), the largest order, include bark beetles (weevil subfamily Scolytinae), longhorn beetles (Cerambycidae), jewel or flatheaded beetles (Buprestidae), powderpost beetles (Bostrichidae, including Lyctinae), weevils (Curculionidae) and white grubs (Scarabaeidae). Lepidoptera include most major defoliators, shoot borers and cone moths. Hymenoptera include sawflies and wood wasps, which can be pests, and the parasitoid wasps that are among the most important natural enemies. Hemiptera include aphids, adelgids, scales, psyllids and other sap-suckers. Termites, traditionally the order Isoptera and now classified within the cockroach order Blattodea, damage seedlings, trees and timber, especially in the tropics. Diptera include gall midges and many beneficial parasitoid flies, and Thysanoptera (thrips) include a few leaf pests. Identification to order and family is the first step in diagnosing insect damage.
Defoliators are insects that eat leaves or needles. Most are the larvae of Lepidoptera or sawflies, with some beetles and grasshoppers. Defoliation reduces photosynthesis and therefore growth; a single defoliation of a broadleaved tree rarely kills it, because deciduous trees can refoliate, but repeated defoliation over several years can reduce increment greatly, weaken trees and predispose them to secondary insects and diseases, and kill them. Conifers, which retain needles for several years and cannot easily replace them, are more likely to be killed by heavy defoliation. Damage is assessed by the proportion of foliage lost and the number of successive years of attack.
The teak defoliator, Hyblaea puera (Lepidoptera: Hyblaeidae), is the most important pest of teak in India and other teak-growing countries. Outbreaks typically begin at the onset of the monsoon, often around the first rains when teak has produced new flush, and the insect may pass through several generations in a season, with successive outbreaks moving through plantations. Young larvae feed on tender leaves; older larvae cut a flap of leaf, fold it over and feed from within this shelter, and can strip trees of foliage over large areas within weeks. Although teak refoliates, studies at the Kerala Forest Research Institute showed that protecting plantations from defoliation can substantially increase volume increment, so the economic loss over a rotation is considerable. Natural enemies include parasitoids, predators and a nucleopolyhedrovirus (HpNPV), which has been developed as a biological control agent; early detection of the first outbreaks and timely application of microbial agents is the basis of recommended management in some programmes.
The teak skeletoniser, Eutectona machaeralis (Lepidoptera: Crambidae), feeds on the leaf tissue between the veins, leaving a network of veins (skeletonisation). It generally becomes abundant later in the season than the defoliator, after the monsoon, and its impact on growth is usually less. Other defoliators of importance in South Asian forestry include the poplar defoliator Clostera species on Populus in plantations of northern India, defoliators of sal, and various sawflies and moths on conifers in the Himalaya. Many plantation species have characteristic defoliators, and their outbreaks often follow the planting of large areas of a single species.
Some of the world's best-studied forest pests are defoliators. The spruce budworm, Choristoneura fumiferana, has periodically defoliated vast areas of spruce and fir in eastern North America in outbreaks recurring at intervals of several decades. The spongy moth (gypsy moth), Lymantria dispar, native to Europe and Asia, became a major invasive defoliator of oaks and other broadleaves in North America after its introduction in the nineteenth century. The pine processionary moth, Thaumetopoea pityocampa, defoliates pines around the Mediterranean, and its urticating hairs are a public-health concern. The larch budmoth in the European Alps shows remarkably regular population cycles. These cases have shaped much of the theory of insect population dynamics and of pest management in forests.
Bark beetles (Curculionidae: Scolytinae) are small, cylindrical beetles whose adults bore through the bark and construct galleries in the phloem and cambium, where the females lay eggs; the larvae then mine outwards, creating a gallery pattern characteristic of each species. Because the phloem and cambium are destroyed, a successful attack girdles and kills the tree. Most bark beetles breed in weakened, dying or freshly felled trees, but a few aggressive species can kill healthy trees by mass attack: beetles release aggregation pheromones that attract others, and the combined attack overwhelms the tree's resin defences. Bark beetles also carry blue-stain fungi, which help overcome the tree and stain the sapwood.
The mountain pine beetle, Dendroctonus ponderosae, killed pine over millions of hectares in western North America in an outbreak favoured by mild winters and extensive mature pine; the European spruce bark beetle, Ips typographus, causes large losses in Norway spruce in Europe, especially after storms and droughts. In the Himalaya, bark beetles attack conifers such as spruce, fir and blue pine, particularly after felling, fire or drought. Prompt removal or debarking of felled and windthrown trees, maintaining tree vigour, and using trap trees or pheromone traps are the main management measures.
Ambrosia beetles, also scolytine and platypodine weevils, bore into the sapwood (and sometimes heartwood) of freshly felled logs or stressed trees and cultivate symbiotic 'ambrosia' fungi in their galleries, on which adults and larvae feed. The small round holes surrounded by dark stain, known as pinholes or shot holes, degrade timber value. Logs left lying in the forest in warm, humid weather are quickly attacked, so prompt extraction, conversion, water storage or prophylactic treatment of logs is important.
Wood borers are larger larvae that tunnel into the wood of living or dead trees. Longhorn beetles (Cerambycidae), whose larvae are called roundheaded borers, include major pests: the sal heartwood borer, Hoplocerambyx spinicornis, has caused heavy losses in the sal forests of central and northern India, its larvae boring into the sapwood and heartwood of sal trees, especially weakened or felled trees, during outbreaks. The trap-tree method, in which freshly felled sal billets are laid out to attract beetles, which are then collected and destroyed, was developed against it. Other cerambycids include the poplar stem borer Apriona and, internationally, the invasive Asian longhorned beetle Anoplophora glabripennis. Jewel beetles (Buprestidae), with flatheaded borer larvae, include the emerald ash borer, Agrilus planipennis, an Asian species that has killed hundreds of millions of ash trees in North America. Moths of the family Cossidae, such as the beehole borer of teak (Xyleutes ceramica), bore large tunnels in living trees. Wood wasps (Siricidae), such as Sirex noctilio, lay eggs in pine with a symbiotic fungus; Sirex became a serious pest of pine plantations in the southern hemisphere.
Borers degrade timber through tunnels, holes and associated stain and decay, and can kill trees by girdling or weaken them so that they break. Many are secondary, attacking trees already stressed by drought, fire, defoliation or poor site, so maintaining vigour through species-site matching, thinning and protection from other damage is the first line of defence. Felled timber should be extracted and converted promptly, or debarked or treated. Trap trees and pheromone traps can reduce populations of some species. Classical biological control has succeeded against Sirex in Australia, using a parasitic nematode and parasitoid wasps.
Sap-sucking insects (Hemiptera) feed on phloem or xylem sap through piercing-sucking mouthparts. Aphids, adelgids, scale insects, mealybugs, psyllids, whiteflies and leafhoppers are the main groups. Damage includes loss of vigour, leaf curling and yellowing, dieback, honeydew on which sooty moulds grow, and in some cases injection of toxic saliva. Many sap-suckers transmit plant pathogens, including viruses and phytoplasmas (see forest-pathology). Because they reproduce rapidly, often by parthenogenesis, populations can explode. The leucaena psyllid, Heteropsylla cubana, spread across Asia and the Pacific in the 1980s and severely damaged plantings of Leucaena leucocephala, a widely planted fodder and agroforestry tree. The hemlock woolly adelgid, introduced to eastern North America from Asia, has killed large numbers of eastern hemlock.
Gall-forming insects induce abnormal plant growths (galls) in which their larvae develop, protected and fed by the plant. Gall wasps, gall midges, some psyllids, aphids and mites form galls on leaves, shoots, buds or roots. Most galls cause little harm, but some are serious. The eucalyptus gall wasp, Leptocybe invasa (Hymenoptera: Eulophidae), an invasive species of Australian origin, spread through many eucalyptus-growing countries in the 2000s, including India, where it formed galls on the leaf midribs, petioles and shoots of young eucalypts, especially in nurseries and young plantations, causing deformation, stunting and loss of growth. Management combined the use of resistant clones, nursery hygiene and the introduction of parasitoids.
Shoot borers are larvae, usually of moths, that tunnel into the growing shoots of young trees, killing the leading shoot and causing forking, multiple stems and poor form. The mahogany or toon shoot borer, Hypsipyla robusta (Lepidoptera: Pyralidae), attacks the shoots of trees of the mahogany family, including toon (Toona ciliata), mahogany (Swietenia) and Chukrasia, across tropical Asia and Africa, and is the main reason why plantations of these valuable species have often failed. Its American relative Hypsipyla grandella plays the same role in the Americas. Repeated attack on the leader can prevent the formation of a straight bole. Silvicultural approaches, such as planting under light shade or in mixtures and corrective pruning, are used because chemical control of insects inside shoots is difficult and rarely economic. Pine shoot moths attack the shoots of young pines in temperate regions.
Termites, treated more fully in the nursery chapter, also attack the roots and stems of young plantation trees, especially eucalypts in dry tropical regions of India and Africa, where they can cause high mortality in the first years after planting. Ring-barking by termites at ground level is a characteristic symptom. Root-feeding larvae of beetles, such as white grubs, damage young trees as well as nursery stock.
Seed and cone insects destroy seeds before or after they are shed, reducing natural regeneration and the supply of seed for nurseries. Losses can be especially serious in seed orchards and seed production areas, where genetically improved seed is concentrated and valuable. Damage often goes unnoticed because the seed looks normal from outside; cutting tests or X-ray examination reveal the empty or infested seeds.
The main groups are: seed chalcids (Hymenoptera, such as Megastigmus species), tiny wasps whose larvae develop inside single seeds of conifers and some broadleaves; cone and seed moths and coneworms (Lepidoptera, such as Dioryctria species), whose larvae tunnel through cones and eat seeds; seed bugs (Hemiptera), which suck the contents of developing seeds; cone beetles and weevils, including acorn weevils in oaks; and seed beetles (bruchids, Chrysomelidae: Bruchinae), which develop in the seeds of legumes such as Acacia, Albizia, Prosopis and other leguminous trees and can destroy a high proportion of stored seed. Gall midges and flies attack seeds and fruits of some species.
Management of seed and cone insects concentrates on seed orchards and seed stores. Measures include monitoring cone and seed damage by sampling cones and cutting seeds; timing seed collection to minimise exposure; prompt processing and drying of seed; fumigation or controlled-atmosphere treatment of stored seed (following national regulations); cold storage, which slows insect development; and, in seed orchards, insecticide applications timed to vulnerable stages where justified. Removing unharvested cones and infested seeds reduces carry-over populations. Seed testing (see tree-seed-technology) should account for insect damage when estimating viability.
Nurseries concentrate large numbers of small, tender plants in a small area, so pests can cause rapid and complete losses. The main insect pests of forest nurseries are: white grubs, the larvae of scarab beetles (Scarabaeidae, such as Holotrichia and related genera in India), which live in the soil and feed on roots, causing seedlings to wilt and die, often in patches; cutworms (larvae of noctuid moths such as Agrotis), which cut seedlings at ground level at night; crickets, including the large brown cricket Brachytrupes portentosus in South Asia, which cut seedlings and drag them into burrows; termites; defoliating caterpillars, grasshoppers and beetles; and sap-suckers such as aphids, scales and mealybugs. Root-knot nematodes, although not insects, are also important nursery pests.
Prevention is central. Measures include siting nurseries away from heavily infested land; using clean, well-prepared or treated growing media (for example sterilising potting mixture by solarisation or other approved methods); deep ploughing or digging to expose white grubs to birds and desiccation; light traps to catch adult scarab beetles and moths during their flight seasons; regular inspection and hand removal of pests; maintaining plant vigour with proper watering and nutrition; and, where pests exceed thresholds, carefully targeted use of approved insecticides or biological agents such as entomopathogenic fungi (Beauveria, Metarhizium) or nematodes. Container nurseries raised above the ground on benches are less exposed to soil pests.
Termites are social insects that live in colonies with castes of workers, soldiers and reproductives. They feed on cellulose, digested with the help of gut microorganisms or, in the fungus-growing termites, with fungi cultivated in their nests. In forestry they are both decomposers, valuable in recycling dead wood, and pests. Subterranean termites, including the mound-building, fungus-growing genera Odontotermes and Microtermes in India, attack seedlings and young trees by eating roots and ring-barking stems at ground level, and damage timber in contact with the soil. Drywood termites, such as Cryptotermes, live entirely within dry wood and attack timber in buildings and furniture without contact with the soil. Dampwood termites infest wet, decaying wood.
Termite damage to eucalypt plantations in the drier parts of India and Africa can cause high mortality in the first years. Management includes planting healthy, vigorous stock with well-developed roots; avoiding damage to roots during planting; removing woody debris that harbours termites; maintaining soil moisture through mulching and irrigation where possible; and, where justified, protecting the root zone of planting stock with approved treatments, following current national registration, since several older soil insecticides formerly used against termites have been banned or restricted because of persistence and toxicity.
Signs of termite attack include earthen runways (mud tubes) on stems or walls, sheeting of soil over bark, hollowed roots and stems filled with soil, wilting and death of young plants, and, in timber, galleries following the grain with thin outer shells of sound wood remaining. Drywood termites leave small, hard, six-sided faecal pellets. Correct identification of the termite type is necessary for choosing control methods.
Freshly felled logs are attacked quickly by insects that need moist wood. Ambrosia beetles (pinhole borers) bore into sapwood and sometimes heartwood within days in warm, humid conditions; longhorn beetles and jewel beetles lay eggs under the bark, and their larvae bore into the wood; and bark beetles colonise the inner bark. These attacks degrade timber value and introduce stain fungi. The main defences are rapid extraction and conversion, debarking, storing logs under water or water sprays (which keep the wood too wet for insects and fungi), end coating, and prophylactic chemical treatment of logs where approved.
Seasoned timber is attacked by a different set of insects adapted to dry wood. Powderpost beetles of the subfamily Lyctinae (Lyctus and related genera) attack the starch-rich sapwood of hardwoods with large vessels, reducing it to fine flour-like powder while the surface remains intact apart from small exit holes; heartwood and wood with little starch are not attacked. Other bostrichid beetles, such as Sinoxylon and Dinoderus, attack seasoned hardwoods and bamboo, which is highly susceptible because of its starch content. The common furniture beetle, Anobium punctatum, attacks seasoned softwoods and hardwoods in older buildings and furniture in temperate climates. Drywood termites attack timber in buildings in the tropics and subtropics, and subterranean termites attack any wood in contact with or near the ground.
Timber in seawater, such as piles, boats and jetties, is attacked by marine borers, which are not insects: shipworms (molluscs of the family Teredinidae, such as Teredo) bore long tunnels lined with shell, and gribbles (small crustaceans, Limnoria) erode the surface. Damage can be rapid in warm seas. Naturally durable timbers and preservative treatments rated for marine use are required.
Protection of stored timber relies on preventing infestation rather than curing it. Measures include using naturally durable heartwood where appropriate; removing sapwood or bark from susceptible timbers; kiln drying, which kills insects present in the wood at sufficient temperature; preservative treatment by approved methods (see wood-seasoning-preservation); good storage hygiene, such as removing infested material, raising stacks off the ground and inspecting regularly; and, for bamboo, harvesting at times of low starch content and leaching or treating culms. Infested items can be treated by heat, freezing or fumigation, following regulations.
An insect population grows when births and immigration exceed deaths and emigration. The factors that regulate populations are commonly divided into density-independent factors, whose effect does not depend on population density (such as weather, extreme cold or drought), and density-dependent factors, whose proportional effect increases as density rises (such as competition for food, natural enemies and disease). Density-dependent factors can regulate populations around an equilibrium; density-independent factors cause fluctuations. Life tables, which record survival through each stage of the life cycle, help identify the stages and factors that drive population change (key-factor analysis).
Most forest insects remain at low, endemic densities most of the time. Outbreak (epidemic or eruptive) species occasionally increase dramatically and cause extensive damage. Outbreaks may be cyclical, recurring at fairly regular intervals, as with the spruce budworm in eastern North America (intervals of several decades) and the larch budmoth in the Alps (about eight to ten years), or irregular, triggered by events such as drought, storms that create abundant breeding material, or the introduction of a pest without its natural enemies. Bark beetle outbreaks commonly follow storms or droughts that weaken trees and provide breeding material, after which populations grow large enough to attack healthy trees. Invasive species, freed from their natural enemies, may cause sustained outbreaks in their new range.
Whether a stand is attacked and damaged depends on its condition. Susceptibility is the likelihood that a stand will be attacked; vulnerability is the likelihood of damage or mortality once attacked. Factors that increase risk include large areas of a single host species, especially even-aged and mature or overmature stands; off-site planting of species poorly adapted to the site; stress from drought, overcrowding, poor nutrition or other damage; and the presence of abundant breeding material such as windthrown or felled trees. Hazard-rating systems use stand characteristics to identify stands at high risk, so that preventive silviculture can be targeted.
Climate change is altering forest insect dynamics. Warmer temperatures speed insect development, allowing more generations per year in some species, and milder winters reduce overwinter mortality, as in the mountain pine beetle's expansion in western Canada. Insects can extend their ranges poleward and upslope into forests that have not co-evolved with them and lack effective defences. Drought and heat stress weaken trees and make them more susceptible to bark beetles and borers. At the same time, climate change may disrupt the synchrony between insects and their host plants or natural enemies, with unpredictable effects. For forest managers, these changes mean that historical outbreak patterns are a less reliable guide, that monitoring is more important, and that silviculture for vigorous, diverse stands is part of climate adaptation (see forests-climate-carbon).
Not every insect presence justifies action. The economic injury level (EIL) is the lowest pest population density that causes economic damage equal to the cost of control. The economic threshold (action threshold) is the density at which control should be applied to prevent the population from reaching the EIL; it is set below the EIL to allow time for action. Thresholds depend on the value of the crop, the cost and effectiveness of control and the expected damage, and are harder to define in forests than in agriculture because of long rotations, non-market values and the difficulty of sampling large areas. Nevertheless, the principle of acting only when monitoring shows that damage will exceed the cost of control underlies integrated pest management.
Integrated pest management (IPM) is a decision-based approach that combines several methods to keep pest populations below damaging levels in an economically and environmentally sound way. Its principles are: prevention through good silviculture; monitoring of pests and natural enemies; decision-making based on thresholds; use of a combination of compatible tactics (silvicultural, mechanical, biological, behavioural, genetic and chemical); preference for methods with least harm to people, natural enemies and the environment; and evaluation of results. In forests, where chemical control over large areas is costly and environmentally sensitive, prevention and biological methods carry more weight than in agriculture.
Silviculture is the first line of defence. Matching species and provenances to site keeps trees vigorous and less susceptible. Mixed-species plantations and retention of natural vegetation can reduce the spread of host-specific pests and support natural enemies. Thinning reduces competition stress, which lowers susceptibility to bark beetles and some borers. Sanitation, the removal of infested, weakened or dying trees, and prompt salvage of windthrown or fire-damaged trees remove breeding material. Timing operations (for example felling outside beetle flight periods), avoiding damage to residual trees, and maintaining stand diversity in age and structure all reduce risk. Planting species outside the range of their key pests, or under shade for shoot borer hosts, are further examples.
Mechanical and physical methods include hand collection and destruction of egg masses, larvae or pupae in nurseries and young plantations; trap trees and trap logs that attract borers or bark beetles, which are then destroyed or debarked; sticky bands on stems; light traps for night-flying moths and beetles; and barriers. Genetic methods use resistant or tolerant planting stock: clones of eucalyptus resistant to the gall wasp and poplar clones resistant to defoliators or borers have been selected, and resistance is an important objective of tree improvement programmes.
Chemical insecticides can be effective in nurseries, seed orchards and high-value situations, and against sudden outbreaks, but in forests their use is limited by cost, the difficulty of reaching large or tall stands, effects on natural enemies and non-target organisms, water contamination, development of resistance, and restrictions in certified forests and protected areas. Where chemicals are needed, IPM favours selective products, targeted application (for example stem injection or treatment of individual trees or nursery beds), correct timing against vulnerable stages, and compliance with national registration, labels and safety rules. Aerial application over large areas is now uncommon in many countries and is subject to strict regulation where permitted.
Natural enemies of forest insects include predators (birds, ants, spiders, predatory beetles and bugs), parasitoids (insects, mostly wasps and flies, whose larvae develop in or on a single host and kill it) and pathogens (viruses, bacteria, fungi, microsporidia and nematodes). In most forests, natural enemies keep insect populations at low levels most of the time. Biological control uses natural enemies deliberately to reduce pest populations.
Classical biological control introduces natural enemies from a pest's native range to control an invasive pest in its new range. Introductions require careful host-specificity testing and approval under national regulations, because introduced agents can attack non-target species. A notable forestry success was the control of the wood wasp Sirex noctilio in pine plantations in Australia and elsewhere, using the parasitic nematode Deladenus siricidicola, which sterilises female wasps, together with parasitoid wasps. Parasitoids have been released against the eucalyptus gall wasp in several countries. Augmentative biological control releases large numbers of natural enemies, reared or produced in the laboratory, at a particular time and place. Conservation biological control protects and enhances existing natural enemies, for example by avoiding broad-spectrum insecticides and maintaining diverse vegetation that provides nectar and shelter.
Microbial agents are formulated and applied like insecticides. Bacillus thuringiensis (Bt), especially the subspecies kurstaki, produces crystal proteins that are toxic to the larvae of Lepidoptera when eaten; it is widely used against defoliating caterpillars because it does not harm most other organisms. Baculoviruses, especially nucleopolyhedroviruses (NPVs), are highly specific: the HpNPV of the teak defoliator and the NPV of the spongy moth have been developed for forest use. Entomopathogenic fungi such as Beauveria bassiana and Metarhizium anisopliae infect insects through the cuticle and are used against soil pests, termites and some sap-suckers. Entomopathogenic nematodes are used against soil-dwelling larvae and borers. Microbial agents are slower acting than chemicals and depend on weather and timing, but they are selective and environmentally benign.
Pheromones are chemicals released by an insect that affect the behaviour of others of the same species. Sex pheromones, usually released by females of moths, attract males over long distances; they are used in traps to monitor populations and detect new invasions, and in mating disruption, in which the air is saturated with pheromone so that males cannot find females. Aggregation pheromones, released by bark beetles, attract both sexes to a host tree; they are used in traps to monitor or mass-trap beetles and to bait trap trees. Anti-aggregation pheromones, such as verbenone for some Dendroctonus species, signal that a tree is fully occupied and can be used to protect high-value trees or stands. Host volatiles (kairomones) such as ethanol and alpha-pinene attract wood-boring beetles and are used in surveillance traps. Pheromone-based methods are species-specific and non-toxic, which makes them valuable components of IPM.
Invasive forest insects introduced by trade have caused some of the greatest forest losses of the past century: the emerald ash borer, the Asian longhorned beetle, the spongy moth, the hemlock woolly adelgid and the eucalyptus gall wasp are examples. Pests travel in wood packaging, logs and sawn timber, live plants and soil, and on vehicles and containers. Once established and spread, invasive pests are rarely eradicated, so prevention and early detection, when eradication is still possible, are far more cost-effective than long-term management.
The International Plant Protection Convention (IPPC), a treaty deposited with FAO and first adopted in 1951, aims to prevent the introduction and spread of plant pests and sets International Standards for Phytosanitary Measures (ISPMs). ISPM 15 regulates wood packaging material, such as pallets, crates and dunnage, in international trade: it must be treated, by heat treatment to a minimum core temperature of 56 °C for at least 30 continuous minutes or by other approved methods, debarked and marked with the IPPC mark. Other standards cover pest risk analysis, surveillance, pest-free areas and the movement of wood. National plant protection organisations implement these standards, issue phytosanitary certificates for exports and inspect imports. In India, plant quarantine operates under the Destructive Insects and Pests Act, 1914 and the Plant Quarantine (Regulation of Import into India) Order, 2003.
Surveillance detects pests and tracks their spread. General surveillance relies on reports from foresters, landowners and the public; specific surveys target particular pests or high-risk sites such as ports, airports, timber yards and nurseries. Methods include visual inspection, aerial and remote-sensing detection of defoliation and mortality, traps baited with pheromones or host volatiles, branch and log sampling, and sentinel plantings of native species abroad to detect potential pests before they arrive. Citizen science and smartphone reporting have extended surveillance networks. Data from surveillance feed pest risk analysis and emergency response.
When a new pest is detected, authorities may attempt eradication (for example by felling and destroying infested and nearby host trees, as was done for some outbreaks of the Asian longhorned beetle), containment (restricting movement of wood and plants from infested zones), or long-term management if eradication is no longer feasible. Rapid response depends on contingency plans, trained staff, legal powers and public cooperation. Foresters play key roles in recognising unusual damage, reporting it promptly and implementing control measures.
Learn insect orders with their metamorphosis and mouthparts, then the major pests by host with their scientific names, families, damage and management: Hyblaea puera and Eutectona machaeralis on teak, Hoplocerambyx spinicornis on sal, Hypsipyla robusta on Meliaceae, Leptocybe invasa on eucalyptus, white grubs and termites in nurseries, Lyctinae in stored timber. Know the IPM principles, the types of biological control with forestry examples, pheromone uses and ISPM 15. In descriptive answers, structure each pest as host, identification, life cycle, damage and management.
A forester five years in recognises pest damage in nurseries and plantations, organises monitoring (light traps, pheromone traps, damage surveys), decides when action is justified, carries out silvicultural and mechanical control, applies microbial or chemical agents correctly where needed, protects felled timber in depots, and reports unusual damage that may indicate an invasive species. Practical skills include sampling, identification to family, record-keeping and safe use of control agents.
A senior forester sets pest management policy for an estate or region: hazard rating of stands, species and clone choice for resistance, budgets for monitoring and outbreak response, coordination with plant protection authorities, and decisions on large-scale interventions after storms or outbreaks. The senior forester balances control effectiveness with environmental, certification and public-health constraints.
A senior researcher studies forest insect ecology, population dynamics, host resistance, biological control agents, semiochemicals, climate effects on pests and invasion biology; develops monitoring and decision tools; and advises on quarantine policy and emergency responses. Such a researcher also trains foresters to recognise pests and maintains reference collections.
This manual gives no insecticide product names, doses or schedules, because registrations and recommendations differ by country and change often; follow national guidance and labels. Only selected pests are described; regional pest lists for particular species and states should be consulted. Taxonomic names follow common usage and some have been revised (for example the classification of termites and some moth families). Detailed identification keys, sampling plans and threshold values are not included. Diseases are in forest-pathology and wood preservation in wood-seasoning-preservation.
Original practice questions written to the syllabus and pattern of the exams named in each question's examTags. They are not past papers and do not reproduce any board's questions.
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