Csóka, GY., and Kovács, T. 1999. Xylophagous insects. Forest Research Institute. Erdészeti Turományos Intézet. Agroinform Kiadó, Budapest. 189 pp.
Stag beetles (Lucanidae)
Usually relatively large beetles, ranging from 5 mm (Aesalus scarabeoides) up to 100 mm (Lucanus cervus). Their antenna are stalked, the first segment is elongated and the following segment joins the first at right angles. The last 3-4 segments of the antenna are elongated and disc-like. Sexual dimorphism - mainly difference in size of the mandibles - is common in this group, but in some cases (Aesalus) it is scarcely detectable. Only 6 species represent the family in Hungary, only 0.5 % of the species richness known world-wide. All species are saproxylic. Their larvae are grub-like, curled. The vertically located head is globular, with strong mandibles. All three pairs of legs are well developed. The anus of the larvae is a characteristic longitudinal split. After their usually long development - lasting for up to 4-5 years - the larvae make a pupal case using wood chips and soil fragments. The pupae are free. The adults feed on sap seeping from wood, on nectar of flowers of a range of plants, or they do not feed at all. The species included in this book are active from dusk, and hide during the day.
Dung beetles (Scarabaeidae)
In spite of the misleading name of the family many xylophagous insects belong to this group. The family includes species showing a wide diversity of size, shape and life history. The most characteristic common feature of these species is the terminal bulb of the antennae (which are elbowed, as in stag beetles); this is 3-7 segmented, shiny and smooth. The species included in this book belong to 3 families (with genera in brackets): Trichiinae (Osmoderma, Gnorimus), Cetoniinae (Cetonischema, Liocola, Potosia) and Dynastinae (Oryctes). Their adult body lengths range from 2.5 mm to 45 mm. Sexual dimorphism is evident in some species (Osmoderma and Oryctes for example). All of them are saproxylic, larvae developing in humid decaying wood. They make a pupal case from wood fragments. The larvae are grub-like, the anus - in contrast to stag beetles - is a transversal split. The majority of the adults hide during the day, becoming active at dusk. Other - usually shiny and colourful species favour the sunshine. In flight they search for food such as woodsap, fermenting fruits and flowers. In the subfamily Cetoniinae the wingcases are closed even during flight.
Jewel beetles (Buprestidae)
The highest species richness of jewel beetles is found in tropical regions. The 120 species recorded from Hungary represent less than 1 % of the total number of species known world-wide. As their English name suggests, these are usually beautifully coloured, shiny beetles. Some of the particularly nice tropical species are used in making jewellery. In this family sexual dimorphism is not characteristic, but can be found in a few examples (Anthaxia hungarica for example). The adult body is hard, most frequently elongated, and flattened, cylindrical or triangular in cross section. The body usually gets narrow toward the rear. A characteristic feature for the whole family that the prothorax is strongly connected to the mid-thorax. The size of species occurring in Hungary ranges from 2 mm to 32 mm.
Most species are xylophagous, living in or under the bark or in the heartwood of woody plants. They most frequently attack trees that are water-stressed. Larval development requires 1-3 years. These species can be very difficult to rear due to their habit of developing in living branches.
The larvae are either white or yellow, legless and blind. Their antennae are three-segmented, the lower labial palps are absent - these last two features distinguish them from the larvae of longhorn beetles. Jewel beetle larvae can be divided into two distinct groups. In the first group the body is flattened, the 1st thoracic segment is disc-like and widened, the 2nd and 3rd segments are intermediate in form between the first and the thin abdominal segments. The last abdominal segment is simply blunt. In the second group the body is more or less cylindrical. The 1st thoracic segment is less flattened and widened. The cross-section of the other segments is nearly circular, and two strongly chitinized and pointed appendages can be found on the last abdominal segment.
Their tunnels - except of the "ringbarking" species - are made in the heartwood or under the bark and are similar to those made by longhorn larvae. In the case of jewel beetle larvae the tunnels in the heartwood are more flattened in cross-section. Jewel beetle tunnels under the bark are relatively wide and flat. They pupate either in the bark or in the heartwood. The emergence hole is asymmetrically elliptical, with a flatter upper half. Occasionally it can be a blunt triangle with one angle pointing downwards, or rarely circular. The adults are fast flying, favouring the sunlight and warm temperatures. They can be found resting on flowers, their foodplants or on wood piles.
Eucnemid beetles (Eucnemidae)
Elongated, cylindrical beetles. They are somewhat similar to both click beetles and jewel beetles. Their antennae are inserted close to each other. The head shield is wider toward the front. The larvae develop for several years in dry wood, such as the branches and trunks of broad-leaved trees. Ca. 20 species of Eucnemids are known from Central Europe.
Click beetles (Elateridae)
Elongated beetles, which taper toward their rear end. They have a mobile joint between the first and second thoracic segments. This makes them able to flick themselves into the air giving a clicking noise. Larvae are called "wireworms", and are hard and elongated. They can either be phytophagous or can feed on decaying substrates. Other species are predaceous. Some species of the family are secondarily saproxylic, feeding on wood fragments and frass left behind by other xylophages. The short-lived adults feed on flowers, foliage and plant saps.
Bostrichid beetles (Bostrichidae)
3-15 mm, cylindrical beetles similar to the bark beetles in appearance. The head faces downward and is covered by the front part of the neck shield. The head of the larva is small and globular. They develop in the dead or dying wood of a range of broad-leaved trees, particularly hardwoods. Their typical representative in Hungary is the 6-15 mm long black and red Bostrichus capucinus.
Furniture beetles (Anobiidae)
Small, cylindrical beetles, with thread-, or comb-like antennae. Larvae develop in dead and dry, usually already carpentered timber, such as beams in buildings and furniture. The short-lived adults do not feed.
Timber beetles (Lymexylonidae)
Narrow-, and relatively soft-bodied, cylindrical insects. The larvae are whitish, long, and feed inside dead wood. The family is represented by two species in Hungary. One species cultivates fungus in its tunnels and feeds on it, while the other one feeds on the wood tissues.
Longhorn beetles (Cerambycidae)
The fossil remnants of longhorn beetles are known from the early tertiary. 35, 000 species of them have been described so far. The largest beetle in the World (Titanus giganteus, up to 15 cm long) belongs to this group. More than 220 species of longhorn are known from Hungary. The species occurring in Hungary range from 3-60 mm in size. Longhorn beetles are usually slender with long antennae. They move fast and fly well. Most of them can produce a squeaking noise (the Hungarian name of the family is based on this noise). They create this noise in two different ways. One group rubs the inner edge of the hind femur on the margin of elytra. This method is called "playing a violin" in Hungarian. The other way is moving the prothorax back and forward and rubbing some chitin discs together. Sexual dimorphism is sometimes pronounced. The males have longer antennae, stronger legs and occasionally different coloration from the females. Species with extremely long antennae are found in some genera. For example, the antenna of male Acanthocinus aedillis can be more than 6 times longer than his body. 80 % of the longhorn species occurring in Hungary develop in woody plants, and the other 20 % feed in stalks and roots of herbaceous plants. The majority of the xylophagous species feed under the bark or in the heartwood of dead trees or dead parts (dead branches for example) of living trees. Only species in a few genera develop in living trees and branches. The majority of species are oligo-, or polyphagous, but there are also strictly monophagous species. Most species are neutral from an economic point of view, but serious pests are also in this group (Hylotrupes bajulus for example). Larval development takes 1-5 years, but the environmental conditions (humidity of the wood for example) can have a serious influence on the time required.
Their galleries are characteristic, although less species-specific than those of the bark beetles. Below we list a few characteristic gallery types, using species included in this book as examples.
- larvae feed and pupate in the heartwood (Ergates faber);
- larvae develop in the heartwood, but they pupate in the ground (Prionus coriarius);
- larvae develop and pupate under the bark (Rhagium inquisitor);
- larvae develop under the bark and pupate in the bark (Trichoferus pallidus);
- larvae develop beneath the bark, pupating in the heartwood. The emerging adult leaves the pupal chamber via the larval entrance (Plagionotus arcuatus);
- larvae develop beneath the bark, pupating in the heartwood. The emerging adult leaves the pupal chamber but not through the larval entrance (Monochamus saltuarius).
The flattened larvae of longhorn beetles are ivory-coloured, and taper towards their rear end. Their head capsules are strongly sclerotised and most of it- just like the mandibles - is hidden in the prothorax. The larvae of species in the Laminae subfamily are legless. Their pupae are free.
The majority of the species prefer warm and sunny conditions, and adults can be found on flowers of herbaceous and woody plants, on stems, branches and sap-flows of trees and shrubs and on wood piles. The remaining species typically become active at dusk, and some species are attracted to lights. These species hide during the day beneath bark, in crevices or inside wood piles. Adult longhorn beetles feed on pollen, leaves, pieces of dead or fresh bark, stalks of herbaceous plants, or on woodsap and fermenting fruits. Some species must feed to become sexually mature ("maturation feeding). Adult females oviposit on dead branches, in bark crevices, or on debarked trunks of woody plants. Some species even glue the eggs onto the surface of the foodplant. Some other species prefer branches already ringbarked by the jewel beetle Coraebus florentinus. In some genera (Anaerea, Compsidia, Oberea) species belonging to the subfamily Laminae show relatively advanced care for individual eggs. The ovipositing females carefully prepare oviposition sites and lay single eggs in each one.
Anthribid beetles (Anthribidae)
Small or medium sized beetles ranging from 0.7 mm to 15 mm in length. Rostrum is short, wide and flattened. The wing cases (elytra) do not cover the end of the abdomen. The body is stubby and often covered with hairy spots. More than 2,200 species belong to this family but only 18 of them are recorded from Hungary. Most species are saproxylic. The larvae develop in dead branches of a range of broad-leaved trees. The adults feed either on decaying plant tissues or fungi. In some species (Anthribus for example) both larvae and adults are predaceous, feeding on the eggs of scale insects. The adults can mainly be found on dead branches, stumps and trunks.
This family has the highest number of species (ca. 50,000) in the order Coleoptera, and 1400 of them are recorded from Hungary. This makes the curculionids the most species-rich family of Coleoptera in Hungary. The head is snout-like and elongated into a rostrum, but in some groups the rostrum is very short. All species are phytophagous with a very broad range of appearance and life history. Their larvae are legless.
The broad-nosed snout beetles (subfamily Cossoninae) are represented by quite many species in Hungary. Their larvae develop in dead decaying wood.
In addition to a few of species belonging to the subfamily Curculioninae we pay special attention to the subfamily of bark beetles (Scolytinae) which have the greatest importance as xylophagous insects. Earlier this group was considered as a separate family in its own right.
The bark beetles are small (1-9 mm), usually cylindrical beetles. The family is very diverse, with more than 6,000 known species world-wide. In Europe there are approximately 300 species and ca. 150 in Central Europe. Most of them feed on the tissues of various parts of plants. A very interesting exception is a group commonly called ambrosia beetles. Adults of these species introduce the spores of fungi to their tunnels, and developing larvae feed from a fungal garden that is far more digestible than wood.
The bark beetle species native to Hungary usually have one or two generations per year, although some species have a lifecycle lasting two years. Developmental rate, and so the number of generations per year, are strongly dependent on environmental conditions such as food quality and climate. After emerging from their pupae, bark beetles leave the host tree but are still not sexually mature. Maturation usually follows 1-2 months of feeding in the adult stage, and in some species an overwintering diapause. Mating takes part on the trunk in some species, while in others it occurs under the bark in a chamber excavated specially for this purpose.
Mated females bore egglaying (oviposition) tunnels into species-specific tissues of the tree (bark, sapwood, heartwood) and lay their eggs on the tunnel wall. These tunnels are called egg galleries. In the case of polygamous species, in which a single male beetle may mate with several females, several egg galleries may radiate from one mating chamber. The larval galleries - made by the feeding larvae- radiate from the egg galleries. Bark beetle larvae are small, plump, slightly curved, legless and usually white. Larvae of many species construct a widened pupal chamber at the end of the larval galleries. The size and shape of both egg and larval galleries are typical of a given species, and in many cases are diagnostic enough for safe identification of the beetle species. Bark beetles have a free pupa on which the shape of the beetle and the body parts can be easily recognised.
When healthy trees are attacked by low numbers of beetles, they are able to flood the larval tunnels with resin or sap, and so kill the beetles and stop the attack. Most bark beetle species can therefore only attack weakened or sick trees whose self-defence systems cannot operate effectively. Many bark beetle species overcome tree defences by simultaneous mass colonisation, mediated in many species by an aggregation pheromone. One sex is the colonising sex, and this recruits individuals of both sexes to a single host tree. Colonisation above a certain density is disadvantageous, because the larvae consume the whole food source before development can be completed, and many species secrete anti aggregation pheromones once some threshold density is reached. The aggregation pheromones of one bark species can also act as anti-aggregation pheromones to other bark beetle species. Aggregation pheromones can be used in the control of bark beetle pests - this possibility is discussed in more detail in a later chapter. Other bark beetles weaken their food plant by infecting it with aggressive pathogens.
The bark beetle species feeding on a given host tree species partition the available resources. In case of the four species feeding on spruce (Pityogenes calcographus, Polygraphus poligraphus, Ips typographus and Dendroctonus micans) the smallest species (Pityogenes) colonises the thinnest stems in the crown followed in thicker stems by the slightly larger Polygraphus and later Ips and Dendroctonus which feeds on the thicker barked parts of the trunk. Similar partitioning is known in case of the ash bark beetles (Hylesinus and Leperisinus species) where there is positive correlation between the size of the beetle and the thickness of the bark on the trunk part attacked.
The bark beetles feeding in cambium and sapwood have the greatest economic importance among the xylophagous insects. During the last decade many European countries (Austria, Poland, Slovakia, Romania, the Czech Republic and Lithuania) have suffered massive outbreaks causing the death of many millions of m3 of wood, representing several tens of thousands of hectares of forest. The most common victims have been conifers, particularly spruce. Although the relative importance of spruce is much lower in Hungary than in the countries mentioned above, over the same period we have also experienced serious damage resulting from bark beetles.