Orchestes fagi (Linnaeus, 1758)
POLYPHAGA Emery, 1886
CURCULIONOIDEA Latreille, 1802
CURCULIONINAE Latreille, 1802
RHAMPHINI Rafinesque, 1815
ORCHESTES Illiger, 1798
A native and generally common species across central and northern Europe from France to the west of Russia, Greece and Turkey, extending north the UK and southern provinces of Fennoscandia, and south to Gibraltar, Italy and several of the Mediterranean islands, it also occurs in the Channel Islands and following recent accidental introductions has become established in the United States. Here it is generally common and often abundant throughout the UK including all the islands except for Shetland. Typical habitats are broadleaved woodland with a varied shrub layer, wooded parkland and pasture and mixed hedgerows on agricultural borders etc. where the host is present; development occurs on Beech, Fagus sylvatica, but adults may feed on other foliage and larvae have been recorded developing on introduced oaks. Adults overwinter among leaf-litter or on evergreens such as holly or conifers, at this time females are in a reproductive diapause which will last until they feed in early spring, they become active in early spring and move to hawthorn as soon as the leaf-buds burst, usually a month or so before those of beech. They feed on young leaves as soon as they begin to emerge, producing numerous small holes away from the veins, and although hawthorn is a common host at this time, more than twenty species of tree and soft fruit foliage have been recorded hosting the adults. This early feeding i.e. before beech buds begin to open, is necessary for the eggs to develop (Bale & Luff, 1978) although Neilson (1974), studying Danish populations, demonstrated that adults delaying their emergence until beech buds began to open were able to find the host, develop eggs and oviposit within 48 hours of feeding. It is essential for the female to oviposit quickly as the young leaves soon begin to toughen; within only a week or two after the buds have burst the foliage becomes too tough for the larvae to complete their development, and so despite the larvae growing rapidly there is only a single generation each year. Eggs are laid from April and in severe outbreaks almost every leaf on the earliest breaking trees will be affected, a single egg is placed against a main or lateral vein and is coated with a black secretion, usually on the underside of
Orchestes fagi 1
Orchestes fagi 2
the leaf, and each leaf may host up to four larvae. Each female will produce between 35 and 60 eggs but if deprived of food, or if they migrate to beech too early, some eggs may be reabsorbed. Eggs are laid over a short period, generally about 8 days, and soon after being deposited the vein swells and splits open, larvae emerge after a day or two and initially begin to mine along the vein, soon moving into the leaf tissue where they produce a narrow mine toward the leaf edge and produce a large blotch mine that spreads along the lateral margin. Fresh mines are white and translucent but they soon turn brown and in older mines the entire structure from the vein can be seen, often with the larvae or pupation site obvious within. Larvae are fully-grown within a few weeks and during May they excavate a wide blotch near the edge and form a cocoon from secretions in which pupation occurs, adults eclose soon after and the entire cycle from egg to adults takes between five and six weeks. New-generation adults migrate to the shrub and herbage layers where they can feed on a constant supply of freshly emerging leaves; these adults will remain in reproductive diapause until the following year when they can feed on fresh leaves after overwintering. Sweeping suitable vegetation is the most straightforward way to record the species but such activity should not be confined to beech; in June 2009 we swept a large population of adults from the lower branches of mature (about 12m) birch (Betula pendula) and the surrounding shrub layer near Brockenhurst, Hants, these were growing among young beech and oak, both of which failed to produce the weevil. In general this is the only member of the tribe likely to be found in large numbers and throughout the range, in certain years, it is an occasional serious pest of beech forests.
These tiny weevils are very distinctive among our fauna and should not be confused with any other species; entirely black or very dark brown with dense pale grey dorsal pubescence, antennae, tarsi and sometimes the extreme tip of the rostrum and tibia red. 2.0-2.8mm. Head visible from above, the vertex and temples usually obvious but the rostrum is usually held beneath body, eyes large and closely approximated, rostrum gently curved and a little wider beyond the antennal insertions; in the female about as long as the pronotum, in the male a little shorter. Antennae inserted about the middle of the rostrum; scape as long as the first 3 segments of the funiculus, funiculus 6-segmented and club slender and pointed. Pronotum transverse, broadest about the base and evenly curved to a constriction before the more or less straight apical margin, basal margin straight. Pronotal punctures coarse, shallow and distinct, usually confluent only towards the apical margin. Scutellum tiny and glabrous or almost so. Elytra elongate-oval, about 3X longer than wide, with sloping shoulders and curved lateral margins, striae very strongly punctured and usually obvious among the fine recumbent pubescence, interstices flat or very weakly convex, smooth at the base and weakly transversely rugose towards the apices. Legs long and robust, the hind femora enlarged and with a series of stout spines along the posterior margins, front and middle femora with a small sharp spine on the ventral surface. Tibiae and tarsi short, the front tibiae a little longer than the tarsi. Claws distinct, not connate, each with a distinct basal tooth.