|Orchestes fagi (Linnaeus, 1758)|
|With the exception of Shetland this species is common and often abundant
throughout the British Isles (Morris, 1993). Typical habitat is broadleaved woodland with a varied shrub layer,
wooded pasture, parkland and hedgerows where the host is present, they occur in Whippendell wood and at Sarrat
Bottom and numbers vary widely from year to year. Adults overwinter in leaf litter or on evergreens eg conifers
or holly and at this time the females are in a reproductive diapause which will last until feeding begins in the
late winter or early spring. Despite the specific name the species persists at sites without beech and it has
been shown that they can succesfully breed on introduced oaks (Morris, ibid). They become active on evergreens
during February and move to hawthorn (Crataegus) as soon as the buds burst, typically a month or so before
those of beech. Adults feed on hawthorn leaves as they open although this may not be the only host at this time;
in lab tests winter starved adults have been recorded feeding on twenty species of tree and soft fruit foliage.
Early feeding ie before beech buds burst is necessary for egg development (Bale and Luff, 1978) although neilson
(1974), studying Danish populations, showed that adults not emerging from the leaf litter until beech bud burst
were able to recognise the host plants, develop eggs and oviposit within 48 hours of feeding. Eggs develop
rapidly and in sequence following adult feeding, typically a female will produce between 35 and 60 eggs but if
deprived of food, or if they migrate to beech to soon, some of these may be reabsorbed. In one study (Bale, 1984)
oviposition occured over a period of 8 days. The relative utility of hawthorn will depend upon the difference in
timing of bud burst between this and beech but as soon as the beech buds begin to burst, or shortly before this,
the weevils move to this host, on a single tree the leaf buds burst over a period of about ten days and the
weevils start to feed as soon as the tissue is exposed. Eggs are laid within the underside of the midribs or
occasionally within a lateral vein and soon after the vein swells and splits along a few mm. The young larvae
begin to mine the vein but soon move into the leaf tissue and tunnel towards the leaf edge or tip. The generally
straight mine is initially narrow then widens towards the edge and a central line of dark frass is conspicuous.
The the white translucent mines soon turn brown and in older leaves may be difficult to see but the oviposition
scars and at least some parts of the mine remain obvious. During May the larvae excavate a wide blotch near the
edge of the leaf in which they pupate within a secreted cocoon. See British Leafminers and Bladmineerders for
excellent colour photographs of these. Mining is only possible in the youngest leaves; as the leaves harden the
young larvae are unable to mine and have been observed to turn back towards the petiole, here young and soft
foliage is essential (Bale, 1984). Overall development is rapid with new generation adults emerging between five
and six weeks after oviposition. Fresh adults migrate to the shrub and herbage layers where there is a supply of
soft new leaves which are preferred to the older, hardened beech leaves, raspberry has been recorded as a host
at this time. New generation adults are in reproductive diapause which prevents them ovipositing on unsuitable,
older leaves and this persists until the following spring, thus the species is univoltine.
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 pendulata) and the surrounding shrub layer near Brokenhurst, Hants, these were growing among young beech and oak, both of which failed to produce the weevil.
These are small but very distinctive weevils, entirely black or very dark brown with antennae, tarsi and sometimes the extreme tip of the rostrum and tibial apices red.
2-2.8mm. Rostrum gently curved, a little wider beyond antennal insertions, in female about as long as the pronotum, in the male a little shorter. Eyes large and, on dorsal margin, very close together, separated by less than half the width of the rostrum near its base. Puncturation coarse and dense. Antennae inserted at or before middle, the scrobes being mostly hidden from above. Scape short; about as long as segments 1-3 of funiculus, and gradually thickened from base to apex. Funiculus 6 segmented; 1 nad 2 elongate, 4-6 becoming more quadrate before a slender and pointed club. Pronotum transverse, evenly curved laterally and broadest at or a littlebehind middle. Puncturation coarse but shallow, distinct with flat and shining cuticle between, below the front margin it may be transversely confluent. Lateral margin without, or with only a few, outstanding setae (cf O.pilosus, O.quercus ). Pubescence yellow, short and recumbent. Scutellum glabrous or nearly so. Elytra elongate-oval, about three times longer than wide, and much broader at shoulders than the base of the pronotum. Striae impressed and punctate to apex, interstices flat or very slightly convex, shiny or, especially towards apex, weakly transversely rugose. Pubescence evenly distributed, golden and backwardly recumbent, mostly in fine longitudinal rows. Hind femora enlarged for hopping, hind edge with a series of stout spine-like setae. Front and mid femora with a small sharp spine underneath. Tibiae and tarsi short, front tarsi shorter than front tibiae. Claws distinct ie not joined at base, each with a distinct tooth at base.
Description from 10 Watford specimens at X20
Bale, J.S. 1984 Bud burst and success of the beech weevil, Rhynchaenus fagi: feeding and oviposition. Ecological Entomology 9:139-148
Bale, J.S. and Luff, M.L. 1978 The foodplants and feeding preferences of the beech leaf mining weevil Rhynchaenus fagi. Ecological Entomology 3:245-249
Morris, M.G. 1993 A review of the British species of Rhynchaeninae. Ent.Mon.Mag 129:177-197
Neilsen, B.O. 1974 The phenology of beech canopy insects in Denmark. Videnskabelige Meddeleser fra Dansk Naturhistorisk Forening 137:95-124.