Observations on the Hibernation of the Beech Weevil

(Rhynchaenus fagi L.) in

Studies on the Fauna of Beech Foliage 3

By B. OVERGAARD NIELSEN Zoological Institute, University of , Denmark

Abstract The estimated density of beetles hibernating in the Hibernating beech weevils were recorded from beech forest floor was about I40.ooo/ha, while miscellaneous habitats. Preliminary quantitative in- about 35.ooo/ha were hibernating in the spruce vestigations on weevils hibernating in a spruce stand. Thus planting of spruce in beech woods stand in the middle of a beech wood and on such creates favourable hibernation sites for the beech hibernating in the beech forest floor were made. weevil.

Introduction Morris (ig68) specimens were collected among the needles of evergreens (Juniperus communis In connection with current investigations on and Pinus sylvestris) during February, March, the beech foliage fauna in Denmark (Nielsen, and October. 1966, 1968) some observations on the hiber- During the winter seasons (December- nation of the beech weevil (Rhynchaenus fagi March) 1965-66, 1966-67, and 1967-68 pre- L.) have been made. The hibernation habits of liminary field studies were carried out in order this species are insufficiently known, and al- to demonstrate some of the hibernation sites though not exhaustive, the present paper used by the beech weevil. In the winter of makes some contributions to our knowledge of 1968-69 this work was intensified thanks to the subject. the assistance of stud. scient. Jens-Ole Frier, Scattered information on the hibernation stud. scient. Finn Mogensen, and stud. scient. sites of the beech weevil is found in text books Nils Skyberg of whose invaluable aid the of forest entomology and in a few papers deal- author here wishes to express his sincere ap- ing with this problem. According to the liter- preciation. ature, hibernation takes place in the forest These studies were carried out in a number floor including soil and litter layer (Ratzeburg of woods in eastern , mainly in the 1839, Boas 1923, Tr?gArdh 1939, Brauns 1964, neighbourhood of Aarhus, viz. Skaade skov, Morris 1965, and Bejer-Petersen 1966), in moss Storskoven, and Marselisborg skov (S of (Ratzeburg 1839, Brauns 1964, and Morris Aarhus), Lisbjerg skov (NW of Aarhus), Son- 1965), in bark crevices and under bark (Ratze- dervore (N of Hammel), Tinning skov (E of burg 1839, Tragardh 1939, Brauns 1964, Weber Hammel), Lyngballe skov (SE of Hammel), 1964, and Bejer-Petersen 1966). Thus several Hemstok skov (E of Rye), Rye Norreskov (W and authors state that the forest floor, moss, of Rye), the woods at Engelsholm (W of bark are the principal hibernation sites; Farsky, ), and Hestehave (S of Ronde); (skov= (1921), however mentions beech weevils hi- wood). bernating in the leaf mines of the larvae, and The hibernating beech weevils were col- according to Morris (1965) specimens were lected in the following way: beaten from Hedera helix in February. Ross- massler (1913) and Fautek (1913) state that (i) By standardized beating of branches of hibernation takes place in bark crevices and young beeches and of spruce growing in under needles of spruce stems, and according to or close to a beech wood; a beating tray 224

Fig. i. Storskoven 5 km S of Aarhus. During the winter of 1968-69 a high number of hibernating beech weevils was found in this spruce stand adjoining a beech wood.

was used and about 25 strong beats con- another, the number of specimens recorded stituted a sample. from the various hibernation sites are not di- (2) Moss, leaf litter, and the upper few centi- rectly comparable. However, the great number metres of soil was also sampled; the size of weevils collected in moss on beech stems, of each sample was about 300 cm2. At on young beeches retaining their leaves during room temperature the weevils left the samples and the remaining specimens were collected by handsorting. Table z. Number of samples collected and number (3) Beech weevils hibernating in the soil and of hibernating beech weevils recorded from various litter layer were also collected by means habitats. of emergence traps. Details of these traps used by the author for sampling soil Dip- tera will be published elsewhere. (4) Moss on beech stems, stumps, and stones was collected; the size of each sample was about 300 cm2. The weevils were collected as above (2).

Results

Table i presents the number of samples col- lected in each habitat and the number of beech weevils recorded. As different habitats have been examined and the collecting methods used consequently varied from one habitat to