On a Pine Sawfly and its Parasites

PINE SAWFLY AND ITS PARASITES

177

Long-tailed Mouse (M. sylvaticus, Linn.).—Common and damages bulbs.

[Harvest Mouse (M. minutus, Pall.), though not observed, is nearly sure to occur. It was (Trans. Norf. Nat. Soc. ix, p. 455) plentiful in eastern Suffolk during 1911.]

Water Vole (Microtus amphibius, Linn.).—Common.

Field Vole (M. agrestis, Linn.).—Common : they have been caught inside Fakenham rectory.

Bank Vole (Evotomys glareolus, Sch.).—Have seen them uncommonly in the bank between Fakenham rectory grounds and the Drygrounds : 28 June 1899, Oct. 1919, etc.

Common Hare (Lepus Europaus, Pall.).—Decreased greatly about 1924 ; but recovered after the Duke took to coursing, and very numerous during 1928-30 : two hundred and seventeen killed between Fakenham and West-farm in Bamham on 4 February 1930.

Rabbit (L. cuniculus, Linn.).—Very numerous formerly ; but they have been much killed off of late years, a mistake because a great deal of the land, especially in Euston Park, is fit for nothing eise. Increasing again in 1930, when nearly six hundred were killed in the first time over Hercles, a large field between Fakenham and Euston.

ON A PINE SAWFLY (Diprion sertifer, AND ITS PARASITES. BY

JOHN

C.

ROBBINS,

Fourc.)

F.E.S.

THE larvae of the rufous Pine Sawfly, D. sertifer (Lophyrus rufus, Latr.), appeared during 1926 to 1928 in large numbers on young plantations of Pines (Pinns sylvestris, L.) belonging to the Forestry Commission at Tangham near Woodbridge ; and a considerable amount of money was spent upon crushing them by hand, as the infestation was sufficiently severe to cause some alarm. Fortunately a disease arose, which killed many of the larvae before they became fully grown, making them to turn yellow, then blackish, and finally to shrivel and adhere to the pine-needles ; this disease appeared to reduce the numbers of the pest considerably.

Upon visiting Tangham on 20 May 1929 I could find only four trees whereon larvae were feeding ; but later they became fairly numerous, although less abundant than the previous year. In the following month Mr. C. Hankins, the Forester there, to whom I am indebted for much help, sent me several hundred larvae, which I reared in confinement. I went again to Tangham on 10 May 1930 and found more young larvae

178

PINE SAWFLY AND ITS PARASITES

than in the preceding season. Some of those that I obtained during 1929 died of that disease which arose in the field in previous years; but a large number spun cocoons, and these were nearly all completed by the end of June. Most of them produced adult sawflies in the course of the following autumn: about 275 females and 52 males emerged between 1 September and 19 November. A few cocoons, however, remained unopened through the winter of 1929-30 ; and, between the ensuing 24 April and 30 May, six Hymenopterous parasites emerged.

A few cocoons still continued intact and, in October 1930, several more sawflies came out, fifteen months after the cocoons' construction. On the last day of that month, two yet contained living sawfly larvas, so possibly these will produce adults in the autumn of 1931 if left undisturbed. [One emerged 12 x 1931.]

Considerable difficulty was experienced in obtaining copulation and oviposition in captivity ; but some eggs were laid during the first half of October 1929 by imagines sleeved on a Pine-tree in the open, and I saw one female, that was confined on a young potted Pine indoors, pair on 10 November and oviposit on the two following days. The potted tree was kept in the open during the winter months. Eggs were deposited in the needles of the new growth, each being inserted into a separately-excavated pocket; and, although several eggs were laid in each needle, no connection existed between the pockets. At first the eggs' depositories could scarcely be detected, unless the needles were held to the light; but, after a week or two, the leaf-tissue around the ova turned yellowish.

On 18 April 1930 I noticed that the eggs in the needles were apparently swelling, and on 25th they began to hatch. Upon emergence the larvae have greenish heads but, within twentyfour hours, these assume the jet-black appearance that is characteristic of the species throughout the rest of its larval life. Hatching seemed to be completed by about 4 May; and, by 2 July, all the larvae that survived had spun cocoons.

The above results indicate that in Suffolk D. sertifer normally has one generation a year, and passes the winter in the egg State.

In the latter respect it differs from the common Pine Sawfly {D. pini, L.) and, indeed, from almost all others ; for D. pini* follows the general rule in hibernating in its cocoon as a fully-developed larva. In another habit also, it differs strikingly from D. sertifer: its eggs are laid in each needle in a continuous slit, which is closed with a coyering consisting of * Since 1908, when this injurious species was found to be delightfully rare in Suflolk (cf. Entom. xxxi, p. 175), we have bred Lophyrus pini from only a few cocoons taken in Blythburgh Wood on 14 September 1912.

L. sertifer, Geoff. (for whose life-history cf. Ivar Trägardh's " Roda tallstekeln, L . sertifer " in Entomol. Tidskr. 1910, pp. 272-8) occurs on Scots Pine-trees in our Monks' Soham garden.—Ed.

179 material excavated from the tree by the saws and cemented with an adhesive secretion of the parent female. Its larvae vary considerably in colouration ; but the head is never, I believe, entirely black.

The parasites, that emerged from my cocoons of D. sertifer during 1930, belonged to three species of the Ichneumonid tribe Tryphonides ; and were kindly identified for me by Dr. Ch. Fernere :—Exenterus marginatorius, Fab., one male emerged on 24 April and two females on 24 April and 21 May; Mesoleius (Torocampus) eques, Htg., one male on 26 May and one female on 30 t; and Perilissus (Lophyroplectus) luteator, Thunb., one female on 21 May. The first is a common parasite of D. sertifer and other species of its genus in northern and central Europe ; but Mr. Claude Morley, who kindly confirmed the determination, knew (lehn. Brit. vol. iv, p. 206) only two records of its occurrence in England. The two latter parasites are both recorded from D. sertifer and D. pini on the Continent, but appear to be new to Britain.

I exhibited speeimens of E. marginatorius and T. eques at a Meeting of the Suffolk Naturalists' Society on 1 August last; my sole L. luteator is now in the British Museum.

BIRD NOTES IN 1931.

BIRD NOTES IN 1931 FROM A BUXHALL GARDEN.

BY C. E. HARVARD.

RESIDENTS.—Mistle-Thrush (Turdus viseivorus) : a winter visitor only. Song-Thrush (T. musicus) :firstegg 7 April, a month later than in 1930. Blackbird (T. merula) :firstegg 10 April; very late in nesting. Redbreast (Erithacus rubecula) :' first nest 13 April. Hedge-Sparrow (Accentor modularis) : a nest found, containing one egg and the egg of a Cuckoo. Tits, Great (Parus major) and Blue (P. caruleus) and Marsh (P. palustris), nest in boxes ; the Coal (P. ater) is a winter visitor only ; and the Long-tailed (Acredula caudata) has been very scarce since the aretie spell of 1928-9. TreeCreeper (Certhia familiaris) : nest of four eggs on 5 May. Pied Wagtail (Motacilla lugubris) : a pair nest regularly in the creeper on the house,firstbrood hatched on 18 May. Finches, such as Greenfinch (Ligurinus chloris), Chaffinch (Fringilla fWe have examined these two species and are satisfied that the latter is a mere form of Mesoleius bicolor, Grav. (lehn. Brit. iv, 149) with developed alar areolet, an extremely variable and unrehable character throughout the tribe Tryphonides, whereon Continental authors place quite unwarranted stress.—Ed.