115 



MuNRO (J. W.). The Structure and Life-History of Bracon sp. : a Study 

 in Parasitism.— Separate, dated 1st March 1917, from Proc. R. 

 Soc. Edinburgh 1915-1916, xxxvi, pt. 3 (no. 20), pp. 313-333, 

 2 plates. [Received 16th January 1918.] 



The first appearance of a Braconid parasitising the larva of Hylobius 

 abietis in this country was recorded by the author in 1914 [see this 

 Review, Ser. A, ii, p. 661]. The species was then beheved to be Bracon 

 hylobii, Ratz., but is now thought to be distinct. 



Hylobius abietis (pine weevil) is the worst insect pest of forestry in 

 Scotland, attacking and killing newly-formed coniferous plantations, 

 especially those of larch and Scots pine, and occasionally even birch, 

 beech and oak. The adult weevil only is harmful, attacking young 

 trees 3-7 years old during its sw^arming periods, and reducing or 

 stopping the flow of sap by gnawing the tender bark of stem and 

 branch. Eggs are laid in or under the bark of the stumps of trees that 

 have been recently felled, and the larva feeds, bores and pupates in 

 the bark, thus doing no harm. 



The system of forestry now in vogue, by which whole woods are cut 

 down in one felling provides extensive breeding areas for H. abietis, 

 while the immediate replanting of the same areas furnishes the weevils 

 on emergence wath an abundant food supply. 



The species of Bracon concerned is not easily studied in the field, 

 owng to a large pai-t of its life being passed in the tunnels of the host, 

 but observations in the laboratory have proved that pairing takes 

 place almost immediately after emergence. The eggs are always 

 deposited on the hard chitin of the dorsal prothoracic surface of the 

 half- or full-grown grub, and not, as previously stated [loc. cit.], on 

 those only in the resting stage. The act of oviposition, during which 

 an average of seventeen eggs is laid, causes no inconvenience to the 

 host, which continues feeding for 4-6 days and then passes into a 

 quiescent stage, becoming flaccid, and finally, when the parasite is 

 fully fed, being reduced to an empty sac. The hatching of the eggs 

 takes place within 2-4 days, and the larval period, during which there 

 are five stages, lasts for 6-9 days. The cocoon is spun in the cavity 

 of the bark previously occupied by the host. The period of pupation 

 is 3-6 weeks in summer, and 4-6 months in winter, this long duration 

 being a feature of this Braconid's life-history. This parasite is 

 extremely hardy and can endure any conditions suitable for its host 

 (which, so far as the insects inhabiting Scots pine stumps are concerned, 

 appears to be H. abietis only), its distribution coinciding with that of 

 the weevil. So far it has been reported from the eastern counties of 

 Scotland from Ross to IVIidlothian, as well as from Peebles and 

 Renfrew. 



MuNRO (J. W.). The Genus Hylastes, Er., and its Importance in 

 Forestry : a Study ia Scolytid Structure and Biology. — Proc. R. 

 Physical Soc. Edinburgh, December 1917, xx, part 3, pp. 123-158, 

 5 plates, 28 figs. 



From the point of view of the forester, the five species of Hylastes 

 may be divided into three groups — H. ater, Pk., H. cunicidarius, Er. ; 

 H. paUiatus, Gyll. ; and lastly H. opacus, Er., and H. angustatus, 

 Hbst., both of which are rare. 



