154 



native of Britain. The formation of the brood-galleries of M. minor, 

 which is described in detail, has already been dealt with in a previous 

 paper [see this Review, Ser. A, iv, p. 47.]. The length of the life-cycle 

 varies according to the season, the temperature and conditions of 

 nutrition. In Central Europe the duration is given as 75 to 84 days ; 

 in Scotland the author observed a hf e-cycle of 95 days. While 31. minor 

 breeds in weakened stems, the author has not found it breeding 

 in stumps, -^here M. piniperda breeds freely. The host-trees of 

 M. minor in Continental forests include several species of pine ; in 

 Scotland the author has found it only in Scots pine. The question 

 of the number of annual generations or broods of M. minor has 

 given rise to some discussion ; the author's observations have led 

 him to conclude that in Scotland the occurrence of a third ammal 

 generation is imjjossible, but that there may be two broods a year. A 

 proportion of the adult beetles, after laying the eggs from which the 

 first brood will develop, leave the parent-galleries and return to the 

 young pine shoots at the top of the tree, and after a nutritious diet a 

 second o\nposition period may follow in a newly made mother-gallery. 

 It is 230ssible that from this second series of eggs a second issue of 

 adults may take place within a year. The same process was obtained 

 experimentally with adults of M. piniperda. 



Both M. minor and M. piniperda are dangerous enemies of the 

 pine and sometimes cause the death of the tree. The periods of 

 greatest damage are from mid- August onwards and from late June 

 onwards ; during each of these periods the adults are feeding on the 

 young shoots prior to oviposition. Additional damage is done in 

 boring the mother and larval galleries. The increase of M. minor 

 may be checked by the use of trap-trees. These should be standing 

 trees selected at intervals throughout the wood, and their use should 

 be continuous from March to October. At regular intervals these 

 traps should be felled and the bark removed and destroyed ; this 

 must be done before the larvae become full grown. Natural enemies 

 of these two species include a Clerid beetle, Clerus formicarius, L., 

 which in both the larval and adult stages is predaceous upon larvae, 

 pupae and adults. The Nitidulids, Rhizophagus ferru-gineus, Payk., 

 R. depressus, F.,and Pityophagusferrugineus, F., as well as Glyschrochilus 

 (T^js) quadripustulatus, L., at times completely clear the galleries of eggs. 

 A small Staphylinid beetle effects similar depredations. A Neuropteron, 

 Rhaphidia sp., is another enemy of the eggs, while a Hymenopterous 

 parasite is foimd feeding externally as a larva on the larvae and 

 pupae of both species. M. minor seems to be almost immune to 

 fungus attack, but M. piniperda breeding on the stumps of felled 

 trees is largely destroyed by fungus mycelia. 



Steven (H. M.). Contributions to the Knowledge of the Family Cher- 

 mesidae, No. i ; the Biology of the Chermes of Spruce and Larch 

 and their Relation to Forestry. — Separate, dated 13th June 1917, 

 from Proc. R. Soc. Edinburgh, xxxvii, part iii, no. 21, pp. 356-381. 

 [Received 5th February 1918.] 



This paper records an introductory research on Aphids of the genus 

 Chermes and their allies, which have already been extensively studied 

 on the Continent in recent years [see this Review, Ser. A, v, p. 592], 



