158 



originally polyphagous and that the present migrations are remnants 

 of that ancestral condition. The relative suitability of the hosts as 

 regards food and breeding is the impulse inducing any particular 

 migration. He divides modern Aphids into groups on the following 

 lines : — 



A. A group in which there are no real migrations ; two different 

 host-plants are not necessary, but the species are widely polyphagous. 

 Here come numerous Aphidinae, some Lachninae and Schizo- 



NEUKINAE. 



B. A group in which there is facultative migration; two host- 

 plants may be utilised, while the polyphagism of the species is limited ; 

 e.g., Siphocoryne xylostei, Schr., according to Mordwilko, can complete 

 uninterruptedly its life-cycle on honeysuckle. The portion from the 

 first winged parthenogenetic females to the sexuparae and the winged 

 males can, however, be passed on an umbeliiferous host. 



C. A group in which migration is obligatory ; two host-plants are 

 necessary, while the species are only slightly polyphagous. Here 

 come a few Aphidinae, some Schizoneurinae and Pemphiginae. 

 Here also come the species of Chermes. 



Mordwilko's theory is based on wide data, but assumes that the 

 same phenomena within this diverse group (Aj)hids in its widest 

 sense) arose in the same way. All the species of Chermesidae that 

 possess a sexual generation pass that generation on spruce. On the 

 other hand, the parthenogenetic development has arisen on a number 

 of other genera of conifers. In the author's opinion the early theories 

 of spruce as the original host of Chermesids explain this phenomenon 

 more satisfactorily. 



Macdougall (R. S.). Insect and Arachnid Pests of 1916.— ^Tmws. 



Highland & Agric. Soc. Scotland, 1917, pp. 1-38, 39 figs. 

 [Received 5th February 1918.] 



The various insects injurious to agriculture or agricultural products 

 dealt with in this paper include Magdalis jMegmatica, Hbst., of which 

 very little is known. The weevil oviposits on the tops of old pine 

 and spruce trees, and the larvae upon hatching gnaw a gallery below 

 the bark, penetrating sometimes into the pith ; here pupation takes 

 place, the adult eating its way to the outside. Myelophilns {Hylurgiis) 

 'piniperda (pine beetle) has been observed on pine, spruce and larch. 

 The breeding habits and damage caused by this beetle are very similar 

 to those of the allied species M. minor [see this Review, Ser. A, vi, 

 p. 153]. The Scolytid, Cryphalus abietis, occurs on spruce {Picea 

 excelsa) and on noble silver fir {Abies nobilis). Two species of 

 Megastigmus have been reared from cones of silver fir and larch. 

 Perrisia (Cecidomyia) strobi oviposits in young spruce cones, and the 

 larvae feed on the seed and pupate in the cones under cover of a very 

 delicate cocoon. An unidentified Cecidomyid infests larch cones, 

 while the buds are also frequently injured by a Cecidomyid larva. 

 It is hoped to rear the adults of these. Cydia (Tortrix) strobilelki, L., 

 o^dposits on the scale of spruce cones in May and June, and the larvae 

 on hatching jDass to the centre of the cone and eat into the axis, 

 destroying it before it has hardened. The whole life-cycle is passed 

 within the cone, the larvae feeding during summer and early autumn. 



