371 



The fluctuating occurrence of these injurious insects, due to the 

 quantity and quality of food present, meteorological conditions and 

 the presence of natural enemies, is discussed, many examples being 

 quoted. In forests composed of a single species of tree, the parasites 

 of injurious insects may continue to increase while the host remains 

 numerous, but decrease to such an extent when there is a reduction 

 in number of the host that they are often incapable of effecting 

 anything against the next generation ; in a mixed forest on the 

 other hand some parasites may find another host that is infesting 

 another species of tree. For example, in 1917 the author observed 

 that in a pure pine-forest there were only 10 per cent, of parasitised 

 eggs of Dendrolimus remota, while in a mixed one there were 68 per 

 cent., the count being made from 6,000 eggs in each case. In another 

 investigation the percentage of parasitism in 1,000 eggs of Dendrolimus 

 remota was 24-37 and of D. superans 61, and in 1,000 pupae of 

 Dendrolimus remota 41, of Zethenia rufescentaria 31, and of Caligula 

 japonica 21. 



Haviland (M. D.). On the Life-History and Bionomics of Myzus ribis, 

 Linn. (Red-Currant Aphis). — Proc. R. Soc. Edinburgh, xxxix, no. 

 1, 1918-1919, pp. 78-112, 9 figs. [Received 1st July 1919.] 



The red blisters found on red currants {Ribes rubrum) are probably 

 caused by the fundatrix stage of Myzus ribis. The dimorphic characters 

 of the antenna and of the abdominal and wing dimensions of this 

 Aphid are probably determined by the nature of the food, whether 

 healthy or bhstered ; the forms from healthy leaves are therefore 

 probably those that have been recognised as M. whitei, Theo., and 

 M. dispar, Patch, in England and America respectively. 



Observations have led to the conclusion that certain Labiatae and 

 other weeds form the summer food-plants of M. ribis, this form having 

 been previously described as Phorodon galeopsidis, Kalt. The entire 

 life-Cycle may be passed on the currant, but if transferred from the 

 summer food-plant back to currant, the Aphids die. The disappearance 

 of the Aphid in the late sunmaer is partly due to the diminished birth- 

 rate and partly to the increase of insect enemies. In the open 4 

 and 5 generations have been noticed ; in laboratories as many as 7. 



The principal natural enemy of M. ribis is a Braconid, Aphidius 

 ribis, Hal., but it does not attack the alate forms. Other enemies 

 are Cecidomyiids, Chrysopa, a mite, Anystis cornigera, Koch, and 

 a fungus, Empusa aphidis. 



Spraying as soon as the buds open in April with nicotine solution, 

 paraffin emulsion or soft-soap is advised. All bhstered leaves should 

 be picked off where possible and the spray repeated in May. Spraying 

 in October with paraffin jelly is suggested to destroy the sexuales. 

 All weeds such as Lamium, Polygonum and Veronica should be 

 removed from the vicinity of currant bushes. 



Lees (A. H.). Phyllopertha horticola, Linn. — Gardeners^ Chronicle,. 

 London, hxv, no. 1699, 19th July 1919, p. 36, 1 fig. 



Phyllopertha horticola, L. (June bug) has been causing great damage 

 to many crops, including wheat, in the neighbourhood of Wisley. 

 The eggs are laid in the ground and the larvae feed on roots of grasses. 



