450 



why the chemical remained on the plants for as long as 12 days, while 

 similar sprays containing free nicotine quickly disappeared. It was 

 found that nicotine sulphate is non-volatile, and when hard water and 

 soap are used in the spraying mixtures the alkalis contained in these 

 substances set free the nicotine. The effects will vary according to 

 the alkalinity of the water, the amount of alkali in the soap and 

 the brand of commercial nicotine sulphate used, and this explains the 

 different results obtained in the use of tobacco extracts and the reasoi 

 why soap greatly increases the efficiency of sprays containing nicotine 

 sulphate. As nicotine vapour is the principal cause of the death of 

 insects in spraying with tobacco extracts, the maximum efficiency of 

 those containing nicotine sulphate can best be obtained by rendering 

 the spra}^ alkaline before use. Commercial tobacco extracts containing 

 nicotine sulphate should not be applied on greenhouse plants intended 

 for use as food, though tobacco extracts or tobacco papers containing 

 free nicotine may be employed with safety. Plants so sprayed, how- 

 ever, should not be cut for the market imtil the day after spraying. 

 If the temperature of the house be low, a longer period should be 

 allowed for the nicotine to evaporate from the leaves. 



Baker (A. C.) & Davidson (W. M.). A Further Contribution to the 

 Study of Eriosoma pyricola, the Woolly Pear Aphis. — Jl. Agric. 

 Research, Washington, D.C., x, no. 2, 9th July 1917, pp. 65-74, 

 2 plates, 1 fig. 



In the present paper, which is a continuation of an earlier one [see 

 this Review, Ser. A, iv, p. 369], the history of the various forms of 

 this Aphid recorded on pear roots is discussed. A description is given 

 of the stem-mother and the spring migrant of Eriosoma pyricola and 

 these forms are particularly contrasted wath those of E. lanuginosum. 

 In the earlier paper it was mentioned that the autumn sexuparous 

 migrants leave the pear roots upon which they have developed and 

 fly to elm trees, where they deposit the sexual forms on the trunks 

 and limbs. Ulmus americana and U. campestris are both used as hosts, 

 but the latter is preferred. The female after pairing deposits a single 

 egg in a crack in the bark or underneath a bud- scale. From this egg 

 the stem-mother hatches in late March or April and ascends the trunk 

 or limb to an expanding leaf. After it has fed for a few days on the 

 under-surface, the leaf curls over, and by the time the insect is in the 

 third instar the leaf has entirely closed round it, forming a gall. The 

 stem-mothers feed 4 or 5 weeks in the immature stages and after 

 maturity is reached the gall grows rapidly. The mature fundatrix 

 deposits young prolifically, sometimes as many as 300 during the 

 4 or 5 weeks of her adult life. The young, -wingless forms mature in 

 about 3 weeks inside the gall, and apparently give rise to another 

 generation, which later acquires wings. By the end of June nearly every 

 gall examined contained winged forms ; these begin to fly off at this time 

 and practically all had disappeared by the end of July. Many larvae 

 and pupae are destroyed by predatory insects, such as the Coccinellid, 

 Scymnus sp., and Chrysopid larvae, which gain admittance to the 

 interior of the galls after mid-June. Spring migrants were observed 

 on pear foliage and deposit their young on pear trunks at or near the 

 soil surface. Root-feeding generations were bred in the laboratory in 



