396 



control b}^ natural enemies, and it is now realised that immunity 

 from insect attack, produced by the injection of caustic potash, 

 promises to be the most successful means of obtaining copious flushes 

 of tea [R.A.E., A, viii, 204 ; x, 153]. While the older methods have 

 a certain value as accessory measures, it is far better pohcy to attempt 

 to control Helopeltis by careful cultivation, improved drainage, the 

 use of proper agricultural implements and the application of suitable 

 substances to the soil. 



Severin (H. H. p.). Control of the Leafhopper. — Facts about Sugar, 

 New York, xiv, nos. 16 & 17, 22nd & 29th April 1922, 

 pp. 312-313 & 332-333. 



A study of the beet leaf-hopper, Eutettix tenella, Baker, and of its 

 role in the dissemination of curly-leaf, has shown that many of the 

 nymphs and adults are non-infective under natural conditions, and 

 it is evident that certain plants growing in the areas where beet is 

 cultivated do not harbour the virus of curly-leaf and that the hoppers 

 breeding on such weeds are non-infective. The transmission of the 

 disease by infective over-wintering adults from plants in the cultivated 

 areas to vegetation on the plains and foothills of California has already 

 been described [R.A .E., A, vii, 474]. It has also been proved, however, 

 that an infective leaf-hopper, having completed all the nymphal 

 instars on an infected beet plant, does not transmit curly-leaf daily ; 

 in an experiment on these lines only five plants developed the disease 

 out of 49 beets used. 



In years with heavy, early autumn rains, winter treatment may 

 have to be adopted if a large number of leaf-hoppers remain behind 

 in the cultivated areas, but if no green vegetation is available the 

 number of stragglers will be almost negligible. 



Experiments with nicotine dust as a remedy, made after careful 

 study of the flights and seasonal appearances, show that from four to 

 six applications are necessary to control the spring brood, and this 

 would become too expensive in a natural breeding area. The possi- 

 bility of sugar companies reducing the cost of nicotine dust by using 

 the waste lime from the manufacture of beet-sugar to replace the 

 kaolin, and suggestions for a combined dusting and mixing machine 

 are discussed. If these methods proved practicable, there would 

 still be the difficulty of shortage of nicotine, and the possibility of 

 sugar companies growing their own tobacco for the purpose is briefly 

 touched upon. 



MozNETTE (G. F.). The Red Spider on the Avocado.— C/.5. Depl. 

 Agric, Washington, D.C., Bull. 1035, 17th February 1922, 

 15 pp., 11 figs., 1 plate. 



These observations on Tetranychus yothersi, McG., were carried out 

 during 1918 and 1919 in Florida. Some food-plants have already 

 been recorded for this mite [R.A.E., A, iii, 3061 ; the author found 

 it on West Indian and Guatemalan varieties of avocado (Persea 

 gratissima), mango {Mangifera indica), camphor {Cinnamomum 

 camphora), Australian silk oak {Grevillea robusta), Eucalyptus sp., 

 Terminalia arjuna, Anona squamosa, Cucumis sativus and Icacorea 

 paniculata. Descriptions are given of the various stages. 



The incubation period varies from 4 to 11 days according to tem- 

 perature and general climatic conditions ; during April and May, 



