533 



understood. Failure of food supply has been suggested as causing the 

 development of a high proportion of winged forms, and the presence of 

 solutions of various salts has been thought to have the same result. 

 Experiments have been recorded in which 100 per cent, of winged 

 forms were produced by watering the food-plants with certain sub- 

 stances such as the salts of magnesium, antimon3% nickel, tin, zinc 

 and sugar, while tap-water, alcohol, tannin, urea, salts of strontium, 

 potassium, calcium, etc., are reported to be non-wing producing 

 substances. The Aphids were susceptible to the treatment for three 

 or more days after birth, according to the species. 



In 1920, the author, wishing to obtain a number of winged females, 

 experimented with Myziis ribis (red currant aphis), placing individuals 

 newly born from stem-mothers on cuttings of red currant watered, 

 some with tap-water and some with magnesium sulphate. The results 

 are shown in a table, where it is seen that the percentage of winged 

 individuals varies from 70 per cent, to 4 per cent, on cuttings watered 

 with magnesium sulphate, and that the largest proportion (90 per cent.) 

 was obtained where nothing but tap-water was used. A further 

 experiment seemed to show that magnesium is not the only determinmg 

 factor in wing production, although it is quite possible that the x\phids 

 may react to metabolic changes in the food-plant induced by an 

 abundance of such salts in the soil. The proportion of winged females 

 of the pea Aphid, Acyrthosiphon {Macrosiphitm) pisi destructor, has 

 been raised by periodically starving the parent during its development, 

 but it is pointed out that periods of total abstinence, alternating with 

 periods of normal feeding, w^ould not necessarily produce the same 

 effect as continuous feeding on an inadequate diet. 



It is known that the maximum production of winged forms in many 

 species takes place in the third and fourth generations, when food is 

 abundant, and then diminishes in a marked degree [R.A.E., A, vii, 

 371] ; it is also pointed out that in most species the last individuals 

 of the cycle (the oviparous females) appear just before the leaves fall 

 and are invariably apterous. 



It is concluded that the factors controlling the production of winged 

 forms cannot yet be considered as determined, and may prove in part 

 to be cyclical. 



CuNLiFFE (N.). Preliminary Observations on the Habits of Oscinella 

 frit, Linn. — Aiui. App. Biol., Cambridge, viii, no. 2, August 1921, 

 pp. 105-133, 1 fig., 12 tables. 



A study of the frit-fly, Oscinella frit, L., has been made in Britain 

 in view of the fact that most of the data published in recent 3'ears have 

 been of Russian origin. Adults were found to be prevalent in the 

 field throughout the year except from November to April. The pre- 

 valence curves indicate that high prevalence is associated with high 

 temperatures, while emergence is dependent on rainfall, and should 

 not be associated with any particular generation. The first generation 

 becomes abundant in the first week in June, and it seems from experi- 

 mental data obtained in 1919 and 1920 that three, or even four, genera- 

 tions may be produced in a favourable season. The periods between 

 emergence of successive generations are about 50 days in spring, 35 

 days in summer and 230-250 days in winter. Summer food-plants 

 include Arrhenatherum avenaceum, Festuca pratcnsis, Lolium italic urn, 

 L. perenne and Poa annua ; and in the winter, Alopecttrus myosnroides, 

 Arrhenatherum avenaceum, Hordeum pratense, L. italicum and 



