362 



frequently found are T. oleracea, T. varipennis, T. gigantea, T. luiescens 

 and Pedicia rivosa, L. The adults of T. paludosa emerge during June 

 to September. The larvae hatch in about 14 days and immediately 

 begin to feed. The larval stage varies in length, but probably occupies 

 about nine months, larvae being found in the soil all the year round. 

 In England there are apparently two generations, while in Scotland, 

 probably owing to the difference in climate, there appears to be only 

 one. Damage to crops may be negligible even though the larvae of 

 T. paludosa are present in the soil, and expenments have shown that 

 these larvae can exist in soil and complete their development inde- 

 pendently of the presence of a growing crop in the ground. 



Migration is brought about by scarcity of food in spring, but whether 

 the larvae migrate normally in appreciable numbers in the search for 

 food is as yet uncertain. The opinion has been expressed that the 

 larvae are not migratory [see this Review, Ser. A, ii, p. 606], but the 

 author is convinced that this theory is erroneous. The circumstances 

 determining a destructive attack on a crop seem to be a combination of 

 conditions favourable for the survival of large numbers of young, 

 which in their early days are very susceptible to drought, excessive 

 sunlight, etc., unfavourable conditions for competitors, a ready supply 

 of food and the absence or scarcity of natural enemies. Oats are 

 destroyed only when attacked in the early days of their growth ; 

 after the adventitious root system is established, the plants suffer 

 very little damage. Any conditions which tend to extend the period 

 of germination therefore render the crops more liable to attack. Early 

 sowing is for this reason attended by a certain amount of risk. 



Experiments with insecticides were inconclusive in this connection. 

 A change of seed has been found useful as a control ; seed grown on 

 the coast and sown inland has proved more resistant to the larvae 

 than locally grown oats. 



The subject of remedial measures will be dealt with in a subsequent 

 paper. 



Lees (A. H.). Accessory Wetting Substances with Special Reference 

 to Paraffin Emulsions. — Ann. App. Biol., London, iii, no. 4, April 

 1917, pp. 141-149, 3 tables. [Received 9th June 1917.] 



The wetting power of a fluid is increased by the addition of soft 

 soap provided that there is no substance in the fluid which can pre- 

 cipitate it. Soap alone is however insufficient to cause the wetting 

 of the woolly aphis [Eriosoma lanigenmi] on apple trees, or of the 

 American gooseberry mildew, while paraffin emulsions are liable to 

 scorch the foliage. In published formulae of liquids containing both 

 soap and paraffin, the proportion varies from 100 parts of paraffin to 

 1-2 parts of soap on the one hand, to 100 parts of paraffin to 240 parts 

 of soap on the other. Solutions containing a very small proportion 

 of soap (I per cent.) de- emulsify on standing and are dangerous to 

 use, while those with 1| per cent, soap and 20-25 per cent, paraffin 

 are unsafe as they de- emulsify on being sprayed. Experiment has 

 shown that the best mixture contains 2 per cent, soap, i.e., 20 lb. to 100 

 gals, water, and 2 per cent, paraffin, i.e., 2 gals, to 100 gals, water. 

 The value of this solution lies not only in its own killing power, but 

 in the fact that it acts as a carrier for other fungicidal or insecticidal 



