PETROLEUM-SOAP EMULSIONS. 303 



ally very sensitive to petroleum, and easily destroyed. According to 

 Bretscher the caterpillars do not resist a 3-6 per cent petroleum 

 emulsion. According to Schoyen a cupro-arsenical bouillie of 005 

 per cent of emerald green is superior in its action to milk of lime 

 emulsions. According to Moor the grubs touched appear for some 

 time to be dead, but recover after a while. 



Pierides. — White cabbage butterfly grubs are not killed 'except by 

 a 6 per cent emulsion of jjetroleum. At that concentration 75 per 

 cent of the caterpillars are killed. More concentrated emulsions are 

 injurious to the leaves (Alvood). It is preferable to preserve cabbages 

 by keeping off the butterflies. For that purpose it suffices, according 

 to Prins's experiments, to sprinkle cabbages with a weak emulsion. 



Ocneria dispar, Sch. (gipsy moth). — Petroleum emulsion is of great 

 service. Berlese found that a 5 per cent emulsion kills them outright. 

 To destroy the eggs, pure petroleum must be used. 



NockcidcB {Noctiia). — Petroleum emulsions kill the numerous 

 caterpillars of Noctuae. 



Agrotis Segettim, W. V. (the common dart-moth grey-worm).- — -Not 

 only are the caterpillars of the common dart-moth called grey-worms 

 but also those of many other species of noctua, because they all have 

 the same nocturnal habits and much resemble each other. These cater- 

 pillars often hibernate, and make considerable ravages in the spring 

 by nibbling the young shoots of cultivated plants. The ravages are 

 often so great that their destruction by petroleum is always necessary 

 unless there be many toads on the spot, which are always great 

 destroyers of these caterpillars. According to Decaux' experiments 

 made in 1892, three toads suffice per acre to defend a crop. Eiley 

 advises to kill grey-worms on the large scale by an emulsion contain- 

 ing 0-5 per cent of soap and 1 per cent of petroleum, which is sprayed 

 on the fields at the rate of about 1000 litres per hectare (88 gallons 

 per acre). Degrully advises a mixture of sulphur 6 lb., lime 4 lb., 

 petroleum 10 gallons. Burning rags steeped in petroleum drives 

 them away without destroying them. 



Charaeas graminis. — The caterpillar of this butterfly devastates 

 meadows when it appears in great numbers (Bremen, 1816 and 1817). 

 Eeuter found that they resist a 6-6 per cent emulsion. 



Mamestris Brass'icce, L. (the cabbage moth). — The invaded cabbages 

 must be sprinkled with a 6 per cent petroleum emulsion. A weaker 

 emulsion may be used as a preventive before the butterflies lay their 

 eggs on the young cabbage. Petroleum emulsions have likewise been 

 tried to combat Tortricides. 



ConcJn/lis ambignella, Hubn. (cochylis of the vine). — Zecchini and 

 Silva found that its caterpillar, the worm of the vintage, is destroyed 

 by an emulsion of 2*5 per cent of petroleum and 1 per cent of soap. 

 The vine leaves are sensitive to greater strengths; this dose should not 

 be exceeded. 



Amongst the Tineides or Tinea : — 



Plutella cruciferarum, Zell. (diamond-back moth). — Petroleum is 

 used in the same way as to combat the cabbage noctua. They are 

 easier killed if the emulsion contains quassia extract (Fleischer). 



