THE INSECT WORLD. 



121 



proper food-plant. In the case of plants which do not lose their 

 foliage at any period, or in conservatories, or where winter treat- 

 ment for any reason is not feasible, we must attack the insects 

 when the larvae are crawling about, and before they are fixed. 

 At that time, while not protected by a scale, they may be easily 

 killed, almost any of the contact insecticides being effective. 

 Soapsuds, a dilute kerosene emulsion, or a mixture of both, are 

 satisfactory, and a good formula is : kerosene emulsion one part, 

 soapsuds ten parts, the suds being of the strength of one pound 

 of soap to six gallons of water. Whale or other fish-oil soap is 

 better than common laundry soap, and the latter is better than 

 high-grade articles containing only a minimum amount of caustic. 

 This would not hurt any except very delicate plants, while it 

 would be absolute death to larval scales. It is useful in the con- 

 servatory on palms, which are often much infested, and for some 

 of these it might be well to reduce the amount of kerosene to 

 one part of the emulsion with from twelve to fifteen parts of soap- 

 suds. Where the insects are viviparous, or bring forth living 

 young, the spraying must be done systematically, at intervals of 

 four or five days, until no more young appear. On out-door 

 plants the same mixture may be used, but the spraying, if the 

 larvae come from eggs, need not be done more than twice, since 

 as a rule the eggs hatch at about the same time. On the Pacific 

 Coast lime, salt, and sulphur mixtures, and various resin washes, 

 have proved effective, but they are troublesome to make, and 

 hardly cheaper, all things considered, than the soap mixtures 

 above referred to. They act largely by sealing the scales to the 

 tree, so that the young cannot emerge or the adults are stifled ; 

 hence they are most effective where rains are few and far between. 

 The formulae for their preparation will be found in the chapter on 

 insecticides, where their range of usefulness is also stated. 



The species belonging to the family Aleyrodidce resemble 

 scale insects in the immature condition, but are not fixed to the 

 plants, and in the adult stage both sexes are winged, somewhat 

 resembling minute plant-Hce. The striking character by which 

 they may always be recognized is a covering of white, flour-like 

 powder, which renders them easily visible upon the leaves. 

 They are not common on out-door crops in the North, but are 

 not infrequent on house or conservatory plants, becoming more 



