216 THE PRINCIPLES OF FLORICULTURE 



(4) Exterminated by poisonous fumes or contact mixtures. 

 White Flies, Aleyrodes vaporarium Westw. 

 Thrips, Heliothrips haemorrhoidalis Bouche. 

 White Mealy Bugs, Orthezia insignis Dougl. 

 Yellow Mealy Bugs, Dactylopius destructor Comst. 



f Aspidiotus, various species. 



I Diaspis, various species. 

 Scale Insects j Chionaspis, various species. 



Lepidosaphes, various species. 



[ Lacanium, various species. 



242. Method of attack. It will be observed from the above 

 classification that few greenhouse insects are injured by direct 

 poisons such as Paris green and arsenate of lead. The larger 

 part are killed by contact poisons or by fumes of poisonous gases. 

 Formerly, fumigation by gases was looked upon with suspicion, 

 because of the deadly character of the fumes, but now, with 

 improved methods of control and application, it has come into 

 more general favor. The practice of spraying with poisonous 

 solutions is rarely followed in greenhouse work. 



243. Pests exterminated by hand picking or arsenical sprays. 

 Among the larvae of insects which cause much injury to flower 



crops, are various so-called caterpillars. Many of them feed 

 on leguminous crops, such as the sweet peas ; some feed on chrys- 

 anthemum foliage and others on the rose. 



Among insects destructive to rose foliage is the oblique- 

 banded leaf -roller, Archips rosaceana, which is especially trouble- 

 some at times. The leaf-roller causes the greatest amount of 

 damage during the fall and spring. It is of a light cinnamon- 

 brown color, with three broad, oblique, dark brown bands across 

 the wings. The moth deposits the egg masses on the bark, and 

 from these the larvae hatch. These are light green in color, 

 varying in some specimens to a red- or brown-green. They feed 

 on the foliage, and it is during the larval stage that most of the 

 damage is done. Before pupation, the larva draws the leaves 

 together, thus forming a cocoon. From the pupa, the moth 

 emerges, and the round of the life cycle is complete. 



244. Remedial measures. Experiments in fumigation with 

 hydrocyanic acid gas prove that the larvae are not seriously 

 injured by this treatment. During the feeding season, the 

 foliage may be sprayed with arsenate of lead, using three pounds 

 of lead to fifty gallons of water. This, however, may spot the 

 foliage, and unless the plants are seriously infested, it would 

 hardly be advisable to use poisons of this sort. 



