INSECTS AFFECTING CITRUS FRUITS 451 



The remedies for the insect pests must be such as will kill 

 them by external contact, or by suffocating them. The spray- 

 ing of arsenical poisons on the trees would have no effect, for 

 the food is drawn by the insects from below the surface. 

 Fumigation by hydrocyanic gas, the application of kerosene 

 emulsions or similar contact poisons, and recourse to dis- 

 tributing and encouraging the natural insect enemies of the 

 pests, are the remedies chiefly used. 



The following paragraphs give brief accounts of the character 

 and life of a number of the more important of the pests. 

 They should enable those students who have opportunities to 

 visit orange and lemon groves to become acquainted with the 

 insects, and to understand the means of controlling them. 

 Most of the citrus fruit pests, it will be noted, are scale-insects 

 and, therefore, the general account of these insects given in 

 Chapter XXXII should be referred to in connection with 

 the accounts in this chapter of various species of the group. 



The White-fly (Aleyrodes citri). This is by far the most 

 important pest of the citrus trees in the Gulf states. The 

 adults are small white insects with two pairs of wings covered 

 with a white waxy powder, which has suggested the popular 

 names of "white-fly" or "mealy -wings." These insects prefer 

 to rest in quiet shady places, hence they are less common in dry 

 open groves than they are in groves where the foliage is dense 

 and there is considerable moisture. The eggs are laid on the 

 underside of the leaves, preferably on new leaves. The young 

 larvae are similar in appearance to young scale-insects, and 

 move about freely for a short time before they settle on the 

 underside of the leaves and begin feeding. As they are 

 whitish-green in color and translucent they are hard to see. 

 The pupal stage, which is entered a few weeks later, is similar 

 in appearance to the later larval stages. There are usually 

 three broods during the year. As the undersides of the leaves 

 are often almost completely covered with these pests, the 

 injury that they may do by sucking the juices from the leaf 

 tissues is often very great. Perhaps the greatest injury, how- 

 ever, is caused by the sooty mould that grows in the honey-dew 

 that is secreted by these insects. This honey-dew drops on the 



