332 ANNUAL REPORT SRHTHSONIAN INSTITUTION, 194 



Mealybug wilt of pineapples is another important example of a 

 disease caused by the toxic injections made by an insect when it feeds 

 (pi. 3). By 1930 this disease had made such inroads that the pine- 

 apple industry in Hawaii was in serious jeopardy, and even now con- 

 trol metliods must be rigorously maintained. The mealybug, carefully 

 fostered by several species of ant, moves into the pineapple field from 

 the weedy field margins and establishes itself on the pineapple 

 plants on which it feeds. The mouth parts of the mealybug are 

 very long — almost twice as long as the insect itself — and when not 

 being used are curled up like a lasso. Their great length is of 

 value to the mealybug since it can remain in one place on the leaf 

 and yet reach a considerable leaf area with its long probing mouth 

 parts, sucking the juice from particular cells in the leaf. 



During the feeding process, and probably as part of it, the insect 

 injects into the leaf some substance which is powerful enough to 

 pass down the leaf to the roots and kill them. The natural conse- 

 quence of this is that the plant wilts down in a manner very similar 

 to wilt due to extreme drought. In this stage the plant is low in 

 sap, and the mealybugs leave it and move on to adjacent healthy 

 plants. These in turn wilt and the process goes on until, without con- 

 trol measures, a field may be ruined. When the mealybugs have 

 left a plant, new healthy roots are put out and the plants makes a gal- 

 lant effort at recovery. If wilt has occurred while the plant-was only a 

 few months old, worth-while recovery sometimes occurs, but usually 

 the fruits are too small to be of commercial value. Recovery is of 

 principal interest in demonstrating that the removal of the mealybug 

 and, with it, the toxic substance it injects, results in new wilt-free 

 growth. 



Psyllid yellows and mealybug wilt are cases in which the effect 

 of the injected toxin is general throughout the plant affected, but 

 the more common examples of the toxic effect of insect feeding are the 

 almost innumerable cases where the effect is localized to a very small 

 area around the actual feeding point of the insect or, at most, a short 

 distance away. The stippling effect on leaves fed upon by leaf- 

 hoppers, the spotting of leaves by the scale insects and mealybugs, 

 and the curiously varied symptoms produced by the so-called mosquito 

 bug on tea and many other crops, are all cases in point, but only 

 the last-named can be discussed here. 



The mosquito bug is not even related to the mosquito, but derives 

 its name from its general appearance — long narrow body and un- 

 usually long legs and feelers. Actually it is one of the sucking plant 

 bugs of which the chinch bug is a better known example. The list 

 of plants which the mosquito bug affects is noteworthy because of the 

 extremely diverse symptoms which result. Typically, a red spot on 

 the leaf follows the insect's feeding. This spot dies and withers. In 



