IXSECTS AFFECTING PARK AND WOODLAND TREES '245 



direct service 1)\- intentionally tlrivino- a\va\- various enemies of one kind or 

 anotluM", hut it also draws wasps and lices, insects which, while they may not 

 intentionally render a service, in all probability aid to some extent in Scarintif 

 away jjarasites which mi^ht otherwise bt: attracted to the leaves in search 

 of pre\'. 



The honeydew is a disad\ antai^e in certain respects, since it occa- 

 sionally collects on the trees in immense cpiantities and may Ijecomc the 

 mediiun for the growth ot a black sooty fungus which clogs the leaf pores 

 and interferes with the growth and development of th(; tree, something 

 which can hardly be considered favorable to the aphids. Occasionally 

 this honeydew is excreted so copiously that it collects in large drops on the 

 leaves, evaporates and forms semisolid gelatinous masses. This has been 

 repeatedly observed by the writer on Norway maples in particular, infested 

 by a species of Chaitophorus. 



Protective devices. Plant lice or aphids resort to a number of protective 

 devices of one kind or another. Not a few species are covered with a 

 whitish, ])owdery matter which is evitlently an excellent shelter from the 

 wet, since it is almost impossible for moisture to penetrate this excre- 

 tion. This is of the greatest value perhaps to the inhabitants of galls, 

 where the insects are overcrowded ami there is considerable dampness 

 resulting not only from the excretions from the plant lice themselves but 

 also from the interior walls of the gall. Fhese particles of moisture 

 become coated Avith this powdery matter antl roll about among the crowded, 

 struggling plant lice and yet do not wet the individuals because of the 

 enveloping excretion. This is undoidjtedh' of very gn>at imptirtance to gall 

 inhabitants since it is a fact well known to collectors that almost any insect 

 placed in an empt\' corked xial will soon become stuck to its sides b)' the 

 accumulated moisture ami jjerish much sooner than if placed in one with a 

 piece of grass or other footing on which it can sustain itself and jjrevent 

 contact with dampness. In other words, the constant presence of moisture 

 on the bodies of the insects is certainlv very unfavorable to life and may 

 result in sj^eedy death, either from suffocation or possibly by development 



