THE HEMIPTERA 



179 



difficult to determine. It may be that the disease is not already present 

 where it is desired to introduce it because conditions there are such that 

 it will not thrive. Fungous diseases at least are influenced to a very 

 large degree by the weather, most of them thriving best in warm, moist 

 weather and if these conditions are not present they will amount to little. 

 At the present time it would appear that the success of artificially 

 introducing diseases to control insect attacks is so dependent upon 

 weather conditions that man can do little more than supply the disease 

 and trust that the needed kind of weather may follow. Unfortunately 

 the very conditions under which injurious abundance of the insect takes 

 place, appears in too many instances to be those distinctly unfavorable 

 to the spread of the disease. 



Family Tingididae. — The insects (Fig. 167) of this family are delicate 

 little bugs, usually having the pronotum broadly expanded and, with the 



Fig. 167. — Example of a Tingidid Bug (Gargaphia solani Heid.), enlarged about ten times 

 (From U. S. D. A. Farm. Bull. 856.) 



hemielytra, covered with reticulated marks, giving them something the 

 appearance of a bit of lace and this has been responsible for their com- 

 mon name — lace-bugs. They are rarely more than an eighth of an inch 

 long, usually whitish in color, and suck the sap from various plants, 

 being generally found on the under side of the leaves. Their eggs are 

 placed on the leaves, generally at the tops of small, brown, rather conical 

 projections produced by the bugs, and which somewhat resemble places 



