FAM. MEMBRACID^ 41 



structures. We believe, also, that the general distribution of the Membracida over the surface of the 

 earth may be explained largely on the basis of migrations regulated and governed bj' the size and 

 positions of the land masses and land bridges of previous geological periods. 



ECONOMIC IMPORTANCE 



The Membracidse, as a family, are of little economic importynce. Since they are not flower- 

 visiting insects they are of no value in the cross-pollination of plants, and they produce no materials 

 valuable to man; on the other hand, they destroy no food products, the damage which they may cause 

 to vegetation is so insignificant that except in the case of a very few species it is negligible, the}' do not 

 feed on plant tissues, and so far as is known they are not carriers of disease. 



The manner in which membracids may cause damage to plants is limited to tvvo habits, feeding 

 and oviposition. Of these the latter is the more harmful. 



So far as feeding is concerned, there is little evidence that Membracidce cause any injury to the 

 host. The quantity of sap consumed by the insects is negligible, and the wounds made by the incisions 

 of their beaks are neither large eiiough to destroy tissue nor extensive enough to offer opportunity for 

 infection. In fact such incisions cannot usually be found even with a microscope a few hours after 

 the process. Trees that are literally covered with Membracida seem in no way less healthj' than those 

 on which no insects are found. Careful examination of trees in the field shows absolutely no indication 

 of injury from feeding habits. 



The egg-laying process may be more destructive, but even this process in most species is of 

 little concern. In most cases the sht made by the ovipositor is clean and sharp and very superficial, 

 seldom extending to the cambium and usually heahng at once leaving onl}' a faint scar. The phloem 

 tissue if injured is not so extensively damaged as to interfere with its function, and the injured part, 

 in dicot^ledons at least, would usually slough off naturally within the first or second season. The ovi- 

 positor in most of the species is neither long nor powerful, and in those forms in which the eggs are 

 laid in the stems of trees — which include the larger nuniber of species — the organ does not reach 

 the xylem or, reaching it, is not able to penetrate the harder wood and slips to one side, leaving the egg 

 between the wood and the bark. In the cases in which the eggs are laid in buds, the part of the bud 

 usually chosen is the outer scales, which are not thereby prevented from performing their functions as 

 protective structures and are of little importance in the later development of the plant. 



There are, however, exceptions to the foregoing general statements. Certain species of the 

 genus Ceresa in North America are known to cause rather serious damage to young stems and twigs 

 because of the fact that the eggs are laid in curving, parallel rows and the bark is cut in such a fashion 

 that it fails to heal and leaves a conspicuous line of scars. These scars persist for several years and 

 are occasionally infected with fungi and offer an entrance for other insects. If such punctures are made 

 in very young twigs or in the soft stems of annuals, especially if made close enough together to girdle 

 the stems, the results may be serious. In a somewhat similar maniier, damage may be done to buds 

 by those species which lay their eggs in buds, particularly if the buds happen to be small ones in which 

 the internal tissues may be reached. Species oi Slictocephala and Etichenopa in the United States have 

 been known to destroy small buds of fruit trees and of the butternut in this manner. In most cases, 

 however, the buds chosen for oviposition are the large terminal buds and the eggs are so lightly inserted 

 that they may be seen projecting on the outside of the bud. In these cases very little damage can 

 result. In a few instances, on the other hand, the buds chosen have been so small and the eggs so 



