ON CERTAIN SEED-INFESTING CHALCIS-FLIES 



Order Hymenoptera. Superfamily Chalcidoidea 



The members of the superfamily Chalcidoidea or Chalcis-fiies, to 

 which the species treated in this bulletin belong, are mostly parasitic 

 on other insects and closely allied forms. While these minute creatures 

 exist everywhere in almost countless numbers, until recently they have 

 received comparatively little attention from entomologists owing to 

 their small size and to the scattered and confused condition of the liter- 

 ature relating to them. Although only a small proportion of the forms 

 existing in the world are known to science, between 5,000 and 5,500 

 nominal species have been described. 



Of this number, the great majority may be considered as beneficial, 

 since they prey as parasites on other insects, while a much smaller 

 number, probably not over 100 species, are known to have vegetable- 

 feeding habits. 



The practice of deducing the probable habits of a given insect from 

 its systematic relationship, while of undoubted value, especially as a 

 basis for a working hypothesis at the beginning of a study, must be em- 

 ployed nevertheless with the greatest caution and the conclusions 

 checked by exact observation and careful rearing. The current classifi- 

 cation of insects, based primarily on structure, represents or should 

 represent their blood relationships. While there is usually a close 

 correlation between habits and structure, habits are more divergent 

 and more readily adapted to special conditions than are the less plastic 

 structural characters. Considering the relative ease with which an 

 organism may change its habits of life while retaining the same type 

 of structure, we should not be surprised to find forms so closely related 

 in structure as to belong to the same genus yet with habits so divergent 

 that some are vegetable-feeding while others are parasitic, that is 

 animal-feeding. Such conditions exist among the Chalcis-flies and at 

 first glance appear highly anomalous. 



Aside from the Agaonidae or Fig-insects, whose larvas infest the 

 seeds of figs, the first Chalcis-flies definitely proved to be vegetable 

 feeders were the Isosomas or Joint-worm flies studied by Harris, Fitch 

 and Riley. More recently a number of forms have been found which 

 in the larval condition devour the kernel of various seeds. Of special 

 interest, as throwing light on the habits of these forms, are the recent 

 papers of MacDougall on the Megastigmus of the Douglas Fir seed,* and 



» Trans. Roy. Scot. Arbor. Soc, XIX., pp. 52-65, 1906, 



