USINCER: HEMIPTERA 535 



The growth of collections marks the development of most of the systematic 

 sciences and this is trne in hemipterology as well. The great collections of the 

 present time are the collections of the British jMnseum (Natural History) in Lon- 

 don, the Natnrhistoriska Riksmnsenm in Stockholm, and the great museums in 

 Helsinki, Vienna, Berlin, Paris, Budapest, Leyden, Genoa, and to a lesser extent 

 elsewhere on the European continent. In the United States great collections were 

 developed somewhat later, and among these may be mentioned those of the United 

 States National IVIuseum, the Museum of Comparative Zoology, the American 

 Museum of Natural History, the Academy of Natural Sciences at Philadelphia, 

 the California Academy of Sciences, the Carnegie Museum, the Chicago Natural 

 History Museum, the Museum at Cornell University, the Snow Museum at the 

 University of Kansas, the Museum at the University of Michigan. 



Progress in the classification of Hemiptera may be marked not only by the 

 traditional taxonomic works but also by great landmarks in improved ap- 

 proaches to the subject. One of these was the pul)lication by Singh Pruthi on 

 male genitalia in the Hemiptera. This work was published in 1925 and provided 

 a new set of data upon which to base classifications. Another new set of charac- 

 ters was discovered by Tullgrcn (1918) and Ekl:)lom (1928). These authors 

 found the maxillary levers to be of significance in the higher classification of 

 the Hemiptera, and also found that the arrangement and position of the tricho- 

 bothria were of significance in the over-all classification. 



During the period of taxonomic progress, other students were furthering our 

 knowledge of the biology of the Hemiptera. Among these the first was Dufour 

 (1883). Later Hungerford, Hoffman, Miller, Readio, Butler, and Weber con- 

 tributed greatly to this field. The subject of the physiology of insects was also pur- 

 sued during much of the period covered by this century. Dufour (1833) did 

 the first significant work in this field but classical studies awaited the researches 

 of Wigglesworth. Wigglesworth selected as his experimental animal the bug 

 Rhodnius prolixus. RJiodnius, being a blood-sucking insect, was especially well 

 adapted to studies of this kind because it could be reared in the laboratory and 

 fed only once between each instar. Wigglesworth studied the moulting of in- 

 sects and many other details of the physiology of insects. 



The subject of genetics should be mentioned because bugs were used very 

 early in the development of this science. The Pentatomids, in particular, were 

 used for cytological studies in the early part of the present century. Recent 

 work of this kind is much more far-reaching and concerns the chromosomes of 

 many other families of Hemiptera. It is too early to say what significance this 

 work may have on our final classification, but certainh^ karyology will provide 

 an additional set of taxonomic characters. 



Economic investigations have always played an important part in ento- 

 mology, but this has come to be more striking during the twentieth century. In 

 the Hemiptera the most important pests are the bedbug, which was studied 

 from earliest times; the chinch bug, which is so injurious to agriculture in the 

 Middle West and was one of the earliest insects of economic importance to be 

 studied in the United States; lygus bugs, which have come to the fore only in the 

 last few years. Among the numerous other pests are the squash bug and the harle- 

 quin cabbage bug. Of great importance in biological control in the 1920's was a bug 

 of the genus Cyrtorhinus. This bug had the remarkable property of sucking the 



