PKEVIOUS WORK WITH INSECT PARASITES. 17 



1730) was apparently the first to discover the real nature of this phe- 

 nomenon and to realize the existence of true parasitic insects. Reau- 

 mur (1683-1757) and De Geer (1720-1778) each studied the life his- 

 tories of living insects with great care and among these worked out 

 the biology of a number of parasites. Very many descriptive works 

 on parasites were published in the closing years of the eighteenth 

 century and the beginning of the nineteenth century, especially by 

 Dalman (1778-1828), Nees ab Esenbeck (1776-1858), Gravenhorst 

 (1777-1857), Walker (publishing from 1833 to 1861), Westwood 

 (pubhshing from 1827 on through nearly the whole of the century), 

 Forster (pubhshing from 1841 on), and Spinola (1780-1857). 



Many later writers have contributed to the systematic study of 

 these insects, among them Holmgren and Thomson, of Sweden; 

 Mayr, of Austria; Motschulsky, of Russia; Ratzeburg, Hartig, and 

 Schmiedeknecht, of Germany; Wesmael, of Belgium; Haliday, 

 Marshall, and Cameron, of England; Rondani, of Italy; Brulle, 

 Giraud, Decaux, and others in France; Provancher, of Canada; and, 

 in America, Cresson, Riley, Howard, Ashmead, Crawford, Viereck, 

 Brues, Girault, and others. 



The best contribution appearing in Europe and devoted to the 

 biology of hymenopterous parasites, and especially consideration of 

 their relations to their hosts, was that by Ratzeburg, whose great 

 work entitled "Die Ichneumonen der Forstinsekten," was a standard 

 for many years. Ratzeburg understood the role played by parasites 

 in the control of forest insects, but did not believe that this control 

 could in any way be facilitated by man. 



EARLY PRACTICAL WORK. 



Froggatt has pointed out that probably the earliest suggestion 

 made regarding the artificial handling of beneficial insects was printed 

 in Ear by and Spence's entomology (1816), where the authors called 

 attention to the value of the common English ladybird as destroying 

 the hop aphis in the south of England. "If we could but discover a 

 mode of increasing these insects at will, we might not only clear our hot- 

 houses of aphides by their means, but render our crops of hops much 

 more certain than they are now." As a matter of fact, gardeners 

 and florists in England for very many years have recognized the value 

 of the ladybirds and have transferred them from one plat to another. 



Prof. A. Trotter, of the Royal School of Viticulture at Avellino, 

 Italy, has recently pointed out in an interesting paper entitled "Two 

 Precursors in the Application of Carnivorous Insects," published in 

 Redia, in 1908. 1 that probably the first person to make a practical 

 application of the natural enemies of injurious species was Prof. 



i Redia, vol. 5, pp. 126-132, Florence, 1908. 

 62188°— Bull. 91—12 2 



