PREVIOUS 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. Réau- 
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 
(publishing from 1827 on through nearly the whole of the century), . 
Forster (publishing 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; Brullé, 
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 réle 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 Kirby 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.! that probably the first person to make a practical 
application of the natural enemies of injurious species was Prof. 
/ 1 Redia, vol. 5, pp. 126-132, Florence, 1908, 
95677 °—Bull. 91—11 2 
