PREFACE TO THE 1940 EDITION 



INCREASING interest in the biological control of insects has cre- 

 ated an insistent demand for a wider knowledge of the parasitic 



forms active in destroying those insects which are injurious to 

 agriculture. The greater number of these parasitic species is found in 

 the order Hymenoptera. Opportunity has, therefore, been taken in 

 this edition (1940) to revise and extend the discussion of the superf ami- 

 lies Ichneumonoidea, Proctotrupoidea and Chalcidoidea, the groups 

 which contain the most important parasites. In addition, a shorter 

 key to the commoner families of the suborder Clistogastra together 

 with keys to the subfamilies of the Ichneumonidae and Chalcididas 

 have been included. 



The text for the keys and for the new matter on the parasitic 

 Hymenoptera has been contributed by Dr. Henry K. Townes, who 

 has given much study to these groups. It is hoped that the keys 

 will prove helpful to those interested in the parasitic forms. 



Glenn W. Herrick 

 Ithaca, June IQ40. 



PREFACE TO THE 1936 EDITION 



IT SEEMED opportune with this reprinting (1936) of the Intro- 

 duction to make some slight revision, more specifically of the 



orders of the wingless insects. 



The class Myrientomata of Berlese has been advanced to its 

 more logical position as the order Protura of Silvestri, under the 

 Hexapoda. This has been done with some reservation, but in 

 accord with the trend of opinion among morphologists and probably 

 most systematists. 



Probably the data for treating the suborder Entognatha of the 

 Thysanura as a definite order are more numerous and more reliable 

 than for the foregoing change in position of the Protura. Out of 

 respect, however, for the careful conservatism of Professor Comstock, 

 the writer has retained the Entognatha as a subordinate group in the 

 Thysanura. This is, no doubt, illogical because Professor Comstock 

 always kept pace with legitimate progress in his field of science. 



