210 E. A. HARTLEY Vol. XXII, No. 8 



These parasites, so far as known, are limited to the aphids 

 as hosts, and most, if not all of them, are confined to a few 

 species. Aphelinus mail was long considered an exception, 

 appearing many times in the records as a scale parasite, also. 

 However, Dr. Howard,* authority on the group, now believes 

 these records to be in error, and further states that it is probably 

 not only confined to aphids, but is likely restricted to the woolly 

 forms, especially the common Eriosoma lanigera Hausm., of the 

 apple, a species often associated with scale insects; a fact which 

 may account for the confusion in the records. 



The group, on the whole, are extremely minute and incon- 

 spicuous insects, not often met with by the average entomol- 

 ogist. Many of the species are quite rare, even to the specialist 

 on the alert for them. At best they rank secondary to the 

 Braconid subfamily Aphidinini as a factor in the control of 

 aphids; although they have been known (Prof. T. H. Parksf) 

 to play a considerable part in some outbreaks (Toxoptera in 

 Kansas during 1909). For these reasons, they have practically 

 escaped attention from a biological standpoint, and most of 

 them have been known systematically but a few years (since 

 1908). 



With the hope of contributing something to the knowledge 

 of the bionomics, life-history, economic importance, and rela- 

 tionship to the aphid complex in general, work was begun on 

 Aphelinus semiflavus in the greenhouse insectary of the Ohio 

 State University, Department of Zoology and Entomology, in 

 the fall of 1920, as part of a thesis for the degree of Master of 

 Science in Entomology. This was continued throughout the 

 winter to the middle of May, 1921 ; when the thesis was written. 

 After graduation in June, part of a series of parthenogenetic 

 generations of the parasite was taken to Oak Lane, Philadel- 

 phia, Pennsylvania, where rearing and study was continued at 

 intervals until the time of this writing, February, 1922. 



ACKNOWLEDGMENTS. 



The writer here wishes to express appreciation for the kind 

 assistance of Dr. Herbert Osborn, who directed the work with 

 many valuable suggestions and criticisms, and to Dr. R. C. 



* Private communication, 

 t Private communication. 



