COMPARATIVE STUDY OF THE AMOUNT OF FOOD EATEN 

 BY PARASITIZED AND NONPARASITIZED hARVJE OF 

 CIRPHIS UNIPUNCTA 



By Daniel G. Tower, 

 Scientific Assistant, Cereal and Forage Insect Investigations, Bureau of Entomology 



INTRODUCTION 



The aim of an experiment which was conducted at the United States 

 Entomological Laboratory in West La Fayette, Ind., during the summer 

 of 1 91 5, vras to determine whether lar\'ae of the army worm (Heliophila) 

 Cirphis unipuncta Haworth, when attacked by an internal parasite, 

 Apanielcs militaris Say, ate less, as much as, or were stimulated to eat 

 more than when nonparasitized ; and as a sequence, to determine whether 

 this or a similar parasitism is directly beneficial in the generation para- 

 sitized or only indirectly, resulting in subsequent smaller generations. 

 Although only 9 of the 25 parasitized larvae with which the experiment 

 was started lived until the emergence of the parasites, the others dying 

 soon after oviposition took place, the records of these 9 lar\^ae are suf&- 

 ciently definite to satisfy the purpose of the experiment. 



The excellent work of Mr. J. J. Davis and Mr. A. F. Satterthwait ^ in 

 determining the total amount of food eaten by healthy larvae of C. uni- 

 puncta under different feeding conditions has been used to compare with 

 the amount of food eaten by parasitized larvae. 



The results of the experiments have been drawn up in tabular form to 

 show the life of the host larvae from the time they were oviposited in 

 until their death coincident with the emergence of the parasite and the 

 life history of the parasite in relation to its host (Table I).^ 



EXPERIMENTAL METHODS 



The parasites were induced to oviposit in the host larva while confined 

 in test tubes into which a larv^a was introduced and left until recognized 

 as a host and parasitized. Often this occurred immediately, and three 

 or four ovipositions might take place before the larv^a could be removed. 

 In other cases it would be some minutes before the parasite could be 

 induced to oviposit. 



These parasitized larvae were confined separately in large vials, placed 

 in the shade in a well-aired room, and fed pieces of mature corn leaves, 

 conveniently cut out so as to measure i square inch each. 



In order to obtain unfertilized females, individual cocoons were placed 

 in gelatin medicine capsules previous to the emergence of the adults, the 

 sex being easily determined through the transparent gelatin, when the 

 adults emerged. 



' Data as yet unpublished; may appear in a later issue of this Journal. 



2 The author was ably assisted in the care and feeding of the larvae by Mr. H. J. Hart, who was tem- 

 porary assistant at the laboratory during the summer of 1915. 



Journal of Agricultural Research, Vol. VI. No. 13 



Department of Agriculture, Washington, D. C. June 19, 1916 



eg (455) K-36 



