THERSILOCHUS CONOTRACHELI, A PARASITE OF THE 



PLUM CURCULIO 



By R. A. Cushman, Entomological Assistant, Deciduous Fruit Insect Investigations, 



Bureau of Entomology 



INTRODUCTION 



During the seasons of 191 4 and 191 5 the ichneumonid Thersilochus 



conotracheli Riley (PI. CIX) has been by far the most abundant and 



effective parasite of the plum curculio at North East, Pa. In 191 4 a 



very large percentage of the fruit on a few plum trees (Prunus spp.) that 



stand on the premises of the Bureau of Entomology laboratory at that 



place was infested by the curculio. In the spring the adults of the parasite 



were abundant on these trees and parasitized a large percentage of the 



curculio larvae in fruit that was still on the trees when the parasites became 



#. 

 active. 



Under date of June 13, 191 4, the writer's notes contain the following: 



Very few of the larvae of this species have been found in host larvae more than one- 

 eighth inch long, although many of larger size than this have been examined. This 

 indicates that the parasite does not begin oyiposition until some time after the 

 curculio has begun its attack on the fruit, and therefore does not exercise any control 

 over the early curculio larvae. 



The season of 191 5 found the curculio much reduced in numbers. 

 The cold, wet season, however, retarded the emergence of the para- 

 sites to such an extent that they attacked only the latest of the larvae, 

 practically all of these being parasitized. 



HISTORICAL REVIEW 



The first mention of Thersilochus conotracheli in literature appeared in 

 1871, when Riley (1) x published his original description of the species, 

 referring it to the genus Porizon, and recorded it as a parasite of the 

 plum curculio (Conotrachelus nenuphar Herbst) in New Jersey. Riley 

 (2, p. 18) again referred to it in a paper written in German and published 

 in St. Louis. In 1880 Gott (3, p. 57) reported that in his work with the 

 plum curculio in Canada he had not found this parasite. Riley and 

 Howard (4, p. 63-64) in 1889 referred the species to the genus Thersi- 

 lochus, gave a brief life history, and recorded the species as nearly as 



1 Reference is made by number to "Literature cited," p. 855. 



Journal of Agricultural Research, Vol. VI, No. 23 



Department of Agriculture, Washington, D. C August 28, 1316 



fd K-41 



(847) 



