THE KANSAS INIYERSITY 



SCIENCE BULLETIN 



Vol. XIV.] October, 1922. [No. 16. 



The Larva of a Chironomid {Trissocladius equitans n. 

 sp.) Which Is Parasitic upon a May-fly Nymph (Rith- 

 rogena sp.).* 



BY p. W. CLAASSEN. 



IN AUGUST, 1919, while spending a few weeks in Colorado, the 

 writer was collecting aquatic insects in the Big Thompson river 

 in Estes Park. This river is a typical mountain stream. The water 

 is very cold and rushes along in a swift current over a stony bed. 

 Aciuatic insects of the swift-water type were very abundant. Among 

 the May-fiy nymphs collected there were found about a dozen speci- 

 mens of one species which presented a curious appearance. Upon 

 examining some of these nymphs it was found that each one carried 

 upon its back a large, white dipterous larva. These larvae had at- 

 tached themselves to the thorax of the nymphs underneath the wing 

 pads. The large size of the larva forced the wing pads of the May- 

 fly nymph upward at a very decided angle and gave the nymph a 

 humped-up appearance as it rested upon the stone. 



All the collected material was preserved in alcohol and taken back 

 to Ithaca, N. Y., for study. When the material was examined more 

 closely in the laboratory, some of these May-fly nymphs were found 

 to carry larvae, while others of the same species carried pupae of the 

 dipterous insect. 



The May-fly nymph proved to be a species of the genus Rithro- 

 gena. Although it was impossible to determine definitely the genus 

 of the diptcron, Dr. 0. A. Johannsen, who examined it, felt certain 

 that it belonged to the family Chironomidse. The scarcity of mate- 

 rial and the lack of adult forms, however, made it impossible to sat- 



* Read before the joint session of the Entomological Society of America and Ecological 

 Society of America, January, 1922. Withdrawn for publication in this bulletin. 



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