32 GRASSHOPPERS IN GENERAL. 



PARASITIC INFLUENCES ON MELANOPLUS.* 



The relation existing between the host and its parasite is an ever- 

 interesting source of study from a biologic standpoint. Multiplied 

 numbers of the former tend toward greater increase of the latter. 

 When the parasites predominate, the individuals of the host tribe de- 

 crease ; should the host disappear, the parasite must follow or adapt 

 itself to new environments. Absence of the parasite grants license to 

 the increase of the host. The prevalence of one is directly dependent 

 upon the other. 



In order that an estimate of the influence of this condition upon 

 Melanoplus differentialis might be gained, the writer, while conduct- 

 ing the summer field-work of this department during the two seasons 

 past, collected a number of the Differential Locust. Fifty were taken 

 the first week of October, 1897 ; 130 were collected September 3, 1898. 

 Twelve per cent, of those captured in 1897 had been parasitized by 

 diptera. Of those taken in 1898, 20 per cent, had been attacked by 

 parasitic diptera. When it is taken into consideration that the dates 

 of capture were before the close of the active season of the parasites, 

 and that by reason of capture and confinement, some of the locusts 

 taken were doubtless saved from attack, the estimate can be regarded 

 as conservative. The duration of observation and number of individ- 

 uals considered -will not yet allow favorable deductions to be made 

 from the eight per cent, increase recorded this year. In localities 

 where this locust was superabundant in October, 1897, the number of 

 dead forms showing an unmistakable evidence of the work of dipter- 

 ous parasites was nearly equal to those moving about. The number 

 of Melanoplus differentialis that appeared in the same localities this 

 season was equal to, if not greater than, those existing the year pre- 

 vious. This species of locust has been of economic importance an- 

 nually in those regions for some years past. This is, in a measure, 

 due to the peculiarly favorable condition existing there, environments 

 which appear to be highly suitable to the rapid multiplication of this 

 species. The ultimate effect of parasitism upon Melanoplus differ- 

 entialis with such surroundings is yet to be demonstrated. 



Observations on this subject will be continued by the department. 

 It is the purpose of this paper to record the data observed and diptera 

 concerned. Dr. S. W. Williston and Dr. Garry de N. Hough have very 

 kindly examined the specimens bred. The descriptions and determi- 

 nations of the Sarcophagidse made by Doctor Hough appear below, 

 The description of the Tachinidse which appear to be new will shortly 

 be given by Doctor Williston in a paper on the museum types of 

 Tachinidse. 



*Kan. Univ. Quar., vol. vn, No. 4, Oct., 1898, series A, pp. 205-210. 



