juneis. I9IS New Wheat Thrips 223 



indicating that they had successfully passed the winter as both adults 

 and larvae, no eggs could be found on or in wheat leaves. 



Both adults and larvae have been found hibernating beneath the 

 sheaths of the following grasses: Triticum vulgare (wheat), Andropogon 

 scoparius, A. furcatus, Poa pratensis, thick mats of Agropyron smithii, 

 and Tripsacum dactyloides. No stages of thrips have been found hiber- 

 nating in Panicum crus-galli or Syntherisma sanguinalis , which become 

 quite dead and dry after the first frost and are abandoned, the thrips 

 continuing to feed on other plants during the warm days that usually 

 follow. 



ENEMIES 



Among the more important enemies of Prosopothrips cognatus are 

 Triphleps insidiosus Say and the larvae of Chrysopa oculata Fab., which 

 consume large numbers. When the thrips are numerous, the fields are 

 literally swarming with the Triphleps. No coccinellid adults or larvae, 

 not even of the smaller species, have been observed feeding on them, 

 either in the field or in confinement. No parasites have been reared, 

 although it is possible that some parasite materially assisted in reducing 

 their numbers in 19 10. No birds have been observed feeding on them. 



CONTROL 



At this time no thoroughly practical remedy can be offered for the 

 control of this pest. Large numbers of thrips may be destroyed by 

 burning off all grasses, but the young wheat fields, where most of the 

 pests are located, can not, for obvious reasons, be burned; nor is it 

 practicable to spray wheat since the expense of the operation would be 

 greater than the returns. 



Careful observations on plowing at different times from the middle of 

 June until September seem to favor early plowing, for, although all 

 fields under observation were infested, the two plowed in June and har- 

 rowed in late July were attacked to a lesser degree, and these fields con- 

 tained practically no volunteer wheat. 



Where this species becomes numerous, it appears that when stubble 

 fields are burned over and plowed early, destroying all grasses, and 

 especially volunteer wheat, there is less opportunity for the thrips to 

 increase in numbers sufficient to damage the crop. 



