REPORT OF THE ENTOMOLOGIST. 313 



Others at long intervals, but tliey were all tritlci and like those pre- 

 viously bred from the other straws. 



To settle the matter beyond the possibility of an error, after the 

 adults had ceased to emerge, we proceeded to slit open the straws with 

 a view of learning if any pup?e of grande remained to emerge later in 

 the season, or if any had died and thus failed to appear. 



As we cut open the last straw, and found it, like all of the others, 

 devoid of Isoso^na in any condition or stage of development, the last 

 clue to the enigma we sought to unravel seemed to vanish. 

 . Up to the 20th of A-phl inclement weather during a large portion of 

 the time kept us from making extensive observations, but during the 

 remainder of this month we were almost continually in the fields, search- 

 ing carefully any young wheat x)lants showing injuries at all suggestive of 

 the work of Isosoma. As much of the wheat had been seriously affected 

 by the extremely severe winter just passed (not only were many of the 

 plants killed to the ground, but many others even up to the time of 

 ripening showed the effects of less serious injuries), our task was alike 

 tedious and uuremunerative ; although, had we at that time known 

 what we have since learned, and directed our attention to the healthy 

 plants instead, the results might, possibly, have been more satisfactory. 



After the 1st of May, previous labors in this direction having been 

 so discouraging, we devoted less time to inspection of the plants, but 

 such as gave evidence of unnatural or retarded development were 

 critically examined, and, as we were almost daily in the wheat-fields 

 searching for the wheat and grass saw-flies, our attention, though not 

 exclusive, was continually directed to the matter. On the 1st of June, 

 from a narrow strip of timothy and blue-grass, bordering a small field 

 of spring wheat, on the university farm, we swept two females of 

 Isosoma grande, and on the next day, in a field of wheat that had been 

 swept qver on the 29th of May without capturing a single one, several 

 more were taken — all females. Determined now to solve the mystery 

 of these insects having so long evaded search, a thorough examination 

 of the growing wheat was begun, excepting only the very few now in 

 head. 



We found (1) that it was the apparently healthy plants that were in- 

 fested, and (2) that little or no trace of the insect was to be discerned 

 from outside appearance until after the adult had emerged, and (3) that 

 the larva did not as a rule attack the culm after the manner of others 

 of the same genus, but confined its work to the undeveloped head, and, 

 as the upper sheath and leaf continued to grow, the affected part was 

 concealed until later in the season. We now found the species grande in 

 all of its stages in the plants, and also found plants from which the adult 

 had emerged, and, while the wheat head was almost invariably entirely 

 eaten away, in some cases the larva had evidently pupated before the 

 work of destruction was complete, and a distorted, misshapen head was 

 IDut forth, and while all infested plants were more or less dwarfed, it by 

 no means followed that all such plants were infested. 



As nothing definite respecting the previous history of this field could 

 be learned, our attention was directed to one of the experiment plats 

 on the university farm. 



This plat was sown on the 29 th of September, 1884 ; much later, we 

 were informed, than the field previously mentioned, and at the beginning 

 of winter the plants were much smaller, ilfotwithstanding this, it was 

 fully as difficult to distinguish the infested plants by a superficial in- 

 spection, although they were nearly if not quite as numerous. 



Whether the females of tritici exercise any discrimination in the 



