October, '14] WOLCOTT: ECOLOGY OF TIPHIA 389 



Peoria, Allentown, Henry, Putnam, Sheridan, Rockford, Freeport, 

 Winnebago and Belvidere, Elis is much more abundaht and Tiphia is 

 found in smaller numbers. Conversely, Elis is found in small numbers 

 on the black clay and brown silt loam to which Tiphia is better adapted. 



Still another factor which is of great importance in restricting the 

 range of Tiphia is that only a single generation of the dominant species 

 of Lachnosterna is present in some localities. For most species of Lach- 

 nosterna three years are required for the completion of the life cycle. 

 The year that full grown grubs are abundant there would be an ample 

 supply of hosts for Tiphia, but the next year only beetles, eggs and 

 very small grubs would be present. Just this condition occurs in 

 northwestern Illinois and every third year the farmers suffer great 

 losses from the grubs. Probably the condition existing in this region 

 some time ago was that parasites, such as Tiphia and Elis, were 

 present, feeding in the years when the dominant species occurs as 

 beetles or very small grubs, on the full grown grubs of some other 

 species of Lachnosterna. In the year when the grubs of the dominant 

 species were abundant, the numbers of Tiphia increased greatly. 

 The next year the grubs of the non-dominant species would be only 

 a meager supply to the large numbers of Tiphia and practically all 

 the grubs would be parasitized. This would eliminate the non- 

 dominant species, and in the coming years Tiphia would have no 

 host in the years when the dominant species did not occur as large 

 grubs, and it also would be exterminated. The elimination of the 

 non-dominant species may also have been caused by the cutting down 

 of trees that formed the food supply of their adults. Whatever 

 caused the elimination of the non-dominant species, until condi- 

 tions are again favorable for their increase no possible assistance 

 can be expected from Tiphia in the destruction of the dominant 

 species. 



There appear to be at least five important factors controlling the 

 abundance of Tiphia inornata: (1) Scarcity of large grubs in the years 

 when the dominant species occurs as beetles and small grubs. (2) A 

 permanent scarcity of grubs caused by unfavorable agricultural prac- 

 tices, or the absence of trees to furnish a food supply for the adults. 



(3) Unfavorable soil — which favors other parasites of Lachnosterna. 



(4) Parasites on Tiphia and the Tiphia fungus, Isaria sp. (5) Fall 

 plowing — which causes premature emergence of adults and exposure 

 of cocoons to predators. 



