October, '14] WOLCOTT: ECOLOGY OF TIPHIA 387 



In addition to the fungus, Tiphia is attacked by at least two para- 

 sites — a bee-fly, Exoprosopa fascipennis Say (Bombyliidse) and a 

 beetle (Rhipiphoridse). Riley identified the beetle emerging from 

 cocoons collected in Missouri as Rhipiphorus pedinatus Fabr., but 

 determinations have not yet been made of the beetles which emerged 

 from cocoons collected in Illinois. The details of the life histories of 

 neither of these parasites have ever been worked out. They seldom 

 infest more than 1 or 2 per cent of the Tiphia cocoons. In one field,^ 

 however (near Randolph, 111.), a large number of the older cocoons in 

 the field, instead of having a side emergence hole, showed the entire 

 blunt end of the cocoon cut off. This was evidence of heavy parasitism 

 by the Rhipiphorid, as Exoprosopa leaves its pupal case in a hole in the 

 side much similar to that cut by the Tiphia adult. Cocoons showing 

 no emergence hole are often found in the field pierced with a consider- 

 able number of small holes less than 1 mm. in diameter. The interior 

 of such cocoons is entirely empty. What causes this is not known, 

 although it may result from the grass roots which are often found 

 wrapped round cocoons, or possibly the mites which often infest the 

 grubs attack the cocoon when their normal host is destroyed by 

 Tiphia. It has been suggested that ants might also cause this type 

 of injury. 



Although the parasites and the fungus are important in controlling 

 the numbers of Tiphia, the most important check to the natural 

 increase of the species is the lack of host grubs. Lachriosterna grubs 

 are not present in noticeable abundance in the great majority of fields 

 in central Illinois. Frequent plowing, rotation of crops, heavy pastur- 

 ing of meadows and fields to horses, cattle and especially to hogs, which 

 root in the soil after the grubs and destroy large numbers of them, and 

 the absence of nearby trees to furnish a food supply to the adult beetles, 

 may be mentioned as the more important checks on Lachnosterna. 



The last mentioned factor seems to be of greater importance than 

 is generally realized. The grubs of the species of Lachnosterna of 

 which the adults prefer to feed on the leaves of willow and cottonwood 

 iPopulus deltoides Marshall) are almost invariably found abundant in 

 those fields in which there are several large cottonwood trees. In the 

 more hilly portions of Illinois, where fewer trees have been cut down, 

 or even in fields near orchards or woods of oak, elm, ash, birch, linden^ 

 locust and walnut, Lachnosterna grubs are sufficiently abundant to 

 cause serious loss to the farmers. Hedge (Osage orange), box elder and 

 maple are the only three common trees that are not acceptable food 

 plants to a.ny Lachnosterna beetles, while cottonwood and willow are pre- 

 ferred by most of the common species. Oak and elm are a good third 

 and fourth, but other trees are of minor importance. Despite the state- 



