Nov. 5. I92I Pale Western Cutworm 313 



be a natural condition such as is found on knolls and ridges where the 

 soil is generally light and easily drifted. In fields where a crop is re- 

 moved during July or August the surface crust may become broken and 

 pulverized in numerous places by the disturbance of the soil in connec- 

 tion with harvesting, thus offering the moths many desirable spots for 

 egg laying. Injury may be least expected to occur in fields in which the 

 surface soil is hard or crusted during the egg-laying period. In most 

 instances this condition can be brought about by not disturbing the 

 ground in any way between July 15 and September 15. If farmers in 

 preparing their grain fields for seeding will be governed by these prin- 

 ciples it is believed that Porosagroiis orthogonia injury can be greatly 

 reduced. Fortunately this method of handling summer-fallowed fields 

 does not interfere with approved farm practices, and in fact agrees very 

 closely with the recommendations of the agronomists. 



NATURAL ENEMIES 



Unlike most of our common cutworms, Porosagroiis orthogonia suffers 

 comparatively little from attack by natural enemies. Much difficulty 

 has been encountered in rearing various other species taken in the field 

 as larvae, particularly the army cutworm, Chorizagrotis auxiliaris, on 

 account of the high percentage that developed disease or parasites. 

 This has not been the case with the present species. Our records for 

 19 15 show that out of a large number of army cutworms reared indi- 

 vidually only 35 per cent were brought through to the moth stage, 

 parasites emerged from 24 per cent, 2 1 per cent died of disease, and the 

 remaining 20 per cent died in the pupa stage, mostly on account of in- 

 sect parasites. In 1919, 55 per cent of P. orthogonia larvse handled 

 in the same way were reared to adults. Of the 45 per cent that died, 

 very few seemed to die of any disease, and parasites emerged from only 

 two larvae. 



In 1920, out of 960 Porosagroiis orthogonia larvae collected in the 

 field, 13.7 per cent were parasitized, 12.2 per cent by Diptera and 1.5 

 per cent by Hymenoptera. The parasites which emerged were 14 Bon- 

 netia compta Fall and i Peleteria robusta Wied. 



The common wild birds of the prairie are the most beneficial natural 

 check that we have observed. The western grasshopper sparrow, Am- 

 modramus savannarum bimaculatus Swainson, particularly, has been 

 watched while digging out the larvae and carrying them away to its 

 young. In many parts of the cutworm-infested regions it has been a 

 common sight toward the last of June to see thousands of small excava- 

 tions made by the western grasshopper sparrow, horned larks Otocoris 

 alpestris leiicolaema Coues (PI. 30, C), and possibly other wild birds in 

 their search for the larvae. 



Although the common ground squirrel, Citellus richardsoni Sabine, has 

 at times been known to seek out and devour large numbers of cutworm 



