12 



CIRCULAR 8 4 9, U. S. DEPT. OF AGRICULTURE 



The larvae begin to feed soon after the wheat has begun to turn 

 green in the spring. In outbreak years bare spots appear, usually on 

 knolls with southern exposure, and severe infestations soon involve 

 entire fields. From a distance these bare spots have the appearance 

 of drought injury. In spring barley, particularly that sown in wheat- 

 stubble ground, the attack reaches its greatest intensity about the 

 time the plants have developed two or three leaves. Entire fields 

 may be completely destroyed in a very short time. 



Seasonal history. — The pale western cutworm has only a single 

 generation annually. The eggs are deposited in the soil late in 

 September or early in October. The larvae develop within the eggs, 

 but do not hatch until the following March. For a time the young 

 larvae feed above ground, skeletonizing the leaves of wheat or other 

 host plants, but after the first instar they assume the subterranean 

 habit. During the rest of their development the larvae remain below 

 ground unless forced to the surface by excessive moisture. They 

 mature late in April or early in May and descend 3 to 5 inches in the 

 soil, depending on the depth of the plow sole or hardpan. Here they 

 form earthen cells and remain quiescent until late in July or early in 

 August, when they begin to pupate. The adults emerge during the 

 latter part of September and deposit eggs soon thereafter. 



Natural enemies. — As might be expected, because of the subterra- 

 nean habit of this species, only slight parasitization was noted. During 

 1936-40 large numbers of larvae were collected in infested fields and 

 reared individually to determine the degree and kind of parasitization 

 and disease. The results are summarized in table 1. 



Table 1. — Mortalities of larvae of Agrotis orthogonia caused by various 

 natural enemies, 1936-40 





Larvae 

 observed 



Larvae killed by — 



Total 



Year 



Hyme- 

 noptera 



Diptera 



Xema- 

 toda 



Disease 



mortal- 

 ity 



1936 



Number 

 322 

 788 

 467 

 475 

 596 



Percent 

 6 



. 3 

 3 



1 

 1 



Percent 

 5 

 1 



. 2 

 6 

 2 



Percent 

 2 

 _____ 



Percent 

 41 

 10 

 28 

 10 

 5 



Percent 

 51 



1937 



11 



1938 



31 



1939 



18 



1940_ 



8 







Many parasites could be determined only to the order because of 

 the difficulty of inducing the adults to emerge. The following para- 

 sites and disease organisms were reared from field-collected larvae: 



Hymenoptera — Meteorus vulgaris (Cress.), Netelia ocellata (Vier.), Apanteles 

 griffini Vier. 



Diptera — Xeophorocera claripennis (Macq.), Phosococephalops tcre/tsis (Rein- 

 hard), Salmacia sequax (Will.), Bombyliidae (species unknown), Tachinidae 

 (species unknown). 



Disease organisms — Undetermined wilt, Metarrhizium anisopliae (Metsch), 

 Beauvaria sp., Isaria sp., Sorosporella uvella (Krass). 



