June, '21] SMITH: FALL ARMY WORM 301 



ter was unusually dry and the rainfall in the spring somewhat below 

 nonnal. There was little rain until after harvest, when the precipita- 

 tion during the month of August was unusually heavy. As a result 

 of this, there was much volunteer wheat and oats over the state and 

 in newly sowtq alfalfa fields which followed wheat. There was also a 

 heavy growth of crab grass, foxtail, and similar grasses. Alfalfa like- 

 wise made a heavier growth than had either of the two previous cut- 

 tings. 



In all infested fields seen, the larvae began their destructive work in a 

 small spot, and then worked outward over a fanshaped area, or, under cer- 

 tain conditions, in all directions. In some fields, the volunteer wheat 

 arotmd a straw stack was their starting point. At the college, the lar- 

 vae appeared at one side of the fields, generally at one of the lowest 

 spots. As food became scarce they spread out over the field, leaving 

 the alfalfa and grasses in the fields completely defoliated. 



The larvae fed first on the young leaves at the crown of the alfalfa 

 plants, then climbed up the plant, defoliating as they went, and devouring 

 the uppermost leaves last. They climbed up the plants and began feed- 

 ing about three o'clock on clear days, while in the morning there were 

 only a few larvae upon the plants. During the day, most of the lar- 

 vae rested at the crou-n of the plant, under the dried leaves or other 

 trash, imder clods or the loose earth. When the plants were jarred, 

 as when one walked through the field, or when bran mash struck the 

 plants, the larvae dropped to the ground. They generally dropped 

 also when attacked by the Tachinid flies, probably as a protective 

 measure, but the flies usually followed and often deposited their eggs 

 on them. Their work was evident first where the alfalfa was thinnest 

 on the ground Since there was less food in such places per unit of 

 area, their migration was most rapid here. This explained, to some 

 extent at least, the peculiar contour of the defoliated areas in some of 

 the fields. 



The larvae disappeared almost as suddenly as they came. By the 

 twenty -third of the month, practically all larvae were full grown, and 

 they were ven,^ scarce on the twenty-fifth. Larvae collected when the 

 outbreak was first noticed were all prepupae or pupae on the twenty- 

 fifth. In two days more there was only an occasional larva to be 

 fotmd. 



The first adults appeared in rearings on September 30th. By Oc- 

 tober 7 th, about half of the reared pupae had yielded adults. It was 

 concluded that the maximum emergence of moths in the field occurred 

 on this date. They appeared to be about as numerous as the larvae 



