290 



JOURNAL OF ECONOMIC EXTO^IOLOGY 



\yo\. s 



In several fields observed,, flax was stripped of its foliage, but new 

 leaves were very quickly developed and the yield was not materi- 

 ally reduced. 



Gooseberries, raspberries, and currants were attacked only where 

 the worms were very abundant and other food was scarce. 



COXTEOL 



The outbreak was so sudden, unexpected and of such short duration 

 that experimental work in control could be carried on only in a very 

 hmited manner. 



Paris green at the rate of 1| pounds in 50 gallons of water, and arse- 

 nate of lead at the rate of 4 pounds (paste) in 50 gallons of water AA'ere 

 effective in killing loopers, but in the case of heavy migrations some 

 method more immediately effective must be employed. 



One farmer reported that a dry ditch with the soil at the sides well 

 puh'erized was an efl^ctive barrier. Another reported kilhng many 

 worms in his beet field by rolling as it is practiced at thinning time to 

 break the surface crust. 



The most successful method of preventing the larvse from invading 

 crops other than alfalfa was to keep a stream of water flowing through 

 the main irrigating ditches. On the Bureau of Plant Industry farm 

 at Huntley, a count was made of the worms carried past a certain 

 point on an irrigating ditch three feet in width. It ran close to four 

 hundred worms per minute or 576,000 per day. Xearly all of these 

 were drowned and those that escaped were carried into a section where 

 there were no farms. Some of the worms sink immediately when 

 placed in water, while others will float for some time. Once in the 

 water, they seem unable to get out, unless they become lodged against 

 projecting weeds, sticks, etc. 



The immediate cutting of infested alfalfa, followed by cHscing and 

 dragging, as is practiced in Utah for the alfalfa weevil, was recom- 

 mended, but because of the presence of natural enemies no data as to 

 the eft^ctiveness of these measures were secured. 



Xatueal Enemies 



Birds destroyed great Ciuantities of looper larvae. Brewer's black 

 bird was of great benefit in this respect and could be seen in large 

 flocks feeding upon the caterpihars at haying time. 



Insect parasites and disease were deadly in their attacks upon the 

 hordes of worms, killing them oft' in such numbers that the second 

 brood of larvse did no damage and in fact was never seen, although a 

 few adults were observed in September. The most eft'ective of these 

 natural enemies were two species of Apcniteles and a bacterial chsease. 



