INSECT ENEMIES — rACKARD 327 



and multiply in the volunteer wheat that would otherwise grow in the 

 stubble fields. 



Certain tillage practices may sometimes be utilized in breaking the 

 annual cycle in the development of certain species. Plowing, for in- 

 stance, may be extensively and profitably applied in the control of 

 grasshoppers. These insects are not as improvident as Aesop's fable 

 about the gi-asshopper and the ant would imply. During late summer 

 and early fall most species deposit their egg pods in the gi'ound (pi. 8), 

 sometimes in enormous numbers, and thus having provided for tlie 

 succeeding generation, die naturally of old age. The eggs normally 

 remain well protected in the soil until the following spring without 

 need of any food supply. In fact, the common injurious species spend 

 6 to 8 months of the year as eggs in the top 8 inches or so of soil. If, 

 sometime during this long period, preferably in the fall, the soil is 

 turned over by plowing to a depth of at least 5 inches and the surface 

 layer well compacted by subsequent cultivation, the little hoppers 

 hatching from the eggs can be effectually prevented from emerging. 



The pale western cutworm, a serious pest of small grains in the 

 Great Plains, provides another example of how knowledge of an in- 

 sect's habits may lead to inexpensive and practical cultural control 

 methods. It is known that most cutworms hide in the soil during the 

 day but come out to crawl around on the surface at night. They can 

 be cheaply and easily controlled, therefore, by spreading poison-bran 

 bait in the infested fields, the worms eating it during the time they 

 spend above ground. But the pale western cutworm cannot be con- 

 trolled by this method because it stays underground both day and 

 night, and progresses from plant to plant by burrowing along just 

 underneath the surface. A Canadian investigator discovered, how- 

 ever, that these worms quickly die after they hatch out in the early 

 spring if the newly sprouted vegetation is all killed by thorough cul- 

 tivation as soon as the worms have had a little time to feed. Strangely 

 enough, they can survive for some time if they have had no food, but 

 die quickly if they have once fed and are then deprived of food. The 

 infested fields may therefore be cleanly fallowed for about 3 weeks 

 soon after the w^orms have hatched, and then sown to spring grains 

 with little subsequent injury to the crop, which otherwise would have 

 been ruined by this cutworm. 



A different strategy has also been used successfully against the pale 

 western cutworm in the southern Great Plains where fall-sown wheat 

 is the principal grain crop. In studying the insect's habits it was 

 discovered that the adult moths, which emerge in the fall, tend to fly 

 to, and lay their eggs in, fields or portions of fields that had been 

 allowed to produce a growth of vegetation during the summer. ■ Win- 

 ter wheat sown in such fields was severely injured by this cutworm 



