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In the entire area mentioned, reductions in the grasshopper potential aver- 
aged from 25 to 50 percent. 
Effect of egg predators on the infestations 
In most of the M. nexicanus area proper egg predators, especially 
heefly larvae ( Bombyliidae ) have reduced the number of good eggs 20 to 75 
percent, as recorded. The heefly occur in the greatest numbers in western 
Forth Dakota in the vicinity of Dickinson. They are not as numerous out- 
side of the four M. moxicanus States as you go southward. Table 6 is a 
summary by States, of records made of the average number per square foot 
of each of the three egg predators found during the survey. These records 
wore neither uniformly kept nor regularly recorded, so it was with difficul- 
ty that any semblance of a summary table was made. Blister beetle larvae 
were most important in Wyoming, Forth Dakota, Colorado, Febraska, and Iowa, 
as recorded in the survey notes. Carabid. larvae were generally numerous 
only in Iowa. 
In the most severely infested, areas of eastern South Dakota in 1938 
where populations of active hoppers numbered in the thousands per square 
yard, the egg reduction by egg predators during the fall and winter of 1937 
and 1938 amounted to less than 10 percent. In the Dickinson, F. Dak., area 
1 flax field averaged 8 pods per square foot altogether, with 6 of those 
wholly or partially destroyed by beofly. If it were not for the becfly, 
the 8 pods per square yard would theoretically produce about 1,500 nymphs per 
square yard, which would equal some of the populations found in eastern 
South Dakota in June 1938. With the 75-pcrccnt destruction of eggs by 
becfly, as observed, the population cannot possibly number over 350 per 
square yard. This, of course, is still a heavy population but not uncommon 
in local outbreaks where in the past large migration has not been the 
fe„ctor that it was in July 1938. In other words, the enormous numbers 
of grasshoppers found in the summer of 1938 will not be so general or over 
so wide an area in 1939. Furthermore, the Forth Dakota-Montana areas arc 
old established grasshopper areas and egg predators, especially beefly, 
are also well established. This probably accounts for their abundance in 
these places. It is also believed that with increased numbers of eggs . 
comes a greater chance of egg predators finding the eggs and this includes 
skunks, field mice, horned larks, or any other creature that will feed on 
grasshopper eggs when it cones across them. There must be some degree of 
chance in the finding of egg pods by all these egg predators, and by in- 
creasing the number of eggs not only is the chanco of finding them increased 
but the numbers of those taking part in the egg destruction, other than 
insect predators, is also increased. Therefore, the end result would be 
the product of the increased chance times the increased numbers of predators 
taking part in the egg destruction. For example, in light infestations a 
skunk or lark may accidentally dig up a pod but, where the infestations 
arc heavy and the pods numerous and congregated, a single animal would 
feed on a much greater number of eggs and actually look for then. This all 
adds up to the fact that grasshopper populations do get cut down enormously, 
often suddenly. 
