NINETEENTH ANNUAL YEAR BOOK— PART IX 



485 



INJURY FROM WHITE GRUBS IN IOWA. 



By E. D. Ball and E. V. Walker. 

 The serious outbreaks of white grubs that have occurred in northeastern 

 Iowa during the past ten years are part of a general outbreak appearing in 

 a number of more or less timbered areas in a belt running from Minne- 

 sota and Iowa east to New York, Connecticut and New Jersey. These 

 grubs first appeared in unusual number in 1909, increased in severity in 

 1912 and reached a climax of injury in 1915. In 1918 the damage was con- 

 siderably less than in the previous outbreak and it is probable that the 

 parasites and other enemies of the grubs will reduce their numbers to a 

 nearly normal amount by 1921 or 1924 at the latest. 



THE WHITE GRUB AREA. 



June bugs and white grubs occur in all parts of Iowa every year, but 

 usually in small numbers. These insects require three years for their de- 

 velopment, but there are three different broods, one appearing each year. 



In the wooded area of northeastern Iowa one of these broods has become 

 enormously abundant, while the other two have not increased materially 

 in numbers. Figure 1 shows the area in which this increase has occurred 

 and also a few scattering places in other parts of the state where damage 

 has been reported. 



It must be remembered in using this circular that it applies only to the 

 area shown on the map and to the brood occurring every three years as 

 shown in figure 2, and that bad infestations seldom occur very far froto 

 timber. 



Fig. 1 — Showing region in which wliite grub may be expected. 



