TWENTY-SEVENTH REPORT OF STATE ENTOMOLOGIST 25 



Investigations are under way at the North Montana Branch 

 Station to discover if the shortening of the Russian thistle-tum- 

 bling mustard period of the reversion cycle by the planting of 

 abandoned crop land to crested wheatgrass will affect plant bug 

 populations. 



SUGAR BEET WEBWORM 



(Loxostege sticticalis L.) 



The outbreak of sugar beet webworms in 1938 was the heav- 

 iest since the state-wide infestation of 1932. In many respects 

 it could be classified as a more severe outbreak than the one 

 in 1932. While most of the damage this year was confined to 

 the Flathead and Bitterroot valleys and an area around Great 

 Falls, in many cases beets were entirely destroyed, which was 



Figure 9. — Sugar beet webworm in case. 



not the case in 1932. Usually in a moderate outbreak the beets 

 are defoliated, but in time new leaves are produced; thus the 

 damage is due to delaying the growth of the plant. In most cases 

 a lighter crop of beets is produced following such an infesta- 

 tion. No data are available as yet to show the effect of feeding 

 on the sugar content of the beet. In many cases this year bothj 

 in the Flathead and Bitterroot valleys the beets were entirely 

 destroyed by the worms eating the crown out of the plant. 

 In some fields entire areas were destroyed in this manner, while 

 in others only occasional beets were entirely destroyed. 



Contrary to the general rule, most of the eggs were de- 

 posited on the plants in the field rather than on bordering weed 

 patches. This may be accounted for by the fact that the adults 

 did not emerge until much later this year, and considerable 

 foliage was present in the beet fields at the time they were 



