TWENTY-FIFTH REPORT OF STATE ENTOMOLOGIST 29 



SAY'S PLANT BUG 



The first injury to grain crops in Montana by Say's plant bug 

 {CJdorochroa saiji Stal.), also known as the grain bug (see front 

 cover), evidently occurred in lij;52. During that season a number of 

 wheat fields in Hill County were severely attacked. In V.)'o-i the 

 damage was more severe and over a wider range. By 1934 sevtval 

 thousand acres of wheat were left uncut in the north-central counties 

 because the wheat berries had been destroyed by this insect. 



It is a very insidious pest for it sucks the milky juice out of the 

 heads of grain. The field attacked may look quite normal, in fact 

 it may appear to i)e a good crop, but at harvest time the heads are 

 found to be practically empty or possessing very shrunken berries. 



The grain bug is known to occur in all the Rocky Mountain states 

 except Wyoming but its greatest abundance has been reached in I'tah, 

 Colorado, Arizona, and New ^Mexico. Prior to 1932 only three speci- 

 mens were in the collection of the ^Montana Agricultural Experiment 

 Station. All came from west of the Continental Divide. Recent 

 correspondence with entomologists of Western states indicates that 

 the grain bug has been of practically no importance for many years 

 except in western Utah where great swarms occurred in 1932 and 

 caused severe damage to grain. It is evidently one of those insects 

 which is of very spasmodic occurrence, reaching great abundance for 

 a few seasons and then dwindling to unimportance for many succeed- 

 ing years. It is hoped that this will be the case in Montana. A point 

 of great significance in this connection is whether it has always been 

 in the north-central counties or has been introduced there. The 

 former is by far the sounder of the two possibilities. But the nature 

 of its apparent spread from Hill County during the past three years 

 and the fact that no such damage in any degree whatever had been 

 reported from those counties during the previous twenty years seems 

 to lend strength to the introduction idea. 



Only the adults and the last instar nymphae attack grain, the 

 younger stages living almost entirely on Russian thistle. Hibernation 

 of the adults takes place under weeds and any other protection which 

 may be found in fields or along roadsides. Accordingly the best, if 

 not the sole control measure, consists in the destruction of all weeds 

 by burning in the late fall so as to expose any hibernating adults. 

 The eradication of Russian thistle as a host i)lant is of course out 

 of the question so that all efforts must be directed against the over- 

 wintering adults. Fortunately they do not burrow into the soil. 



