58 



GRASSHOPPERS AND OTHER INJURIOUS INSECTS OF 1911 AND 1912. 



The Common Flat-headed Borer. 



The footless grubs of the common Flat-headed Borer with 

 their large flat heads are found working just beneath the bark on 

 a number of such trees as maple, boxelder, oak, 

 basswood and apple trees- The adults fly during 

 the period from May 15th to July 15th and deposit 

 eggs in the crevices of the bark. The larval life 

 is spent beneath the bark where the injury is 

 done. In each instance where these grubs have 

 been found in Minnesota, it 

 was noticed that the infested 

 area had been previously in- 

 jured in some way, either by 

 sun scald or by mechanical in- 

 jury. The insect rarely or 

 never attacks and kills a 

 healthy uninjured tree. 



Fig. 40. Common Flat- 

 headed Borer, larva, 

 about twice enlarged 

 Ruggles. 



The Rustic Borer. 



The grubs of the Rustic 

 Borer have always been found 

 associated with the Two-lined Chestnut Borer, pj^ 4^_ Fiat-headed Borer, 

 particularly in oaks. This insect has never ''''^"''- ^"^^^^^■ 

 been known to attack and kill a healthy tree. The grubs live 

 beneath the bark and often penetrate the wood to a depth of half 

 an inch or more. The adult beetles are found in the spring at 

 about the same time as the Two-lined Chestnut or Oak Borer. 



Thunderbolt Beetle. 



The Thunderbolt Beetle is very common. Its grubs burrow 

 beneath the bark in the sapwood of oaks. They probably follow 

 another insect's injury. The adult insects have been captured dur- 

 ing the months of June, July and August. The life history is not 

 well known. 



In conclusion the following points are to be remembered : 



1. The larvffi or grubs of these beetles make galleries in the 

 growing layer between the bark and wood. 



2. When these burrows are made across the grain of the 

 wood, it is very evident that the food supply will be cut off" and the 

 tree practically girdled. The grubs of the oak borer and the birch 

 borer work in this way. 



