EXPERIMENTS WITH SPRAY SOLUTIONS FOR GREEN LOGS. 3 



problem and the preliminary experiments conducted during the 

 years 1916 to 1919 are here presented. 



REQUISITES OF A PRACTICAL SPRAY. 



It may be impossible to find a single spray solution that can be 

 used with success under all conditions, but it may be possible to 

 obtain good results by using several solutions, each of which is effec- 

 tive under certain conditions. Any spray to fulfill all the requisites 

 necessary for practical effectiveness must possess the following qual- 

 ities : 



IT MUST BE EFFECTIVE AGAINST SEVERAL TYPES OF INSiECTS. 



Many species of insects attack green timber. Some attack only 

 certain kinds of wood while others show little discrimination. In 

 some cases the injury is caused by the grubs or larvae feeding be- 

 neath the bark or in the wood, or by an adult which bores through 

 the bark and produces larvae that feed under the bark. According 

 to their method of attacking the wood, boring insects may be divided 

 into the following four groups : 



Type 1. Those that lay eggs in crevices of the bark. The larvae 

 hatching from these eggs then bore through the bark and later into 

 the wood. 



Tyi^e 2. Those that gnaw a hole through the bark and insert the 

 egg beneath. The larvae start feeding directly beneath the bark and 

 later bore into the wood. 



Type 3. Those that bore through the bark and wood as beetles, 

 to make a suitable place for developing a new brood. The grubs in 

 this case never cause injury. 



Type 4. Those that bore through the bark as beetles and lay the 

 eggs beneath the bark. The resulting larvae feed beneath the bark 

 and loosen it. 



The only spray that could possibly be effective against all these 

 types would be one of a disagreeable odor acting as a repellent, thus 

 driving away the adult beetles and preventing oviposition. Poison 

 sprays that will penetrate the outer layers of bark will kill the young 

 larvae of type 1, but experiments have demonstrated that such mate- 

 rials are not effective against types 2, 3, and 4. In these types most 

 of the beetles do not eat any of the bark or wood as they chew 

 through it and consequently are not poisoned. Possibl}^ a poison 

 combined with a sticky substance that would form a film over the 

 bark and adhere to the mouth parts of the insects might kill them. 



Insects of type 4 are not very injurious to saw logs, as they only 

 work beneath the bark and do not enter the wood, but they are 

 important in loosening the bark from rustic work. The others are 

 all injurious to both classes of timber. 



