No. 4.] THE GYPSY MOTH. 249 



determined that it could not be depended upon to exter- 

 minate. Though, like other insecticides, it proved effectual 

 in destroying other insects, it did not kill all gypsy moth 

 caterpillars on trees that had been sprayed with the poison 

 of a strength' of fifteen pounds to one hundred and fifty 

 gallons of water. It is recorded that where forty pounds 

 were used to one hundred and fifty gallons of water the 

 caterpillars all disappeared. In this case they were pre- 

 sumably destroyed by the poison, although some may have 

 been driven away by the excess of poison on the foliage. 

 In any case such an amount of the poison would be very 

 expensive, and could not be used without incurring some 

 risk of poisoning domestic animals or fowls. Its general 

 use at such a strength is therefore out of the question. 

 Arsenate of lead has two advantages as an insecticide : it 

 can be applied at any desired strength without injuring 

 foliage, and a strong mixture containing glucose will with- 

 stand showers and remain on the foliage throueh an entire 

 season. Thus, although the application of a strong mixture 

 of arsenate of lead is more expensive than that of London 

 purple or Paris green, it may be safer and more economical 

 in the end. For the gypsy moth ten to fifteen pounds to 

 one hundred and fifty gallons of water must be used to have 

 much effect. Its action is slower than that of Paris green, 

 and it should therefore be used early in the season, and of a 

 strength sufiicient to check the ravages of the insect as soon 

 as possible. 



Although this is the most effective poison yet used on the 

 gypsy moth caterpillars, doubtless it would have failed, like 

 Paris green, to check their ravages when they were in full 

 force. After four years of experimenting I am constrained 

 to believe that no form of arsenic, unless used in unsafe 

 quantities, can be relied upon to hold the gypsy moth in 

 check, much less to exterminate it. The effect of other 

 poisons on the moth has been and is still being investigated, 

 and the results will eventually be made public. 



Summer Work. 

 The killing of caterpillars under the " burlaps," which 

 was begun in June, was continued throughout July and 



