WHEN TO SPRAY. 157 



more effective if applied soon after the caterpillars hatch. 

 As the young gypsy-moth caterpillars hatch at intervals 

 from the latter part of April until the middle of June, and 

 as the leaves are constantly growing during the early part 

 of the season, thereby offering daily more fresh unpoisoned 

 surface upon which the caterpillars may feed, it may be neces- 

 sary to spray once or twice more in May or June. Spraying 

 with the best insecticides known (arsenate of lead excepted) , 

 if done late in the season, has little effect on the gypsy-moth 

 caterpillars where they are numerous, as they will strip all 

 foliage from the trees before being seriously affected by the 

 poison. The uselessness of such spraying is shown by the 

 illustrations in plates IX., XI. and XVI. The caterpillars 

 thus destroyed the foliage in the Swampscott woods early in 

 August, after the trees had been sprayed twice with Paris 

 green.* 



It is well not to spray fruit trees when in blossom. If 

 sprayed at all at that time, the work should be done with a 

 nozzle throwing a fine, mist-like spray. A coarser spray is 

 likely to injure the blossoms, as well as to wash off the 

 pollen. There is danger also of 'poisoning bees. Prof. F. 

 M. Webster, entomologist of the Ohio experiment station, 

 has experimented by spraying apple trees in full bloom and 

 giving bees access under natural conditions to the sprayed 

 blossoms. Many of the bees which visited the trees died 

 suddenly, as well as the young larvae of a brood from 

 uncapped cells. Arsenic was found in the contents of the 

 abdomen as well as on the external parts. The bees all gave 

 evidence of having died from the effects of arsenic which 

 could only have been introduced from without the hive. If 

 the pollen is washed off tlie blossoms by the spraying and 

 the bees which distribute pollen are killed by the poison, the 

 spraying of fruit trees when in blossom will affect their 

 fruitfulness. 



Spraying should not be done during showers or after 

 showers before the leaves dry, or when a heavy dew is 

 on the foliage. When spraying is done during showers, 



* Many of the failures that have been recorded in spraying for other insects may 

 be traced to the fact that the work was done too late, and not until after the injury 

 was so serious that the spraying could not stop it in time to save the foliage. 



