The Pear Tree Psylla. 249 



water. It was found tliat every nympli was killed by the emul- 

 sion even when diluted with, twenty-five parts of water, and thus 

 containing less than three per cent of kerosene. The nymphs died 

 alruost immediately after the liquid touched them. These labora- 

 tory results were thus very encouraging. 



Field experiments were soon begTin to test the practicability of 

 the emulsion. No trees could be found that wei^ very badly 

 infested. But by cai'efully exaniining the trees before and isoon 

 after spraying it was estimated that from seventy-five to ninety 

 per cent of the nymphs were killed by one spraying with 

 kerosene emulsiou diluted with twenty-five parts of water. Some 

 of the nymphs had by this time become nearly full grown, but 

 these were as quickly and effectually destroyed as were the young 

 ones. The habit of the nymphs of feeding in the leaf axils made 

 it easier for the spray to reach them; the liquid would naturally 

 run down the leaf petioles and twigs and gather ia the axils, and 

 thus become very effective. It was found that two quarts of the 

 dilution was sufficient for a large dwarf tree; and thirteen such 

 trees could easily be sprayed in half an hour with a knapsack 

 sprayer. It would, of course, take more time and material to spray 

 the large standard trees, but the whole cost for each tree would 

 not be more than one cent a tree for time and material. The 

 experiments with the kerosene emulsion against the nymphs were 

 so successful that no other insecticides were tried. The emul- 

 sion is the cheapest effective insecticide now known for sucking 

 insects; and our expeiiments have shown that it wiU prove a 

 very practical and efficient means for checking the ravages of the 

 Pear-tree Psylla if it be used thoroughly and in time. 



The honey-dew did not interfere with the action of the insec- 

 ticide this year, 1892. This was probably due to the fact that 

 many hard showers fell during the early part of the season. The 

 raia washed off much of the secretion. This fact should be taken 

 advantage of ^by fruit growers in spraying for the pest. Spray 

 soon after a heavy rainstorm, if possible; a shower soon after 

 spraying will not lessen the destructiveness of the emulsion as 

 the nymphs are kiUed almost instantly. There is not the least 



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