CORNELL UNIVERSITY EXPERIMENT STATION BULLETINS. 265 



crawled into the buds out of the reach of the insecticides. It was feared 

 that all the young and tender nymphs would thus get out of reach. But a 

 majority of the eggs did not hatch this year until many of the leaves had 

 -expanded, thus leaving the nymphs exposed. During a warm early spring 

 the eggs might hatch early but many of the leaves expand in a few days 

 and thus the nymphs would be exposed before they had become more than 

 one third grown. 



Our experiments against the young nymphs were first carried on in the 

 insectary upon infested branches brought in from the field. It was soon 

 found that the young nymphs were very tender and very susceptible to 

 kerosene. A kerosene emulsion was prepared according to the Hubbard- 

 Hiley formula.* The nymphs were dipped in the emulsion diluted with 

 "different quantities of water. It was found that every nymph was killed 

 by the emulsion even when diluted with twenty-five parts of water, and 

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

 almost immediately after the liquid touched them. These laboratory 

 results were thus very encouraging. 



Field experiments were soon begun to test the practicability of the 

 ^m'alsion. No trees could be found that were very badly infested. But 

 by carefully examining the trees before and soon after spraying it was esti- 

 mated that from 75 to 90 per cent, of the nymphs were killed by one spray- 

 ing with kerosene emulsion diluted with twenty-five parts of water. Some 

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

 a,s 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 in 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 per tree for time and material. The experiments with 

 the kerosene emulsion against the nymphs were so successful that no other 

 insecticides were tried. The emulsion is the cheapest effective insecticide 

 now known for sucking insects; and our experiments have shown that it 

 will prove a very practical and efficient means of 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 insecticide this 

 year, 1892. This was probably due to the fact that many hard showers 

 fell during the early part of the season. The rain washed off much of the 

 secretion. This fact should be taken advantage of by fruitgrowers in 

 spraying for the pest. Spray soon after a heavy rain-storm if possible; a 

 shower soon after spraying will not lessen the destructiveness of the emul- 



* The formula is \i poand hard or soft aoap, 1 gallon water, 2 gallons kerosene. 



First, thoroaghly dissolve the soap in boiling water. While this solution is still very hot add the kero- 

 sene; if the whole is then left over the fire for a few moments to raise the temperature of the kerosene 

 slightly, it will facilitate the emulsifying process. Remove from the fire and quickly begin to agitate the 

 whole mass through a syringe or force pump of some kind ; draw the liquid into the pump and force it 

 back into the dish. Continue this operation for five minutes or until the whole mass assumes a creamy 

 color and consistency which will adhere to the sides of the vessel, and not glide off like oil. If desired 

 for use immediately, it may now be readily diluted with cold water, preferably with rain water. Or the 

 whole mass may be allowed to cool when it has a semi-solid form, not unlike loppered milk. This stock 

 if covered and placed in a cool dark place will keep for a long time. In making a dilution from this 

 cold stock emulsion, it is necessary to measure out the amount of the emulsion required, and first dis- 

 solve it in three or four parts of boiling water ; if cold water be used a large quantity of a white floccu- 

 lent mass rises to the surface and does not dissolve. After the stock emulsion is dissolved, cold water 

 may be added in the required quantities. IE all the utensils are clean, and the directions followed closely, 

 no free oil will rise to the surface of the dilution. 



34 



