ANNUAL REPORT, 1937 



67 



Temper- Average Average Average Percentage Average .Average Number of 



*Only 1 larva completed growth at 60° F. 



Oviposition approximately doubled with each increase of 10° in temperature, 

 and the number of days required for larvae to hatch from eggs was IY2 times as 

 many at 60° as at 80° F. Although the percentage of eggs from which larvae 

 hatched in these studies was low, it was significantly higher at 70° than at either 

 80° or 60°. At 60° only 1 larva completed development and, therefore, the results 

 at this temperature should not be considered representative. At 80° the average 

 larva ate 1217.4 mealybug eggs or 37.6 per day for 32.3 days; while at 70°, 29.2 

 eggs were eaten each day for 43.9 days, making a total of 1279.8 eggs eaten by 

 each larva and thus indicating the greatest protection against mealybug damage. 



Preliminary experiments in feeding adult beetles on adult mealybugs indicate 

 that a beetle will eat about XYi mealybugs per day at 80°, and half a mealybug 

 per day at 60° and 70° F. 



Control of Red Spider. (\V. D. Whitcomb, Waltham.) In studies of insecticides 

 used for the control of red spider on carnations and greenhouse plants, materials 

 containing rotenone continued to show a high toxicity' against this pest and 

 generally became more effective as the. temperature increased. The addition of 

 wettable sulfur as a fungicide to one of the rotenone sprays caused no 'material 

 change in the number of red spiders killed. In comparable tests most of the newer 

 commercial insecticides containing rotenone were inferior to the older standard 

 mixtures or to laboratory preparations. Suspensions of derris, cube, or pyrethrum 

 powder in water were less effective than the extracts of these materials, and the 

 addition of a wetting agent did not increase their effectivness in the laboratory. 



A commercial potassium-seleno-sulfide spray was only moderately effective, 

 and the addition of wettable sulfur increased the value of the combination only 

 slightly. With this material the percentage of spiders killed was greater 5 days 

 after spraying than it was after 10 or 15 days, but the number of live spiders on 

 the sprayed plants was much smaller after 15 than after 5 days. 



Lubricating oil emulsions were more effective at 60° F. than at 80° but the more 

 volatile kerosene emulsion was more effective at 80°. 



Naphthalene and Similar Compounds as Greenhouse Fumigants. (W. D. 



Whitcomb, Waltham.) Preliminary studies of naphthalene derivatives indicate 

 that these materials are quite toxic to red spider and have promising possibilities 

 as greenhouse fumigants. 



In experimental fumigations using the materials at the rate of Yi ounce per 

 1,000 cubic feet vaporized in 6 hours at a temperature of 70° F. and a relative 

 humidity of 60-65 percent, 75 to 95 percent of the red spiders were killed in one 

 fumigation, and 95 percent or more in two fumigations. Naphthalene base ma- 

 terials in the form of oils or light waxes vaporized satisfactorily, but the heavier 

 waxes gave of? a thick smoke and a powdery precipitate which made them un- 

 desirable for practical use. When 1 part of wax was dissolved in 2 parts of oil, each 

 of the combinations used killed 60-70 percent of the spiders in one fumigation, 

 and about 95 percent in two fumigations. The addition of naphthalene or paradi- 

 chlorobenzene crystals to the oil gave similar results. Crude forms of the naphtha- 



