ANNUAL REPORT, 1934 51 



Naphthalene as a Fumigant for the Control of Greenhouse Insect Pests. 



(W. D. Whitcomb, Waltham.) When naphthalene was used in experimental 

 fumigations at a rate of 2 ounces per 1000 cubic feet for 6 hours, the vaporization 

 of the total amount in the first 3 hours and none in the last 3 hours killed 85 

 percent of the red spiders in a 3-hour exposure; three-fourths of the total amount 

 in the first 3 hours and one-fourth in the last 3 hours killed 85 percent in a 4-hour 

 exposure; and the total amount in 6 equal hourly applications required an ex- 

 posure of 5 hours to kill 85 percent or more of the red spider. 



These experiments indicate that an exposure of at least 3 hours to an atmos- 

 phere saturated with naphthalene is necessary to cause an appreciable mortality 

 of red spider, and since saturation exists when 0.64 ounces of naphthalene are 

 vaporized in 1000 cubic feet of air at 77°F., it is apparent that about twice as 

 much vapor is lost and absorbed as is retained in the air during a 6-hour fumi- 

 gation. 



A homemade naphthalene fumigator has been developed in which warm air 

 is blown over trays of naphthalene crystals by an electric fan. The air is heated 

 to 165°F. by being blown over a resistance heating unit, and the dosage is reg- 

 ulated by the amount of crystals in the trays or by the time the apparatus is in 

 operation. Experimental fumigations with this apparatus indicate that sensitive 

 plants are less likely to be injured than when the application is made with lamps. 



Typical injury in the form of blindness which occurs in some varieties of 

 chrysanthemums following naphthalene fumigation appears to occur only during 

 the bud formation stage, and buds which have developed to 1/8 inch diameter 

 or larger are not blasted or otherwise injured by the treatment. In addition to 

 the standard varieties which have been susceptible to this type of injury, Yellow 

 Frost, Garnet King, Olivette, and Pride of Tokio were found to be moderately 

 susceptible this year. 



Biology and Control of the Carrot Rust Fly. (W. D. Whitcomb, Waltham.) 

 The field infestation of the carrot rust fly in 1934 was closely related to the 

 weather. Dry, hot weather in early summer was so unfavorable to the develop- 

 ment of this pest that early planted carrots were practically uninjured while 

 late planted carrots which were exposed to the favorable cool, wet weather of late 

 August and September suffered from 10 to 27 percent moderate and severe injury. 



It was apparent from control experiments that seed treatments with calomel 

 mixed in varying quantities with inert clay are not active long enough to give 

 protection from the attack of the second or third generation, even though they 

 have shown many beneficial results on the early plantings. 



Influence of Temperature on Development and Control of Red Spider. (W. D. 

 Whitcomb, Waltham). Preliminary studies of the influence of temperature on 

 the effectiveness of sprays used for combating the red spider have shown that 

 the number of spiders killed usually varies between 60° and 80° F., and that this 

 difference may be as great as 60 percent. The effectiveness of some materials 

 varied directly with the increase in temperature and others inversely. Out of 34 

 materials or types of materials so far observed, 16 were consistently more effective 

 at 60° than at 80°. 



Heavy lubricating oil emulsions were more effective at the higher temperature 

 probably due to the greater spreading and penetrating action, while light oil 

 emulsions were distinctly superior at 60°F., evidently due to suppressed volatility 

 and longer contact. Soaps were rather inconsistent in their response to tempera- 

 ture but showed a tendency toward greater effectiveness at 60°. Soluble sulfurs 

 as represented by liquid lime-sulfur and carbon disulfide-sulfur emulsion were 



