ANNUAL REPORT, 1935 53 



Naphthalene as a Fumigant for the Control of Greenhouse Insect 

 Pests. (W. D. Whitcomb, Waltham.) A report on previous studies with 

 naphthalene as a greenhouse fumigant has been published as Bulletin 326. 



Further work with an electric fumigator in which a fan is combined with a 

 heating unit determined that in the experimental equipment about 20 percent 

 of the naphthalene placed in the trays was vaporized in an average exposure of 

 6 to 8 hours. Since air can hold only a limited amount of naphthalene vapor, 

 the vaporization of the crystals can be increased within certain limits, (1 ) by 

 enlarging the air draft capacity of the apparatus, (2 ) by lengthening the period 

 of exposure, and (3) by raising the air temperature. On the other hand, it was 

 found that when the air draft and the air temperature remained constant, the 

 percentage of naphthalene vaporized in a given length of time decreased as the 

 amount of napthalene crystals was increased. 



Experiments with two commercial liquid fumigants containing materials 

 similar to naphthalene indicate that they are very efficient for the control of 

 red spider, and that the mortality following one fumigation is generally greater 

 than from naphthalene. It was also found that these materials could be used 

 satisfactorily at any of the lower temperatures at which greenhouse plants 

 are grown. 



Plum Gurculio in Apples. (W. D. Whitcomb, Waltham.) In 1935, plum 

 curculio beetles emerged in large numbers during the petal fall period, and 

 consequently the calyx spray was more effective in combating this insect in 

 apples than normally. An extended period of cool wet weather during the 

 normal period of curculio activity made two applications, one just before the 

 rainy period and one just after it, necessary for the best control. 



Experimental spraying for timeliness of application at the Waltham Field 

 Station orchard, using lead arsenate and fish oil, showed that the most timely 

 two-spray applications were made June 3 and 15, while the most effective single 

 spray was applied June 7. 



The susceptibility of varieties all receiving the same control treatments was 

 as follows: average percentage of apples stung by plum curculio, Gravenstein 

 25.84; Wealthy 16.35; Baldwin 10.12; and Mcintosh 6.51. 



Influence of Temperature on Development and Control of Red 

 Spider. (W. D. Whitcomb, Waltham.) Studies of the influence of tempera- 

 ture on the effectiveness of spray materials for controlling the red spider were 

 continued in constant temperature cabinets at 60°, 70°, and 80°F. 



Miscible pine oil, an ingredient in several of the newer sprays, gave a very 

 low kill of red spider and apparently adds very little to the toxicity of the 

 materials with which it is combined. The effect of temperature was irregular, 

 but slightly better control was obtained at 80°F. 



A concentrated pyrethrum paste containing 1.95 percent pyrethrins plus 

 .5 percent of neutral soap killed about 30 percent of the spiders and the majority 

 of the dead spiders apparently were killed by the soap. Another pyrethrum 

 extract in acetone (2.15 percent pyrethrins) diluted 1-200 was only slightly 

 effective, and the mortality was not increased by the addition of pine oil 1-400. 



When pyrethrum was combined with derris or cube extractives in alcohol 

 an excellent mortality resulted. With this commercial product the mortality 

 increased about 5 percent with each increase of 10 degrees in temperature, and 

 increased about 10 percent when the dilution was raised from 1-400 to 1-200. 

 Another commercial product containing 1.5 percent rotenone in acetone gave 

 good control at 80°F. but showed a 20 percent decrease in mortality at 60°. 



