24 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE, 1952 
aphid is able to infect plants for only about one hour after it leaves the 
disease-source plant. Tests with other aphids are underway. It is 
possible that chrysanthemum may serve as a reservoir for this diseasi 
from which aphid vectors could carry it to tomato and tobacco where 
the symptoms arc very severe. 
Dipping Narcissus Bulbs Controls Bulb Fly 
Tests have been continued in Washington and Oregon to develop 
a practical means of preventing infestation of narcissus bulb- by 
larvae of the narcissus bulb fly. For application during the late 
spring period of adult activity naphthalene flakes applied to the soil 
surface around the growing plant- has been the only material which 
has given a consistently high degree of control against this stage of 
the insect. Summer-type spray oils, technical benzene hexachloride, 
and toxaphene, applied to the growing plants, are the most promising 
of the materials tested so far, but the degree of control obtained from 
their use has been only fair and attempts to improve control by in- 
creasing the number of applications or the dosages have not been 
successful. However, the method of soaking narcissus bulbs 10 
minutes or longer in a solution of aldrin, chlordane. dieldrin, hepta- 
chlor, or lindane, prior to planting gave complete protection to the 
bulbs. Xo injurious effects were apparent in the bulbs treated with 
aldrin, chlordane, or heptachlor. Some injury occurred to bulbs 
soaked in lindane, probably due to the solvent. Stimulation of plant 
growth of the dieldrin-treated bulbs rendered them susceptible to 
injury from cold weather. The highly satisfactory results from this 
method of approach to the problem give the best promise of develop- 
ing practical recommendations for control of the narcissus bulb fly. 
Weevil-Resistant Sweetpotatoes Studied 
In investigations on the varietal resistance of sweetpotato plants 
to the sweetpotato weevil, two sweetpotato seedlings. L187 and L/244, 
developed in cooperation with plant breeders of the Louisiana Agri- 
cultural Experiment Station, showed a high degree of resistance to 
attack of the sweetpotato weevil in experimental-plot tests. 
Thrips Infestations in Tomato Fruits Largely a 
Plant-Breeding Problem 
Research work in cooperation with the Bureau of Plant Industry, 
Soils, and Agricultural Engineering and the Utah Agricultural Ex- 
periment Stat ion to develop methods of preventing thrips infestations 
within tomato fruits was completed and the project is being discon- 
tinued. It was shown that thrips infest tomatoes only whim the 
tomatoes, while green, develop open cavities. The thrips feed in the 
cavities of the green fruits. As the tomatoes grow and ripen the 
Cavil ies tend to close and t rap the thrips, thereby causing the marketed 
product io lie contaminated. Experiments indicated that it is not 
practical to prevent the ocurrence of thrips within tomatoes by con 
trolling the insect with insecticides. It was also shown that plant 
thai produce tomatoes without cavities can be developed by select'™ 
Thus the problem has become one largely for the plant breeder. 
un- 
ion. 
