40 MASS. EXPERIMENT STATION BULLETIN 417 



averaging 1L16 days. There are five nymphal stages, the first four requiring 4 

 to 6 days and the last averaging 12.8 days. 



In the late planting the white and yellow varieties of celery were more heavily 

 infested than the green varieties, averaging 73 more bugs per 100 plants in the 

 semi-weekly counts. The most heavily infested variety was FuUheart, with 3749 

 bugs per 100 plants during the season and 320 per 100 plants at the maximum 

 infestation on September 11. The most resistant variety appeared to be Morse's 

 Utah, a coarse green variety which does not bleach well. It had only 538 bugs 

 per 100 plants throughout the season, and 44 per 100 plants at the height of the 

 infestation. The standard variety, Summer Pascal, had a low infestation through- 

 out the season. 



Spraying and dusting experiments against the first brood of bugs on early 

 celery showed satisfactor\' protection from nicotine dusts and sprays, and from 

 nicotine-pyrethrum dust in three applications. The nicotine-pyrethrum dust 

 reduced the number of bugs 97 percent, and only 4 live bugs per 100 plants were 

 found in counts made one day after treatment. Black Leaf 155-bordeaux 

 mixture spray, and Black Leaf 155-lime dust also gave good protection. On the 

 untreated plants the infestation increased 81.3 percent during the period. 



On the second planting, the nicotine-pyrethrum dust again gave the best pro- 

 tection. When applied at weekly intervals between July 19 and September 20, 

 only 95 bugs per 100 plants were found during the season, compared to 350 bugs 

 per 100 plants on the untreated check. Counts on the day following application 

 showed a 95 percent reduction in the number of bugs from this dust. The addi- 

 tion of 2 pounds of soap flakes dissolved in each 100 gallons increased the effective- 

 ness of nicotine sulfate spray 1-800 by 28 percent, and of a commercial pyrethrum 

 spray 1-400 by 17 percent. The least effective treatment was nicotine sulfate 

 1-800 without soap, in weekl)^ applications. 



Applications with a spray gun which drove the spray into the heart of the 

 celery were 5 to 10 percent more effective than applications with a mist nozzle. 



Applications at intervals of 2 and 3 weeks reduced the number of bugs found 

 24 hours after treatment as much as weekly applications, but permitted greater 

 reinfestation in proportion to the interval between treatments. 



Investigations on the Effect of Insecticides on Honeybees. (A. I. Bourne and 

 F. R. Shaw.) In feeding tests to determine the relative toxicity of arsenicals 

 and fluosilicates to bees, fluorine compounds at the rates recommended for con- 

 trol of shade tree pests seemed to be fully as toxic as arsenicals. In a comparison 

 of the effects of dusts on bees, rotenone and pyrethrum dusts were most toxic, 

 nicotine was third, sulfur fourth, and DN dust fifth in order of toxicity. Since 

 DN dust would be applied during the summer when bees are active, the fact that 

 it did not cause appreciable death is significant. 



Tests of materials suggested as bee repellents included creosote at various 

 dilutions, carbolic acid, and a proprietary phenol compound known as Milkol. 

 All creosote applications produced blossom injury. The heavier concentrations 

 produced some leaf injury, which soon disappeared, however, because of the drop- 

 ing of the affected leaves. Materials applied shortly after full bloom did not 

 materially affect the set. 



Experiments to determine the effect of the materials suggested as repellents 

 on the length of life of bees were conducted by feeding the "repellent" material 

 in sugar syrup. The length of life of bees fed these materials was compared with 

 that of check lots receiving sugar syrup. In all instances the addition of the 

 "repellent" shortened life. Whether this was due to insecticidal action or to 

 starvation was not determined. 



