408 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 14 



It was afterwards found that "Nicodust" manufactured by the Wal- 

 nut Growers Spray Manufacturing Company was not uniform in 

 strength. Beet leafhoppers were confined in screen wire cages (PI. 8, 

 fig. 1) and the dusting machine passed over these cages in a beet field. 

 Five sacs of "5% Nicodust" applied at the rate of about 125 pounds per 

 acre showed a variation in the killing of the adults from. 8-72%. 



With the use of" 10% Nicodust" one of the men working on the dust- 

 ing machine was overcome with nicotine. The army gas m.ask was then 

 employed and no further trouble was experienced by the operator. 



During 1921, Hartung and Schwing conducted a series of experiments 

 in order to make a dust mixture which is uniform, in strength and efficient 

 in killing the beet leafhopper. The same ingredients were employed in 

 the dust preparation as were used last year. 



Preliminary tests with reference to the effectiveness of the dust mix- 

 tures in killing the beet leafhopper were conducted in Little Panoche 

 Pass, The vegetation was dry for the most part on the foothills but 

 nymphs and adults had congregated on green Filaree growing in the 

 gullies. An area about 20 x 10 feet was swept with an insect-net at the 

 rate of 100 sweeps and an average of 34 hoppers was estimated : then the 

 plot was dusted and the niim.ber of bugs captured in 100 sweeps was again 

 ascertained. One hundred hoppers were also confined in screen wire 

 cages (PI. 8, fig. 2) and after dusting the percentage of kill was determin- 

 ed. A dust containing 8% "Black Leaf 40" was applied with an Ameri- 

 can Beauty hand duster. The percentage of leafhoppers that were killed 

 in four cages varied from 87-97%. It was found that a few adults re- 

 covered but most of these died at the end of 20-45 hours when further 

 observations were discontinued. Nymphs and adults were rarel}^ cap- 

 tured in an insect-net by sweeping the dusted area. 



Preliminary experiments conducted with a dusting machine in a beet 

 field at King City showed that dust mixtures about six weeks old kept 

 in closed tin receptacles and containing from. 6-10% of "Black Leaf 40" 

 were not as effective as the newly m.ade m.aterial. The percentage of 



EXPLANATION OF PLATE 5. 



(1) Dusting machine in operation. The nozzles are enclosed in a sheet-iron fumi- 

 gation box. Insert shows screen wire cage which was rolled below dusting machine 

 in operation to determine the percentage of beet leafhoppers killed with nicotine 

 dust. The hoppers were put into the cage through the hole in the cover plugged 

 with cotton. 



(2) Front sheet-iron turned over showing nozzles. The nozzle ending in two 

 forked flattened tubes dusts the lower surface of the leaves of two rows of beets. 

 The nozzle ending in a funnel is provided with a sieve-plate which forces the dust 

 between the petioles. 



