54 ANM AL Ki:i'nlC l S OK l^lil'AK'J .MKN i ( H" A( iUICl LTUUi:, 1037 
fectioii, iimdc in soiuh-cciil nil Idaho tluriiiji tl»o T-ycar iKrioil 1030-30, it was 
coiiclu(l('(l that t-ariy spiiiig inoveiiu'iits of the beet leafhopiKT were followed 
by rapid and widespriad curly top infection, result ini; in low yields of sugar 
beets, wheri'as late spriii},' movements were followed \>y seasons in which sugar 
beets escaped serious curly top infection and produ<-ed good average yiehls. A 
comparison of the acreages of sugar beets planl«'d, thinned, abandoned, and 
harvested, and the resultant yields \Hir acre, during seasons of high curly top 
infection, with th«)se of low infection, showed that nnu'h abandonment of 
sugar-l)eet acreage occurred during those years when the curly top disease ap- 
peared early in the season and spread rapidly, and that low tonnages of beets 
resulted, whereas very little abaudonmeiit occurred in years when curly top 
infection was late and slow in spreading, and that good average yields were 
obtained under these conditions. In comparing the average yields of sugar 
beets in ]03r>, during which resistant strains of beets were planted, with the 
yields obtained in 1030 and 1932, during which susceptible strains were 
grown, it was shown that high curly top infection reduced the average yield 
of susceptible beets i?i 1030 to a point below the margin of profit, and that 
low curly top infection allowed the production of a highly satisfactory aver- 
age yield in the .same strains of sugar beets in 1032; also, that the resistant 
strains of sugar beets produced a good average yield in 103r>. despite a high 
infection early in the season. 
As a result of a survey made in Texas, approximately 2.7(X) square miles of 
territory were added to the known breeding areas of the beet leafhopper. 
Leafhoppers from this area have been primarily responsible for the curly top 
disease epidemics which have been prevalent in the spinach fields of Texas. 
The known breeding areas (*f the beet leafhopper in this section now occupy 
approximately 10.700 scjuare miles north of the Rio Grande in New Mexico and 
Texas in addition to the unknown extent of adjacent areas in .Mexico. 
Field observations in California indicated that the curly top disease, of 
which the beet leafhopper is the vector, is more prevalent in tomatoes planted 
in sandy soils than in those planted in soils of the heavier types, and that 
fields of tomatoes planted before the spring migration of the leafhoppers were 
infected by curly top to a greater extent than those planted after the prin- 
cipjil leafhopper migration. Biological investigations disclosed that the beet 
leafhopper can exist for long periods late in the fall on v.-irious species of 
deciduous trees grown in or adjacent to the San Joaquin Valley, in addition 
to the previously known host ])lants of this insect. High populations of the 
beet leafhopper which occurred during the fall of 10.30 on Russian-thistle grow- 
ing ad.incent to the winter l)reeding grounds of the in.sect necessitated the 
spraying of large areas of this weed to destroy the leafhoppers congregated 
thereon. 
TOBACCO INSECTS 
Extensive field-plot tests against tobacco fiea beetles [llijUrir panuln V. 
and E. cucutneris Harr. ) in Florida. Tennessee, North Carolina. South Caro- 
lina, and Connecticut indicated that these pests could be controlle»l in the 
plant bed, as well as on newly set plants and on the growing crop, by timely 
applications of dust mixtures containing rotenone derived from derris or cube, 
with steriliz(>d tobacco dust as the diluent. In the wrapper-tobacco districts 
of Coiniecticut and I'lorida the growers have adopted dusting with cube or 
derris mixtures for flea beetle control, but in the flue-cured and other sun- 
grown tobacco areas these insecticides are not as yet reconunended for gen- 
eral use. From data obtained to date, dust mixtures containing rotenone 
gave a higher initial degree of control than insecticides containing arsenical or 
fluorine conipoinuls. In a series of experiments designed to show the relative 
toxicity of cube dust nnxtures containing 0..!. 1.0. and 1.5 percent of rotenone, 
respe<-tively. against the tobacco flea beetle on shade-grown tobacco in Florida, 
it was shown that the dust mixtures containing 1.0 and 1.5 percent of rotenone. 
re.si)ectively, were much UKU'e l<>xic and gave a higher degree of control of 
tlie flea beetles than the dust mixtures which contained 0..") percent of rotenone. 
These conclusions were reacln'd as a result of a detailed stmly of tlie har- 
vested jiroduct. in which it was shown that the percentages of injured leaves, 
together with the i>ercentages (tf the commercial gradings. served as a satis- 
factory method for obtaining a relative comparisim of the elTt'ct of the dif- 
ferent dilutions used. Incidentally. thes(» studies demonstrated that a flea 
beetle infestation of only mo(hrat«' intensity may cause a loss, ba.sed on an 
average croj) return in cigar-wrajijier tobacco. whi< h reaches J?47."» imm' acre. 
Laboratory studies to determine the comparative t(>xicity of certain ar.senlcals 
and iKtiiarsenical conii»onnds to the lar\ ae of tobacco honnvorms ( Prntoparce 
