INSECT PESTS OF CIGAR-TYPE TOBACCOS 43 
the insect lives on numerous wild plants indigenous to uncultivated 
fields and woodlands. The most likely host plants for breeding sources 
are tobacco, peanuts, cocklebur, beggarweed, Gnaphaliwm sp., and 
several native grasses. 
The tobacco thrips passes the winter in the adult form, and can be 
found in limited numbers on weeds and grasses throughout the winter 
months. The insects are found also in a semiquiescent condition in 
such protected places as the bases of sods and sheaths of grasses. The 
majority apparently hibernate in the surface soil in close proximity 
to their last feeding place. 
CHARACTER OF THE INJURY 
The injury caused by thrips on cigar-wrapper tobacco is known as 
“white vein,” because of the whitened and silvered appearance of 
the veins (fig. 48). While the veins themselves may be bleached to 
a certain extent, the discoloration is due mainly to the injured tissue 
immediately adjacent to the midvein, the lateral veins, and the 
veinlets. This injury, which is produced by the feeding of the larvae 
and adults, occurs on the upper surface of the leaf. It is quite com- 
mon on the outer marginal areas near the tip, which, unfortunately, 
are the most valuable portions for wrapper purposes. The insects, 
feeding in a very hurried and energetic manner, rasp open the outer 
tissues and remove the cell contents. The injured tissues later become 
shrunken and take on the characteristic silvered appearance when 
cured. Cigars wrapped with noticeably affected leaves have an un- 
desirable appearance. 
CONTROL 
While control measures for the tobacco thrips are unnecessary 
during most seasons, safe and efficient remedial methods would be of 
benefit during occasional severe outbreaks. Unfortunately no entirely 
satisfactory methods are yet available. 
SPRAY APPLICATIONS 
A spray which has given a moderate degree of control under both 
experimental and commercial conditions consists of 114 pounds of 
40-percent nicotine sulfate by weight and 6 pounds of laundry soap 
to 100 gallons of water. In field experiments this spray killed about 
86 percent of the adults and a somewhat higher percentage of im- 
mature individuals that were thoroughly wetted with the material. 
- Under actual field spraying conditions, however, many escape the 
spray and the mortality is much lower. The eggs, which are pro- 
tected from the spray within the leaf tissues, are also a source of 
reinfestation. 
The nicotine sulfate and soap spray has been applied extensively 
to shade-grown tobacco, and only slight foliage injury has followed 
its use. The spraying of tobacco buds that have had the usual appli- 
cations of lead arsenate and corn meal for budworm control involves 
some slight risk of burning, and it is evident that the spray should 
be directed away from the buds as much as possible. , 
While knapsack sprayers (fig. 49) may be utilized with some 
success in tobacco spraying, their operation on large acreages is ex- 
