42 CIRCULAR 639, U. S. DEPARTMENT OF AGRICULTURE 
seasons. These insects feed also upon sun-grown types of tobacco 
but cause them no appreciable commercial injury. 
Within the Georgia-Florida producing region the severity and extent 
of thrips damage on wrapper tobacco has varied greatly from year to 
year, depending mainly on climatic conditions. Certain years have 
stood out prominently as “thrips years,” while during the intervening 
seasons the insect has caused little damage. 
DESCRIPTION AND HABITS 
The adult tobacco thrips (fig. 47) is a minute, brownish-colored 
insect about one twenty-fifth of an inch in length. Some of these 
insects have wings which apparently are seldom used, while others 
possess only short wing pads. During warm, dry weather the adults 
spend most of their time on the upper surfaces of ‘tobacco leaves, being 
found usually in the depressions of the veins, where they do most of 
their feeding. 
Adult females begin to deposit eggs soon after they have become 
established on the tobacco plants. The eggs are deposited in the epi- 
dermis, usually of the upper sur- 
face of the leaf. The incubation 
period during May, June, and 
" July in the southern districts re- 
Ovi Guires an average period of about 
= S414 days. 
OP y 
\\ 
\ 
a. 
i 
Wy 
a i 
oy ‘O22 
fi 
CHL 
NA 
\ 
N 
bib sn yy 
i e, 
fay HS a i, 
if 
I 
-— most colorless and difficult to dis- 
= cern, but after they have fed 
3 they become yellowish and are 
(EN more easily detected. They 
TK crawl about both surfaces of the 
tobacco leaves but the greater 
Figure 47.—Adult of the tobacco number are found on the upper 
thrips, X 32. surfaces. 
The larval stage is followed by 
nonfeeding prepupal and pupal stages. Both these stages are spent 
on the leaf in a semiquiescent condition, and the lower surface seems 
to be preferred at this time. The total developmental period for the 
immature stages of the insect during the spring months averages 
about 13 days. 
By the first week in May many individuals of the first generation 
bave completed their development, although overwintered females are 
usually still emerging at this time. Overl rlapping broods then follow 
one another throughout the tobacco-growing season. From the lower 
leaves the thrips oradually ascend to the leaves above , and the height 
which they attain depends mainly upon the climatic conditions. “In 
seasons with abundant rainfall the limited number of individuals that 
survive confine their attacks mainly to the lower leaves, while in ex- 
tremely dry seasons the heavy infestations spread upward to the high- 
est leaves on the plants. Six or seven generations may attack the 
tobacco crop during its growing period. 
The tobacco thrips feeds on many plants, both wild and cultivated. 
While it is mainly a foliage feeder, it is found also in the blooms of 
many plants, especially the legumes. As tobacco set on newly cleared 
land becomes immediately infested with this species, it is evident that 
Newly emerged larvae are al-— 
