two P, sexta males andone P, quinquemaculata 
female in 1961 and 8,1 and 8,2 miles for two 
P, sexta males in 1962, 
It was evident from these data why previous 
attempts to control hornworms with traps on 
small areas had failed, Such areas would be 
subjected to a continuous influx of moths from 
outside, and only part of these would be caught, 
The size of area required for a useful ex- 
periment can be estimated from the marking 
and recapture data, provided some allowance 
is made for the movement of moths over a 
larger and larger area as they dispersed from 
a central point, In correcting for the distance 
factor, it was assumed that moths dispersed at 
random and the effective range of all traps 
was the same and circular, If the diameter of 
this circle is ''d'' and the distance of a trap 
from the point of release is "r,''thenthe catch 
of the trap should be approximately propor- 
tional to d/2mr, Since "d"' and "27" are con- 
stants, an approximate correction can be ob- 
tained by multiplying the catch by "r." If this 
correction is,applied to the data for P, sexta 
males, the regression equation then becomes 
log Y = 2,003 - 0,266 X, and the regression 
coefficient is highly significant, From this it 
can be calculated that 5 percent of a dispers- 
ing population will travel 4,89 miles, Thenina 
circle with a radius of 4,89 miles, 5 percent 
of the moths at the center willhave come from 
outside the circle, 
After estimating the increase in total catch 
to be expected from increasing the number of 
traps, it was concluded that about three traps 
per square mile were necessary to control 
the population of P, sexta, 
Since a certain minimum area is needed to 
measure a population, the experiment as set 
up in 1962 consisted of two tangent circles, 
each 12 miles in diameter, The westerncircle 
had 6 light traps placed at about l-mile 
intervals in each of four directions from the 
center outward, with a total of 24 traps in 113 
square miles, The eastern circle had 324 light 
traps in an area of the same Size, or about 3 
per square mile, In addition, six traps were 
placed at about l-mile intervals, extending out 
6 miles from the outer edge of the eastern 
circle to the north, south, and east, The center 
of the eastern circle was 6 miles west of 
Oxford, N.C. 

196 
The size of the trapped area was increased 
to a circle 20 miles in diameter in 1964 and 
the legs were extended 10 miles beyond the 
circle, but this experiment was putinto opera- 
tion too late in the season to yield much use- 
ful data, Each trap was equipped with a 15- 
watt black-light lamp, 
EFFECT OF LIGHT TRAPS AND 
STALK CUTTING ON HORNWORM 
POPULATIONS AND DAMAGE 
TO TOBACCO 
Since it was not possible to count all the 
moths caught in all traps, moth counts were 
made daily or every 3 days in only 52 traps, 
These traps were located in four radii ex- 
tending outward from the center of the circle, 
a distance of 12 miles in 1962 and 1960 and 
20 miles in 1964, In 1964, the number of traps 
in which moths were counted was increased to 
62, 
When the data were examined, it was found 
that the numbers of hornworms caught per trap 
tended to be lowest at the center ofthe trapped 
area and gradually increased outward in all 
directions as far as the trap lines extended, 
although there were differences between 
species, sexes, and years, The data are il- 
lustrated in figures 1 and 2, 
The same general pattern of distribution was 
also seen in counts of eggs madeon 12 tobacco 
fields in 1962, 45 in 1963, and 48 in 1964 (fig. 
3). For the first 2 years these counts were 
made on farmers’ tobacco, which in many 
fields was treated with insecticides, Hence, 
although estimates of damage were made, no 
significant differences between damage in the 
light-trap area and that in the area outside the 
light traps could be established, In 1964, the 
samples were taken on half-acre plots of un- 
treated tobacco, Figure 4 shows the number of 
plants attacked by hornworms, Again, the 
general gradient in extent of damage was the 
same, 
There was a marked depression in mothand 
egg populations and in damage in the area 
covered by light traps, This depression ex- 
tended for a considerable distance outside the 
area trapped, The reduction in populations 

