Counts of hornworms were also made on tobacco fields inside and outside the 
trapped area during this period. When these were plotted, they also indicated 
a gradual increase in populations from the center outward, but the number of 
hornworms found was highly variable, primarily because the condition of the 
plants and the suitability for hornworm Oviposition were also variable. The 
regression of number of hornworms on distance was not significant. 
The mean numbers of hornworm eggs and first-instar larvae per 50 tobacco 
plants in seven counts in 12 fields at varying distances from the center of the 
trapped area between July 27 and August 16, 1962, were as follows: 
Miles from center Number of hornworm 
eges and larvae 
Q- 32--------------------------- 23 
3-6---------------------------- 29 
6-9---------------------------- 4g 
9-12--------------------------- 66 
The percent reduction for 9-12 and O-3 miles was 57.6. Differences between 
these means were not significant, but the percent reduction was about the same 
as the reduction in female populations indicated by the trap catch in table 7. 
Table 7 indicates that the reduction in population in the trapped area was 
much greater for males of both species than for females. It might be expected 
that the fertility of females would be reduced by the destruction of so many 
males. Two methods were used to capture moths for dissection. Some were caught 
in the ordinary trap cages where most moths remained alive until removed, and 
they frequently mated after being caught. Some traps were equipped with a can 
containing dilute alcohol in which the moths were killed when captured. The 
spermatophore in these species is easy to find. It is about the size of a 
grain of barley with a tube nearly an inch long. 
Table & indicates that the percentage of mated P. sexta was higher in the 
cages than in alcohol, but there was no difference in P. quinquemaculata. This 
result is somewhat odd, since both species were often found in copulation in 
the cages. There was little, if any, difference in the fertility of females 
caught in the trapped area and outside. Table 9 indicates that multiple mating 
is not common in either species, but it does occur. 
DISCUSSION AND TENTATIVE CONCLUSIONS 
The role that light traps might play in the practical control of hornworms 
on tobacco cannot be determined on the basis of results obtained during 1 year 
in one location. The preliminary data obtained in the sizeable area of approxi- 
mately 113 square miles utilizing about 3 light traps per square mile, indicate, 
however, that male hornworm populations in the center of the trapped area might 
be expected to be reduced by 76 and 89 percent, respectively, for P. sexta and 
P. guinquemaculata. The corresponding reductions in the population of females 
were 55 and 56 percent, respectively, for the two species. The population 
levels of eggs and small larvae on tobacco in the trapped area in comparison 
with tobacco in the surrounding untrapped area were about the same as the 
reduction in female hornworm population in the trapped area. 
ae 
