Sr.pt. 15, 1925 
Distribution of the Colorado Potato Beetle 
545 
Apparently the adult insects drop into a potato field without 
deliberation and are satisfied if they find potato plants. Obser¬ 
vations made in the Solanaceae garden at Ithaca in 1923 indicate 
that distinction is made within the family. A common idea is 
current among growers that Colorado potato beetle adults manifest 
a preference for early varieties when offered a choice of host plants, 
but it would appear from variety tests that the insect does not have 
any particular preference when offered the opportunity of wide 
choice of varieties. It would seem that the insect arrives on some 
varieties only after trial and error, and that it does not make a dis¬ 
tinction between varieties. This has been indicated in variety-test 
plots where all factors remained the same except variety. 
THE VOLUNTEER 
That early spraying of potato sprouts soon after they come up is 
effective in reducing infestation, is a common observation among 
growers and in the literature of the subject. In addition to the lethal 
effect of the spray there is a certain amount of protection afforded 
by the deterrent influence of the Bordeaux-arsenical sprays. Re¬ 
dispersal flights often closely follow spray applications. Repelled 
from further feeding by either the spray residues or alimentary dis¬ 
turbances occasioned by arsenic ingestion, the beetles take flight for 
a more hospitable environment. One may locate them sometimes 
resting on nearby foliage, as if contemplating what to do next. Such 
redispersal flights afford an opportunity for infestation of other 
fields and wild Solanaceae, the most common of which is the wild or 
“ volunteer” potato. 
The “volunteer” potato is a plant which has grown from tubers 
remaining overwinter in the ground or from tubers thrown away in 
waste areas. In a northern latitude they occur most frequently in 
fields sown to oats, wheat, and other similar grain crops following 
potatoes. Low temperatures prevent decay in the fall, an early 
snow blanket protects from heavy ground frost, and tubers missed 
during the previous fall harvest develop plants the following spring 
which come up with the new crop. It is not unusual for the plant 
to perpetuate itself; volunteers may be found in the third and some¬ 
times the fourth year after the field was originally planted in pota¬ 
toes. Great fluctuation in the numbers of volunteers per acre occurs, 
due to the fact that in some years the ground freezes deeply before 
the snow comes and the tubers are killed and “volunteers” are 
either very scarce or absent the following year. Dispersing adult 
beetles are then forced to choose between wild species of Solanum 
and the cultivated crop. After a deliberate hunt for infested species 
of wild Solanaceae, the writer is convinced that the beetles do not 
accept them within smelling distance of cultivated potatoes. This 
opinion, based on observation, is confirmed by the fact that high 
rates of infestation follow years favorable to the development of 
volunteers, such as were the years in which the data reported in 
this paper were taken. The importance of the volunteer potato 
plant as a refuge and reservoir for the potato beetle is not overdrawn. 
In one locality the writer counted 202 volunteers per acre in wheat, 
with an average infestation of 36 per cent; in wheat in another 
locality they ran 3,360 per acre, with an average infestation of 16 
per cent, and, in clover 621, with 54 per cent infestation. 
