July i, 1925 Overwintering and Dissemination of Cucurbit Mosaic 
17 
of this infection being carried by those making the observations, and 
as no further infection appeared until late in August, it is quite 
probable that the original infection came from a distant source, such 
as the mosaic wild-cucumber plants, and that, owing to the chance 
nature of infection from beetles over such distances, no further infec¬ 
tion occurred for some time. 
Perhaps such an irregularity in infection is to be expected if we 
consider the beetles to have been the agency concerned in the trans¬ 
mission of the disease, for, as already stated, the percentage of infec¬ 
tion due to these insects is always low as compared with that due to 
aphids. On this basis a certain element of chance may exist, and it is 
possible that a greater number of insects might visit a nearby plat 
v without necessarily causing immediate infection, while a smaller 
number might reach a more distant plat and produce infection at an 
earlier date. In most cases it is improbable that great numbers of 
insects feed on Micrampelis and immediately travel to the cucumbers 
in the field. Recent investigations by Dudley, of the United States 
Bureau of Entomology ( 12 ) indicate that the beetles may travel as 
far as one-half mile and also that they' perhaps pass over nearby 
cucumber fields when moving with the wind. Under such circum¬ 
stances the above results probably are to be expected. 
If we accept the results of these experiments at their face value, 
they indicate the possibility of infection being carried at least a quarter 
of a mile from groups of mosaic Micrampelis plants and at a date 
sufficiently early to allow for destructive development of the disease. 
In the plats within 350 yards of the Micrampelis plants, it was practi¬ 
cally certain that infection must have been carried a distance equal 
to that of the known source on the wild cucumber. We can not be 
sure, however, that insects other than the cucumber beetles were not 
concerned in its transmission. This latter point is of minor signifi¬ 
cance, however, as regards the practical importance of the wild 
cucumber as a source oi primary infection. 
The source of infection for tne most distant plats (plat 7 of 1920 
and plat 5 of 1921), is less certain, perhaps, especially as the disease 
developed comparatively early at this point each year. These 
plats occupied approximately the same locations and were close to 
a small piece of wooded land which contained many wild plants. 
Careful inspection at various times failed to show any known host 
f fiants of cucurbit mosaic, but the possibility of their being over- 
ooked is not beyond question. The general evidence, however, 
seems to indicate that infection was traceable to the wild cucumber. 
In theory, the distance over which the beetles may carry infection 
is limited only by the extreme range of their flight. Field observa¬ 
tions, however, indicate that a range of 400 to 600 yards represents 
the limits within which there is a reasonable expectation of infec¬ 
tion on the cultivated hosts, since at these distances fields have 
often remained free from mosaic for the greater part of the summer. 
IMPORTANCE OF THE WILD CUCUMBER AS A SOURCE OF INFECTION OF THE CULTI¬ 
VATED CUCURBITS 
The present evidence has shown that the mosaic disease is carried 
over winter in the seed of the wild cucumber and that certain insects 
are able to transmit the disease from this host to the cultivated 
