14 
Journal of Agricultural Research 
Vol. XXXI, No. 1 
the disease from the wild cucumber to cultivated cucurbits. This 
is due to the fact that this insect emerges from hibernation each 
year at approximately the time at which the wild cucumber seedlings 
appear. Observations during the last five years have shown that 
the beetles may often be found feeding on the cotyledons of 
Micrampelis lobata when the first leaf is still only partially developed. 
The striped beetle occurs in considerable numbers in most cucumber¬ 
growing sections and is usually found on the wild cucumber through¬ 
out May and June. The beetles apparently feed on the wild 
cucumber and other host plants until the cultivated cucurbits come 
up, and the majority then appear to migrate to the cultivated hosts. 
This migration from the wild to the cultivated cucurbits probably 
continues to a small extent throughout the season. When wild 
cucumbers have been grown within a few yards of cultivated cucum¬ 
bers, a constant flight from one host to the other has frequently been 
noted and, as will be shown later, it is probable that considerable 
distances may be covered between the wild and cultivated plants. 
The lesser importance of the 12-spotted beetles in this relation 
is due to the fact that they are not as frequently found on Micrampelis 
in May and June, when compared with the numbers of Diabrotica 
vittata , as the 12-spotted beetle does not appear in any considerable 
numbers in the vicinity of Madison, Wis., until about July 1. On 
this account much of the experimental work has been done with 
Diabrotica, vittata . There is no reason to believe that the 12-spotted 
beetle is not an agency in the dissemination of mosaic from the wild 
cucumber later in the season, and to some extent at an earlier date 
as well. In any case, the results with one species seem directly appli¬ 
cable to the other, if both species are present at the same time. 
The cucumber aphis, Aphis gossypii , is probably not of much 
importance in carrying infection from the wild cucumber over any 
cbnsiderable distance. The aphids are rarely found on Micrampelis 
Until after mosaic has appeared on cucumbers in the field and are 
not of common occurrence on the wild host, so that while they are 
almost Certain to produce infection if they move from mosaic 
Micrampelis to the cucumber, their actual importance is limited. 
The winged generations are the only ones likely to cover any great 
distance and their migrations are apparently limited when compared 
to those of the striped beetle. In view of the greater numbers and 
activity of the beetles it is probable, therefore, that the aphids are 
of minor importance in the dissemination of the disease from the 
wild cucumber. 
INFECTION OF CUCUMBER PLANTS BY STRIPED BEETLES COLLECTED ABOUT MOSAIC 
MICRAMPELIS PLANTS IN THE OPEN 
The rdle of the striped beetle as a means of transmitting primary 
infection from the wild cucumber to the cultivated cucurbits has 
been demonstrated to some extent by experiments in which the 
beetles were collected from groups of Micrampelis plants containing 
mosaic individuals and placed in cages containing healthy cucumoer 
plants. No effort was made to collect the beetles from mosaic 
plants alone and the insects were taken from all plants in the vicinity. 
The results of these experiments, as shown in Table YI, indicate that 
beetles from such mosaic centers were able to transmit the disease in 
a number of cases. s 
