BACTERIAL WILT OF CUCURBITS. 41 
SUMMARY. 
As a result of our studies on bacterial wilt of cucurbits during the 
period 1914-1918, considerable new information regarding the disease 
and its relations to insects has been obtained. 
The disease occurs in 31 States, including the territory from Ver- 
mont and Canada to Florida and west to Minnesota, Nebraska, Colo- 
rado, and Texas. It also probably occurs in parts of California. 
Of our common domestic cucurbits the disease affects cucumbers, 
cantaloupes, summer and winter squashes, and pumpkins, but not 
watermelons. 
The severity of the disease varies widely in different seasons and 
localities from an occasional wilted plant up to a destruction of 75 to 
95 per cent of the crop. There is very little direct relation between 
percentage of infections and severity of the disease and ordinary 
weather conditions in the North, but there is a direct relation to prev- 
alence of cucumber beetles and condition of vigor in the host plant. 
Careful and extensive experiments have shown that infection does 
not come through soil or seed; that the squash bug (Anasa tristis), 
squash lady bird (EpilacTina lorealis), melon aphis (Aphis gossypii), 
potato flea-beetle (Epitrix cucumeris), and honeybee (Apis mellifera) 
are not wilt carriers; but that the striped cucumber beetle (Diabrotica 
vittata) and the 12-spotted cucumber beetle (D. duodecimpunctata) 
are both summer carriers and probably the only means of summer 
transmission of the disease in the localities studied. Infection 
through the breathing pores of the plant does not occur, introduc- 
tion of virulent bacteria into the interior plant tissues being neces- 
sary for infection. 
It has been definitely proved that bacterial wilt of cucurbits does 
not winter over in the soil, and all seed tests have given negative re- 
sults. The disease has been carried experimentally for six weeks by 
striped cucumber beetles hibernated artificially in cold storage. We 
have thus far been unable to hibernate the beetles for a longer period. 
Considerable circumstantial evidence, however, points to cucumber 
beetles as winter carriers. For example, among the first collections 
of beetles in the spring a small percentage were found to be wilt car- 
riers. The earliest cucurbits were still very small and no wilt was 
anywhere in evidence. Futhermore, a careful record of spring se- 
quence of wilt was kept in all field and garden plats of cucurbits in 
two localities and in all cases the leaves first showing wilt in the spring 
had typical cucumber-beetle injuries; the wilt had plainly started 
from these injured points, and there was a tendency for wilt to spread 
in groups around the original cases, in each new plant starting from 
beetle-injured leaves. In many of the cases such beetle injuries had 
not become general at this time throughout the fields. 
