2 BULLETIN 828, U. S. DEPARTMENT OF AGRICULTURE. 
SUMMER TRANSMISSION OF WILT. 
DIRECT INSECT TRANSMISSION EXPERIMENTS. 
The earlier experiments on insect transfer of the wilt disease have 
been repeated many times during the past three years (1916-1918) 
with results similar to those already published. As an example of 
the method used the following details may be given: 
September 17, 1916. Twelve squash bugs (AnasatristisDeG.) were fed four days upon 
cucumber plants wilted from pure culture inoculation. Two bugs were then caged 
(PI. I) with each of six healthy cucumber plants for two days, during which time they 
were all observed to have fed. The plants at this time had become slightly flabby as 
a direct result of the insect feeding. However, this condition practically always 
results from squash-bug injury to young cucumber plants and is in no way connected 
with bacterial wilt. Cultures and microscopical examination in such cases fail to 
show bacteria present; the flabbiness often begins to appear within a few hours after 
the bugs start feeding, while wilt at the very earliest does not appear sooner than three 
to five days after inoculation ; this flabbiness at once affects the plant as a whole, 
while in the bacterial disease the wilting is progressive from the point of inoculation; 
and finally, unless too far gone, plants always recover their turgor after the squash bugs 
are removed, while vigorous young cucumber plants inoculated with virulent strains 
of bacterial wilt have never been known to recover. In this experiment the squash 
bugs were all removed after two days and the plants soon regained their turgor. Al- 
though under observation until October 13, no wilt developed. This experiment was 
repeated many times with like results. 
The squash lady bird (Epilachna borealis Fab.) was tested in 10 or more further sets of 
experiments, but no wilt ever followed its injuries to healthy cucumber plants, and 
negative results were obtained by inoculation with intestines of wilt-fed individuals 
(see p. 24). 
The cotton aphis (Aphis gossypii Glov.) and the potato flea-beetle (Epitrix cucumeris 
Harr.) were also retested by similar methods and the negative results confirmed by 
observations in the experimental fields. Furthermore, in the field cage experiments 
they have always had access through the wire netting to the cucurbit plants within, 
but have never carried the disease from the numerous wilt cases in the surrounding 
field. These observations corroborate the results of the direct experiments. 
During August, 1917, honeybees (Apis mellifera L.) were collected at random from the 
experimental cucurbit field where wilt was prevalent, and many were taken directly 
from blossoms of wilting vines. One to several bees were placed in 15 large cages 
containing cucumber or cantaloupe vines (PI. II, fig. 1). No wilt followed in any 
case. It might be noted in passing that the cucumber fruit set very much more freely 
in these cages than where bees were excluded. 
These five different species have all given constantly negative 
results, while the striped and 12-spotted cucumber beetles tested in 
the same way have repeatedly given positive results. For example, 
using the striped beetle in 10 direct experiments (1916 and 1917) 
similar to the one detailed above for the squash bug, 7 out of the 10 
tests gave positive results. In these cases the beetles were fed upon 
wilted leaves and then caged with cucumber plants for a sufficient 
length of time to determine the result. These experiments were 
entirely separate from the successive infection experiments detailed 
later (cf. p. 21, 22). The 12-spotted cucumber beetles have not 
