42 BULLETIN 828, U. S. DEPARTMENT OF AGRICULTURE. 



After one initial feeding, striped cucumber beetles are sometimes 

 capable of infecting at least four healthy cucumber plants successively 

 fed upon, and after one wilt feeding some individuals in the active 

 condition have still been capable of giving infection as long as 23 

 days afterwards. 



Dissection and inoculation experiments have shown virulent wilt 

 bacteria present in the intestines of a portion of the beetles fed on 

 wilted plants, and isolations of intestinal bacteria so far as tried 

 showed in most cases an acid-forming -and gas-forming flora antago- 

 nistic to the wilt organism; but in 10 per cent (one experiment only) of 

 the beetles used the intestinal bacteria were not inimical to the wilt 

 organism, the latter remaining alive and causing infection in cucumber 

 plants after three weeks' growth in mixed culture with the intestinal 

 bacteria. 



In the extensive virulence tests the various isolations of Bacillus 

 tracheiphilus from different hosts and localities have shown wide and 

 fairly constant differences in relative virulence to a given host variety. 

 While in these tests the individual isolations have not preserved ex- 

 actly the same order of relative virulence when inoculated into the 

 different host species and varieties, the tendency has been in that 

 direction. That is, isolations highly or weakly virulent to one variety 

 of cucumbers have tended, respectively, to be highly or weakly viru- 

 lent to another variety, and many though not all isolations highly 

 virulent to cucumbers have been found capable of infecting squashes 

 to a greater or less degree, while isolations of low virulence to cucum- 

 bers have invariably given no infection at all in squashes. It is en- 

 tirely possible that in addition to the many races of the parasite ex- 

 hibiting varying degrees of relative virulence to any particular host 

 species there may be also two distinct strains for cucumber and 

 squash. 



Cucumbers are the most susceptible host species thus far tested 

 and watermelons the most resistant of any species which has shown 

 any host reaction at all. No authentic report of natural infection 

 on watermelon has been found, and inoculations have given either 

 negative results or at most a very slight local wilting. Cantaloupes 

 are slightly more resistant than cucumbers, while the squash group 

 stands next to watermelons in order of resistance. 



In greenhouse tests, given similar plants to start with, very little 

 difference in the percentage of infection or progress of the disease oc- 

 curs between wet versus dry inoculations or between those made in 

 sunlight versus shade. On the other hand, badly stunted or old plants 

 have in general shown a much lower percentage of infection and slower 

 progress of wilt than young, vigorously growing plants of the same 

 variety. Ordinary variations in weather conditions have very little 

 direct effect on percentage of infection, but may possibly have some 



