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



There is a tendency for wilt to spread in groups around the plants 

 first developing the disease, and in all observed cases it always starts 

 from beetle-injured plants. The facts that a careful record was kept 

 of all cucurbits in these localities and that the first wilt to appear 

 was from beetle injuries on the earliest plantings of the season pre- 

 clude the possibility of a transfer of the disease from previously 

 wilted cucurbits of the current season. These results, added to the 

 data presented in our previous papers, negative the possibility of 

 transmission of bacterial wilt of cucurbits through the soil from 

 season to season and give strong circumstantial evidence in favor of 

 the cucumber beetles as winter carriers. 



Until the striped or 12-spotted cucumber beetles can be hiber- 

 nated successfully in considerable numbers and under experimental 

 conditions, absolute experimental proof that these insects are winter 

 carriers can not be obtained. However, it would appear from the 

 evidence given that either the beetles must have carried the wilt 

 organism over winter or must have brought it directly from previous 

 cases of the current season. The second assumption is eliminated 

 so far as cucurbits are concerned by the facts that in neither locality 

 were cucurbits grown under glass, that our observations covered a 

 considerable territory, and that the wilt appeared on the very earliest 

 plantings of the season only after the plants were bitten by the 

 beetles. In one locality no wild cucurbits were present within at 

 least 10 miles. 



Apparently the only loophole remaining is the possibility that the 

 organism may live over winter in some perennial noncucurbitaceous 

 host. In his early work upon this organism, Dr. Erwin F. Smith 

 obtained infections by pure-culture inoculations on various species 

 of Cucumis and Cucurbita and on Benincasa cerifera, Sicyos angulatus, 

 and IFicrampelis lobata, and failed to infect or obtained only local 

 injury on the following cucurbits: Melothria scabra, Cucumis erina- 

 ceus, Luifa acutangula, Momordica halsamina, Lagenarla vulgaris, 

 Tricliosanihes cucurneroides, and Apodanthera undulata. 1 He states 

 further: 



"Inoculations into noncucurbitaceous plants such as Solatium tuberosum, Lyco- 

 persicum esculentum, Datura stramonium, Passiflora incarnata, Vigna catjang, Nico- 

 tiana tabacum, Pyrus orientalis, and Hyacinthus orientalis yielded only negative 

 results. The disease is not known to occur outside the Cucurbitacese, and probably 

 many species of plants within the limits of this family are not subject to it. " 



The present writers have no data concerning the possible occur- 

 rence of this disease outside the Cucurbitacese. 



1 Smith, Erwin F. Bacteria in relation to plant diseases, v. 2, p. 209. Washington, D. C, 1911. 

 (Carnegie Inst., Washington. Pub. 27, v. 2.) 



