THE BLACK FLY OF CITRUS. 51 
The fifth possible means of introduction, namely, the bringing in of 
adults on freight cars from Cuba via the railroad ferry plying between 
Habana and Key West, is one worthy of consideration. The writers 
have seen what they believe to be " train borne" infestations at Mira- 
flores and Frijoles, though there is no proof, except that all other possi- 
bilities were eliminated as far as practicable. In the first place, the 
infestation in the Canal Zone could be " train borne" much more 
easily than it could be carried from Cuba to Florida. Frijoles is about 
midway between Panama and Colon, or about an hour's run by train, 
while Miraflores is but 15 to 20 minutes distant from Panama. On the 
other hand, Habana is over 10 hours away from Key West with all the 
trip across the ocean. Whether the adults could weather such a trip 
is open to question. Again, in the Canal Zone the " train borne" 
infestation took place in a region where the insect had already success- 
fully established itself. Doubtless if introduced at Key West or at the 
lower end of Florida, the black fly would, under proper conditions, 
become established, but whether it would be able to maintain itself 
in the more northern portions of the State is debatable for here there 
is a factor with which the writers have not had any experience in the 
Canal Zone or adjoining parts of the Republic of Panama. That fac- 
tor is much lower minimum and mean minimum temperatures than 
are ever reached in the regions where A. woglumi now occurs. 
Then too, if only unfertilized females were introduced the insect 
would die out after the first generation, for owing to parthenogenesis 
all the individuals would be males. And finally, the question of the 
influence of different climatic conditions, other than temperature, on 
the mortality in the various developmental stages of the insect comes 
into play. All in all there is at present nothing to warrant the idea that 
there is great danger of AleurocantJius woglumi becoming introduced 
into and established in the United States through adults brought from 
Cuba on freight cars via the railroad ferry plying between Habana 
and Key West. The matter is one where there are two points of view. 
The removal of citrus and other host plants from the vicinity of the 
terminal freight yards and railroad sidings in Habana, however, would 
absolutely insure freight cars being free from A. woglumi. 
In conclusion, the method by which the black fly is most apt to 
become introduced into the United States and through which it will 
have the greatest opportunity of becoming established in favorable 
localities, is on undefoliated, infested nursery stock of various kinds, 
Or individual infested plants for ornamental or other purposes. This 
includes also undefoliated parts of plants like cuttings for propagation. 
This is the way it has spread from the Tropics of the Old World to 
those of the New and the way it has continued its spread over widely 
separated parts of its new home. Bragdon (5) has pointed out the 
