CONTROL OF TABANIDS 489 



only by men who spend the day in the forest, and is most prevalent 

 in May and June, a time corresponding to the appearance of 

 many tabanids, points strongly to these insects as the carriers 

 of the infection, since they are the only diurnal insects exclusively 

 found in forest regions. The forest leishmaniasis of Paraguay 

 may also be due to tabanids. 



In one other case a tabanid is implicated in the spread of a 

 disease. In the tropical jungles of Africa certain species of 

 Chrysops locally known as 

 mangrove flies, serve as in- 

 termediate hosts for filarial 

 worms. Leiper and other 

 investigators have found 

 that the larvae of the loa 

 worm, Loa loa, which 

 swarm in the peripheral 

 blood of the host in the 

 daytime only, undergo 



rapid development in Sev- FIG. 227. A deerfly, Chrysops callidus. 



eral Chrysops, especially 



C. dimidiata and C. silacea (see p. 309). 



It has recently been shown by Francis that tularemia, a rodent 

 disease of western United States, caused by Bacterium tularense, 

 and transmissible to man, may be transmitted, and probably 

 commonly is, by the deerfly, Chrysops discalis. These flies are 

 infective from a few seconds to at least fourteen days after biting 

 an infective rabbit. 



Control. Prevention of bites from tabanids, especially dur- 

 ing an epidemic of anthrax, or where diseases believed to be 

 transmitted by tabanids are prevalent, is important. Practi- 

 cally the only means that can be employed is the use of repellents, 

 as for other insect pests (see p. 455). According to Herms, re- 

 pellents efficient against tabanids usually contain fish oil. 



In a recent publication Poutchinsky, a Russian entomologist, 

 having found that tabanids have the peculiar habit of skimming 

 over pools, touching the lower side of their bodies to the surface, 

 advised the conversion of such pools into traps by pouring oil 

 on them to produce a surface film, so that the insects would be 

 caught in it, and the spiracles (openings of the tracheae through 

 which air is absorbed) closed up. In an experiment which he 



