CONTROL OF TABANIDS 



489 



A deerfly, Chrysops callidus. 

 X4. 



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. 

 eral Chrysops, especially 

 C. dimidiata and C. silacea, and probably also C. centurionis 

 (see p. 309). It is probable that other species of Chrysops, 

 including our own deerflies (Fig. 227), would be able to serve as 

 intermediate hosts for the worms, in which case there is danger 

 that this form of filarial disease, if introduced into America or 

 other countries, might become endemic. 



Control. Prevention of bites from tabanids, especially dur- 

 ing an epidemic of anthrax, or in places where diseases believed 

 to be transmitted by tabanids are prevalent, is an important mat- 

 ter. Practically the only means that can be employed is the 

 use of repellents, as for other insect pests (see p. 455). Accord- 

 ing to Herms, repellents efficient against tabanids usually con- 

 tain fish oil. 



In a recent publication Portchinsky, 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 trachese through 

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



