NO. I 



BLACK FLIES OF GUATEMALA — DALMAT 



21 



eral trends can be indicated. The average annual temperature descends 

 as the altitude ascends. The rainfall is greatest in those areas between 

 1,500 feet and 4,000 feet where the great wall of volcanic mountains 

 serves as a barrier to the moisture-laden air currents. In all cases the 

 heaviest rainfall is reported in September, the second heaviest rain 

 usually being recorded in June. All the areas for which data are given 



Map 9. 



are on the Pacific versant except Bananera, which is near the Gulf of 

 Honduras. Bananera, exposed to the tradewinds, receives much 

 heavier rainfall than Tiquisate. 



The similarities of conditions in areas within the onchocerciasis 

 zones and outside of them would tend to show that the meteorological 

 factors are not in themselves sufficient to explain the presence or 

 absence of onchocerciasis. However, they do have a marked effect. 

 Thus, in regions as high as Quezaltenango (table i), it is quite possi- 

 ble that the great variation between mean maximum and mean mini- 



