I INSECTS AND HUMAN DISEASE 89 



parasite is continuous and the result is an endemic disease. 

 A second, and more striking example, is afforded by the 

 large Brazilian bug Lamus megistus, which transmits a 

 dangerous human trypanosome disease. It is the only 

 American member of the genus which shows a close 

 association with man. It lives in houses, lays its eggs 

 there, and never, naturally, occurs apart from man, on 

 whose blood its young feed from birth. A curious circum- 

 stance is, that nearly all the wild species of the genus 

 to which this disease-carrying bug belongs have very 

 painful bites, but this species is specially adapted for 

 giving such painless bites that they will not awaken a 

 sleeping man. 



At first sight the malaria mosquitoes do not appear to 

 fulfil this condition of close association with man. A 

 study of the habits of the various species of Anopheles, 

 however, reveals the fact that they differ widely, and that, 

 whilst some species do not habitually seek man's blood, 

 for other species it appears to be a necessity; moreover, 

 it is only those species which habitually associate with 

 man, "domestic" species they have been called, that 

 transmit malaria. Let us consider the mosquito question 

 in the tropics, and see how much more dangerous, from a 

 health point of view, the " domestic " species of mosquitoes 

 are than the wild ones. In the Isthmian Canal zone of 

 Panama, we have a country eminently suited to a mosquito 

 fauna, as is evinced by the fact that no less than one 

 hundred and twenty-five species are found there. This 

 district is characterised by a typically tropical climate, 

 high humidity, a short dry season, and a rich virgin soil, 

 clothed with dense, luxuriant vegetation. Under these 

 favourable conditions the mosquitoes breed continuously 

 throughout the year, oviposition taking place whenever 

 opportunity, in the shape of water, is to be found. Of 

 the economically important mosquitoes to be found in this 

 region are nine species of Anopheles, Stegomyia fasciata, 



