Comparative biology of two populations of Lutzomyia umbratilis (Diptera: Psychodidae) of Central Amazonia, Brazil, under laboratory conditions.

Abstract

Lutzomyia umbratilis is the main vector of cutaneous leishmaniasis due to Leishmania guyanensis in northern South America. It has been found naturally infected with this species of Leishmania only east of the Rio Negro and north of the Rio Amazonas. However, populations of this sand fly species are also present in areas south of the Amazon river system, which may act as a geographical barrier to the Leishmania guyanensis cycle. With the aim of looking for possible biological differences between populations of L. umbratilis from each side of this river system, their biology in the laboratory was investigated. Progenitors collected on tree bases in Manaus and Manacapuru (east and west, respectively, of the Rio Negro) were reared in the laboratory. Results from observations of the life cycle, fecundity, fertility, and adult longevity at 27 degrees C and 92% RH were analyzed by descriptive statistics and z, t, U, and chi2 tests. Although the Manaus and Manacapuru colonies showed a longer developmental time than most Lutzomyia species reared at similar temperatures, length of time of egg and 4th instar larva of the two populations differed significantly (p < 0.01). Females of the latter retained significantly (p < 0.001) less mature oocytes, and the general productivity (% adults from a known number of eggs) of the colony was significantly (p < 0.01) higher than that of the former. These results show that the L. umbratilis population of Manaus is more productive, and thus a better candidate for future mass-rearing attempts. The two populations differ in their life cycle, fecundity, fertility, adult longevity, and emergence. These differences may reflect some divergence of intrinsic biological features evolved as a result of their geographical isolation by the Rio Negro. It is expected that further investigations on morphometry, cuticular hydrocarbon, isoenzyme, molecular and chromossomal analyses, infection, and cross-mating experiments with these and other allopatric populations of both margins of the Amazon river system will help reveal whether or not L. umbratilis has genetically diverged into two or more reproductively isolated populations of vectors or non-vectors of Leishmania guyanensis.