Age Structure, Population Dynamics and Vector Potential of Phlebotomus in Northern California Part II. Field Population Dynamics and Natural Flagellate Infections in Parous Females1

Abstract

The 3 known species of sandflies in California use burrows of a large ground squirrel, Citellus beecheyi, as breeding and diurnal resting sites. In 1965 there were 3 annual field generations with adults being active from May-November. Their annual population peaked near the middle of this period and coincided with emergence of the second adult generation. Adults were primarily crepuscular and nocturnal in their above-ground activities. Although such adult activities were associated with dispersal, feeding and probably mating, the results suggest that feeding and mating of flies also may occur within burrows during the day. Field capture of parous ♀♀ showed that some flies survived long enough to take a second blood meal, but the small percentages of such ♀♀ captured also indicated die short duration of each generation's blood-sucking activities. Flagellate infections in only parous or gravid ♀♀ of P. v. occidentis strongly implies that this species serves as an intermediate host of a protozoan infecting 1 of its natural hosts. The presence of crithidial forms in the midgut indicates a trypanosome infection in the vertebrate host. Trypanosomes were not isolated from a number of reptiles examined, but all studies indicate that the most probable vertebrate host is a species of reptile or anuran on which these flies feed. As fly infections were confined to the posterior station, and because the ♀♀ excrete small droplets from the anus while feeding, the vertebrate host must acquire its infection either by contamination of a wound or by ingesting infected flies.