Seasonal and nocturnal landing/biting behaviour of Phlebotomus argentipes (Diptera : Psychodidae)

The nocturnal activity of Phlebotomus argentipes (Diptera: Psychodidae), th e main vector of Leishmania donovani in India, was studied throughout a yea r, with monthly collections, between 18.00 and 06.00 hours, of the sandflie s landing on 15 humans and 15 cows in the villa ge of Bahapur, Patna distri ct. The cattle appeared to be better as bait, since more than five female P . argentipes were caught on them for each one caught on the human bait. Overall, although P. argentipes were caught during each collection hour fro m 18.00-06.00 hours, the numbers caught landing/biting peaked at 23.00-24.0 0 hours. There were, however, slight seasonal variations in the timing of t his peak in activity. The numbers of P. argentipes caught/collection night also varied with season, being significantly higher during the summer than during the rainy season or win ter (P < 0.01 for each), and apparently inve rsely correlated with rainfall. Male P. argentipes were caught in much high er numbers than the females of this species, with female: male ratios of 1: 8 for the flies caught on human bait and of 1:13 for those collected from c attle. If the probability of a female P. argentipes being infected with L. donovani does not vary with season, peak transmission of this parasite to h umans probably occurs between February and May, at the middle of night.