Phlebotomine sandfly ecology on the Indian subcontinent: does village vegetation play a role in sandfly distribution in Bihar, India?

Visceral leishmaniasis (VL) is a disease that results in approximately 50 000 human deaths annually. It is transmitted through the bites of phlebotomine sandflies and around two-thirds of cases occur on the Indian subcontinent. Indoor residual spraying (IRS), the efficacy of which depends upon sandfly adults resting indoors, is the only sandfly control method used in India. Recently, in Bihar, India, considerable sandfly numbers have been recorded outdoors in village vegetation, which suggests that IRS may control only a portion of the population. The purpose of this study was to revisit previously published results that suggested some sandflies to be arboreal and to rest on outlying plants by using Centers for Disease Control light traps to capture sandflies in vegetation, including banana plants and palmyra palm trees, in two previously sampled VL-endemic Bihari villages. Over 3500 sandflies were trapped in vegetation over 12 weeks. The results showed the mean number of sandflies collected per trap night were significantly higher in banana trees than in other vegetation (P = 0.0141) and in female rather than male palmyra palm trees (P = 0.0002). The results raise questions regarding sandfly dispersal, oviposition and feeding behaviours, and suggest a need to refine current control practices in India and to take into account an evolving understanding of sandfly ecology.