Insecticide resistance and human blood meal preference of Anopheles annularis in Asom-Meghalaya border area, northeast India.

(ITNs) and indoor residual spray (IRS) have made significant decrease in the number of malaria cases, but these efforts are subsided by the development and spread of insecticide resistance among major malaria vectors1. Currently, DDT and synthetic pyrethroids are used widely for IRS and ITNs throughout the malaria endemic countries including India, which insist unconditional need of regular monitoring of the insecticide resistance in mosquito vectors. Anopheles (Cellia) annularis Van der Wulp is widespread in Asia and recently emerged as an important vector of malaria in India and neighbouring countries1–2. In northeastern states, An. annularis is abundant and recently has been presumed to be an important vector of malaria in addition to An. minimus and An. dirus2–3. Continuous and indiscreet use of DDT for IRS has led to the development and spatial spread of physiological resistance among many efficient malaria vectors in India4–6. Furthermore, the use of synthetic pyrethroids in ITNs and long-lasting insecticidal nets (LLINs) has also led to the development of resistance in some known mosquito vectors5–6. Although metabolic mechanisms play a major role in conferring resistance, behavioural changes in the vector mosquito population might have an impact on the efficacy of the insecticides7. Insecticide resistance is a dynamic phenomenon and the resistance level among the mosquito species differ even between the nearby areas8. Hence, the extrapolation of insecticide resistance results from one geographical area to another may be inappropriate. In addition to monitoring insecticide resistance among wild caught Anopheles mosquitoes, human host preference and malaria parasite detection remain integral components in understanding the transmission dynamics. Such data provide vulnerable parameters for estimating transmission intensity and serve as a relative measure of the disease risk in an area of interest. Anopheles annularis is primarily considered as a zoophilic mosquito, however, its host preference and incrimination data in many parts of India are still scanty and only a few systematic studies have been carried out previously2, 9. Identification of human host preference and vectorial status are useful in understanding the role of different Anopheles mosquitoes in malaria transmission at local level. The present study was carried out to collect information on DDT and deltamethrin susceptibility status, human host preference and possible role in malaria transmission of An. annularis mosquito along AsomMeghalaya border in northeast India. This study was conducted at five villages each in Chandubi and Rani areas (GPS location: 25° 52' 23" N to 91° 26' 36" E) along Asom-Meghalaya border area in Khasi hills during June–August 2011 (Fig. 1). Ecologically, Chandubi area has predominately mixed thicket and dense forest, whereas Rani area is relatively plain interspersed with precambrian residual hills covered with thin forest and settlement areas. Humid climate, vast paddy fields, irrigation drains and duck rearing ponds provide suitable environment for vector mosquito breeding. Adult Anopheles mosquitoes were collected inside the human houses using CDC miniature light-trap model 512 (John W. Hock Inc., USA), installed for at least 12 h (1800 to 0600 hrs). A total of four trappings were conducted at four randomly selected houses in each of the study villages. The mosquitoes landed on the wall, roofs, wooden pillars and other temporary structures including clothings and bicycles which were kept inside the houses were collected using hand held aspirators (John Hock, USA) and torch-light. The collected Anopheles mosquitoes were identified to species based on morphological characteristics. To monitor the susceptibility status against DDT and J Vector Borne Dis 51, June 2014, pp. 133–136