Monitoring Susceptibility Status of Phlebotomus argentipes (Diptera:Psychodidae) at Bihar (India) for the Procurement of Homozygous DDT Resistant Colony

Abstract

Brisk and continuous application of routine insecticide i.e., dichlorodiphenyltrichloroethane (DDT) for long had evoked the problem of resistance among Indian Visceral Leishmaniasis (VL) vector Phlebotomus argentipes (Diptera: Psychodidae) in Bihar, affecting DDT based strategies for controlling vector population. In this way, strong resistant colony of P. argentipes would provide fundamental platform to reveal the mechanistic reason behind the arousal of DDT resistance among sand flies. Present report summarizes our experiences with baseline establishment and maintenance of DDT resistant colony of P. argentipes after studying susceptibility profile for districts of Bihar. The district with lowest susceptibility or highest resistance against DDT would inculcate the collection of resistant sand flies for procuring resistant colony of P. argentipes, the foremost objective of the present study. For this, DDT susceptibility test were carried out at seven districts of Bihar (India), followed by the selection of Vaishali district as a ‘perfect site for resistant sand fly collection’. Here Percentage Mortality Range (PMR) and Corrected Mortality Rate (CMR) i.e., 41.00-52.73 and 44.83 % respectively were recorded to be lowest indicating the presence of sand flies highly resistant to DDT. Single blood-fed female and a male P. argentipes, collected from the selected site were confined together for oviposition and rearing of developmental stages for obtaining its next generation.. Inherited DDT resistant character of progenies of highly resistant parent was estimated and compared by quantifying Mortality Frequency Rate and DDT Resistant Rate through the insecticide susceptibility test conducted at its subsequent generations. Significant fluctuation within DRR (with 67.29 ± 17.28; 95% C.I=54.49-80.09) was observed throughout the 7th generation establishing intrusion of susceptibility factor in homozygous resistant colony of P. argentipes after achieving absolute resistant in F4 generation of P. argentipes. Though invaded with insecticide susceptibility, resistance dominate the colony. So far, colony has reached its 7th generation and culturing well in the laboratory.