BackgroundIndoor residual spraying (IRS) with DDT has been the primary strategy for control of the visceral leishmaniasis (VL) vector Phlebotomus argentipes in India but efficacy may be compromised by resistance. Synthetic pyrethroids are now being introduced for IRS, but with a shared target site, the para voltage-gated sodium channel (VGSC), mutations affecting both insecticide classes could provide cross-resistance and represent a threat to sustainable IRS-based disease control.Methodology/Principal findingsA region of the Vgsc gene was sequenced in P. argentipes from the VL hotspot of Bihar, India. Two knockdown resistance (kdr) mutations were detected at codon 1014 (L1014F and L1014S), each common in mosquitoes, but previously unknown in phlebotomines. Both kdr mutations appear largely recessive, but as homozygotes (especially 1014F/F) or as 1014F/S heterozygotes exert a strong effect on DDT resistance, and significantly predict survivorship to class II pyrethroids in short-duration bioassays. The mutations are present at high frequency in wild P. argentipes populations from Bihar, with 1014F significantly more common in higher VL areas.Conclusions/SignificanceThe Vgsc mutations detected appear to be a primary mechanism underlying DDT resistance in P. argentipes and a contributory factor in reduced pyrethroid susceptibility, suggesting a potential impact if P. argentipes are subjected to suboptimal levels of pyrethroid exposure, or additional resistance mechanisms evolve. The assays to detect kdr frequency changes provide a sensitive, high-throughput monitoring tool to detecting spatial and temporal variation in resistance in P. argentipes.

Background: Indoor Residual Spraying (IRS) and Insecticide Treated Nets (ITNs) are important tools in the fight against insect vectors of important diseases. In spite of having operational and logistic limitation(s), IRS and ITN are still in practice as conventional tools with mixed results for controlling Phlebotomus argentipes, the vector of Visceral Leishmaniasis (VL) in the Indian subcontinent. A combination of both tools might results better for reducing VL vector densities during the attack phase of the VL elimination initiative. Methods: A comparison-based study was designed for analyzing the field efficacy of a combination strategy of IRS+ITN (PermaNet 3.0 ®) versus single interventions with IRS and ITNs alone comparing with control respectively. The study was conducted at the villages of Samastipur district of Bihar (India) using aspiration and light traps techniques (i.e., AT and LTT respectively) for collecting sand fly. The numbers of all types of sand flies (male, unfed, fed and gravid female) were recorded during a period of 12 months after the intervention in the three study arms. The bioavailability of insecticide for IRS as well as ITN was also observed at the interval of 3 months with the help of cone bioassay technique established by World Health Organization (WHO). Results: The observed highest percent-reduction of sand flies (93.59%-100%) at the sites with combined intervention of IRS+ITN, as compared to the sites without any intervention at control (with 0% reduction) or with single control intervention either with IRS (4.29%-86.77%) or with ITN (60.18%-97.07%) followed by the reduction in bioavailability of insecticide in IRS (i.e., 52.38%, 58.33%, 45.45% & 50.00%) and ITN (84.44%, 82.50%, 77.78% & 83.33%) over the period of 12 months since intervention, establishes the success of IRS plus ITN as a combined approach for contaminating vector population. Also, through the house-to-house survey at the end of study period, the acceptance of combined approach for IRS plus ITN by the community was accessed to be highest i.e., 100% as compared to the single-intervention approaches for IRS (87%) and ITN (100%). Conclusions: Study results advocate the use of the combined strategy during the attack phase of the VL elimination initiative in order to reduce or interrupt disease transmission. It may also be a valid approach during the maintenance phase in hot-spots of VL transmission.

online | memorias.ioc.fiocruz.brPhlebotomus argentipes, the vector of Indian kalaazar, has received much attention because of its transmission of Leishmania donovani (Mukhopadhyay & Mishra 1991). Surprisingly, very little information is available on the breeding habitats of P. argentipes. Consequently, the lack of information on the breeding of sandflies prevents us from locating these habitats and inhibits the targeting of prevention measures against the pre-imaginal stages of sandflies.To study sandfly biology and behaviour and to search for new methods of vector control, it is necessary to maintain large laboratory colonies of sandflies. In this respect, it is important to note that oviposition behaviour is a neglected aspect of the biology of sandflies. Pheromones influence oviposition behaviour in the females of haematophagous insects. These pheromones are produced by the ovipositing female or by conspecific eggs that co-occur with gravid females. Moreover, there has been no definitive information from laboratory studies of the oviposition of P. argentipes (Ghosh & Bhattacharya 1992, Dinesh et al. 2009, although it is thought that the insects select the oviposition site based on chemical factors released by the emerging progeny. It has been observed that in the wild, the behavioural ecology of P. argentipes is similar to that of Lutzomyia longipalpis (the corresponding South American vector) in terms of lek formation on the blood-feeding hosts, to which females are attracted. Dougherty et al. (1993), with the help of a bio-assay, demonstrated the semichemical-mediated oviposition attraction of gravid Lu. longipalpis. When determining the location of a suitable oviposition site for egg laying (Dougherty et al. 1993) or a potential host for blood feeding , haematophagous insects primarily use their olfactory senses. Previous research conducted by Elnaiem and Ward (1992) demonstrated that Lu. longipalpis preferred sites for oviposition that contain frass or rabbit faeces, which act as its larval rearing medium. More recently, Wasserberg and Rowton (2011) demonstrated that in choice and no-choice oviposition chambers, the effect of old sandfly colony remains (frass), conspecific eggs and their combination affected the oviposition rates of sandflies (Peterkova-Koci et al. 2012). The present study will contribute to the development of a methodology for the maintenance of sandfly colonies, which is a major challenge for scientists working on different biological aspects of sandflies. Additionally, this study may provide promising tools for the monitoring and control of target insects using integrated vector management strategies involving the use of traps baited with pheromones, infusions and insecticides. In the present study, experiments were conducted in Hilton's pots that contained old remains of colonies, including eggs, larvae and larval foods, with empty pots serving as the control group. Hence, in the present study, an attempt was made to observe the possible role of pheromone/odour in the oviposition beha...

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Background: After the decades of Dichlorodiphenyltrichloroethane (DDT) use, Phlebotomus argentipes reportedly developed resistance against it affecting every aspect of vector control at grass-root level. Although DDT based Indoor Residual Spray (IRS) has been replaced with Alphacypermethrine-a Synthetic Pyrethroid (SP) based insecticide, since 2016 but its successful implementation at the Visceral Leishmaniasis (VL) endemic regime of Bihar doesn’t cause much effect upon VL vector density. Furthermore, the outcomes of existing operational research works, it had been observed that VL vectors are continuously changing its behavior under the pressure of insecticides. Methods: For validating the hypothesis, present study has been carried out at Vaishali and Patna being highly and semi-endemic sites respectively for quantifying the oriental behavior among VL vectors persuaded by the IRS and enforce them to remain alive and get trapped in light trap even after changed chemical composition of IRS i.e., SP-IRS from routine DDT-IRS. Results: Following results, a significant reduction in sand fly density (i.e., 33.09% and 29.16%) was observed for outdoor and indoor caught sand flies, collected with light trap and aspirator respectively. Significant higher no. of sand fly collection in terms of per light traps per night was recorded from the outdoor sites than those from indoor habitat for each village of Vaishali and Saran district of Bihar. Higher no. of male sand flies than to that of female ones were collected from outdoor sites and only unfed female sand flies (i.e., 100%) were caught following SP-IRS from each study villages of Vaishali and Saran districts of Bihar. Conclusions: The results of higher no. of sand flies collection from the outdoor sites as compared with the indoor habitat validate the hypothesis of gradual shifting of habitat of VL vectors from endophilic to exophilic which is undoubtedly followed due to the fact of developed resistance among them against chemical constituent of IRS. Results  provide very useful information about the sand fly dynamics under the impact of IRS and accordingly, advocates the combined approach of IRS along with insecticidal fogging together at a same time that could be an effective dividend for maximum VL vector control along for negotiating VL cases at par for longer duration during the maintenance phase at the VL foci.

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Female sand flies Phlebotomus argentipes are well-established pathogen transmitter for Visceral Leishmaniasis (VL) among humans and Dichlorodiphenyltrichloroethane (DDT) served as an important tool for controlling their population. After the decades of DDT use, P. argentipes has developed resistance against it affecting every aspect of vector control at grass-root level. In a way of exploring new 'strategic weapon' against sand flies, Novalurone -a noble Insect Growth Regulators (IGRs), inhibiting life-cycle and checking insect population at their non-infective stage has been evaluated for the first time ever against the laboratory colonized DDT resistant sand flies. It was observed that DDT resistant sand flies tolerating insecticide pressure successfully exhibited susceptibility at highest concentration of Novalurone processed larval diet (i.e., at 150000 ppm) following slowed growth rate that doesn't allowed them to metamorphed into the pupal stage. Moreover, their survival (1.8±94.50) was observed to be lasted till 2 nd stage only in which they attained absolute mortality. These preliminary laboratory based results certifies Novalurone to be very much effective for nailing effective checks upon natural growth process of immature DDT resistant sand flies and hence could be incorporated as an important preposition as alone or as a synergist with insecticide for total and long-lasting control over the VL vector population.