Less is more: modelling the impact of species-targeted versus broadcast larviciding approaches for malaria control in rural settings

BackgroundLarval source management (LSM) was once central to malaria control before insecticide-treated nets and indoor residual spraying dominated. Renewed interest in LSM raises questions about its effectiveness in rural Africa, where habitats are dispersed, and vector species contribute unequally, and whether species-targeted larviciding could offer greater gains than broadcast approaches. MethodsThis modelling study quantified the potential impact of larviciding in African settings where multiple vector species contribute unequally to malaria transmission. We modeled malaria transmission in southeastern Tanzania using agent-based simulations incorporating seasonal dynamics, insecticide resistance, and semi-field biolarvicide efficacy. Outcomes were entomological inoculation rate, malaria incidence in under-fives, and operational larviciding costs. FindingsLarge-scale deployment of biolarvicides with >1-week residual activity substantially reduced malaria transmission, with disproportionately greater gains when control efforts were preferentially focused on the dominant vector species, Anopheles funestus, compared to broadcast approaches treating both An. funestus and An. arabiensis habitats. In the absence of ITNs, a four-month fortnightly larviciding campaign targeting An. funestus at 80% coverage reduced EIR by 58% and incidence by [~]40%, versus [~]55% incidence and [~]70% EIR reductions under broadcast strategies; targeting An. arabiensis alone yielded [≤]30% EIR and [≤]13% incidence reductions. Starting with pre-existing 80% ITN coverage, funestus-targeted larviciding further reduced peak EIR by [~]70% and incidence by [~]77%, versus [~]90% and [~]85%, respectively, with broadcast strategies, suggesting broadcast larviciding provided limited additional reductions beyond those achieved by the funestus-targeted approach. At 40% ITN coverage, additional reductions were [~]62% of EIR and [~]46% in incidence (funestus-targeted) versus [~]76% and 63%, respectively (broadcast). The targeted campaigns preserved a 30-50% cost advantage while sustaining >50% dry-season transmission reductions. Finally, high-coverage (e.g., 80%) funestus-targeted larviciding campaigns achieved greater impacts than lower-coverage (e.g., 40-60%) targeting both species. ConclusionsIn settings where multiple vector species contribute unequally to malaria transmission, preferentially targeting larviciding against the dominant vector species can deliver substantial epidemiological impact, with greater resource efficiency than broadcast approaches targeting multiple vectors. In Tanzania, where An. funestus drives most transmission; concentrating larviciding efforts on its characteristic aquatic habitats may offer a scalable, low-cost complement to established tools such as ITNs.