Sink trap: duckweed and dye attractant reduce mosquito populations

Abstract

Duckweeds, such as Lemna minor Linnaeus (Alismatales: Lemnaceae), are common in aquatic habitats and have been suggested to reduce larval mosquito survivorship via mechanical and chemical effects. Furthermore, pond dyes are used increasingly in aquatic habitats to enhance their aesthetics, although they have been shown to attract mosquito oviposition. The present study examined the coupled effects of L. minor and black pond dye on the oviposition selectivity of Culex pipiens Linnaeus (Diptera: Culicidae) mosquitoes in a series of laboratory choice tests. Subsequently, using outdoor mesocosms, the combined influence of duckweed and pond dye on mosquito abundances in aquatic habitats was quantified. Mosquitoes were strongly attracted to duckweed, and oviposited significantly greater numbers of egg rafts in duckweed-treated water compared with untreated controls, even when the duckweed was ground. The presence of pond dye interacted with the duckweed and further enhanced positive selectivity towards duckweed-treated water. The presence of duckweed caused significant and sustained reductions in larval mosquito numbers, whereas the relative effects of dye were not evident. The use of floating aquatic plants such as duckweed, combined with dye, may help reduce mosquito populations via the establishment of population sinks, characterized by high rates of oviposition coupled with high levels of larval mortality.

Aquatic plant extracts and coverage mediate larval mosquito survivorship and development

“…Certain aquatic or riparian plants have been shown to significantly alter mosquito colonisation dynamics and directly influence survivorship of immature stages (Cuthbert et al, 2019a;2020a). In particular, floating aquatic plants such as duckweed (Lemna spp.)…”

“…and water fern (Azolla spp.) have been linked to increased larval mortality rates and physical deformations (Eid et al, 1992a, b;Ravi et al, 2018;Cuthbert et al, 2020a). Indeed, the presence of duckweed has been suggested to impart a mosquito population sink effect, owing to combined oviposition attraction and larval mortality (Cuthbert et al, 2020a).…”

“…have been linked to increased larval mortality rates and physical deformations (Eid et al, 1992a, b;Ravi et al, 2018;Cuthbert et al, 2020a). Indeed, the presence of duckweed has been suggested to impart a mosquito population sink effect, owing to combined oviposition attraction and larval mortality (Cuthbert et al, 2020a). The insecticidal properties of floating aquatic plants may be either driven by their physical characteristics, whereby they form a mechanical barrier which prevents mosquito respiration or egg hatching at the surface (Hobbs and Molina, 1983), or through chemical processes which directly induce mortality via toxicities (Eid et al, 1992a, b;Cuthbert et al, 2020a).…”

“…Culex pipiens is a widespread and abundant mosquito complex which colonises a range of aquatic habitat types, including artificial containers in urban and peri-urban environments (Townroe and Callaghan, 2014). This species complex is an important vector of West Nile virus from bird to human populations (Becker et al, 2010), and has been previously shown to be sensitive to cues from aquatic plants when selecting oviposition sites (Turnipseed et al, 2018;Cuthbert et al, 2020a). Further, mortality in this species has been shown to be associated with the presence of floating aquatic plants, such as duckweeds (Eid et al, 1992a, b;Cuthbert et al, 2020a); however, whether these effects arise from physical or chemical processes remains largely unclear.…”

“…Based on previous studies (e.g., Cuthbert et al, 2019a;2020a) and piloting, overall, we hypothesise that: (1) extracts from selected aquatic plants will drive larval mosquito mortality and reduce development to subsequent life stages; (2) higher concentrations of plant extracts will enhance any larvicidal effects associated with efficacious species; (3) surface coverage of Lemna species will cause high mosquito mortality rates and reduced development through the presence of a physical barrier to respiration, and; (4) higher levels of plant coverage will enhance the efficacy of physical effects in driving mortality, irrespective of mono-or polyculture treatments.…”