Survival-Larval Density Relationships in the Field and Their Implications for Control of Container-Dwelling Aedes Mosquitoes

Abstract

Population density can affect survival, growth, development time, and adult size and fecundity, which are collectively known as density-dependent effects. Container Aedes larvae often attain high densities in nature, and those densities may be reduced when larval control is applied. We tested the hypothesis that density-dependent effects on survival are common and strong in nature and could result in maximal adult production at intermediate densities for Aedes aegypti, Aedes albopictus, and Aedes triseriatus. We surveyed naturally occurring densities in field containers, then introduced larvae at a similar range of densities, and censused the containers for survivors. We analyzed the survival-density relationships by nonlinear regressions, which showed that survival-density relationships vary among seasons, sites, and species. For each Aedes species, some sites and times yielded predictions that larval density reduction would yield the same (compensation), or more (overcompensation), adults than no larval density reduction. Thus, larval control targeting these Aedes species cannot always be assumed to yield a reduction in the number of adult mosquitoes. We suggest that mosquito control targeting larvae may be made more effective by: Imposing maximum mortality; targeting populations when larval abundances are low; and knowing the shape of the survival-density response of the target population.

Sterile Insect Technique (SIT) field trial targeting the suppression of Aedes albopictus in Greece

“…This is also in line with observations from increased larval mortality in Ae. albopictus and is considered to be related to density-dependent compensation of mortality [ 14 , 21 , 30 ]. Specifically, a reduction in egg sterility could lead to a decrease in larval density within breeding sites, which can have varying effects on the overall adult population density.…”

Different demographic responses of three species of container Aedes (Diptera: Culicidae) larvae to timing of extrinsic mortality

“…Gato et al (2021) reported sterile egg frequency only exceeded ∼50% and larval density began to decline after ∼10 weeks of releases of sterile males, when the relative abundance of fertile wild-type males was presumably reduced compared to released sterile males. Thus, as noted by Evans et al (2023) and Bouyer (2023), SIT and IIT programs should use approaches that minimize the likelihood of overcompensation (or compensation) by rapidly achieving high levels of egg sterility (>70% induced sterility recommended by Bouyer 2023), targeting populations when larval densities are low, rather than high (as done by Gato et al 2021), and gathering preliminary data on the responses of target species populations to density reductions. The heterogeneity of population responses among Aedes species (this study; Neale and Juliano 2019), and among different experimental studies (McIntire and Juliano 2018, Bouyer 2023, Evans et al 2023) indicates that understanding the specific responses of target species populations in their specific environments can contribute to successful mosquito control.…”

“…Populations of container Aedes are often impacted by negative density-dependent effects on adult production, adult traits, and per capita population growth (Dye 1984, Juliano 2007, Legros et al 2009, Walsh et al 2011, 2012, 2013, Hancock et al 2016, Sauers et al 2022, Evans et al 2023). Negative density dependence reduces population growth as population density increases, often via increased intraspecific competition (Murdoch and Briggs 1996).…”

“…Servanty et al 2010, Sandercock et al 2011, Peron 2013, Grosholz et al 2021) for a wide array of animals. Compensatory or overcompensatory mortality may be important for vector control efforts as well (Agudelo-Silva and Spielman 1984, Washburn 1995, Juliano 2007, Phuc et al 2007, Legros et al 2009, Alphey et al 2010, McIntire and Juliano 2018, Neale and Juliano 2019, Paton and Bonsall 2019, Bouyer 2023, Evans et al 2023).…”

“…Compensatory or overcompensatory mortality would render control efforts ineffective at best or counter-productive at worst, respectively. A few field studies have investigated the likelihood of overcompensation by mosquitoes in nature (e.g., Washburn et al 1991, Nannini and Juliano 1998, Ower and Juliano 2019, Evans et al 2023). The most commonly postulated cause of overcompensatory mortality is the timing of extrinsic mortality (Abrams 2009).…”