Ecology of invasive mosquitoes: effects on resident species and on human health

Abstract

Investigations of biological invasions focus on patterns and processes that are related to introduction, establishment, spread and impacts of introduced species. This review focuses on the ecological interactions operating during invasions by the most prominent group of insect vectors of disease, mosquitoes. First, we review characteristics of non-native mosquito species that have established viable populations, and those invasive species that have spread widely and had major impacts, testing whether biotic characteristics are associated with the transition from established non-native to invasive. Second, we review the roles of interspecific competition, apparent competition, predation, intraguild predation and climatic limitation as causes of impacts on residents or as barriers to invasion. We concentrate on the best-studied invasive mosquito, Aedes albopictus, evaluating the application of basic ecological theory to invasions by Aedes albopictus. We develop a model based on observations of Aedes albopictus for effects of resource competition and predation as barriers to invasion, evaluating which community and ecosystem characteristics favour invasion. Third, we evaluate the ways in which invasive mosquitoes have contributed to outbreaks of human and animal disease, considering specifically whether invasive mosquitoes create novel health threats, or modify disease transmission for existing pathogen-host systems.

Figure 1

Model of predation after invasion by a superior competitor (I) into a community consisting of a resident prey (R), a predator (P), and micro-organisms (M). This model is an extension of that of Leibold (1996), adding a lower trophic level (M) that is a resource for the competitors, and incorporating type 2 functional responses for competing prey (R, I), P and M. Conversion efficiencies indicate the rate at which consumed food is converted into growth for micro-organisms (c_M), invader (c_I), resident (c_R), and predator feeding on invader (c_PI) and resident (c_PR). Feeding rates of micro-organisms feeding on the resource [f_M (C)], invader and resident feeding on micro-organisms [f_I(M) and f_R(M), respectively], and predator feeding on invader [f_P(I)] and resident [f_P(R)] are all hyperbolic functions of the general form: f(X) = F X/(K + X), where X = food abundance, F = maximum feeding rate and K = food abundance yielding one half maximum feeding rate. The two species functional responses for the predator feeding on resident and invader are f(R) = F_PR R/(R + K_PR + I K_PR/K_PI) and f(I) = F_PI I/(I + K_PI + R K_PI/K_PR), respectively. Lower Ks result in greater competitive ability for the consumer (i.e. ability to feed at low food availability) and greater vulnerability for the prey. Death rates (d_P, d_R, d_I, d_M) for each species are density-independent. Resources (C) for micro-organisms (e.g. plant detritus) become available at a rate logistically dependent on their abundance, with a maximum availability of S (supply).

Figure 2

Simulations of invasion of a stable predator–prey system by a superior competitor, illustrating the sensitivity of the outcome to the invader’s vulnerability to predation (increasing vulnerability with decreasing K_PI) and environmental productivity (S), the maximal resource availability for the micro-organism population. Simulations ran for 30 000 time steps with the invader invading at time 2000. Parameters are in arbitrary units so results only illustrate the qualitative trends expected in this system. Letters on the graph indicate species combinations attaining stable coexistence (I = invader, R = resident, P = predator, subscript S = stable oscillations, subscript U = unstable expanding oscillations; e.g., RP = resident + predator). Shaded regions indicate combinations of K_PI and S where the presence of the predator fosters coexistence of competing resident and invader via a keystone predator effect. (a) Competitive advantage of invader is large (K_I = 100, K_R = 600). (b) Competitive advantage of the invader is small (K_I = 300, K_R = 600).