Facilitating Wolbachia introductions into mosquito populations through insecticide-resistance selection

Abstract

Wolbachia infections are being introduced into mosquito vectors of human diseases following the discovery that they can block transmission of disease agents. This requires mosquitoes infected with the disease-blocking Wolbachia to successfully invade populations lacking the infection. While this process is facilitated by features of Wolbachia, particularly their ability to cause cytoplasmic incompatibility, blocking Wolbachia may produce deleterious effects, such as reduced host viability or fecundity, that inhibit successful local introductions and subsequent spatial spread. Here, we outline an approach to facilitate the introduction and spread of Wolbachia infections by coupling Wolbachia introduction to resistance to specific classes of insecticides. The approach takes advantage of very high maternal transmission fidelity of Wolbachia infections in mosquitoes, complete incompatibility between infected males and uninfected females, the widespread occurrence of insecticide resistance, and the widespread use of chemical control in disease-endemic countries. This approach is easily integrated into many existing control strategies, provides population suppression during release and might be used to introduce Wolbachia infections even with high and seasonally dependent deleterious effects, such as the wMelPop infection introduced into Aedes aegypti for dengue control. However, possible benefits will need to be weighed against concerns associated with the introduction of resistance alleles.

Figure 1.

Minimum value of p₀ that produces Wolbachia frequency p_t = 0.95 within 20 generations, assuming r_I,0 = 1. In each panel, selection against susceptibility (s) varies as does the dominance of susceptibility (h: 0.9, diamonds; 0.5, squares; 0.1, circles). (a,b) Assume no insecticide resistance in the target population (r_U,0 = 0), and s_f = 0.3 (a) or s_f = 0.4 (b). (c,d) Investigate the effects of a low level of insecticide resistance in the target population: r_U,0 = 0.001 (c) or r_U,0 = 0.01 (d). (Online version in colour.)

Figure 2.

Minimum value of the ‘effective release rate,’ m, that produces Wolbachia frequency p_t = 0.95 within 20 generations, assuming r_I,0 = 1, and s_f = 0.3. In each panel, the selection against susceptibility (s) varies as does the dominance of susceptibility (h: 0.9, diamonds; 0.5, squares; 0.1, circles). (a,b) Assume no pesticide resistance in the resident population (r_U,0 = 0) and investigate the effects of limiting the releases to the first 10 generations (b) versus every generation (a). The reference values, without insecticide resistance, are m_c = 0.0471 for (a) and m_c(10) = 0.0563 for (b). (c,d) Investigate the effects of a low level of insecticide resistance in the target population: r_U,0 = 0.001 (c) or r_U,0 = 0.01 (d). (Online version in colour.)