Fitness of wAlbB Wolbachia Infection in Aedes aegypti: Parameter Estimates in an Outcrossed Background and Potential for Population Invasion

Abstract

Wolbachia endosymbionts are potentially useful tools for suppressing disease transmission by Aedes aegypti mosquitoes because Wolbachia can interfere with the transmission of dengue and other viruses as well as causing deleterious effects on their mosquito hosts. Most recent research has focused on the wMel infection, but other infections also influence viral transmission and may spread in natural populations. Here, we focus on the wAlbB infection in an Australian outbred background and show that this infection has many features that facilitate its invasion into natural populations including strong cytoplasmic incompatibility, a lack of effect on larval development, an equivalent mating success to uninfected males and perfect maternal transmission fidelity. On the other hand, the infection has deleterious effects when eggs are held in a dried state, falling between wMel and the more virulent wMelPop Wolbachia strains. The impact of this infection on lifespan also appears to be intermediate, consistent with the observation that this infection has a titer in adults between wMel and wMelPop. Population cage experiments indicate that the wAlbB infection establishes in cages when introduced at a frequency of 22%, suggesting that this strain could be successfully introduced into populations and subsequently persist and spread.

Figure 1.

Percentage hatch rate of wAlbB-infected (red, dashed line), wMelPop-infected (green, dotted line), and uninfected CNS (black, solid line) Aedes aegypti eggs after 0, 3, 10, 17, 24, 31, 61, 90, and 124 days of quiescence. Error bars are standard error of means. Ten replicates per time point. Egg batches ranged from 25 to 78 eggs. The wMelPop curve, generated from eggs outbred to the Cairns genetic background, is taken from the work of Yeap and others.

Figure 2.

Survival of adult Aedes aegypti males (A) and females (B) infected with wAlbB (red, dashed line), wMel (blue, dotted line), or wMelPop (green, dot–dash line) outcrossed to the Cairns genetic background, represented by CNS (black, solid line). “+” represents right-censored data. Thin dotted lines are 95% confidence intervals.

Figure 3.

Mean hatch rates of Aedes aegypti eggs oviposited by 80 CNS females exposed to populations of males in the following groups: 0% infected (80 CNS males), 50% infected (40 wAlbB and CNS males), and 100% infected (80 wAlbB males). The solid line denotes the null model for the expected hatch rate (no difference in mating ability), whereas the dotted line represents the observed hatch rate and relative mating success (β) of wAlbB to CNS males and its probability (p).

Figure 4.

Wolbachia infection frequency per generation after an initial release of wAlbB females and males (red, open markers: 10%; black, solid markers: 22%) into 10 cages possessing CNS populations.

Figure 5.

Box plot of Wolbachia load for wAlbB, wMel, and wMelPop in laboratory-reared Aedes aegypti (N = 25). Outliers are represented as circles. Medians are indicated by horizontal lines.