Abstract
Trichogramma wasps are tiny parasitoids of lepidopteran eggs, used extensively for biological control. They are often infected with the bacterial symbiont Wolbachia, which converts Trichogramma to an asexual mode of reproduction, whereby females develop from unfertilized eggs. However, this Wolbachia-induced parthenogenesis is not always complete, and previous studies have noted that infected females will produce occasional males in the lab. The conditions that reduce penetrance of the parthenogenesis phenotype are not well understood. We hypothesized that more ecologically relevant conditions of limited host access will sustain female-biased sex ratios. After restricting access to host eggs, we found a strong relationship between reproductive rate and sex ratio. By limiting reproduction to one hour a day, wasps could sustain up to 100% effective parthenogenesis for one week, with no significant impact on total fecundity. Reproductive output in the first 24-hours appears to be critical to the total sex ratio of the entire brood. Limiting oviposition in that period resulted in more effective parthenogenesis after one week, again without any significant impact on total fecundity. Our data suggest that this phenomenon may be due to the depletion of Wolbachia when oviposition occurs continuously, whereas Wolbachia titers may recover when offspring production is limited. In addition to the potential to improve mass rearing of Trichogramma for biological control, findings from this study help elucidate the context-dependent nature of a pervasive symbiotic relationship.
Highlights
Wolbachia is a maternally transmitted, symbiotic bacterium that inhabits numerous arthropods and nematodes
Known reproductive modifications include cytoplasmic incompatibility, male-killing, feminization, and parthenogenesisinduction (Werren, Baldo & Clark, 2008), all of which increase the relative fitness of infected females, allowing Wolbachia to spread through a population (Hoffmann et al, 2011; Turelli & Hoffmann, 1991)
Based on the established relationship between Wolbachia titers and the parthenogenesisphenotype (Pascal et al, 2004; Stouthamer, 1997; Tulgetske & Stouthamer, 2012; ZchoriFein, Gottlieb & Coll, 2000), and previous research on Muscidifurax uniraptor that showed sex ratios changed with reproductive patterns (Legner, 1985), we hypothesized that reproductive rate might mediate the level of male production in an asexual line of Trichogramma
Summary
Wolbachia is a maternally transmitted, symbiotic bacterium that inhabits numerous arthropods and nematodes. Known reproductive modifications include cytoplasmic incompatibility, male-killing, feminization, and parthenogenesisinduction (Werren, Baldo & Clark, 2008), all of which increase the relative fitness of infected females, allowing Wolbachia to spread through a population (Hoffmann et al, 2011; Turelli & Hoffmann, 1991). Parthenogenesis-inducing Wolbachia infect haplodiploid species and result in the production of females without the need for a mate. This is accomplished through converting unfertilized eggs (that would otherwise develop as males) to diploid eggs, which develop as females (Gottlieb et al, 2002; Pannebakker et al, 2004; Stouthamer & Kazmer, 1994).
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