The Costs and Benefits of Two Secondary Symbionts in a Whitefly Host Shape Their Differential Prevalence in the Field.

Insects commonly harbor maternally inherited intracellular symbionts in nature, and the microbial partners often exert influence on host reproduction and fitness to promote their prevalence. Here, we investigated composition of symbionts and their biological effects in the invasive MED species of a whitefly complex. Our field surveys revealed that populations of the MED whitefly, in addition to the primary symbiont , mainly contain two secondary symbionts , which is nearly fixed in the host populations, and with infection frequencies ranging from 0 to 86%. We isolated and established -positive and -free whitefly lines with a similar nuclear genetic background from a field population, and compared performance of the two whitefly lines. The infection of incurred significant fitness costs on the MED whitefly, including reduction of fecundity and egg viability as well as delay in development. We then selectively removed from the -free whitefly line and compared performance of two whitefly lines, one harboring both and and the other harboring only . While depletion of had little or only marginal effects on the fecundity, developmental rate, and offspring survival, the -free whitefly line produced very few female offspring, often reducing the progeny female ratio from about 50% to less than 1%. Our findings indicate that the varying costs and benefits of the association between these two symbionts and the MED whitefly may play an important role in shaping their differential prevalence in the field.