Bacterial endosymbionts may induce female-biased sex ratio in the invasive mitochondrial type Q2 of Bemisia tabaci

The whitefly Bemisia tabaci (Gennadius) is a complex of cryptic species some of which, namely the Mediterranean (MED) and the Middle East-Asia Minor 1 (MEAM1), are highly invasive, and injurious crop pests worldwide, and able to displace local genotypes. Invasiveness of B. tabaci may correlate with the phenotype of inherited bacterial endosymbionts. In a greenhouse crop area of South Italy Q1 and Q2 mitochondrial types of MED, currently the only species found in this area, coexist in the field. Here, the introduction of Q2 (eastern Mediterranean origin) has been very recent and in few years (less than five years) Q2 largely outnumbered Q1 (the indigenous mitotype of western Mediterranean origin). Now 70% of individuals in the field are Q2. Each mitochondrial type is characterized by a specific endosymbiont composition. Hamiltonella and Rickettsia are at near fixation in Q1 and Q2 respectively; Arsenophonus, Cardinium and Wolbachia infect both types although at different frequencies. Contrarily to Q1, with an even sex ratio, Q2 shows a significant female-biased sex ratio. Although different agro-ecological conditions may have favored the invasion of Q2 in South Italy, the female-biased sex ratio may strongly affect the invasion biology of this mitotype. Endosymbionts (i.e. Rickettsia) may have a role in Q2 invasiveness acting as sex-ratio manipulators.