Invasion of the Q2 mitochondrial variant of Mediterranean Bemisia tabaci in southern Italy: possible role of bacterial endosymbionts

BACKGROUND: 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 depend on the phenotype of inherited bacterial endosymbionts. Here, we examined B. tabaci genetic diversity variation occurred in recent years in South Italy. Whitefly were genotyped by PCR-RFLP analysis of COI gene and molecular identification of endosymbionts. Possible factors leading to the observed genetic diversity were examined. RESULTS: Q1 and Q2 mitochondrial types of MED, the only species found, coexisted in the field, while MEAM1 disappeared. A large spreading of Q2 (70% of individuals) was observed for the first time in Italy. Q2 showed a significant female-biased sex ratio and largely outnumbered Q1 on solanaceous hosts, in greenhouses and on insecticide-treated plants. Q1, with even sex ratio, slightly prevailed on non-solanaceous hosts, especially wild and untreated plants. Endosymbiont composition was associated with the mitochondrial type. Hamiltonella and Rickettsia were found at near fixation in Q1 and Q2 respectively; Arsenophonus, Cardinium and Wolbachia were found in both types although at different frequencies. CONCLUSIONS: Q2 invasion seems to have been favored by the agro-ecological conditions of South Italy and by female-biased sex ratio. Endosymbionts may have a role in Q2 invasiveness acting as sex-ratio manipulators (e.g. Rickettsia) and possibly by benefiting the host fitness.