Reproductive differences between Q and B whiteflies, Bemisia tabaci, on three host plants and negative interactions in mixed cohorts

Two cryptic species of Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), B and Q whiteflies, have been invading many parts of the world. In Japan, Q whiteflies are displacing the predominant B whiteflies. To elucidate the mechanism of whitefly displacement, we compared the reproductive capacities of these species at different temperatures on three host plants and investigated negative interactions in the mixed cohort of mated females of both species. We measured their development times and emergence rates at six temperatures ranging from 20 to 35 °C on tomato, cucumber, and sweet pepper. In addition, we measured their life spans and the number of eggs at 20 and 30 °C on tomato and cucumber. On sweet pepper, B whiteflies mostly did not develop and died as first instar, but Q whiteflies completed their development. On tomato and cucumber, the development times, emergence rates, and life spans of B and Q whiteflies at all experimental temperatures did not differ significantly. B whiteflies had a higher intrinsic rate of population increase (rm) and net reproductive rate (R0) than Q whiteflies at 30 °C on these plants. In a mixed cohort of mated females, Q whiteflies had longer development times than B whiteflies. Furthermore, Q whiteflies had a lower proportion of emerged adults (25.4%) and higher progeny sex ratio (i.e., percentage sons) in the mixed cohort (52.8%) than in the single cohort (36.8%). The reduction in female Q progeny suggests that the interaction between B and Q whiteflies negatively affects only Q whiteflies, resulting in a lower Q population in the presence of B whiteflies. This reduction does not explain the recent displacement of B whiteflies by Q whiteflies in Japan.