Mortality and population dynamics of Bemisia tabaci within a multi-crop system.

The population dynamics of mobile polyphagous pests is governed by a complex set of interacting factors that involve multiple host-plants, seasonality, movement and demography. Bemisia tabaci is a multivoltine insect with no diapause that maintains population continuity by moving from one host to another over the year. To better understand the mechanisms governing population development of this insect within the landscape, whitefly “ecosystems” were established in three geographically and climatically distinct areas in Arizona. These systems consisted of a sequence of six representative hosts (winter broccoli, spring and fall cantaloupes, summer cotton, perennial alfalfa, various annual weeds, and the perennial ornamental, lantana). Source and rates of natural mortality were quantified, in situ, on each host plant by life tables. The quantitative contribution of each mortality factor varied among hosts and time of the year, but was relatively consistent among geographic sites. Predation (sucking insects) and dislodgement from the plant surface (largely chewing predation) were consistently the largest sources of mortality. Median generational mortality was generally > 90% except on spring-planted cantaloupe where median mortality was <70%. Low mortality during the spring on cantaloupe appears to act as a biotic release leading to outbreak populations during summer months. Overall, an understanding of the year round spatio-temporal dynamics of this pest and its associated natural enemies will greatly aid the development of better pest management strategies in all affected crops.