Migration and dispersal by the sweet potato whitefly, Bemisiatabaci

Abstract

Research on short-range dispersal (less than 10 km) by supposedly weakly flying insects, e.g., whiteflies, has not enjoyed the attention paid to dispersal by strong flying insects that are capable of migrating more than 100 km, such as some leafhoppers. Possible exceptions are studies concerning dispersal by the sweet potato whitefly, Bemisia tabaci. We wanted to determine to what extent whitefly flight is truly weak and if it meets some of the criteria historically used to define migration. In a flight chamber the majority of whiteflies landed quickly. A portion (6%) flew for more than 15 min (some more than 2 h). In doing so whiteflies ignored vegetative cues and focused on artificial skylight. This was against a downwardly directed airstream exceeding 4.0 cm/s. Attempts to associate wing morphological characteristics with their flight were mostly successful. The shapes of the wings of whiteflies that flew for some time in the chamber, or for some distance in the field, were different than those that did not. In the field B. tabaci was found dispersing more than 5 km. In these experiments whiteflies in a cantaloupe field were marked with fluorescent dust. Large portions of the marked population landed in close proximity to the field and another large group was trapped at 2.2 km. We hypothesized that this conformed to flight behavior observed in the laboratory, i.e., individuals captured near the field quickly responded to vegetative cues and landed, while others dispersed down range, initially ignoring these plant cues. This behavior was thought to be persistent. Additionally, flight in the field was not entirely wind-directed. Whiteflies were sometimes captured in areas away from prevailing winds. These are indicative of strong flight and migration. We found, however, that whiteflies did not possess all the characteristics commonly associated with stronger flyers. Whiteflies do not increase wingbeat frequency to compensate for high wing loading. Whiteflies do not possess an oogenesis-flight syndrome. In spite of these findings, whitefly flight cannot be characterized as weak. Whiteflies flew in a flight chamber against a strong airstream. They also dispersed in field experiments for a considerable distance. There is also information that whiteflies have a migratory form, in the manner of some strong flying insects. Whitefly flight seems to meet many criteria associated with migration in insects. As a final note, although most whitefly flight occurs over short distances, it is no less important biologically and cannot be ignored when developing pest management programs.