Isard Symposium
Comparatively little is known about migration and dispersal by small (less than100 micrograms) insects moving short distances (less than 5.0 km) across agricultural landscapes. This lack of information is being corrected as more scientists address these phenomena. In our laboratory, we have been studying dispersal by sweet potato whiteflies, Bemisia tabaci, as they move from summer crops, such as cotton, into fall vegetables. Our initial conclusions were that these insects were not capable of sustained flight. Reasons included; they were members of a taxon that is almost exclusively associated with perennial hosts in the tropics, they were likely too small (ca. 45 micrograms) to have large quantities of flight fuels, and high surface to volume ratios would result in rapid desiccation in the Southwest. Early studies obtained using a flight chamber proved us wrong on several counts. In these laboratory studies, ca. 6% of the population flew for greater than 30 min. Some sustained flight for greater than 2 hr. These insects seemed to be conforming to classic definitions of insect migration, i.e., during their flight they initially ignored vegetative cues in favor of skylight cues, but eventually focused on cues mimicking plants. Mark-recapture field studies demonstrated that the majority of the population dispersed at least 2.2 km during a 3 hr-period. Further studies have shown that there is an optimal age for flight by Bemisia tabaci. Flight activity was demonstrated to be associated with changes in the flight musculature and mitochondria associated with indirect flight muscles. Other research characterized the vertical component of their dispersal. We demonstrated that aerial density of Bemisia tabaci decreases with height above ground. Aerial whitefly density also decreased with distance from the point of take-off. We captured marked whiteflies at 7.3 m above the ground in traps at the edge of the source field, indicating a rapid rate of ascent for some individuals. Females trapped in this study were also used to determine mean egg load for insects captured at four heights (0 to 7.3 m). A highly significant negative correlation was found between height trapped and egg load, indicating that there may be a trade-off in B. tabaci between production of eggs and the ability to disperse. Recent studies have been undertaken concerning whitefly parasitoid dispersal. The dispersal abilities of Eretmocerus eremicus have been examined in the vertical flight chamber to determine its dispersal potential. It is our plan to eventually compare their flight behavior to that of B. tabaci. Preliminary results clearly indicate that there is a statistical difference in flight duration between males (1 min avg., 10 min maximum) and females (19 min avg., 93 min maximum). Isard Symposium
Comparatively little is known about migration and dispersal by small (less than100 micrograms) insects moving short distances (less than 5.0 km) across agricultural landscapes. This lack of information is being corrected as more scientists address these phenomena. In our laboratory, we have been studying dispersal by sweet potato whiteflies, Bemisia tabaci, as they move from summer crops, such as cotton, into fall vegetables. Our initial conclusions were that these insects were not capable of sustained flight. Reasons included; they were members of a taxon that is almost exclusively associated with perennial hosts in the tropics, they were likely too small (ca. 45 micrograms) to have large quantities of flight fuels, and high surface to volume ratios would result in rapid desiccation in the Southwest. Early studies obtained using a flight chamber proved us wrong on several counts. In these laboratory studies, ca. 6% of the population flew for greater than 30 min. Some sustained flight for greater than 2 hr. These insects seemed to be conforming to classic definitions of insect migration, i.e., during their flight they initially ignored vegetative cues in favor of skylight cues, but eventually focused on cues mimicking plants. Mark-recapture field studies demonstrated that the majority of the population dispersed at least 2.2 km during a 3 hr-period. Further studies have shown that there is an optimal age for flight by Bemisia tabaci. Flight activity was demonstrated to be associated with changes in the flight musculature and mitochondria associated with indirect flight muscles. Other research characterized the vertical component of their dispersal. We demonstrated that aerial density of Bemisia tabaci decreases with height above ground. Aerial whitefly density also decreased with distance from the point of take-off. We captured marked whiteflies at 7.3 m above the ground in traps at the edge of the source field, indicating a rapid rate of ascent for some individuals. Females trapped in this study were also used to determine mean egg load for insects captured at four heights (0 to 7.3 m). A highly significant negative correlation was found between height trapped and egg load, indicating that there may be a trade-off in B. tabaci between production of eggs and the ability to disperse. Recent studies have been undertaken concerning whitefly parasitoid dispersal. The dispersal abilities of Eretmocerus eremicus have been examined in the vertical flight chamber to determine its dispersal potential. It is our plan to eventually compare their flight behavior to that of B. tabaci. Preliminary results clearly indicate that there is a statistical difference in flight duration between males (1 min avg., 10 min maximum) and females (19 min avg., 93 min maximum).