SIMULATING THE DYNAMICS OF BEMISIA-ARGENTIFOLII (HOMOPTERA, ALEYRODIDAE) IN AN ORGANIC CROPPING SYSTEM WITH A SPATIOTEMPORAL MODEL

The dynamics of the whitefly Bemisia argentifolii Bellows & Perring we re studied at a mixed-crop organic farm on Pine Island, FL, between Se ptember 1992 and January 1993. Whitefly populations on tomato, eggplan t, zucchini, cucumber; and pepper were monitored weekly by beat-pan sa mpling and biweekly by visual counts, and parasitism was determined by rearing parasitoids from whitefly infested tomato and eggplant foliag e, Analysis of the sampling data identified tomato and eggplant as the most attractive whitely host plants followed by cucumber, zucchini, a nd pepper. Parasitism of whiteflies on tomato and eggplant reached 80% during the study. Two peaks in population numbers were observed on to mato and eggplant planted by late September, whereas only 1 peak occur red when the same crops were planted later. The suitability of a spati ally explicit population model as a tool for investigating insect dyna mics was demonstrated on whiteflies at the farm. Simulation experiment s conducted to explain the trends in whitefly population numbers obser ved on early and late tomato indicated that these population peaks lik ely resulted from the interaction of planting date and temperature and not from the spatial heterogeneity of the crop system at the farm. Ot her simulation experiments showed that whitely population levels could be lowered by grouping similar crops and maintaining barriers to whit efly movement between crops. The utility; of this type of model for st udying insect dynamics in systems where host plants vary spatially and temporally is illustrated.