GEMINIVIRUS-TRANSMISSION AND BIOLOGICAL CHARACTERIZATION OF BEMISIA-TABACI (GENNADIUS) BIOTYPES FROM DIFFERENT GEOGRAPHIC REGIONS

Eighteen populations of Bemisia tabaci, collected from different geogr aphic locations (North & Central America, the Caribbean, Africa, the M iddle East, Asia and Europe), were studied to identify and compare bio logical and genetic characteristics that can be used to differentiate biotypes. The morphology of the fourth instar/pupal stage and compound eye structures of adults were investigated using scanning electron mi croscopy and found to be typical of the species among all biotypes and populations studied. Setae and spines of B. tabaci larval scales from the same colony were highly variable depending on the host plant spec ies or leaf surface characteristics. The location and the morphology o f caudal setae, characteristic of all B. tabaci studied to date, were present in all colonies. However, differences in adult body lengths an d in the ability to induce phytotoxic disorders in certain plant speci es were found between biotypes or populations. The recently identified ''B'' biotype, characterised by a diagnostic esterase banding pattern and by its ability to induce phytotoxic responses in squash, honeysuc kle and nightshade was readily distinguished from non-''B'' biotype po pulations. None of the non-''B'' biotypes studied, were found to induc e phytotoxic responses. Nine populations examined showed typical ''B'' biotype characteristics, regardless of country of origin. All tested populations, determined as ''B'' or ''B''-like biotypes successfully m ated with other ''B'' biotype colonies from different geographic areas . Non-''B'' biotype colonies did not interbreed with other biotypes. T he B. tabaci populations were tested for their ability to transmit 15 whitefly-transmitted geminiviruses (WTGs) from different geographic ar eas with a wide range of symptom types. All WTGs were transmitted by t he ''B'' biotype colonies and by most non-''B'' biotype colonies, with the exception of three viruses found in ornamental plants which were non-transmissible by any colony. Some non-''B'' biotypes would not tra nsmit certain geminiviruses and some geminiviruses were more efficient ly transmitted than were others.