Quantitation over time of tomato yellow leaf curl geminivirus DNA in its whitefly vector

The amount of tomato yellow leaf curl geminivirus (TYLCV) DNA that accumulated in the vector Bemisia tabaci was studied by quantitative chemiluminescent dot-blot assay, using digoxigenin-labeled specific DNA probes. Large groups of female whiteflies were allowed to feed for 4, 12, 24, or 48 h on TYLCV-infected tomato plants and then were transferred to TYLCV-immune cucumber plants. Insects were sampled at different times during and after acquisition access and tested for TYLCV-DNA content. TYLCV-DNA assays were done either on whole insects or on the head plus prothorax (to include salivary glands) and abdomen separately. The maximum amount of TYLCV DNA, averaging from 0.5 to 1.6 ng per insect, was always attained at the end of the acquisition period. The mean amount then decreased by about 1 to 2% per day, remaining clearly detectable up to 20 days after the end of the acquisition period. Only some whiteflies that were TYLCV-positive in the abdomen were positive for head plus prothorax. In both parts of the body, TYLCV DNA remained detectable up to 18 days after the end of the acquisition period, showing that TYLCV DNA remains in insect tissues much longer than infectivity indicates.