Author
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Castle, Steven |
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Submitted to: Sweetpotato Whitefly Progress Review Proceedings
Publication Type: Proceedings Publication Acceptance Date: 4/1/2002 Publication Date: 6/1/2002 Citation: N/A Interpretive Summary: Technical Abstract: A series of greenhouse experiments were conducted to evaluate host acceptance of melons relative to cotton by Bemisia tabaci. The objectives were to quantify the differences between melons and cotton in terms of the number of adult whiteflies that settled on either plant, then determine the levels of oviposition that occurred over the course of the experiment. Two types of choice assays were used to examine adult settlement and oviposition. For the first, acetate cylinders 0.6 m high by 0.28 m diameter were fashioned with 3 equidistant slots cut into the cylinder wall at a height of 0.46 m, large enough for fully expanded melon and cotton leaves to be inserted into the interior space of each cylinder. The tops of the cylinders were covered with nylon organdy to retain whiteflies within the cylinder space. The leaves projecting into the cylinder interiors remained attached to their plants. A foam-rubber collar was sandwiched around each leaf petiole and then snugly fit into the rectangular slots in the cylinder walls so that no whiteflies would be able to escape from the interiors. Once all cylinders were fitted with their complement of leaves and all openings sealed, they were ready to be infested with adult whiteflies. Adult whiteflies were aspirated from colonies maintained on both melon and cotton plants. Approximately 120 adults were collected into an aspiration tube, then transferred through a sleeve opening to be released inside each cylinder cage. As many as 18 cylinders were set up at one time and infested with adult whiteflies. A series of 5 counts were made beginning at 18:00 on the day of released, then followed by 2 days of counts in the morning and at dusk. Each leaf projecting into the cylinder spaces was closely viewed from outside the cylinder walls. A total of 10 cylinder cage experiments were conducted. For the 2nd type of assays, experiments were conducted in 2 small greenhouses with 16 plants of each type, melon and cotton, arranged into a randomized complete block design with 4 blocks consisting of 8 plants each. The 4 blocks were arranged on a bench on one side of each greenhouse. Whiteflies were collected separately from cotton and melon cultures. Approximately 1200 adults were released into each of the 2 greenhouses. Leaf counts of adults were made over the next 2.5 days, morning and late afternoon. Following the 5th and final count, all leaves were collected from each test plant for egg counts. Whitefly adult and egg counts were expressed as the mean number (±SEM) of whiteflies per leaf at each leaf node. In both the cylinder cage and greenhouse experiments, Bemisia tabaci consistently demonstrated a much higher affinity for melons compared to cotton. Adult settling and oviposition rates were greater on melon in the greenhouse experiments that used whole plants and for which whiteflies were free to move from plant to plant. A similar pattern was observed in the cylinder cage tests, but the differential in adult settling and oviposition between melons and cotton, although highly significant, was not as great as the greenhouse test. Overall, a ratio of 2:1 or greater was observed for mean numbers of adults on the melon leaf relative to either one of the two cotton leaves. In some cases, i.e. experiment 1, the differential was approximately 5:1 in favor of melon leaves. The relative number of whitefly eggs on either host tended to follow the same pattern observed for adults. The differential between cotton and melon plants was more pronounced in the 2 greenhouse experiments in terms of mean whitefly adult and egg densities. The mean numbers of whitefly adults on cotton leaves compared to melon leaves ranged between 8-31-fold greater on melon leaves. Egg densities on melon leaves exceeded those on cotton leaves between 8-56-fold. There was little difference in results with respect to the origin of the wh |
