Gas Exchange of Cucumber, Cucumis sativus L., Impaired by Tobacco Whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae)

Herbivory directly affects plant carbon gain by removing photosynthetic leaf tissues and indirectly by inducing the production of costly defensive compounds and/or disrupting water movement among other mechanisms. Damage to plant productivity was estimated in terms of photosynthesis, respiration and transpiration performances as function of Bemisia tabaci (Gennadius) density and feeding period under greenhouse conditions. Results indicated that cucumber gas exchange was impaired by whitefly feeding. B. tabaci elicited up to 30% decreased photosynthetic rates at 14 days after whitefly release. The degree of photosynthesis injury caused by whitefly generally was proportional to the number of whiteflies and infestation period. Feeding injury by whitefly on cucumber foliage increased respiration rate by 24% to 78%. The influence of whitefly infestation on the respiration rate was dependent upon whitefly density for each date, but it was not evidently enhanced over time. It is obvious that photosynthetic products could be lost not only as a result of phloem removal by whitefly feeding, but also through reduced photosynthetic activity and increasing respiration. The rate of water loss from infested leaves was 3-32% greater than that of the control plants. Increasing number of whiteflies and infestation period led in general to an increase in the transpiration rate. This profligate water loss through infested plant tissues might exacerbate the effects of water stress on plant productivity under semiarid field conditions