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By Philip A. Stansly Printer Friendly Version (whitefly.pdf 366kb Requires Acrobat Reader) Damage caused by Bemisia
Whitefly adults and nymphs feed by piercing the leaf surface and extracting phloem sap from sieve tubes with their sucking mouthparts. Sap contains mostly sugars produced in the leaves on its way to the roots and other structures. High whitefly populations may drain enough nutrients to deplete the plant. Additionally, whiteflies must consume so much sap to obtain scarce amino acids that great quantities of honey dew must be excreted, becoming a substrate for sooty mold that reduce the photosynthetic capacity of the foliage.
In addition to the direct damage mentioned above, salivary secretions of the silverleaf whitefly and perhaps other biotypes of Bemisia tabaci induce various physiological disorders in some plants. The silverleaf disorder seen in many squash and pumpkin varieties is caused by a shrinking of the palisade cells away from the upper epidermis leaving an airspace that gives the silver appearance. Blanching of various plant parts from whitefly feeding has been observed in stems of lettuce and various brassicas, bracts of poinsettias, and other plants. Irregular ripening of tomato is another whitefly induced disorder that can render fruit unmarketable. Moderate to low populations may be sufficient to cause these disorders, but at least they can be quantified.
By far the most damaging consequence of whitefly feeding can be transmission of plant viruses, particularly geminiviruses like tomato yellow leafcurl (TYLCV) and closteroviruses like lettuce infectious yellows. If the proportion of viruliferous whiteflies is high, the number necessary to spread the virus could be quite low. It impossible evaluate the potential damage represented by a certain whitefly populations in the field because one cannot estimate the number of viruliferous whiteflies, although some idea of their origin may provide a rough idea. Virus disease is most damaging when infection occurs early in the crop cycle. |
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