|Chu, Chang chi|
Submitted to: Journal of Chinese Association of Entomologists
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/1/1998
Publication Date: N/A
Citation: Interpretive Summary: Silverleaf whiteflies feed on host plants by sucking plant juice from leaves. The feeding procedure is complex that involves locating probing sites on leaf surface, stylet penetration, searching for phloem and penetration into it. Using light microscope, electron microscopy and confocal image analysis, we have found the sequence of this feeding behavior. First, whitefly larvae use leaf hair and elongated cells on the leaf surface as a guide to find the location of small veins underneath. Then, larvae secret saliva to produce a sleeve-like sheath that guides the stylets going through mesophyll tissue between cells to reach phloems. If the searching of phloems is not successful, the salivary sheeth is always sealed at the end. It has been known that whiteflies prefer melons than lettuce. Part of the reason is that melons have more small veins than lettuce that help whitefly larvae locate the feeding sites.
Technical Abstract: Whitefly feeding biology is complex and includes the location of appropriate sites to probe leaves so that minor veins can be located. Since survival of the nymphal stage of the silverleaf whitefly requires stylet penetration of the smallest veins in host plant leaves, an elaborate series of behavioral acts must be performed for the insect to reach its target. Our studies, using light and electron microscopy as well as confocal imaging, reveal that successful feeding always involves probing of minor veins that contain no more than three xylem elements. We found almost no evidence of stylet or sheath penetration into parenchyma or palisade cells. Sheaths were up to 140 um long and about 2 um in diameter at their widest dimension with the appearance of fused beads. The sheaths were occasionally glued to cell walls and made contiguous contact between the plant leaf surface where penetration originated, proceeding all the way to the veins. Some sheaths terminated blindly without reaching a vascular bundle, and these sheaths were invariably sealed at the end. The relative success of silverleaf whitefly on different species of host plants is, in part, attributable to the geometry of the feeding arrangement in relationship to the availability of minor veins in the host plants. This accounts for the high success of this species on cantaloupe and other cucurbit hosts and the low success on lettuce, the former having more than twice the amount of vascular bundle tissue than the latter.