|Chu, Chang Chi|
Submitted to: Archives of Insect Biochemistry and Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/26/2001
Publication Date: 1/1/2002
Citation: Buckner, J.S., Freeman, T.P., Ruud, R.L., Chu, C., Henneberry, T.J. 2002. Characterization and functions of the whitefly egg pedicel. Archives of Insect Biochemistry and Physiology. 49(1):22-33.
Interpretive Summary: The silverleaf whitefly, Bemisia argentifolii, is a very serious pest of agricultural crops in the southern U.S., including cotton, and a wide range of ornamentals, melons and vegetables. Whitefly nymphs and adults damage crops by extracting large quantities of phloem sap that causes wilting and decreased plant development. Feeding whiteflies also excrete "sticky" honeydew that contaminates the surroundings and serves as a medium for sooty mold, and they serve as vectors to transmit yield-limiting viruses and other plant disorders. Female whiteflies lay eggs on the host plants by making a slit on the underside of the leaf with their ovipositor and inserting the pedicel (stalk) of the egg. For the egg to survive and develop into a nymph, the egg must remain 'anchored' to the leaf and, as many researchers have suggested, the pedicel must receive water from the plant to avoid desiccation. In this study, we clearly demonstrate with radiolabeled solutes and an artificial membrane apparatus for egg oviposition that egg hatch is dependent on water uptake by the pedicel, and that the pedicel has the ability to transport water/solutes into the developing egg. Electron microscopy of the pedicel of eggs oviposited into leaf tissue, artificial membranes and eggs removed from female ovaries revealed structural features that were consistent for the distal portion of pedicels serving as conduits for movement of water and solutes into the developing egg.
Technical Abstract: For the silverleaf whitefly, Bemisia argentifolii (Bellows and Perring) (Homoptera: Aleyrodidae), scanning and transmission electron microscopic techniques were used to observe the characteristics of egg oviposition into both plant cells/tissues and artificial membranes, and to document the morphology of mature egg pedicles removed from the ovaries of females. The exterior of the distal portion of the pedicel consisted of a tangled array of fibrous structures (0.2-0.3 um in diameter) that constituted about 20-25% of the outer diameter of the pedicel. The attachments of the fibers to the core of the pedicle suggested that the pedicel functions as the collector and conduit for water (vapor), and perhaps solute movement into the egg. Silverleaf whitefly eggs on membranes were incubated at various levels of relative humidity and the eggs were scored for egg hatch. At 98-100% rh, the percentage egg hatch was 86-98%. At lower humidity ranges of 0-20% rh, 55-65% rh and 75-85% rh, none of the eggs hatched. Media (solute) uptake by silverleaf whitefly and greenhouse whitefly, Trialeurodes vaporariorum (Westwood), egg pedicels was determined by exposing the pedicel side of eggs oviposited on membranes to media solutions containing the high molecular weight polysaccharide, [14C]-inulin. Solute uptake by the pedicel and movement into developing silverleaf whitefly eggs were demonstrated using [2-14C]-acetate, and assaying for radioactivity in hatched nymphs. These studies, using exposure of pedicels to relative humidity and radiolabeled materials, demonstrate that whitefly egg hatch is dependent upon water uptake by the pedicel, and that the pedicel has the ability to transport solutes into the developing egg.