|Chu, Chang Chi|
Submitted to: Annals of the Entomological Society of America
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/2001
Publication Date: 9/1/2001
Citation: Freeman, T.P., Buckner, J.S., Nelson, D.R., Chu, C., Henneberry, T.J. 2001. Stylet penetration by Bemisia argentifolii (Homoptera: Aleyrodidae) into host leaf tissue. Annals of the Entomological Society of America 94(5):761-768.
Interpretive Summary: The length of the stylets of nymphs and adults was long thought to be the determining factor on selection of leaves for feeding and oviposition by whiteflies. A short stylet length of first instar nymphs (=crawlers), the only mobile stage, was thought to mean that the crawler had to use surface cues on the leaf in order to quickly locate a vein within the leaf on which it could feed before it would dehydrate and die. Thus, leaf morphology was looked at in the selection of cotton varieties for insect resistance. Our findings show that the crawler, as well as all other stages of whitefly, have stylets that are long enough to reach a vein within the leaf, from any position on the leaf. Thus, surface cues based on the leaf morphology are not necessary in order to locate a vein within the leaf. Focus must now be shifted in search of other factors affecting insect resistance.
Technical Abstract: Silverleaf whitefly (Bemisia argentifolii, Bellows & Perring) adults and nymphs both feed on the phloem tissue of host plant leaves. Leaves infested with whitefly adults and nymphs were fixed rapidly so that the insects did not have time to withdraw their mouthparts. The stylet bundle of adults enters the labial groove at the junction between the first and second labial segments and is completely contained within the labium except during feeding. Stylet length is equal to the combined length of labial segments 2, 3, and 4. The whitefly penetrates the host leaf by pushing the stylet bundle down the labial groove. Thus, the depth of stylet penetration into the host leaf can be determined by noting the position of the head along the labial groove. Apparent changes in the length of the labium during feeding may be related to the viewing angle as only the first labial segment showed significant changes in length. Much of the mechanical force necessary for adult stylet penetration comes from the change in position of the head with respect to the labium.. As the head is extended over the labium, the style bundle is pushed down the labial groove into the host tissue. Nymphal stylet length was found to be longer than previously reported, ranging from 113 um for first instar crawlers to 200 um for fourth instar nymphs. Nymphal stylets are long enough to reach the phloem tissue in cotton and hibiscus leaves from essentially any position on the abaxial lead surface, negating need for surface cues to locate a vein.