|Chu, Chang Chi|
|Freeman, Thomas - NORTH DAKOTA UNIV., FARGO|
Submitted to: Southwestern Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 1, 1996
Publication Date: N/A
Interpretive Summary: The silverleaf whitefly causes hundreds of millions of dollars in damage to various crops each year, and have developed resistance to nearly every pesticide registered for use against them. We need alternative ways to combat this serious pest, including ways of taking advantage of idiosyncrasies of feeding behavior to lower their impact so that other methods such as biological control can be used more effectively. We showed that several features on the under-surface of cotton leaves are used by silverleaf whiteflies to find their feeding sites. The cells on the cotton leaf's undersurface are elongated when they are under veins and square- looking when they are under plant tissue other than veins (areoles). The newly hatched individuals, called crawlers, move around on about 1/8-1/4 of the leaf's surface using the elongated cells as guides to help them find the small veins that contain the plant saps that are the whitefly feeding targets. Once the veins are found, the whiteflies have a very strong chanc of surviving to the adult stage, but prior to finding veins the crawlers are most vulnerable. Also, adult females use plant hairs a guideposts for sites in which to lay their eggs (which they insert into the plant surface cells so that the eggs can get water from the plant). The implication of this work is that plant breeders or genetic engineers now have a clear target as to what features they can incorporate into varieties of cotton that will give the plants enhanced resistance to whiteflies.
Technical Abstract: We examined cotton leaves for correlations between surface structures and veins, using light and electron microscopy. Using Bemisia argentifolii Bellows and Perring egg placement, nymphal positions and crawler (first- instar nymph) behavior, we evaluated the responses of whitefly nymphs to leaf surface features. Two kinds of epidermal cells predominated the leaf abaxial surface: those underlying vascular bundles and areoles (regions between veins). Lamina trichomes (simple and complex) originated from elongated epidermal cells overlaying the veins, including minute (single- stranded) veins. All 2,000 lamina trichomes (non-glandular) we examined originated from vascular bundle-associated epidermal cells. Areoles of fully expanded leaves had perimeters of 2.463 mm (ñ 0.1113 S.E., N= 10) and a mean area of 0.382 mm sq (ñ 0.0374). Epidermal cells underlying areoles were isodiametric while those underlying veins were elongated. Eggs were generally deposited on the elongated epidermal cells associated with bundles or on cells within ca. 30 um of those vascular bundle-associated epidermal cells. Crawlers walked about 2300 um per minute until they settled upon feeding sites that were immediately under the minor veins, never more than about 60-80 um from the edge of the abaxial bundle- associated epidermal cells. Crawlers spent at least 80% of their time in contact with bundle-associated epidermal cells, apparently making contact with these cells either with legs or antennae.