Journal of Insect Science (2008) 8 (4), p. 49 (Walker et al.)

G.P. Walker and E.T. Natwick (2008)
Resistance to silverleaf whitefly, Bemisia argentifolii (Hemiptera: Aleyrodidae) in Gossypium thurberi, a wild cotton species
Journal of Insect Science 8 (4), 49-49
in P. A. Stansly and C.L. McKenzie, organizers: Fourth International Bemisia Workshop - International Whitefly Genomics Workshop, December 3-8, 2006, Duck Key, Florida, USA
Abstract: Gossypium thurberi Todaro is a wild cotton species native to Mexico and parts of the southwestern United States. Four years of field studies in California's Imperial Valley revealed consistent high levels of resistance in G. thurberi against silverleaf whitefly, Bemisia argentifolii Bellows and Perring, an important worldwide pest of cotton. Naturally developing field infestations in plots of G. thurberi were significantly lower than in plots of the G. hirsutum L. commercial cotton cultivars, DP 5415, Siokra L23, and Stoneville 474. G. thurberi has two morphological traits that, in past research, have been associated with lower levels of whitefly susceptibility, smooth-leaf and okra-leaf; however, the levels of resistance observed in G. thurberi were significantly greater than the cotton cultivar DP 5415, which is a smooth-leaf cotton, and Siokra L23 which, like G. thurberi, has both smooth-leaf and okra-leaf traits. Therefore, the high level of resistance in G. thurberi seems to be due to factors above and beyond smooth-leaf and okra-leaf. In contrast to the clear results on naturally developing field infestations, experiments comparing nymphal survival among G. thurberi and commercial cotton cultivars did not detect antibiosis and both choice and no-choice oviposition experiments did not detect antixenosis. Immature survival (first instar through adult) was actually slightly higher on G. thurberi than on DP 5415 in the greenhouse test. This test was conducted on very young plants, so it seemed plausible that the unexpected results were due to resistance not being expressed in young plants and/or in greenhouse conditions. However, the next two tests in the field on mature plants also detected little or no resistance in G. thurberi. Likewise choice and no-choice oviposition tests in the greenhouse and in the field did not detect any difference in whitefly oviposition rate between G. thurberi and DP 5415. At this point, while the data conclusively demonstrate a high level of whitefly resistance in G. thurberi, the mechanisms of the resistance remains an enigma. Despite the failure of the oviposition tests to demonstrate non-preference, we suspect that non-preference is the most likely candidate for the mechanism of resistance. The reason for this suspicion is that each year of the field plot tests, the number of adults and eggs early in the season, which would be the initial colonization, were much less on G. thurberi than on the other cotton entries. In our choice and no-choice oviposition experiments in this study, the whiteflies were in a confined space which may have interfered with their normal host selection behavior. We plan additional oviposition tests using less confining conditions to investigate this possibility further.
Database assignments for author(s): Gregory P. Walker, Eric T. Natwick

Research topic(s) for pests/diseases/weeds:
resistance/tolerance/defence of host

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Pest and/or beneficial records:

Beneficial	Pest/Disease/Weed	Crop/Product	Country	Quarant.
	Bemisia tabaci biotype MEAM1	Cotton (Gossypium)	U.S.A. (SW)