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Gossypium thurberi Todaro is a wild cotton species native to Mexico and parts of the southwestern USA. Four years of field studies in California's Imperial Valley revealed consistent very high levels of resistance in G. thurberi against silverleaf whitefly, Bemisia argentifolii Bellows and Perring, an important pest of cotton in many regions of the world. Naturally developing field infestations in plots of G. thurberi were significantly lower than in plots of the commercial cotton cultivars DP 5415, Siokra L23, and Stoneville 474. Gossypium thurberi has two morphological traits that, in past research, have been associated with lower levels of whitefly susceptibility: smooth- and okra-leaf; however, the levels of resistance observed in G. thurberi were significantly greater than in the cotton cultivar DP 5415, which is a smooth-leaf cotton, and Siokra L23 which, like G. thurberi, has both smooth- and okra-leaf traits. Therefore, the high level of resistance in G. thurberi seems to be due to factors above and beyond smooth- and okra-leaf. Siokra L23, which is among the least whitefly-susceptible cotton cultivars, developed whitefly populations over 30 times those on G. thurberi in all 3 years that Siokra L23 was tested. The difference in whitefly population development between G. thurberi and the other two cotton cultivars was even more striking, up to a 475-fold difference. 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. Thus, the mechanisms of resistance in G. thurberi remain unknown. more...

Five upland cotton, Gossypium hirsutum L., cultivars, Deltapine (DPL) 50, 5415 and 5432, Fibermax 832 and Siokra L23, were studied in relation to silverleaf whitefly, Bemisia argentifolii Bellows and Perring, oviposition and colonization. Deltapine 5415 and 5432 had the highest numbers of eggs and nymphs and Siokra L-23 the lowest. Siokra L-23 also had the lowest number of adults compared to the other four cultivars. Over 75% of eggs were oviposited on leaf surfaces between veins and 23% were oviposited in veins that were ≤4 cells wide. Few eggs were found on veins that were five or more cells wide. No eggs were inserted into leaf stomata. more...

Adult whitefly Bemisia argentifolii BellowsPerring trap (CC trap) catches were compared with suction type trap catches. CC trap catches were significantly correlated to the suction trap catches. Higher numbers of B. argentifolii adults were caught in CC traps oriented toward an untreated, B. argentifolii-infested, cotton field as compared with traps oriented toward Bermuda grass fields, farm roads, or fallow areas. CC trap catches at five heights above ground (from 0 to 120 cm) were significantly related to each other in choice and no-choice studies. CC trap catches were low in the Imperial and Palo Verde Valleys from late October to early June each of 1996, 1997, and 1998. Trap catches increased with increasing seasonal air temperatures and host availability. Trap catches were adversely affected by wind and rain. Abrupt trap catch increases of 40- to 50-fold for 1-2 d in late June to early July followed by abrupt decreases in adult catches suggest migrating activity of adults from other nearby crop sources. more...

Seasonal activity of the sweet potato whitefly (SPWF), Bemisia tabaci (Gennadius), was monitored weekly in the Imperial Valley and lower Colorado desert region of California in 1984. Numbers of SPWF caught on traps placed ca. 20 m inside a cotton field were significantly correlated to numbers of SPWF caught on traps located at the perimeter of the cotton field and also on traps 0.4 km away. Although the number of SPWF caught on traps located in the desert was considerably lower than those in the Imperial Valley, seasonal trends between the two regions were highly correlated. SPWF populations exhibited an exponential increase in all locations, and time-series analyses showed that there were no discernible time-lags in population trends from the different areas sampled. more...