The relative resistance of 18 cultivars of Brassica oleracea L. to attack by the sweetpotato whitefly [Bemisia tabaci (Gennadius)] was studied in screen cage (spring), field (autumn), and laboratory tests. The B. oleracea entries consisted of six types, including 16 green and two red cultivars. Cabbage (Capitata Group) and broccoli (Boytrytis Group) were less infested than other crops in a screen cage test, with kale, collard (Acephala Group), and brussels sprouts (Germmiter Group) experiencing relatively high and kohlrabi (Gongtlodes Group) intermediate infestations. Relative ranking of crops was similar in an autumn field study, with the exception of brussels sprouts, which had an intermediate level of infestation. Differences in numbers of whiteflies among cultivars within crops were negligible or inconsistent, except that red cultivars of brussels sprouts (`Rubine') and cabbage (`Red Acre') were much less infested than green cultivars. In a laboratory test, differences of whitefly oviposition and nymphal survival and development were small, indicating that nonpreference factors, rather than antibiosis, are the best explanations for differences in the numbers of whiteflies among the B. oleracea cultivars that were tested,
K.D. Elsey and M.W. Farnham
N. Boissot, D. Lafortune, C. Pavis, and N. Sauvion
The whitefly Bemisia tabaci (Gennadius) B-Biotype is a major pest on cucurbits in the Caribbean islands. Five field trials were conducted to identify resistance among 80 genotypes of Cucumis melo L. from diverse geographic origins. We focused on resistant rather than tolerant genotypes by counting adults on the abaxial side of two leaves of each plant at least three times in each trial, and larval density of under leaf disk samples at least twice in each trial. On the basis of insect density, three Indian accessions, PI 414723, PI 164723, and 90625, and one Korean accession, PI 161375, had field resistance. On those accessions, we observed 3.6 to 6 times fewer adults than on the most susceptible genotypes (`AR Top Mark' or `Délice de Table') and 11 to 29 times fewer larvae than on `AR Top Mark' or B66-5. Those levels of resistance may be sufficient to significantly reduce pesticide use in Guadeloupe (Lesser Antilles) where B. tabaci populations are lower than in the Southern United States or in the Mediterranean Basin. Higher levels of resistance are needed for genetic control, and may be achieved by a combination of different partial resistance genes.
Aliya Momotaz, Jay W. Scott, and David J. Schuster
chromosomes associated with resistance. Literature Cited Alba, J.M. Cuartero, J. Fernandez-Muńoz, R. 2005 Resistance to Bemisia tabaci in L. pimpinellifolium accession TO-937 and advance-backcross line XVth
Rosalía Servín, Jos L. Martínez, E. Troyo-Diguez, and A. Ortega
The sweetpotato whitefly [Bemisia tabaci (Gennadius)] has become a high-risk insect pest in Mexico as well as in other countries, causing serious damage to several crops. Control of whitefly in Baja California Sur, ,Mexico, is usually done by intense insecticides applications, either alone or in mixtures of several kinds. The aim in this work was to determine its susceptibility to cypermethrin, endosulfan, methamidophos, and methyl-parathion. LC50 was obtained to identify the resistant and susceptible populations. A group of 20 whiteflies were introduced in a 20-ml scintillation vial coated in the inner surface with a known concentration of the insecticide. Mortality readings were obtained 3 h after exposing the insects to the residual activity at five concentrations. Five replications and control were run in different consecutive days for each bioassay. Results indicated that cypermethrin was the most toxic to B. tabaci and metamidophos the least. Data will be considered for further evaluations.
David J. Schuster, James B. Kring, and James F. Price
The sweetpotato whitefly, Bemisia tabaci (Gennadius), was associated with symptoms of a silverleaf disorder of acorn squash (Cucurbita pepo L. cvs. Table King Bush and Table Ace) in cage studies in the greenhouse. Symptoms appeared on uninfested leaves that developed after plants were infested with the whitefly. When the infested lower leaves were removed and the young leaves protected from infestation with insecticides, new growth was asymptomatic or nearly so and symptomatic leaves remained symptomatic. Symptom expression was related more to nymphal density than to adult density since the relationship between log nymph density and symptoms was linear when adult densities were equal.
Harry S. Paris, Peter J. Stoffella, and Charles A. Powell
Summer squash (Cucurbita pepo L.) plants were grown in pots with high (290% capacity) or low (45% to 70% of capacity) soil moisture. The plants were exposed or not exposed to sweetpotato whiteflies (Bemisia tabaci Genn.). Only the plants exposed to whiteflies developed leaf silvering. Silvering was more severe in plants subjected to low soil moisture.
Charles A. Powell, Peter J. Stoffella, and Harry S. Paris
Zucchini squash (Cucurbita pepo L.) fruit yield and the incidence of sweetpotato whitefly (SPWF) [Bemisia tabaci (Gennadius)], squash silver leaf (SSL) disorder, and zucchini yellow mosaic virus (ZYMV) were measured during Spring and Fall 1991 in experiments containing various plant populations. In both experiments, as the within-row spacing increased from 30.5 to 76.2 cm or the number of plants per hill decreased from three to one, the number of marketable fruit per hectare decreased, and the marketable fruit per plant increased. Adult SPWF populations increased with decreased within-row spacing in the spring but not the fall experiment. The incidence of SSL or ZYMV infection was not affected by plant population in either experiment. The results indicate that increasing zucchini squash plant population can increase yield without affecting the incidence of SSL or ZYMV.
Harry S. Paris, Peter J. Stoffella, and Charles A. Powell
`Striato d'Italia' (cocozelle group) and `Clarita' (vegetable marrow group) summer squash were grown in the greenhouse and field in the presence of sweetpotato whiteflies (Bemisia tabaci Germ.) and their susceptibility to leaf silvering was compared. Silvering was less severe in `Striato d'Italia' in the greenhouse and field.
Charles A. Powell and Peter J. Stoffella
Mature-green and mature-red tomato (Lycopersicon esculentum Mill.) fruit were harvested from spring- and fall-grown plants infested with sweet potato whitefly (SPWF; Bemisia tabaci Gennadins). The mature-green fruit were either ripened at 20 to 22C or cold-stored at 10 to 13C for 3 weeks and then were allowed to ripen at 20 to 22C. There was no significant difference in the appearance of either external or internal tomato irregular ripening (TIR) symptoms between the two storage–ripening regimes or in the appearance of internal TIR symptoms among the two storage regimes and vine-ripened tomatoes. Thus, removing the tomatoes from the SPWF during ripening does not reduce TIR symptoms. About half of the mature-green tomatoes, ripened with or without cold storage (10 to 13C), developed no external TIR symptoms, but about half of these tomatoes had internal TIR symptoms. About one-third of the tomatoes developed external symptoms during ripening, but these symptoms disappeared after ripening was complete. A high percentage (71%) of these tomatoes with external symptoms also had internal symptoms. The remaining tomatoes developed external TIR that did not disappear, and almost all of these tomatoes had internal symptoms. These data suggest that culling tomatoes that develop external TIR during ripening will reduce but not eliminate tomatoes with internal TIR from the fresh-fruit market.
J.C. Palumbo and C.A. Sanchez
Imidacloprid is a new, chloronicotinyl insecticide currently being used to control sweetpotato whitefly [Bemisia tabaci Genn, also known as silverleaf whitefly (Bemisia argentifolii Bellows and Perring)]. Large growth and yield increases of muskmelon (Cucumis melo L.) following the use of imidacloprid have caused some to speculate that this compound may enhance growth and yield above that expected from insect control alone. Greenhouse and field studies were conducted to evaluate the growth and yield response of melons to imidacloprid in the presence and absence of whitefly pressure. In greenhouse cage studies, sweetpotato whiteflies developed very high densities of nymphs and eclosed pupal cases on plants not treated with imidacloprid, and significant increases in vegetative plant growth were inversely proportional to whitefly densities. Positive plant growth responses were absent when plants were treated with imidacloprid and insects were excluded. Results from a field study showed similar whitefly control and yield responses to imidacloprid and bifenthrin + endosulfan applications. Hence, we conclude that growth and yield response to imidacloprid is associated with control of whiteflies and the subsequent prevention of damage, rather than a compensatory physiological promotion of plant growth processes. Chemical names used: 1-[(6-chloro-3-pyridinyl)methyl]-4,5-dihydro-N-nitro-1-H-imidazol-2-amine (imidacloprid); [2 methyl(1,1′-biphenyl)-3yl)methyl 3-2-chloro-3,3,3-trifluoro-1-propenyl]-2,2-dimethylcyclopropane carboxylate (bifenthrin); 6,7,8,9,10,10-hexachloro-1,5,5a,6,9,9a-hexahydro-6,9-methano-2,4,3-benzodiaxathiepin 3-oxide (endosulfan).