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J. Farías-Larios, M. Orozco-Santos, and N.R. Ramírez-Vazquez

Bemisia argentifolii is a major pest of melon crop in key production areas of Mexico. Foliar applications of chemical insecticides for their management have been ineffective. The purpose of this research was to evaluate the use of commercial formulations of Beauveria bassiana and different rates for biological control of silverleaf whitefly in cantaloupe melon grown under tropical conditions. Experimental plots were treated with three rates of Mycotrol ES and only an of Naturalis-L or Endosulfan as conventional insecticide. Treatments were arranged in a randomized complete-block design with four replicates. Effects of the treatments on B. argentifolii larval and adult populations and the amount of damage to the foliage and yield melon were recorded. There was not a significant difference between Mycotrol ES rates in nymphs and adults killed. Mycotrol ES, Naturalis and Endosulfan have a similar effect on nymphs and adults control. The nontreated control melon plants had significantly greater number of silverleaf whitefly nymphs and adults than Mycotrol ES, Naturalis-L and Endosulfan treatments. Also, marketable yield was lower for the nontreated control melon plants due to higher whitefly infestations. Results from this study indicate that B. bassiana use resulted in consistently lower whitefly infestations compared to the control. The field results are promising and confirmed the potential of B. bassiana as a microbial control agent against B. argentifolii in melon crop under tropical conditions.

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Charles G. Summers, Albert S. Newton Jr., and Kyle R. Hansen

Six table grape (Vitis vinifera L.) cultivars and 10 species of tree fruit were evaluated in cage tests to determine their susceptibility to colonization by the silverleaf whitefly (Bemisia argentifolii Bellows and Perring). The table grape cultivars Thompson Seedless, Perlette, Flame Seedless, Ruby Seedless, Christmas Rose, and Redglobe were all colonized. In a field nursery, with naturally occurring silverleaf whitefly populations, `Zinfandel', `Sirah', and `Chardonnay' were more heavily colonized than were `Merlot', `Thompson Seedless', or `Redglobe'. The tree crops `Kerman' pistachio (Pistacia vera L.), `Calimyrna' fig (Ficus carica L.), `Nonpareil' almond [Prunus dulcis (Mill.) D.A. Webb], and `Fuyu' persimmon (Diospyros kaki L.) were colonized in cage tests. Silverleaf whitefly failed to establish colonies on caged `O'Henry' peach [Prunus persica (L.) Batsch.], `Fantasia' nectarine [P. persica (L.) Batsch. var. nectarina (Ait.f.) Maxim.], `Casselman' plum (P. salicina Lindl.), `Tilton' apricot (P. armeniaca L.), `Granny Smith' apple (Malus domestica Borkh.), and `Hayward' kiwifruit [Actinidia delicoisa (A. Chevalier) C.F. Liang et A.R. Ferguson].

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Barbara E. Liedl, Darlene M. Lawson, Kris K. White, Joseph A. Shapiro, William G. Carson, John T. Trumble, and Martha A. Mutschler

Acylsugars, the primary components of the exudate secreted by type IV trichomes of Lycopersicon pennellii (Corr.) D'Arcy LA716, mediate the resistance of this accession to silverleaf whitefly, Bemisia argentifolii Bellows & Perring, n. sp. Reduction in the settling of the adult silverleaf whiteflies correlates with the concomitant increase in applied acylsugars. Oviposition of B. argentifolii is also affected by acylsugars, resulting in a reduction in the number of eggs and nymphs found; however, acylsugars do not affect hatching of nymphs. The threshold amount of acylsugars required for deterring settling and oviposition is under the amount of acylsugars (50 to 70 μg·cm–1) required for control of other insects.

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A.A. Csizinszky and D.J. Schuster

Field studies were conducted for three seasons, Fall 1994, Spring 1995, and Fall 1995 on the effect of UV-reflective films (mulches) on fruit yields and on the silverleaf whitefly [Bemisia argentifolii (Bellows and Perring)] of staked, fresh-market tomatoes (Lycopersicon esculentum Mill). The UV-reflective mulches were metallized aluminum (ALU) and painted aluminum (PAL) on either black or white plastic film. The AL and SL mulches were evaluated with and without a white (fall) or black (spring) 25-cm-wide painted band in the bed center. Controls were the conventional white (fall) or black (spring) polyethylene mulches. Highest reflected energy (μmol·m–2·s–1) to the plants at 25 cm from the mulch surface was measured on the ALU without white painted band or on PAL on white or black mulch with white painted band. Lowest energy was reflected from the white or black controls. Whitefly populations in the fall were lower on the ALU than on the PAL mulches. In the spring, when whitefly populations were low, number of whiteflies on tomato leaves were similar with all treatments. The proportion of plants with symptoms of the silverleaf whitefly transmitted tomato mottle virus (TMoV) were highest on controls. Yields in the fall were similar with UV-reflective or with white mulch. In the spring, fruit size and marketable yields were greater (P < 0.05) on plants with PAL on white plastic film without black band than on black control.

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David J. Schuster

The silverleaf whitefly (Bemisia argentifolii Bellows & Perring) is an important pest of tomatoes in Florida and elsewhere. Associated with populations of the whitefly is an irregular ripening disorder of fruit characterized by inhibited or incomplete ripening of longitudinal sections of fruit and by an increase in the amount of interior white tissue. Experiments were conducted during the spring and fall tomato production seasons of 1995 and 1996 to elucidate the relationship of nymphal and pupal density with severity of the disorder. Insecticides or insecticide combinations were applied at predetermined densities of whitefly nymphs and pupae and the subsequent severity of the disorder was rated separately for external and internal symptoms on red ripe fruit harvested weekly. Expression of irregular ripening symptoms, especially external symptoms, were correlated positively to the density of whitefly nymphs and pupae (number·10-1 terminal leaflets on the seventh to eighth leaf from the top of a main or lateral stem) increased. Expression of external symptoms tended to be better correlated with whitefly density when symptom severity was rated 1 and 3 weeks after estimating whitefly density for the spring and fall seasons, respectively. Expression of internal symptoms tended to be more consistently correlated with whitefly density when symptom severity was rated 2 and 3 weeks after estimating whitefly density for the spring and fall seasons, respectively.

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Shahab Hanif-Khan, Robert C. Bullock, Peter J. Stoffella, Charles A. Powell, Jeffrey K. Brecht, Heather J. McAuslane, and Raymond K. Yokomi

Silverleaf whitefly (SLW) (Bemisia argentifolii Bellows and Perring) feeding was associated with development of tomato irregular ripening (TIR) symptoms. `Micro-Tom', `Florida Basket', `Florida Lanai', and `Florida Petite' dwarf cherry tomatoes (Lycopersicon esculentum Mill.) were infested with adult SLW to observe oviposition preference, plant tolerance, and TIR symptom development in two experiments. There was no oviposition preference among the cultivars in either of the trials. TIR fruit symptoms were expressed as longitudinal red streaks with yellow, green, pink, or red blotches externally and white tissue internally. External TIR symptoms at the pink stage of ripening ranged from 32% (`Micro-Tom') to 82% (`Florida Basket') in Expt. 1 and 44% (`Micro-Tom') to 93% (`Florida Petite') in Expt. 2. In Expt. 1, external TIR symptoms disappeared from 18% (`Florida Lanai') to 37% (`Micro-Tom') and, in Expt. 2, 16% (`Micro-Tom') to 39% (`Florida Basket') of the fruit during ripening. SLW-infested plants exhibited 82% (`Florida Lanai') to 99% (`Florida Basket') and 76% (`Micro-Tom') to 90% (`Florida Petite') of fruit with internal white tissue regardless of external symptoms in Expts. 1 and 2, respectively. Tomatoes with severe TIR symptoms rarely ripened to full red. Postharvest characteristics of ripening SLW-infested and control fruit were evaluated (Expts. 3 and 4). Generally, the SLW-infested fruit were lighter in color than the control fruit. The control fruit developed normal red color while the SLW-infested fruit developed a blotchy, streaky color that was overall more of an orange-red. SLW-infested fruit were firmer than the control fruit in both experiments. Ethylene production was higher in SLW-infested fruit. While the total soluble solids contents were not significantly different between the treatments, the SLW-infested fruit were more acidic than the control fruit. Each cultivar was susceptible to oviposition by SLW and induction of TIR symptoms. However, TIR symptom expression differed among the cultivars. Despite higher ethylene levels, the ripening process in the SLW-infested fruit appeared slower or may have been inhibited by factors induced by the SLW compared with the control fruit, which ripened normally.

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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).

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Susan S. Han and Jennifer Konieczny

Eggs, larvae, pupae, and adult stages of greenhouse whitefly (Trialeurodes vaporarium Westwood) and silverleaf whitefly (Bemisia argentifolii Bellows & Perring) were exposed to insecticidal controlled atmospheres at 20 °C or 30 °C. Mortality data were calculated for each stage and results demonstrated that reduced-O2 atmospheres (an O2 level of <2 μL·L-1 balance in N2) resulted in faster and higher mortality than elevated-CO2 atmospheres (25% or 50% CO2). Responses, from the least to most tolerant stage was adult < larvae < eggs = pupae, regardless of the species of whitefly and treatment temperature. At 20 °C, treatment time required to kill >90% of adults, larvae, and eggs and pupae was 2, 4, and 8 hours, respectively. Increasing the treatment temperature from 20 to 30 °C reduced the treatment time to one-half that of 20 °C. Treatment time required to achieve complete elimination of the insects also caused phytotoxicity symptoms on poinsettias (Euphorbia pulcherrima Willd. ex Klotzsch), thus, limiting use of insecticidal controlled atmospheres as the sole means for managing whitefly.

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A.A. Csizinszky, D.J. Schuster, and J.E. Polston

Field studies were conducted for three seasons, Fall 1994, Spring 1995, and Fall 1995, on the effect of ultraviolet (UV)-reflective films (mulches) on the silverleaf whitefly (Bemisia argentifolii Bellows and Perring), the incidence of tomato mottle virus (ToMoV), and on fruit yields of staked, fresh-market tomatoes (Lycopersicon esculentum Mill.). The UV-reflective mulches were metallized aluminum (aluminum) and painted aluminum (silver) on either black or white plastic film. The aluminum and silver mulches were evaluated with and without a white (fall) or black (spring) 25-cm-wide painted band in the bed center. Controls were the conventional white (fall) or black (spring) polyethylene mulches. Highest reflected energy (μmol·m–2·s–1) to the plants at 15 cm from the mulch surface was measured on the aluminum mulch with or without a white painted band. Lowest energy was reflected from the white or black controls and from silver on black mulches with or without a black painted band. Whitefly populations in the fall were lower (P ≤ 0.05) on the aluminum than on the silver mulches. In the spring, when whitefly populations were low, whiteflies were more numerous on the black control and silver on white, than on the aluminum mulches. In the fall seasons, the proportion of plants with symptoms of ToMoV transmitted by the silverleaf whitefly were higher on the controls than on the aluminum mulch. In the spring, the proportion of plants with symptoms was not affected by mulch treatments. Yields in the fall were similar with UV-reflective or white control mulches. In the spring, fruit size and marketable yields were greater (P ≤ 0.05) on plants with silver on white mulch than on the control black mulch.

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Claudio C. Pasian, Daniel K. Struve, and Richard K. Lindquist

The effectiveness of two application methods of the insecticide imidacloprid in controlling 1) melon aphids (Aphis gossypii Glover) on `Nob Hill' chrysanthemum (Dendranthema ×grandiflora Ramat) plants and 2) silverleaf whitefly (Bemisia argentifolii Bellows & Perring) on `Freedom Red' poinsettia (Euphorbia pulcherrima Wild.) were compared. Plants were grown in containers with their interior covered by a mixture of flat latex paint plus several concentrations of imidacloprid (0, 10, 21, 42, and 88 mg·L−1), or treated with a granular application of the insecticide (1% a.i.) according to label recommendations. All imidacloprid treatments effectively reduced aphid survival for at least 8 weeks. The two most effective treatments were the granular application (10 mg a.i.) and the 88-mg·L−1 treatment (0.26 mg a.i). All imidacloprid treatments effectively reduced whitefly nymph survival. The 42- and 88-mg·L−1 treatment and the granular application (1% a.i.) were equally effective in reducing nymph numbers in lower poinsettia leaves. None of the plants given treatments with paint exhibited any phytotoxicity symptoms. These results suggest the possibility of a new application method for systemic chemicals with the potential of reducing the release of chemicals to the environment. Paint and imidacloprid mixes are not described in any product label and cannot be legally used by growers. Chemical name used: 1-[(6-chloro-3-pyrimidil)-N-nitro-2-imidazolidinimine (imidacloprid)