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John L. Coffey, Alvin M. Simmons, B. Merle Shepard, Yaakov Tadmor, and Amnon Levi

important vectors of numerous plant viruses ( Kousik et al., 2012 ; Togni et al., 2010 ). The sweetpotato whitefly, Bemisia tabaci (Gennadius), is particularly abundant in warm habitats ( McKenzie et al., 2004 ) and feeds on over 1000 plant species ( Abd

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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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Alvin M. Simmons and Amnon Levi

The B-biotype sweetpotato whitefly, Bemisia tabaci (Gennadius), feeds on and damages numerous vegetable crops including watermelon (Citrullus sp.). Seven watermelon cultivars, a triploid line, and 16 U.S. Plant Introduction accessions (PIs) of C. lanatus var. lanatus; 10 PIs of C. lanatus var. citroides; and eight PIs of C. colocynthis, were evaluated for resistance to B. tabaci. Bioassays were based on nonpreference and performance of the whiteflies on the 42 Citrullus genotypes. Most of the watermelon cultivars and C. lanatus PIs tested were highly susceptible to whitefly infestation, while the C. colocynthis accessions exhibited whitefly resistance. Among the C. colocynthis accessions tested, PI 386015, PI 386018, and PI 386024 were most resistant to B. tabaci. This study identified useful sources of germplasm that can be used for the improvement of watermelon for resistance to whiteflies.

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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.

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Javier Farias-Larios, Mario Orozco-Santos, and Salvador Guzman-Gonzalez

Muskmelon (Cucumis melo L.) is the major cucurbit crop in the Colima state, Mexico. The use transparent plastic mulch continues to increase in that region for high production technology systems of muskmelon, and more recently floating rowcovers were introduced to protect cucurbits from insects (direct pests or vector of viruses) and to increase yield of cucurbit crops. During 1993, yield was evaluated of three cultivars of muskmelon (`Crushier', `Laguna', and `Durango') growing on transparent polyethylene mulch alone or with floating rowcover. The cultivar Crushier showed the higher yield 40 ton/ha (77% for export market), followed by `Durango' with 28.5 ton (77% for export quality) and `Laguna' with about 23 ton (only 40% of export fruit). There was no significant difference in yield between cultivar growth on transparent mulch plots alone and combined with floating rowcover. Also, floating rowcover excluded (until perfect flowering) beetles leafminers, sweetpotato whitefly, and aphids, reducing the use of insecticide by 50%.

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Chang-chi Chu*, Kai Umeda, Tian-Ye Chen, Alvin M. Simmons, and Thomas H. Henneberry

Insect traps are vital component of many entomological programs for detection and monitoring of insect populations. We equipped yellow (YC), blue (BC) sticky card (BC) with 530 nm lime green (LED-YC) and 470 nm blue (LED-BC) light-emitting diodes, respectively that increased trap catches of several insect pests. The LED-YC traps caught 1.3, 1.4, 1.8, and 4.8 times more adult greenhouse whitefly Trialeurodes vaporariorum (Westwood), sweetpotato whitefly Bemisia tabaci (Gennadius) biotype B, cotton aphids Gossypium hirsutum (L.), and fungus gnats Bradysia coprophila (Lintner), respectively, compared with standard YC traps. The LED-YC traps did not catch more Eretmocerus spp. than the standard YC traps. Eretmocerus spp. are important B. tabaci parasitoids used in greenhouse biological control programs. For whitefly control in greenhouse the 530 nm lime green LED equipped plastic cup trap designed by Chu et al. (2003) is the better choice than LED-YC trap because it catches few Eretmocerus spp. and Encarsia spp. whitefly parasitoids released for B. tabaci nymph control. The LED-BC traps caught 2.0-2.5 times more adult western flower thrips Franklinella occidentalis (Pergande) compared with the standard BC traps.

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J. Farias-Larios, M. Orozco, S. Guzman, and J. Perez

This work was conducted for evaluate the influence of clear and black polyethylene mulches, used alone or combined with floating rowcover (FRC) and plastic perforated microtunnels, on insect populations, growth and yield of muskmelon. Treatments evaluated were 1) clear plastic + FRC, 2) polyethylene perforated microtunnel, 3) clear plastic + polyethylene not perforated microtunnel, 4) black plastic + FRC, 5) clear plastic, 6) black polyethylene, 7) clear plastic + oil, and 8) bare soil. Aphids and sweetpotato whitefly adults and nymphs were completely excluded by floating rowcovers while the plots covered. The export and national quality fruit yield was major in the mulched beds in relation to control. Clear polyethylene mulch + FRC increased number of fruit and export marketable fruit of cantaloupe (45.2% and 44.8%) with respect to black plastic + FRC, respectively. It is proposed that, under tropical conditions and under high insect stress, mulches combined with floating rowcovers should be selected for their effects on insects in addition to their effects on melon yield. Polyethylene microtunnels were found not economical for cantaloupe production in western Mexico.

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Mario Orozco-Santos, Octavio Perez-Zamora, and Oscar Lopez-Arriaga

The effect of floating rowcover and transparent polyethylene mulch was evaluated on insect populations, virus disease control, yield, and growth of muskmelon (Cucumis melo L.) cv. Durango in a tropical region of Colima state, Mexico. Aphids (Aphis gossypii Glover and other species), sweetpotato whitefly (Bemisia tabaci Gennadius), beetles (Diabrotica spp.), and leafminer (Lyriormyza sativae Blanchard) were completely excluded by the floating rowcover while the plots were covered (until perfect flowering). Transparent mulch reduced aphids and whitefly populations, but did not show effect on leafminer infestation. The appearance of virus diseases of plants was delayed for 2 weeks by floating rowcover with respect to control (bare soil). Also, the transparent mulch reduced the virus incidence. The yield and number of fruit were positively influenced by floating rowcover and transparent mulch. Plot with transparent mulch combined with floating rowcover yielded nearly 4-fold higher (50.9 t·ha–1) than that plots with bare soil (13.1 t·ha–1). The yield from plots with floating row cover on bare soil was of 38.3 t·ha–1, while in the transparent mulch plots it was of 23.1 t·ha–1. The results of this work shows the beneficial effects of floating rowcover and transparent mulch in dry tropical conditions.

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James D. McCreight and William M. Wintermantel

Melon (Cucumis melo L.) is a fresh vegetable and dessert fruit that may also be cooked or dried, processed for juice and flavoring, and the seeds of which are a source of high-quality cooking oil and high protein seed meal. Melon production throughout many parts of the world is now threatened by the crinivirus Cucurbit yellow stunting disorder virus (CYSDV) in tropical and subtropical areas favorable to its whitefly vector. CYSDV is transmitted by the sweetpotato whitefly, Bemisia tabaci Gennadius, biotypes A, B, and Q. CYSDV first appeared on melon in the 1980s in the United Arab Emirates and emerged on melon in the Yuma, AZ, and Imperial Valley, CA, regions and western Mexico during the Fall season of 2006 followed by Florida in 2007. PI 313970, C. melo var. acidulus Naudin, a salad-type melon from India, expressed high-level resistance to CYSDV in Yuma and Imperial Valley in Fall 2006, but it was not immune; the virus was detected in asymptomatic plants. Inheritance of resistance to CYSDV in PI 313970 was studied in three naturally infected, replicated field tests in Imperial Valley during the Fall seasons of 2007 and 2008 and the Spring season of 2009. Resistance in PI 313970 was recessive: all F1 PI 313970 (PI) × susceptible ‘Top Mark’ (TM) and BCTM individuals were susceptible, and the F2 and BCPI segregated 3:1 and 1:1 susceptible to resistance, respectively. Frequency distributions of CYSDV symptom severity ratings suggested a single recessive gene in PI 313970 for resistance to CYSDV. PI 313970 was, however, observed to be variable for resistance; a few plants in each test expressed distinct symptoms of CYSDV infection and its frequency distributions overlapped those of ‘Top Mark’. This variation may represent genetic variation selectable for uniform reaction to infection by CYSDV or phenotypic variation in the resistant reaction. The genetic relationship between the genes for resistance to CYSDV in PI 313970 (recessive) and TGR-1551 (dominant) is not known.

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Kristen Young and Eileen A. Kabelka

McAuslane, H.J. 2007 Sweetpotato whitefly B biotype of silverleaf whitefly, Bemisia tabaci (Gennadius) or Bemisia argentifolii Bellows and Perring (Insecta: Hemiptera: Aleyrodidae) 25 Mar. 2009 < http://edis.ifas.ufl.edu/pdffiles/IN/IN28600