Tabaci Biotype Research Articles

Performance of Bemisia tabaci Biotype B on Soybean Genotypes.

Bemisia tabaci (Genn.) (Hemiptera: Aleyrodidae) has been recognized as an important pest of many agricultural systems including soybean [Glycine max (L.) Merrill] crops. As an alternative to chemical control, the use of resistant genotypes represents an important tool for integrated pest management (IPM). This study aimed to evaluate the biological development of Bemisia tabaci biotype B confined on 13 soybean genotypes under greenhouse conditions. Initially, the nymphal period, complete development period (egg-adult), and the viability of the silverleaf whitefly nymphs were evaluated in all genotypes. Then, four genotypes promising for resistance ('Jackson,' UX-2569-159, 'P98Y11,' and 'TMG132 RR') and a susceptible genotype (PI-227687) were selected for further assays, where two insect populations were compared: a first population from the initial rearing (cabbage plants) and another corresponding to insects previously reared out on the selected genotypes. In addition to the parameters evaluated in preliminary tests, we also determined the viability and incubation period of eggs. Moderate levels of resistance (antibiosis/antixenosis) to B. tabaci biotype B were found in three genotypes. 'P98Y11' and 'TMG132 RR' were less suitable for insect development, extending the development cycle, and UX-2569-159 caused high nymphal mortality. We did not observe a significant increase in the level of plant resistance by the use of previously stressed insects. This suggests that the evaluation of a single whitefly generation may be sufficient to make correct decisions on promising soybean genotypes.

Amblyseius tamatavensis Blommers (Acari: Phytoseiidae) a candidate for biological control of Bemisia tabaci (Gennadius) biotype B (Hemiptera: Aleyrodidae) in Brazil

ABSTRACTDespite the great diversity of the Brazilian fauna of phytoseiid mites, studies about their potential as biological control agents of the silverleaf whitefly, Bemisia tabaci (Gennadius) biotype B (Hemiptera: Aleyrodidae), have barely been initiated. The aim of this study was to evaluate the potential of a Brazilian population of Amblyseius tamatavensis Blommers (Acari: Phytoseiidae) to control B. tabaci. In the first part of this study, the biotic potential of the predator was evaluated at 28 ± 1°C, 80 ± 10% RH and 12 h of daily photoperiod, when offered eggs of B. tabaci as food. In the second, the performance of the predator as a control agent of B. tabaci was evaluated on bell pepper (Capsicum annuum L., Solanaceae) plants. Amblyseius tamatavensis completed immature development in 5.1 ± 0.1 days and laid an average of 1.0 ± 0.1 eggs/female/day in its lifetime; calculated intrinsic rate of population increase was 0.21 ± 0.01 female/female/day. Under laboratory conditions, the predator was able to significantly reduce the population density of B. tabaci when released on artificially infested bell pepper plants. Reductions between 60% and 80% of pest population were observed in comparison with densities on plants onto which the predator had not been released. The results suggested that A. tamatavensis is promising as a biological control agent of B. tabaci biotype B.

Biological aspects of Bemisia tabaci biotype B and the chemical causes of resistance in soybean genotypes

In Brazil, the silverleaf whitefly (SLW), Bemisia tabaci biotype B, is a serious soybean pest. SLW management is difficult and new control strategies, such as host–plant resistance, are required. Herein, we aimed to evaluate the biology of SLW, from eggs to adults, on seven soybean cultivars. The emergence of adult insects was monitored daily. Defense-related compounds were identified and quantified from the V3 to the V8 stages in SLW-infested and non-infested plants. The rates of emergence of SLW adults were lower in cultivars ‘IAC 17,’ ‘IAC 19’, and ‘IAC 24’ compared with the susceptible cultivar ‘IAC Holambra Stwart’. Rutin, genistin, genistein, and salicylic acid were identified and quantified in plant extracts. The rutin, genistin, and genistein levels decreased after SLW infestation. Rutin concentrations increased in infested plants of ‘IAC 17’ (V6) and ‘IAC 19’ (from V5 to V8). ‘Barreiras’ showed the highest genistein content in non-infested plants; from V5 growth stage, it was not detected in cultivars Doko (infested), Vencedora, ‘IAC 17’, and ‘IAC 24’ (non-infested). High levels of salicylic acid were observed in ‘IAC ‘19’-infested plants (at V3 and V5). The results suggest that rutin can be related to SLW adults’ emergence only when the feeding source was ‘IAC 19’. Consequently, further studies are needed to access the associated gene expressions and the effect of other secondary metabolites, mainly volatile compounds from SA pathway, including its consequences on feeding preference and mostly in relation to IAC cultivars.

English

The biological control of pests is essential for the use of Integrated Pest Management in agricultural environments. In this context, the objective of this study was to identify biological parameters and quantify the parasitism index of Encarsia hispida on Bemisia tabaci biotype B nymphs in cotton plants. The research was conducted at the Entomology Laboratory of the Federal University of Paraiba, in Areia, Paraiba State, Brazil. For the first bioassay, the treatments consisted of cotton cultivars BRS H8 and BRS Topazio to evaluate the biological development of the parasitoid in its host. In the second bioassay, these cultivars were used to assess the impact of the biological agent in a greenhouse. In the first experiment, there were only female parasitoids with longevity of 24.61 and 22.61 days in BRS H8 and BRS Topazio, respectively. However, they were not statistically different. The life cycle of the parasitoid (egg to adult) was 35.68 and 33.71 days in BRS H8 and BRS Topazio, respectively, and they did not differ from each other. In the second bioassay, there were E. hispida parasitism indexes around 34.33 and 29.63% in BRS H8 and BRS Topazio, respectively. The parasitoid E. hispida develops properly when the nymphs of the host were from the two cotton cultivars. The parasitoid E. hispida has an application potential in the biological control of B. tabaci biotype B whiteflies. Key words: Biological control, whitefly, biological parameters, parasitoid.

Suscetibilidade de adultos de Bemisia tabaci biótipo B a inseticidas

RESUMO: A associação de alguns vírus fitopatogênicos com seus vetores pode ou não alterar a ação do controle químico. Este trabalho objetivou avaliar a suscetibilidade de moscas-brancas virulíferas (com aquisição do begomovirus Tomato severe rugose virus, ToSRV) e avirulíferas (sem aquisição do ToSRV) aos principais inseticidas registrados para o seu controle na cultura do tomateiro. Foram realizados ensaios com plantas de tomateiro e discos foliares de feijão-de-porco. Os tratamentos foram arranjados em esquema fatorial de 7 (seis inseticidas + controle) e de 5 (quatro inseticidas + controle) x 2 {mosca-branca (MB) virulífera (V) ou avirulífera (AV)} e dispostos no delineamento em blocos ao acaso com seis e 25 repetições para o tomateiro e feijão-de-porco, respectivamente. Os inseticidas e concentrações avaliados foram: a) tomateiro: acefato (100 g), clotianidina (20 g), pimetrozina (40 g), piriproxifem (75 mL) e tiametoxam (20 g de i.a./100 L de calda) e diafentiurom (800 g de i.a./300 L de calda); b) feijão-de-porco: acefato (100 g), tiametoxam (20 g), pimetrozina (40 g de i.a./100 L) e diafentiurom (800 g de i.a./300 L de calda). Não houve diferença na suscetibilidade do vetor em razão de sua condição (V ou AV). Os inseticidas diafentiurom (87,68%±4,96) e tiametoxam (43,95%±9,43) proporcionaram maior mortalidade de MB no tomateiro, enquanto no feijão-de-porco diafentiurom (92,01%±2,68) e tiametoxam (86,39%±2,74) apresentaram desempenho similar. Diafentiurom foi o único inseticida que proporcionou controle satisfatório de B. tabaci em ambos os ensaios avaliados.

Survey of indigenous entomopathogenic fungi and evaluation of their pathogenicity against the carmine spider mite, Tetranychus cinnabarinus (Boisd.), and the whitefly, Bemisia tabaci (Genn.) biotype B.

The carmine spider mite, Tetranychus cinnabarinus, and the silverleaf whitefly, Bemisia tabaci, are serious pests of both field- and greenhouse-grown crops in south-western Turkey. Control of these pests has been heavily dependent upon chemical pesticides. The objectives of this study were to investigate the occurrence of indigenous entomopathogenic fungi (EPF) in field populations of T. cinnabarinus and B. tabaci, and to evaluate their pathogenicity against these pests. For this purpose, a survey of EPF isolated from field-collected samples of both pests was carried out in Antalya in 2010 and 2011 using the dilution plating method. Four indigenous Beauveria bassiana isolates (TUR1-B, TUR2-B, FIN1-B, FIN2-B) were recovered. In pathogenicity bioassays with T. cinnabarinus and B. tabaci biotype B, all the isolates tested were pathogenic to some of the biological stages of both pests to varying degrees. FIN1-B and TUR1-B caused mortalities of up to 50 and 45%, respectively, in adults of T. cinnabarinus, and of over 79 and 37%, respectively, in pupae of B. tabaci with 107 conidia mL-1 suspensions under laboratory conditions 10 days after inoculation. FIN2-B and TUR2-B had mortalities of 19.45 and 12.28%, respectively, in adults of T. cinnabarinus, and of 6.78 and 8.18%, respectively, in pupae of B. tabaci. None of the isolates had an effect on eggs of either species and larvae of the mite. Overall results suggest that isolates FIN1-B and TUR1-B have potential for management of T. cinnabarinus and B. tabaci. © 2016 Society of Chemical Industry.

RNA1-Independent Replication and GFP Expression from Tomato marchitez virus Isolate M Cloned cDNA.

Tomato marchitez virus (ToMarV; synonymous with Tomato apex necrosis virus) is a positive-strand RNA virus in the genus Torradovirus within the family Secoviridae. ToMarV is an emergent whitefly-transmitted virus that causes important diseases in tomato (Solanum lycopersicum) in Mexico. Here, the genome sequence of the ToMarV isolate M (ToMarV-M) was determined. We engineered full-length cDNA clones of the ToMarV-M genomic RNA (RNA1 and RNA2), separately, into a binary vector. Coinfiltration of both triggered systemic infections in Nicotiana benthamiana, tomato, and tomatillo (Physalis philadelphica) plants and recapitulated the biological activity of the wild-type virus. The viral progeny generated from tomato and tomatillo plants were transmissible by the whitefly Bemisia tabaci biotype B. Also, we assessed whether these infectious clones could be used for screening tomato cultivars for resistance to ToMarV and our results allowed us to differentiate resistant and susceptible tomato lines. We demonstrated that RNA1 of ToMarV-M is required for the replication of RNA2, and it can replicate independently of RNA2. From this, ToMarV-M RNA2 was used to express the green fluorescent protein in N. benthamiana plants, which allowed us to track cell-to-cell movement. The construction of full-length infectious cDNA clones of ToMarV-M provides an excellent tool to investigate virus-host-vector interactions and elucidate the functions of torradovirus-encoded proteins or the mechanisms of replication of torradovirus genomic RNA.

Development of an antibody-based diagnostic method for the identification of Bemisia tabaci biotype B

The whitefly Bemisia tabaci is a very destructive pest. B. tabaci is composed of various morphologically undistinguishable biotypes, among which biotypes B and Q, in particular, draw attention because of their wide distribution in Korea and differential potentials for insecticide resistance development. To develop a biotype-specific protein marker that can readily distinguishes biotypes B from other biotypes in the field, we established an ELISA protocol based on carboxylesterase 2 (COE2), which is more abundantly expressed in biotypes B compared with Q. Recombinant COE2 was expressed, purified and used for antibody construction. Polyclonal antibodies specific to B. tabaci COE2 [anti-COE2 pAb and deglycosylated anti-COE2 pAb (DG anti-COE2 pAb)] revealed a 3–9-fold higher reactivity to biotype B COE2 than biotype Q COE2 by Western blot and ELISA analyses. DG anti-COE2 pAb exhibited low non-specific activity, demonstrating its compatibility in diagnosing biotypes. Western blot and ELISA analyses determined that one of the 11 field populations examined was biotype B and the others were biotype Q, suggesting the saturation of biotype Q in Korea. DG anti-COE2 pAb discriminates B. tabaci biotypes B and Q with high specificity and accuracy and could be useful for the development of a B. tabaci biotype diagnosis kit for on-site field applications.

A Primary Screening and Applying of Plant Volatiles as Repellents to Control Whitefly Bemisia tabaci (Gennadius) on Tomato.

With the goal of finding a new way to reduce population densities of Bemisia tabaci biotype Q in greenhouses, seven repellent volatile chemicals and their combinations were screened. The mixture of DLCO (D-limonene, citral and olive oil (63:7:30)) had a better cost performance(SC50 = 22.59 mg/ml)to repel whiteflies from settling than the other mixtures or single chemicals. In the greenhouse, in both the choice test and the no-choice tests, the number of adult whiteflies that settled on 1% DLCO-treated tomato plants was significantly lower than those settling on the control plants for the different exposure periods (P < 0.01). In the choice test, the egg amount on the treated tomato plants was significantly lower (P < 0.01) than that on the control plants, but there was no significant difference (P > 0.05) between the number of eggs on treated and control plants in the no-choice test. Compared with the controls, 1% DLCO did not cause significantly statistic mortality rates (P > 0.05) out of different living stages of B. tabaci. The tests for evaluating the repellent efficacy, showed that a slow-releasing bottle containing the mixture had a period of efficacy of 29 days, and the application of this mixture plus a yellow board used as a push-pull strategy in the greenhouse was also effective.

Variation in susceptibility to insecticides in Bemisia tabaci biotype B fed on different hosts

Bemisia tabaci (Gennaadius) biotype B is one of themost important pests due to the number of hosts and economic lossesit produces. Its control is based on the application of chemicals,which has led to resistance problems. However, the host may also influencethe induction of resistance to pesticides. Therefore, the presentstudy evaluated the susceptibility of populations of B. tabaci biotypeB developed indifferent hosts to three insecticides belonging todifferent toxicological groups. Bemisia tabaci biotype B populationswere collected and reared in six different hosts (three crops and threeassociated weeds: Solanum lycopersicum, Solanum nigrum, Phaseolusvulgaris, Melampodium divaricatum, Cucurbita spp. and Heliotropiumangiospermun) in the state of Chiapas, Mexico. By using the dippingbioassay method with nymphs five- to eight-days-old, the CL50 wasdetermined. The higher values of bifenthrin were recorded on M.divaricatum and S. nigrum with 278.74 and 177.76 ppm, respectively.For imidacloprid, S. lycopersicum and S. nigrum recorded 179.59 and168.59 ppm, respectively. Finally for endosulfan, M. divaricatum andH. angiospermun registered values of 134.57 and 156.52 ppm, respectively.Therefore, the host affected the tolerance of Bemisia tabaci biotypeB to insecticides, primarily because of the induced resistance ofeach of the plant species that served as hosts, providing the ability todetoxify the various pesticides by using enzymes.

Identification and distribution of whiteflies (Hemiptera: Aleyrodidae) in tomato crops (Solanum lycopersicum) in Cundinamarca (Colombia)

The main purpose of this study was to determine the presence, distribution and characterization of whiteflies in thirteen tomato-crop producing municipalities in Cundinamarca (Colombia). Immature stages were collected and taken to the laboratory until adults emerged in order to establish their taxonomic identification. The mitochondrial regions were amplified with specific primers, which allowed for the allocation of biotypes in Bemisia tabaci. Genetic similarity analysis was performed in Trialeurodes vaporariorum using RAPD and phylogenetic analysis of the gene sequences mtCOI. The presence of T. vapo- rariorum was established in 100% of the municipalities visited and B. tabaci biotype B was detected in 32%, coexisting with T. vaporariorum. A wide distribution of T. vaporariorum was determined between 653 and 2,680 m a.s.l. B. tabaci was found between 653 and 1,940 m a.s.l distributed in four municipalities in the Sumapaz, lower Magdalena, and Rio Negro provinces. The RAPD analysis established high genetic similarity between the T. vaporariorum insects. The phylogenetic analysis did not allow for the resolution of structured groups inside the analyzed T. vaporariorum samples.

Acyl sugars and whitefly (Bemisia tabaci) resistance in segregating populations of tomato genotypes.

The wild tomato, Solanum pennellii, is an important source of resistance genes against tomato pests. This resistance is due to the presence of acyl sugars (AS), which are allelochemicals that have negative effects on arthropod pests. There are no commercially available tomato cultivars that exhibit significant levels of resistance to arthropod pests. Therefore, this study evaluated resistance to whitefly (Bemisia tabaci) in F2 and F2RC1 tomato genotypes with high AS levels from a cross between Solanum lycopersicum 'Redenção' and the S. pennellii accession, LA-716. Plants were exposed to B. tabaci biotype B at the pre-flowering stage. In both generations, there were significant, negative correlations between AS content and oviposition preference and nymph development. Whitefly exhibited a lower preference for oviposition and produced fewer nymphs in genotypes with high AS levels and the wild parent S. pennellii than in the low AS-level genotypes and Redenção cultivar, demonstrating that the breeding program was effective in transferring resistance to the F2 and F2RC1 generations. RVTA-2010-pl#31 and RVTA-2010-pl#94 in the F2 population are promising genotypes that produced materials with high AS levels in the F2RC1 generation (RVTA-2010-31-pl#177 and RVTA-2010-94-pl#381).

Lethal and Inhibitory Activities of Plant-Derived Essential Oils Against Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae) Biotype B in Tomato.

The silverleaf whitefly Bemisia tabaci (Genn.) biotype B (Hemiptera: Aleyrodidae) is one of the most severe tomato pests in the world. The damage caused by this insect may compromise up to 100% of crop production, and management of this pest has relied on spraying of synthetic insecticides. However, due to the environmental issues associated with this practice, alternative methods such as the use of botanical pesticides are now used as a strategy of integrated pest management (IPM). We evaluated the effects of essential oils of five plant species on B. tabaci biotype B in tomato and demonstrate that the essential oils (0.5%) of Piper callosum (PC-EO), Adenocalymma alliaceum (AA-EO), Pelargonium graveolens (PG-EO), and Plectranthus neochilus (PN-EO) inhibit the settlement and oviposition of B. tabaci biotype B adults in tomato plants. In fumigation tests, A. alliaceum (AA-EO) at 0.4 μL/L of air after 72 h and 0.1 μL/L of air after 6 h was the most effective against nymphs and adults of B. tabaci biotype B, respectively. The major chemical constituents of PC-EO were identified as being safrole (29.3%), α-pinene (19.2%), and β-pinene (14.3%), whereas diallyl trisulfide (66.9%) and diallyl disulfide (23.3%) were the major compounds identified in AA-EO. This is the first report on the reduction of oviposition by the use of P. callosum (PC-EO) and A. alliaceum (AA-EO). In addition, the fumigant effect of A. alliaceum (AA-EO) on nymphs and adults has also been reported here for the first time.

Intra-plant spatial interaction between Delphastus catalinae (Coleoptera: Coccinellidae) and Bemisia tabaci biotype B (Hemiptera: Aleyrodidae) and its effect on predation rates

Predictive models developed to provide recommendations about release rates and application methods for augmentative biological control often assume a constant probability of encounter between prey and predators within plants. We tested the assumed uniform probability of encounter between the coccinellid predator Delphastus catalinae and nymphs of the sweetpotato whitefly (SWF), Bemisia tabaci biotype B (Hemiptera: Aleyrodidae), on tomato plants. We hypothesized that D. catalinae non-random search patterns would result in a spatially non-uniform intra-plant probability of predator–prey interaction that ultimately affects predation rates. Tomato plants infested with a range of 14–50 SWF adult male–female pairs were placed individually in cages and D. catalinae individuals marked with different colors were released on them. The number of SWF nymphs before and after predator release and the predator visit frequency on each leaf and leaflet were recorded. We found that the distribution of predator visits and prey mortality is concentrated towards the mid and mid-lower region of the plant canopy and followed a different within-plant distribution than that of the SWF. The resulting non-uniform probability of prey encounter presumably affected the magnitude of predation rates and the shape of the functional response at the intra-plant scale. Results show that the assumption of uniform probability of encounter among leaves within a plant could be misleading at least for predictive models of the tomato-SWF-D. catalinae system, and that spatially explicit or individual-based modeling approaches could improve prediction accuracy.

Area-wide releases and evaluation of the parasitoidEretmocerus hayati(Hymenoptera:Aphelinidae) for silverleaf whitefly control

Silverleaf whitefly (SLW), Bemisia tabaci biotype B, is a major horticultural pest that costs Queensland vegetable growers millions of dollars in lost production and control measures each year. In the Bowen and Burdekin districts of North Queensland, the major cultivated SLW host crops are tomatoes, melons, green beans, pumpkins, eggplants, and cucumbers, which cover a total production area of approximately 6500 ha. Eretmocerus hayati, an effective SLW parasitoid, was imported into Australia by CSIRO in 2002 and released from quarantine in 2004. In 2006, DAFF established a mass-rearing unit for E. hayati at Bowen Research Station to provide E. hayati for release on vegetable farms within its SLW integrated pest management research program. A total of 1.3 million E. hayati were released over three seasons on 34 vegetable farms in the Bowen and Burdekin districts (October 2006 to December 2008). Post-release samplings were conducted across the release area over this time period with parasitism levels recorded in tomatoes, melons, beans, eggplants, pumpkins, and various SLW weed hosts. Sample data show that E. hayati established at most release sites as well as some non-release sites, indicating natural spread. Overall results from these three years of evaluation clearly demonstrated that E hayati releases played a significant role in SLW control. In most crops sampled, E hayati exerted between 30 and 80% parasitism. Even in regularly sprayed crops, such as tomato and eggplant, E. hayati was able to achieve an overall average parasitism of 45%.

Resistance of cotton genotypes with different leaf colour and trichome density to Bemisia tabaci biotype B

AbstractThe silverleaf whitefly (SLW), Bemisia tabaci biotype B, is considered one of the most serious pests in cotton worldwide. Its control is based on the use of pesticides, which are well‐known for their harmful effects on non‐target organisms and the environment. Here, we examined resistance of several cotton genotypes in terms of antixenosis and antibiosis against SLW. We also investigated the mechanisms of cotton genotypes involved in antixenosis against SLW by correlating with leaf trichome density and leaf colour parameters. In choice tests, we selected resistant cotton genotypes, Gossypium hirsutum palmeri, Aubum 56‐7, G. hirsutum morrilli, Mocó, Nu‐16 (B2 B3 B6)‐ 78/658, Paymaster 53‐816 and ‘IAC 23’, based on SLW oviposition and host preference. No‐choice tests with these genotypes confirmed antixenosis effect on SLW; however, no antibiosis resistance was detected in terms of developmental period and adult emergence rate. We found SLW oviposition preference was positively correlated with trichome density in the abaxial leaf surface, while adult host preference was mostly explained by high levels of green intensity of adaxial surface. Nevertheless, both SLW oviposition and host preference were negatively correlated with the lightness level of adaxial leaf surface. Probably, the underlying mechanism of cotton resistance is based on more than just these two parameters, but our study will contribute to selecting resistant cotton genotypes and helps to understand the mechanisms involved in cotton resistance against SLW. To our best knowledge, this is the first work showing that cotton leaf colour parameters are related to resistance against SLW.

Effectiveness of imidacloprid in combination with a root nitrogen fertilizer applied to tomato seedlings against Bemisia tabaci (Hemiptera: Aleyrodidae)

The whitefly Bemisia tabaci (biotype B) is a worldwide pest of vegetables and field crops. We tested the efficacy of imidacloprid (IM) with a root fertilizer ‘Root Feed (RF)’ (9% N, 7% Ca, 1.5% Mg and 0.1% B) sub-irrigated in the growing medium against the whitefly on tomato. Tomato seedlings (3–4 true leaves) were treated with 0, 3, 6 or 12 mg active ingredient (a.i.) seedling−1 of IM and with RF (0, 0.02, 0.04 or 0.08 ml seedling−1). The efficacy of 12 mg IM seedling−1 was further evaluated in the greenhouse for 60 days. The survival of B. tabaci adults, nymphs, and egg production were negatively affected by the treatments in a dosage-dependent manner. Treatment of 12 mg IM seedling−1 caused >60% adult and nymph mortality 50 days after treatment (DAT). The active ingredient of IM in tomato leaves also increased with the increase of IM dosage. The RF exhibited a limited effect on B. tabaci. However, the mortality of whitefly adults and nymphs treated with RF (0.02 or 0.04 ml seedling−1) positively interacted with IM, and was greater than IM alone. In the greenhouse, 12 mg IM seedling−1 greatly reduced the number of whitefly adults and increased the dry weight of the tomato plants at 30 DAT. In conclusion, application of 12 mg IM seedling−1 on tomato seedlings before transplanting effectively controled B. tabaci for up to 50 days, and the efficacy of IM combined with 0.02 ml RF seedling−1 performed even better. This could be a cost-effective method for managing B. tabaci on tomato and other vegetables.

Host-Specific Relationship Between Virus Titer and Whitefly Transmission of Cucurbit yellow stunting disorder virus.

Cucurbit yellow stunting disorder virus (CYSDV; genus Crinivirus, family Closteroviridae) was identified in the melon (Cucumis melo) production regions of the desert southwestern United States in fall 2006. It is now well established in the region, where it is transmitted efficiently by the sweet potato whitefly, Bemisia tabaci biotype B (MEAM1). In order to evaluate the spread and establishment of the virus, nearly all spring and fall cucurbit fields planted in the Imperial Valley of California from 2007 to 2009 were surveyed and representative plants were tested for CYSDV infection. Incidence of CYSDV in spring melon fields was initially low and limited to a small number of fields in 2007 but increased to 63% of fields by spring 2009. Virus incidence in fall melon fields was 100% in each year. These results suggested that the virus had become established in native vegetation, weeds, and other crop species, and represented an increasing threat to melon production in the southwestern United States. Therefore, a select set of weed and crop species which grow or are cultivated in the Imperial Valley were evaluated as CYSDV reservoir hosts. For each species, we determined the capacity of CYSDV to accumulate, the relationship between virus titer in these source plants and transmission by whiteflies, as well as subsequent accumulation in inoculated cucurbit plants. Among these hosts, there was considerable variation in virus accumulation and transmission rates. Cucurbit hosts had the highest CYSDV titers, were efficient sources for virus acquisition, and showed a positive correlation between titer in source plants and transmission. Noncucurbit hosts had significantly lower CYSDV titers and varied in their capacity to serve as sources for transmission. CYSDV titers in some noncucurbit source plants, specifically common bean (Phaseolus vulgaris) and shepherd's purse (Capsella bursa-pastoris), were not positively correlated with transmission, demonstrating that additional environmental, physical, or biochemical factors were involved. These results demonstrate that multiple factors influence the efficiency with which a host plant species will be a reservoir for vector transmission of virus to crops.

Preference of Bemisia tabaci biotype B on zucchini squash and buckwheat and the effect of Delphastus catalinae on whitefly populations.

Zucchini squash, Cucurbita pepo L., is an important vegetable crop in Florida. Physiological disorders and insect-transmitted diseases are major problems for squash growers in semi-tropical regions around the world. Bemisia tabaci (Gennadius) biotype B is a significant whitefly pest and is largely responsible for transmitting viruses and causing physiological disorders in squash. Several studies have shown that whitefly populations are reduced when crops are interplanted with non-host cover crops or mulches. The aim of the present study was to determine how the presence of buckwheat, Fagopyrum esculentum Moench, and a key predator, Delphastus catalinae (Horn), affect whitefly colonization on squash. Whitefly densities were higher on squash than on buckwheat. The introduction of D. catalinae on squash significantly reduced whitefly populations. Overall, there were higher densities of D. catalinae on squash where the whitefly pest was more concentrated compared with buckwheat. The study provided preliminary evidence that D. catalinae, when used in conjunction with buckwheat as a living mulch, may aid in reducing whiteflies in squash. This greenhouse experiment highlights the need to investigate a multitactic approach of intercropping buckwheat with squash and the incorporation of D. catalinae in the field to manage populations of whiteflies and whitefly-transmitted diseases. © 2015 Society of Chemical Industry.

Effects of culture conditions on conidial production of the sweet potato whitefly pathogenic fungus Isaria javanica

Sweet potato whitefly, Bemisia tabaci biotype Q has been recognized as one of the most destructive insect pests worldwide because of increased resistance to some insecticide groups. To develop an alternative control agent, the effects of different culture conditions such as fermentation methods, culture temperatures, initial inoculum concentrations, substrates and medium supplements on the conidial production of the isolate Isaria javanica Pf04 were assessed. The results demonstrated that conidia of the isolate could be economically produced by single-phase solid state fermentation on barley substrate at 25 °C with 108 conidia/g of initial substrate concentrations. Using optimal conditions, the maximum conidial production obtained was 3.5 × 109 conidia/g dry substrate after 15 d of cultivation. The conidia, which were produced on barley alone and barley with 5% additives of silkworm powder and moth larvae, were virulent against second instar nymphs of whitefly, providing ≥90% mortality.