Bemisia Tabaci Biotype Research Articles

Viral complexity of tomatoes yellow mosaic and leaf curl diseases in lowland and highland areas

AbstractYellow mosaic and leaf curl diseases caused by whitefly‐transmitted begomo virus genera are important problems in tomato (Solanum lycopersicon L.) production in Indonesia, particularly on Java Island. The aims of this survey are to assess the percentages of disease incidence (DI) and disease severity index (DSI), evaluate the spread and complexity of begomovirus and crinivirus infections responsible for yellow mosaic and leaf curl diseases in tomato plants, and identify the species of whitefly insect vectors and their cryptic biotypes in tomato production centers located on Java Island, Indonesia. A total of 43 locations in East, Central, and West Java were surveyed during the dry season from July 2022 to September 2022. Disease incidence and severity were determined by observing 200 samples of tomato plants from five points at each location, with 40 plants per point of land. A total of 116 whitefly samples in microtubes and 215 symptomatic leaf samples were collected. The genus begomovirus and crinivirus infecting tomato were identified by PCR and RT‐PCR using genus‐specific primers. Similarly, whitefly species and their cryptic biotypes were identified by PCR using MCoI gene‐specific primers. Results showed that DI and DSI remarkably differed between the lowlands (66%–89%) and highlands (33%–62%) in the provinces of Central Java and West Java. Furthermore, PCR analysis of 215 infected tomato showing the symptoms of yellow mosaic and curly leaf revealed that three begomoviruses, one crinivirus and their mixed combination both begomoviruses, one crinivirus has been detected in all the samples. Similarly, the whitefly insect vector Bemisia tabaci biotype Q was identified in all areas, whereas Trialeurodes vaporariorum was found only in the East Java and Java highlands, respectively.

Research on Drawing Attention to Overlooked Viruses in Plant Viruses Causing Yellowing-Type Symptoms in Cucurbitaceae

A single-stranded, positive-sense plant RNA virus called the Cucurbit chlorotic yellows virus (CCYV, Crinivirus, Closteroviridae) is comprised of RNA1 and RNA2. It is semipersistently transmitted by the whitefly Bemisia tabaci biotypes MEAM1 and MED. In 2004, CCYV was discovered on melon plants in Japan. Several other cucurbit species, as well as a range of non-species, were subsequently reported from countries such as Saudi Arabia, California, Israel, Taiwan, Sudan, Lebanon, Iran, Greece, Türkiye, Egypt, Spain, and China. Whitefly populations are frequently encountered in cucurbit cultivating areas. Virus plant diseases attributed to whiteflies are common in squash cultivation in the open field and greenhouses in Türkiye, especially in cucumbers and squash. Cucumber vein yellowing virus (CVYV), Cucurbit yellow stunting disorder virus (CYSDV), Tomato leaf curl New Delhi virus (ToLCNDV), Squash vein-yellowing virus (SqVYV) are the leading virus diseases transmitted by Bemisia tabaci. Symptoms caused specifically by these viral diseases are of the yellowing type, although they differ as intervascular yellowing, yellowing of old or young leaves, and upward curling. Besides these viruses, CCYV, a problem in cucurbits, is carried by whitefly like others, causes yellowing type symptoms, and its first record in cucumber was reported in 2017 in Türkiye. However, this virus is ignored in the production of cucurbits, it is a problem in production areas. There are major viruses cause similar symptoms with the presence of the Cucumber chlorotic yellows virus is overlooked in the symptomatological observation. In this study, we tried to reveal the difference of CCYV, which is encountered in cucurbit growing areas in Antalya and whose presence was detected by RT-PCR, from other viruses and emphasized its importance as a virus that should be considered in classical breeding studies.

Synthesis, characterization, and evaluation of derivatives from cardanol as repellents/pesticides agents of Liriomyza sativae (Diptera: Agromyzidae) and Bemisia tabaci (Hemiptera: Aleyrodidae) on melon plants

Hydrogenated cardanol derivatives were evaluated as potentially active insecticides/repellent agents against insect pests such as Liriomyza sativae (Diptera: Agromyzidae) and Bemisia tabaci biotype B (Hemiptera: Aleyrodidae). Benzoylation, acetylation, and methylation were made on the hydrogenated cardanol aromatic ring to synthesize active ingredients with potential insecticide action. Nuclear magnetic resonance spectra (13C and 1H NMR) and infrared (IR) proposed the chemical elucidation of the products. The production of melon seedlings was made and each synthesized products, benzoylated 3-pentadecylphenol, acetylated 3-pentadecylphenol, and methylated 3-pentadecylphenol were applied to seedlings by glass sprayer. Phytotoxicity evaluations were carried out, noting that all the plants showed burnt leaves except for concentration of 1% which the leaves remained healthy look. The insecticidal efficacy as well as the repellent and dissuasive effects were evaluated by a completely randomized design (DIC) and a randomized complete block design (DBCA) with six treatments, five and four replicates respectively. The compounds derived from cardanol did not present insecticidal activity in DBCA for L. sativae; however, they had a noticeable effect on oviposition index (IPO). Ovicidal effect and nymphal mortality only were found for B. tabaci by methylated 3-pentadecylphenol and Mospilan® in terms of dissuasion and oviposition effects in the two bioassays evaluated and, methylated 3-pentadecyl showed a similar behavior as the effect of Abamectin® on the confinement test, with 53.5% - 65.4% repellence of adults, an important data to emphasize that the products synthesized from cardanol are promising in preventing the pests attack such as L. sativae and, B. tabaci.

Development of BC3F2 Tomato Genotypes with Arthropod Resistance Introgressed from Solanum habrochaites var. hirsutum (PI127826)

Arthropod pests are among the biggest problems faced in tomato production worldwide. To overcome the losses caused by these pests, one of the most sustainable and economical strategies is the use of resistance introgressed from wild species. We aimed to develop BC3F2 tomato genotypes with high levels of zingiberene (ZGB) and resistance to whitefly (Bemisia tabaci biotype B), South American tomato pinworm (Tuta absoluta), and the two-spotted spider mite (Tatranychus urticae), from the wild accession of Solanum habrochaites var. hirsutum (accession PI127826). The quantification of ZGB in 520 BC3F2 genotypes and in the parentals yielded the selection of five genotypes with high ZGB content and three with low ZGB content, which were then infested with B. tabaci, T. absolute, and T. urticae. In these eight genotypes and in the parents, the types and amounts of trichomes on the leaves were determined. Additionally, molecular markers were used to identify the genotypes with a higher recurrent genome recovery. The results confirmed the transfer of resistance from S. habrochaites to the BC3F2 genotypes and showed that this resistance seems to be directly related to high concentrations of ZGB and the presence of type IV trichomes.

Clonostachys rosea: Production by Submerged Culture and Bioactivity Against Sclerotinia sclerotiorum and Bemisia tabaci.

Among the prospective biocontrol agents, the saprophytic filamentous fungus Clonostachys rosea is an excellent necrotrophic mycoparasite of numerous plant pathogenic fungi. However, its commercial development has been hampered by mass production difficulties during solid-state fermentation. Conversely, the submerged liquid fermentation shortens the cultivation time while increasing yields of fungal propagules. However, this method has been overlooked for C. rosea. In this work, we investigated the impact of liquid pre-culture inoculum on the spore production by the two-stage fermentation process using rice grains in comparison to the traditional solid-state fermentation. In parallel, we studied the submerged cultivation of C. rosea by manipulating carbon-to-nitrogen (C:N) ratio and nitrogen source, with the further optimization of spore production in a benchtop bioreactor. Additional bioassays included assessing the bioactivity of water-dispersible microgranules (that contained a submerged conidia) against the whitefly (Bemisia tabaci biotype B) and Sclerotinia sclerotiorum (causal agent of the white mold). Our results showed a maximum concentration of 1.1 × 109 conidia/g-dry-matter after 7 days of cultivation by two-stage fermentation process. The liquid fermentation yielded 1.4 × 109 submerged conidia/ml after 7 days using a medium with a 50:1 C:N ratio, and it also induced the production of microsclerotia (MS) up to 1.35 × 104/ml within 6 days with 10:1 C:N ratio; both media were supplemented with dextrose monohydrate and soybean meal. The fermentation batches carried out in a benchtop bioreactor with medium 50:1 C:N ratio and amended with soybean meal rendered a production peak on the fourth day, corresponding to 1.11 × 109 conidia/ml and 4.35 × 108 colony forming units (CFU)/ml. Following air-drying, the conidia production from air-dried microgranules of C. rosea biomass was estimated at 3.4 × 1010 conidia/g of formulated product upon re-hydration for 7 days. Both submerged conidia and MS of C. rosea inhibited 100% germination of S. sclerotiorum sclerotia by direct parasitism. The air-dried submerged conidia exhibited a suppressive activity on sclerotia (88% mycoparasitism) and early whitefly nymphs (76.2% mortality) that rendered LC50 values of 3.2 × 104 CFU/g soil and 1.5 × 107 CFU/ml, respectively. Therefore, the submerged liquid culture of C. rosea may offer a feasible and cost-effective method for its large-scale production, alleviating critical constraints to their commercial use while providing an additional tool for management of B. tabaci and S. sclerotiorum.

Infestação de mosca branca (Hemiptera: Aleyrodidae) biótipo B em cultivares de soja no polo Paragominas grãos, Pará

The aim of this study was to evaluate the infestation of whitefly Bemisia tabaci (Hemiptera: Aleyrodidae) biotype B in 19 soybean cultivars in the Paragominas grain pole, 2017/18 crop year. The cultivars selected for planting are based on those normally planted in the Paragominas grain complex and research institutions. The sampling of the incidence of B. tabaci biotype B started on the 7th day after plant emergence (DAE), and the number of eggs, nymphs and adults was recorded weekly, that is, 10 small leaves of the plant evaluated in each plot, until the end of the crop cycle. The number of eggs and nymphs of B. tabaci type B was recorded in the laboratory with the aid of a stereoscopic microscope and adults made in loco. The values obtained were transformed into (x + 0.5)1/2, for normalization of these and submitted to analysis of variance (ANOVA) by the F test (Fisher). Tukey at 5% probability. The cultivar M 8644 IPRO showed the lowest infestation of eggs of B. tabaci and RK 6813RR was the most infested; for nymphs, the highest infestation was observed in cultivar RK 6813RR while in BRS 9383 IPRO there was less infestation; the highest number of whitefly adults was observed in the cultivar P 99R03, and M 8808 had the lowest average of adult insects and the period of highest incidence of whitefly was in the egg stage, in the first seven days after emergence (DAE); the period of 7 DAE was the most infested by adults and whitefly eggs; 35 and 42 DAE more infested by pest nymphs; meteorological factors mean temperature, rainfall and relative humidity do not showed influence on whitefly infestation, and relative humidity explained only 35.59% for incidence of eggs in soybean and the occurrence of adults explained 81% for the same parameter (eggs).

Análise espaço-temporal de mosca-branca Bemisia tabaci (Genn., 1889) biótipo B (Hemiptera: Aleyrodidae) na cultura da soja, no município de Paragominas - Pará

The objective of this study is to evaluate the progress of whitefly Bemisia tabaci biotype B infestation during the crops of 2015, 2016 and 2017, to identify between crops studied in which they increased or decreased infestation and in which month the infestation was more representative, to identify among the cultivars which one or which are most susceptible to the attack and to map the areas of incidence of the whitefly. The research to obtain the data was carried out in the municipality of Paragominas and the data were obtained from Defense Agency of the State of Pará according to the methodology based on a model predefined by the agency. Climatic data on rainfall (mm) for crops were obtained through a database of the Brazilian Agricultural Research Corporation meteorological station. For statistical analysis of data, a database was built into Microsoft Excel spreadsheets. Data were analyzed through regression analysis and compared by the Tukey and Scott & Knott test. For the preparation of the whitefly infestation maps, the Spatial Analyst extension in the ArcGIS 10.1 software was used. In the studied area, the month of April is the one with the highest incidence of the pest, the crop of 2017 presented greater infestation, the cultivar P99R03 RR was the most susceptible to the attack of whitefly, and the cultivars P98Y51 RR and FT PGM, were more resistant to whitefly (B. tabaci) biotype B than the other cultivars.

Resistance of cotton genotypes to silverleaf whitefly (Bemisia tabaci [GENNADIUS] Biotype B)

Silverleaf whitefly (Bemisia tabaci biotype B) has caused significant damage, year after year, and can be considered one of the major pests responsible for the increase in use of insecticides in cotton. This research aimed to evaluate the biology and preference for oviposition and feeding of Bemisia tabaci biotype B in wild cotton genotypes. The experiments were conducted at the Experimental Farm of the Mato Grosso do Sul State University, Cassilândia-MS, from March 24th to May 13th, 2017. The treatments were composed of the following genotypes:, APGO 01 and APGO 02 (Gossypium barbadense),TEX 1116 and TEX 1964 (G. hirsutum) and G. arboreum acquired in EMBRAPA germplasm, BRS 269 (standard cultivar/control) widely grown in Brazil. The infestations were carried out on plants 25 days after emergence in a no-choice test and at 42 days for the free-choice test, the cages they were infested with 100 whitefly adults per plant. The number of eggs per leaf, the density of trichomes, the viability of nymphs and the duration of the juvenile phases, in days, on the youngest leaf in the upper third of the plant were evaluated. The averages for cotton genotypes were grouped by the Scott Knott test at the 5% probability level. Low preference for oviposition of B. tabaci biotype B on genotypes APGO 01 and APGO 02 was observed in the no-choice test. The genotypes APGO 01, APGO 02, and BRS 269 were the least preferred for oviposition and had the lowest density of trichomes at 43 days after emergence in 24 hours after infestation. It was verified that in the genotypes APGO 01 and APGO 02, there was an increase in the density of trichomes, and consequently, there was an increase in the number of eggs per cm² in 48 hours after infestation. After 72 hours of infestation, a positive and significant correlation (r = 0687**) was observed between the number of eggs per cm² and the density of trichomes. A positive correlation was observed between the density of trichomes and the preference of oviposition. A negative effect of glandular trichomes and preference for oviposition was observed for APGO 02.. Resistance by antibiosis and / or non-preference for feeding in the genotypes APGO 01, APGO 02 and G. arboreum were observed for prolonging the development of the insect in the juvenile/nymph phase.

Silverleaf whitefly-resistant common beans: an investigation of antibiosis and/or antixenosis

ABSTRACT The silverleaf whitefly Bemisia tabaci biotype B is one of the most important sucking pests of common bean, which causes severe damages and requires frequently synthetic insecticides spraying to protect crop productivity. The use of common bean cultivars resistant to whitefly attack is an important strategy within an integrated pest management (IPM) program. The biological development of B. tabaci confined to 17 bean genotypes was evaluated in greenhouse trials to verify the occurrence of antibiosis. Whitefly adults were released on plants of these genotypes to oviposit, afterward the incubation period of eggs, nymphal period, complete development period (egg–adult), and viability of the silverleaf whitefly nymphs were recorded. As main results, genotype CHIP 300 prolonged the developmental period from egg to adult (~10 days) and BRS Estilo, Arcelina 4, IPR Garca, Tybata, CHIP 300, IPR Eldorado, H96A102-1-1-1-52, SCS-202-Guara and CHIB 06 caused nymphal mortality, suggesting high levels of antibiosis and/or antixenosis. These genotypes may be helpful in common bean breeding programs aimed at developing commercial cultivars resistant to B. tabaci biotype B.

The Influence of Visual and Olfactory Cues in Host Selection for Bemisia tabaci Biotype B in the Presence or Absence of Tomato Yellow Leaf Curl Virus

The silverleaf whitefly, Bemisia tabaci, is one of the most destructive agricultural pests in the world, vectoring a large number of devastating viruses, including Tomato Yellow Leaf Curl Virus (TYLCV). When selecting a host, B. tabaci is primarily influenced by a range of visual and olfactory cues. Therefore, elucidating how such cues become modified in the presence of whitefly-vectored begomoviruses is critical to better understanding the epidemiology of many economically important diseases. The goal of this study was to determine how both visual and odor cues interact in the presence of TYLCV. In Y-tube olfactometer assays, whiteflies were submitted to a range of isolated visual and olfactory cues to determine behavioral changes. B. tabaci choices were then compared to both stimuli combined in the presence or absence of TYLCV. Under visual stimuli only, B. tabaci exhibited a visual attraction to the color yellow, TYLCV-infected tomato leaves, and TYLCV-infected tomato volatiles. Attraction was the strongest overall when both visual and olfactory cues from TYLCV-symptomatic tomato plants were combined, as opposed to a single isolated cue. These results highlight the importance of both sensory stimuli during B. tabaci host selection in the presence of an associated begomovirus.

First Report of Cucurbit Chlorotic Yellows Virus Infecting Cucumber and Zucchini in Algeria

This work was supported by the Spanish Ministerio de Ciencia, Innovacion y Universidades, cofunded with FEDER funds (project nos. AGL2017-85563-C2-1-R and RTA2017-00061-0O3-03 [INIA]) and the programa para grupos de investigacion de excelencia from the Conselleria d'Educacio, Investigacio, Cultura i Esport, (Generalitat Valenciana) (Prometeo Program 2017/078). A. Kheireddine thanks the Erasmus+ Programme of the European Union for her mobility project (KA107 2018-20). C. Saez is a recipient of a predoctoral fellowship from Generalitat Valenciana, cofunded by the Operational Program of the European Social Fund (FSECV 2014-2020) (grant no. ACIF/2016/188). Plant Dis. 104: 1264, 2020; published online as https://doi.org/10.1094/PDIS-10-19-2091PDN.Accepted for publication 19 December 2019.

Intervalo de aplicação do Azamax® sobre pragas sugadoras do algodoeiro e seus inimigos naturais

O algodoeiro é atacado por pragas sugadoras que têm sido controladas com inseticidas químicos, causando problemas à saúde do aplicador e poluição do meio ambiente, mas o uso de produtos botânicos como o nim vem sendo estudado nos últimos anos. O efeito do intervalo de aplicação do inseticida Azamax® foi avaliado sobre pragas sugadoras e seus inimigos naturais. O estudo foi conduzido na Embrapa Algodão em Barbalha, Ceará. O Azamax® foi aplicado em dois intervalos de aplicação (sete e 15 dias), em cobertura total das plantas com pulverizador costal manual com bico cônico. As amostragens foram realizadas semanalmente em 40 plantas por parcela dos 13 aos 90 dias após a emergência das plantas. Pulgão, tripes e a cochonilha foram amostrados nos ponteiros das plantas, a mosca branca na folha do 5º nó e o ácaro vermelho na parte mediana, enquanto os inimigos naturais, nos locais onde as pragas foram amostradas. O Azamax® aplicado aos sete e 15 dias reduz a taxa de infestação do pulgão Aphis gossypii, assim como, a mosca branca Bemisia tabaci biótipo B e a cochonilha Planococcus minor, não tendo efeito no ácaro vermelho, para os dois períodos de aplicação. Não foi observado efeito direto do Azamax® sobre a população dos inimigos naturais das principais pragas sugadoras do algodoeiro.

Potential of Entomopathogenic Fungi as Biological Control Agents of Whitefly (Bemisia tabaci biotype B) (Genn.) (Hemiptera: Aleyrodidae)

The efficiency of isolates from entomopathogenic fungus Beauveria bassiana, Lecanicillium muscarium and Metarhizium rileyi in the control of eggs and third-instar nymphs of whitefly, Bemisia tabaci biotype B, was evaluated by pathogenicity and virulence tests, under laboratory conditions. For the pathogenicity tests, five leaflets of bean (Phaseolus vulgaris) plants containing 20 nymphs or 20 eggs of B. tabaci biotype B were used. The leaflets were immersed in suspension containing a concentration of 108 conidia/ml of each fungus isolate. Nymph mortality and egg viability were evaluated after seven days. The isolates that caused nymph mortality and egg viability above 80% were submitted to virulence tests, in order to estimate the lethal concentration (LC50) of each isolate. All isolates were pathogenic to eggs and third-instar nymphs of B. tabaci Biotype B. JAB07 of B. bassiana and LCMAP3790 of L. muscarium isolates presented the best results, with nymphs mortality of 96.68 ± 2.25% and 97.74 ± 1.56%, respectively. Additionally, JAB07 was the most virulent isolate, both for eggs and third-instar nymphs, with LC50 estimated of 0.012 and 0.006 × 103 conidia/ml, respectively. We suggest, future field trials are required in order to analyze the real efficiency of this isolate in the control of eggs and nymphs of B. tabaci biotype B in field conditions.

SELECTIVITY OF INSECTICIDES TO Encarsia hispida (Hymenoptera: Aphelinidae)

ABSTRACT The use of non-selective insecticides in agricultural production can reduce or eliminate biological agents that regulate insects that are undesirable to humans in production processes. Here, the toxicity of synthetic products on the parasitoid Encarsia hispida was evaluated, the host of which is the whitefly, Bemisia tabaci biotype B, found on cotton plants. The study was carried out using bioassays, in a completely randomized design in a factorial scheme. Pupae and adults of E. hispida were used in the bioassays, which had been sprayed with various chemicals (thiamethoxam, deltamethrin, imidacloprid, and pyriproxyfen) at different concentrations (1.0 g L-1, 1.0 mL L-1, 4.0 mL L-1, and 2.5 mL L-1). The control treatment was distilled water. Chemicals were topically placed in the dorsal region of the tegument of 1 and 3-day old pupae. Then, between 1 and 15-days of emergence of adult parasitoids, residual contact bioassay were used to determine the toxicity of the insecticides. The insecticides thiamethoxam and imidacloprid were harmless to the pupal stage of E. hispida, but were harmful to the adult stage. The insecticides deltamethrin and pyriproxyfen were harmful to both pupal and adult stages of E. hispida.

Elicitor-Induced Defense Response in Soybean Plants Challenged by Bemisia tabaci

The whitefly, Bemisia tabaci Biotype B (Hemiptera: Aleyrodidae), is considered one of the world’s major agricultural pest groups, attacking a wide range of crop hosts and causing considerable crop loss. Understanding the interactions between whiteflies and host plants promotes the development of novel strategies for controlling whiteflies. This study aimed to evaluate the biochemical alterations caused by induced resistance in soybean plants, challenged by B. tabaci. The experiment was performed at the Federal University of Technology, Parana. Soybean seeds (cv. BRS 284) were sown in polyethylene pots in the greenhouse. The elicitors sprayed on the soybean leaves were: acibenzolar-S-Methyl (ASM-0.005%); Salicylic Acid (SA-2Mm); foliar phosphite (ULTRA K®-0.004%); Chitosan (CH-1%); and silicon (SI-0.25%); whilst the control group was sprayed with distilled water. Plants were infested with 50 adult whiteflies in the cages that were released after applying the treatments. At 0, 24, 48 and 96 hours after the beginning of the experiment, biochemical analyses of total proteins and the activity of the phenylalanine ammonia-lyase (PAL), peroxidases (PO), phenolic compounds, chitinase, and β-1,3-glucanase were made. The results showed that the application of elicitors increased the route of the phenylpropanoids with the activation of PAL and formation of phenolic compounds. It was also verified the activation of pathogenicity-related enzymes such as peroxidases and chitinase.

Genome-Wide Profiling of Cardinium-Responsive MicroRNAs in the Exotic Whitefly, Bemisia tabaci (Gennadius) Biotype Q.

Although the bacterial symbiont Cardinium has profound effects on the ecological adaptation of its host, the whitefly Bemisia tabaci (Gennadius) biotype Q (hereafter referred to as B. tabaci Q), the molecular mechanism underlying interactions between these two organisms is not yet fully understood. In this study, sRNA libraries were constructed, amplified, and sequenced for Cardinium-infected (C+) and uninfected (C∗−) B. tabaci Q with identical genetic backgrounds. Subsequently, the genes targeted by the differentially expressed miRNAs were predicted by integrating the B. tabaci Q genome data. A total of 125 known and 100 novel miRNAs were identified, among which 23 significant differentially expressed miRNAs were identified in both libraries. It is noteworthy that an analysis of target genes showed that Cardinium-responsive miRNA-regulated genes were functional in apoptosis, reproduction, development, immune response, thermotolerance and insecticide resistance. GO and KEGG pathway analysis revealed that some miRNA-target genes are closely associated with energy metabolism. A major finding of this study was the identification of several miRNAs that may be involved in physiological processes in response to environmental stress, i.e., insecticides and high temperatures. This information will provide a foundation to help further elucidate the functions of Cardinium in B. tabaci Q.

Weeds associated with cotton crop and hosting whitefly

ABSTRACT: The whitefly can be hosted by weeds and cause damage to cotton crops. The objective of this work was to identify which species of weeds among the floristic compositions occurring in the cotton crop are hosts of whiteflies (Bemisia tabaci biotype B). Bi-weekly evaluations were performed in a cotton area (FM 975 WS) in Sinop, Mato Grosso, Brazil, during the reproductive phase of the crop. An inventory square (0.25 m side) was randomly cast 15 times between the cotton rows. The weeds were cut close to the ground, conditioned and taken to the laboratory to identify the family and species, and to quantify the eggs and nymphs of whiteflies. Eleven families were detected, with the most frequent being Amaranthaceae (16.67%), Convolvulaceae (12.5%), Rubiaceae (12.5%) and Poaceae (12.5%). The most frequent species were Amaranthus spp. (13.79%) and Alternanthera tenella, Ipomea spp., Richardia brasiliensis and Eleusine indica, with 10.34% each. From the 15 collected species, the presence of whitefly eggs or nymphs was only not observed in Portulaca oleracea and E. indica. The highest incidence of B. tabaci occurred in Euphorbia heterophylla. The occurrence of these species should be monitored, so that the whitefly population does not interfere in the cotton fiber quality.

Insecticidal and inhibitory effects of dihydrobenzofuran neolignans on Bemisia tabaci

Bemisia tabaci (Gennadius) biotype B (Hemiptera: Aleyrodidae) has developed resistance to numerous conventional insecticides, which has led us to investigate the toxicity of ten dihydrobenzofuran- (DBN) and benzofuran-type (BN) neolignans structurally related to conocarpan against second instar B. tabaci nymphs. At concentrations higher than 5 mg/L, most of the tested compounds killed 100% of B. tabaci biotype B nymphs 6 days after spraying. The contact toxicity of compounds 2 ((±)-trans-dehydrodiferulate dimethyl ester), 3 ((±)-4-O-methyl-trans-dehydrodiferulate dimethyl ester), 5 ((±)-4-O-acetyl-trans-dehydrodiferulate dimethyl ester), 6 ((±)-7′,8′-dihydro-trans-dehydrodicoumarate dimethyl ester), 8 ((±)-4-O-methyl-7′,8′-dihydro-trans-dehydrodiferulate dimethyl ester), and 10 ((±)-7′,8′-dihydro-7,8-dehydro-trans-dehydrodicoumarate dimethyl ester) was higher than the contact toxicity of pyriproxyfen at a concentration of 75 mg/L, which was used as positive control. Repellent (compounds 2 and 7 ((±)-7′,8′-dihydro-trans-dehydrodiferulate dimethyl ester) and oviposition deterrent (compounds 2, 3, and 7) effects were observed for adult whiteflies exposed to leaves sprayed with DBNs for 24 and 48 h, respectively. These results suggest that DBNs have potential application in the development of effective pest management compounds.

Host preference by two Bemisia tabaci biotypes in Costa Rica and Florida

Despite being a polyphagous insect, Bemisia tabaci (Gennadius) shows a marked preference for certain hosts, which in turn may depend upon the particular whitefly biotype involved. The objective of this research was to compare preference towards a selected group of host crops, by two biotypes of Bemisia tabaci , New World in Costa Rica, and MEAM1 in Florida. Therefore, choice experiments were conducted in greenhouses both at Turrialba (Costa Rica) and Immokalee (Florida), in April and June-September, 1998, respectively. The same crops and varieties were exposed to the New World and MEAM1 biotypes, which predominate in each one of these locations, respectively. Host species included green beans ( Phaseolus vulgaris ), bell pepper ( Capsicum annuum ), eggplant ( Solanum melongena ), cucumber ( Cucumis sativus ), tobacco ( Nicotiana tabacum ) and tomato ( Solanum lycopersicum ). Seedlings were transplanted in large pots, which were distributed on the greenhouse floor. B. tabaci adults were released in the late afternoon, and the number of individuals on each plant was recorded the next morning. In Turrialba, tobacco was greatly preferred by New World biotype adults, followed by eggplant, whereas the MEAM1 biotype in Florida preferred green beans and eggplant. Thus, both biotypes showed a strong and significant preference for eggplant, which suggests its possible utility as a trap crop.

Preferencia de hospedantes por dos biotipos de Bemisia tabaci en Costa Rica y Florida

Despite being a polyphagous insect, Bemisia tabaci (Gennadius) shows a marked preference for certain hosts, which in turn may depend upon the particular whitefly biotype involved. The objective of this research was to compare preference towards a selected group of host crops, by two biotypes of Bemisia tabaci, New World in Costa Rica, and MEAM1 in Florida. Therefore, choice experiments were conducted in greenhouses both at Turrialba (Costa Rica) and Immokalee (Florida), in April and June-September, 1998, respectively. The same crops and varieties were exposed to the New World and MEAM1 biotypes, which predominate in each one of these locations, respectively. Host species included green beans (Phaseolus vulgaris), bell pepper (Capsicum annuum), eggplant (Solanum melongena), cucumber (Cucumis sativus), tobacco (Nicotiana tabacum) and tomato (Solanum lycopersicum). Seedlings were transplanted in large pots, which were distributed on the greenhouse floor. B. tabaci adults were released in the late afternoon, and the number of individuals on each plant was recorded the next morning. In Turrialba, tobacco was greatly preferred by New World biotype adults, followed by eggplant, whereas the MEAM1 biotype in Florida preferred green beans and eggplant. Thus, both biotypes showed a strong and significant preference for eggplant, which suggests its possible utility as a trap crop.