Tabaci Biotype Research Articles

Baseline Susceptibility ofBemisia tabaci, Biotype B (Hemiptera: Aleyrodidae) to Chlorantraniliprole in Southern Florida

ABSTRACT Chlorantraniliprole 200 mg ai L-1 (Rynaxypyr® 200 SC) is the first xylem systemic insecticide in the new chemistry class, anthranilic diamides. A laboratory systemic bioassay using cut stems of cotton seedlings was developed to quantify the baseline susceptibility of the sweetpotato whitefly, Bemisia tabaci (Gennadius) biotype B, to chlorantraniliprole. Bioassays were conducted for a susceptible laboratory colony and for 11 field populations collected in 2008 and 2009 in Southern Florida. Baseline data of the susceptible colony (targeting first instar nymphs with initial exposure at the egg stage) for chlorantraniliprole in 2008 and 2009, revealed a pooled LC50 and slope values of 0.033 mg ai L-1 and 1.186, correspondingly. With the implementation of the stabilization period in the bioassay method in 2009, the susceptible colony generated LC50 and slope values of 0.182 mg ai L-1 and 0.972, respectively. LC50 and slope values of field collected populations (targeting nymphs as above) ranged from 0...

New Synthesis: Investigating Mutualisms in Virus-Vector Interactions

Most plant viruses depend on insect vectors for transmission from one host to another. Aphids are the most notable among these insect vectors, transmitting more than half of all described virus species. Virus transmission ranges from simple attachment to the tip of the aphid stylets tomore complicated interactions that involve ingestion of the viruses, passage through the haemolymph to the salivary glands, and subsequent injection into a new host plant. Plant viruses, which clearly benefit from being transported to new hosts, generally do not harm their aphid vectors. To the contrary, the frequent observation of improved aphid growth on virus-infected plants suggests that these interactions can be mutualistic, benefitting both the viruses and their insect vectors. Several studies have demonstrated that plant viruses manipulate plants, thus increasing the number of inoculated insect vectors. This can be accomplished by attracting aphids to infected plants and/or changing plant physiology in a manner that improves aphid reproduction. Increased fecundity and developmental rate of aphids on virus-infected plantswill result in greater dispersal of viruliferous aphids tonewhosts as host plant qualitydeclines andaphids becomecrowded.Crowding also induces the formation of alate aphids, which provide longer-distance virus transmission. Virus-vector interactions can be mediated indirectly by virusinduced increases in plant nutritive value, suppression of plant defense responses, or some combination of these effects. Recent publications provide evidence for active manipulation of herbivore defenses by plant-pathogenic viruses. For instance, the 2b silencing suppressor protein of cucumber mosaic virus compromises jasmonate-regulated insect defenses and improves performance of Myzus persicae (green peach aphid; Lewsey et al. 2010). Similarly, pathogenicity factor βC1, which is encoded in the betasatellite of tomato yellow leaf curl China virus, suppresses jasmonate-mediated defenses and improves growth of Bemisia tabaci (silverleaf whitefly) on Nicotiana tabacum (Zhang et al. 2012). Because arthropod-mediated transmission benefits plant viruses, and there is an apparent reproductive benefit for the insects, in many cases, the virus-vector interaction can be considered a mutualism. For instance, individual aphids that transport viruses to a new host plant would benefit from rapid virus-mediated suppression of plantdefenses. In suchasituation, it clearlywouldbeadvantageous foraphids topick up and transmit viruses. It is also possible that, by transmitting plant-pathogenic viruses, hemipteran insects can expand their ranges to include normally unsuitable host plants.Our ownunpublishedobservations show that, ifNicotiana benthamiana is infected with turnip mosaic virus, the survival of newly arrivingMyzus persicae (green peach aphids) increases from 30% to 90%. Similarly,N. tabacum is a poor host for some B. tabaci biotypes, but whitefly performance is improved greatly through prior begomovirus infection (Zhang et al. 2012). If an insect vector arriving at an uninfected plant benefits from being viruliferous, this suggests that such insects will benefit by acquiring viruses prior to moving to new host plants. For instance, aphids could be feeding from virus-infected tissue in a targetedmanner, or specifically selecting virus-infected cells as they are probing to reach the phloem. When an aphid punctures a cell infected with cauliflower mosaic virus, the virus rearranges itself rapidly, thereby promoting attachment to the aphid stylets (Martiniere et al. 2013). It has been suggested that this is due to viral recognition of some component of the plant defense signaling pathway that is triggered by aphid feeing. However, it also is possible that the aphids acquire viruses by actively manipulating plant cellular metabolism. Conversely, when a viruliferous aphid settles on a new plant, its feeding success may be promoted if viruses are deposited in a cellular location that allows rapid replication and thereby suppression of plant defenses. To date, most research on the molecular mechanisms of virus-vector interactions has focused on studying host plant manipulation by viruses that promotes aphid performance. However, aphids and other insect vectors also may promote virus transmission by altering plant physiology. To initiate progress in this research area, it will be necessary to identify conditions under which there are immediate benefits to insect vectors carrying viruses to newhost plants. Furthermore, future investigation of these ecologically important but relatively under-investigated three-way interactions should include a greater focus on discovering behavioral and molecular mechanisms by which insect vectors can actively manipulate plant-virus interactions for their own benefit.

Monitoring Changes in <I>Bemisia tabaci</I> (Hemiptera: Aleyrodidae) Susceptibility to Neonicotinoid Insecticides in Arizona and California

Bemisia tabaci (Gennadius) biotype B is a highly prolific and polyphagous whitefly that established in much of North America during the 1980s. Neonicotinoid insecticides have been fundamental in regaining control over outbreak populations of B. tabaci, but resistance threatens their sustainability. Susceptibility of B. tabaci in the southwestern United States to four neonicotinoid insecticides varied considerably across populations within each year over a 3 yr period. Using a variability ratio of highest LC50 to lowest LC50 in field-collected whitefly adults from Arizona and California, the ranges of LC50(s) across all tests within compounds were highest to imidacloprid and lowest to thiamethoxam. Patterns of susceptibility were similar among all four neonicotinoid insecticides, but the greater variability in responses to imidacloprid and significantly higher LC50(s) attained indicated higher resistance levels to imidacloprid in all field populations. Further evidence of differential toxicities of neonicotinoids was observed in multiple tests of dinotefuran against imidacloprid-resistant lab strains that yielded significant differences in the LC50(s) of dinotefuran and imidacloprid in simultaneous bioassays. To test the possibility that resistance expression in field-collected insects was sometimes masked by stressful conditions, field strains cultured in a greenhouse without insecticide exposure produced significantly higher LC50(s) to all neonicotinoids compared with LC50(s) attained directly from the field. In harsh climates such as the American southwest, resistance expression in field-collected test insects may be strongly influenced by environmental stresses such as high temperatures, overcrowding, and declining host plant quality.

The virulence of entomopathogenic fungi against Bemisia tabaci biotype B (Hemiptera: Aleyrodidae) and their conidial production using solid substrate fermentation

The virulence of five isolates of Beauveria bassiana, five of Isaria fumosorosea and four of Lecanicillium muscarium from Brazil was determined on whitefly Bemisia tabaci biotype B lifestages on bean leaves under laboratory conditions. The conidial yield (on cadavers or parboiled rice), surface hydrophobicity and enzyme activity were also determined. The isolates of B. bassiana and I. fumosorosea were the most virulent against nymphs (71–86% mortality within 8d), with LT50 values ranging from 3 to 4d after treatment with 107conidia/mL (150conidia/mm2). Spore production on nymph cadavers reached 4–8×105conidia/insect. The L. muscarium isolates demonstrated low virulence toward nymphs. After spraying eggs with 1×108conidia/mL (1674conidia/mm2) of B. bassiana and I. fumosorosea, most nymphs hatched, but then 40–70% of these nymphs were infected by indirect exposure of conidia on the leaves. Adults exposed to treated leaf disks (150conidia/mm2) were more susceptible to I. fumosorosea than to B. bassiana. The enzyme activity (Pr1) and the relative conidial surface hydrophobicity were not correlated with any virulence parameter measured for either B. bassiana or I. fumosorosea. In addition, the highest conidial yields on parboiled rice using solid-state fermentation (4.9–11.4×109conidia/g) were achieved by isolates of I. fumosorosea CG1228 and B. bassiana CG1229. I. fumosorosea CG1228 was highly virulent against whitefly nymphs and adults as well as attained high spore production on insect cadavers and parboiled rice. Our results indicate that I. fumosorosea CG1228 has desirable attributes for the development of a mycoinsecticide against B. tabaci biotype B.

Comparison of the host-handling behavior of Eretmocerus mundus on Bemisia tabaci B biotype, Q biotype and Trialeurodes vaporariorum

Host-handling behaviors of Eretmocerus mundus (Mercet) (Hymenoptera: Aphelinidae) toward first to fourth instar nymphs of the Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) B and Q biotypes and of Trialeurodes vaporariorum (Westwood) (Homoptera: Aleyrodidae) were compared under laboratory conditions. The host acceptance rates differed among host stages but not among host species or biotypes. In all host species and biotypes, the parasitoids stopped their host-handling behavior before oviposition more often with older hosts. The total host-handling time was longer for the fourth instars than for younger instars, mainly due to the longer oviposition times and probing times. E. mundus showed marking behavior for the B. tabaci B and Q biotypes, but not for T. vaporariorum. In conclusion, E. mundus could parasitize all whitefly biotypes and species used in this study, but both B. tabaci biotypes were more suitable hosts than T. vaporariorum. The younger instars were good oviposition targets in all hosts.

Physalis angulata: A New Natural Host of Tomato chlorosis virus in Brazil.

Tomato chlorosis virus (ToCV) and Tomato infectious chlorosis virus (TICV) are the two Solanaceae-infecting Crinivirus species (family Closteroviridae) of worldwide importance. In Brazil, only ToCV has been detected under natural conditions infecting tomato (Solanum lycopersicum), sweet pepper (Capsicum annuum), and potato (S. tuberosum), causing foliar chlorosis (1, 3). However, there are no formal reports of alternative weed hosts of ToCV. During crop surveys in Capão Bonito, São Paulo State, Brazil (May 2011), a high incidence (above 20%) of plants of the weed, cut leaf ground cherry (Physalis angulata L.) growing around and within a tomato (cv. Alambra) field with a high incidence of ToCV, were found displaying interveinal chlorosis on the lower leaves, similar to those induced by magnesium deficiency. The P. angulata plants also had high populations of whiteflies (Bemisia tabaci biotype B). Ten leaf samples were taken from individual symptomatic ground cherry and tomato plants for Crinivirus testing. Total nucleic acids were extracted from 2 g of symptomatic and healthy leaf tissues of both hosts using Whatman CF-11 cellulose (Sigma) as described (4). The purified double stranded RNA samples were used as a template in reverse transcription (RT)-PCR using specific primers targeting the p22 gene region in the genome of ToCV (2). Only the 566-bp ToCV-specific amplicon was detected in all field samples. Sequences of samples from the P. angulata and tomato cDNA amplicons were identical to each other (GenBank Accession No. JX187514) and they showed 99% identity with the ToCV RNA 1 from a tomato isolate from Florida (AY903447). This confirmed the initial hypothesis of Crinivirus infection. Cuttings of symptomatic P. angulata plants were also obtained and kept in a voile cage under greenhouse conditions together with healthy seedlings of P. angulata and the begomovirus-resistant inbred tomato line 'TX-468RG.' Fifty aviruliferous B. tabaci (biotype B) adults were placed in the cage. Similar symptoms were observed 50 days after exposure to whiteflies in both hosts. Transmission to P. angulata and to 'TX-468RG' was also confirmed via sequencing of ToCV-specific amplicon, demonstrating the infectivity of the isolate to both hosts. To our knowledge, this is the first report of P. angulata as a natural host of ToCV in Brazil. This weed is often present in the commercial fields because of its natural tolerance to herbicides currently used in tomato production. The ToCV-infected P. angulata plants might serve as alternative sources of inoculum for the surrounding tomato fields. The environmental persistence of P. angulata combined with its intense whitefly colonization might allow a year-round ToCV exposure for tomato plants under field conditions in this major production area of Brazil where at least 25 million tomato plants are cultivated annually.

Formation of Stylet Sheaths in āere (in air) from Eight Species of Phytophagous Hemipterans from Six Families (Suborders: Auchenorrhyncha and Sternorrhyncha)

Stylet sheath formation is a common feature among phytophagous hemipterans. These sheaths are considered essential to promote a successful feeding event. Stylet sheath compositions are largely unknown and their mode of solidification remains to be elucidated. This report demonstrates the formation and solidification of in āere (in air) produced stylet sheaths by six hemipteran families: Diaphorina citri (Psyllidae, Asian citrus psyllid), Aphis nerii (Aphididae, oleander/milkweed aphid), Toxoptera citricida (Aphididae, brown citrus aphid), Aphis gossypii (Aphididae, cotton melon aphid), Bemisia tabaci biotype B (Aleyrodidae, whitefly), Homalodisca vitripennis (Cicadellidae, glassy-winged sharpshooter), Ferrisia virgata (Pseudococcidae, striped mealybug), and Protopulvinaria pyriformis (Coccidae, pyriform scale). Examination of in āere produced stylet sheaths by confocal and scanning electron microscopy shows a common morphology of an initial flange laid down on the surface of the membrane followed by continuous hollow core structures with sequentially stacked hardened bulbous droplets. Single and multi-branched sheaths were common, whereas mealybug and scale insects typically produced multi-branched sheaths. Micrographs of the in āere formed flanges indicate flange sealing upon stylet bundle extraction in D. citri and the aphids, while the B. tabaci whitefly and H. vitripennis glassy-winged sharpshooter flanges remain unsealed. Structural similarity of in āere sheaths are apparent in stylet sheaths formed in planta, in artificial diets, or in water. The use of ‘Solvy’, a dissolvable membrane, for intact stylet sheath isolation is reported. These observations illustrate for the first time this mode of stylet sheath synthesis adding to the understanding of stylet sheath formation in phytophagous hemipterans and providing tools for future use in structural and compositional analysis.

Tomato Spotted Wilt Virus Infection Reduces the Fitness of a Nonvector Herbivore on Pepper

Plant pathogens and insect herbivores often share hosts under natural conditions. Hence, pathogen-induced changes in a host plant can affect the herbivore and vice versa. Even though plant viruses are ubiquitous in the field, little is known about plant-mediated interactions between viruses and nonvector herbivores. Here we tested whether the performance of the sweet potato whitefly, Bemisia tabaci (Gennadius) biotype Q, was altered when raised on pepper infected with Tomato spotted wilt virus (TSWV). TSWV infection reduced B. tabaci fecundity and longevity and increased B. tabaci developmental time but did not affect the insect's survival or female body lengths. Our results demonstrate that TSWV infection can decrease the fitness of B. tabaci biotype Q on pepper plants.

Brazilian begomovirus populations are highly recombinant, rapidly evolving, and segregated based on geographical location.

The incidence of begomovirus infections in crop plants sharply increased in Brazil during the 1990s following the introduction of the invasive B biotype of the whitefly vector, Bemisia tabaci. It is believed that this biotype transmitted begomoviruses from noncultivated plants to crop species with greater efficiency than indigenous B. tabaci biotypes. Either through rapid host adaptation or selection pressure in genetically diverse populations of noncultivated hosts, over the past 20 years various previously unknown begomovirus species have became progressively more prevalent in cultivated species such as tomato. Here we assess the genetic structure of begomovirus populations infecting tomatoes and noncultivated hosts in southeastern Brazil. Between 2005 and 2010, we sampled and sequenced 126 DNA-A and 58 DNA-B full-length begomovirus components. We detected nine begomovirus species in tomatoes and eight in the noncultivated host samples, with four species common to both tomatoes and noncultivated hosts. Like many begomoviruses, most species are obvious interspecies recombinants. Furthermore, species identified in tomato have probable parental viruses from noncultivated hosts. While the population structures of five well-sampled viral species all displayed geographical subdivision, a noncultivated host-infecting virus was more genetically variable than the four predominantly tomato-infecting viruses.

Multiple forms of vector manipulation by a plant-infecting virus: Bemisia tabaci and tomato yellow leaf curl virus.

For many insect-vectored plant viruses, the relationship between feeding behavior and vector competence may prove integral to an understanding of the epidemiology of the resulting plant disease. While plant-infecting viruses are well known to change host plant physiology in a way that makes them more attractive to vectors, viral manipulation of the vectors themselves has only recently been reported. Previous research suggested that the rapid spread of Tomato yellow leaf curl virus (TYLCV) throughout China has been facilitated by its primary vector, the whitefly Bemisia tabaci. We conducted two experiments testing the impact of TYLCV infection of the host plant (tomato) and vector (B. tabaci biotypes B and Q) on whitefly feeding behavior. Whiteflies of biotypes B and Q both appeared to find TYLCV-infected plants more attractive, probing them more quickly and having a greater number of feeding bouts; this did not, however, alter the total time spent feeding. Viruliferous whiteflies fed more readily than uninfected whiteflies and spent more time salivating into sieve tube elements. Because vector salivation is essential for viral transmission, this virally mediated alteration of behavior should provide TYLCV a direct fitness benefit. This is the first report of such manipulation by a nonpropagative virus that belongs to an exclusively plant-infecting family of viruses (Geminiviridae). In the context of previous research showing that feeding on TYLCV-infected plants harms biotype B but helps biotype Q, the fact that both biotypes were equally affected by TYLCV also suggests that the virus may alter the biotype B-biotype Q competitive interaction in favor of biotype Q.

Role of allelochemicals and trichome density in the resistance of tomato to whitefly

In Brazil, the tomato is cultivated in almost all geographic regions even though its yield is significantly reduced by pests and diseases. Among these pests and diseases, whitefly is a major problem that causes direct and indirect damage due to its role in transmission of geminiviruses. The aim of the present study was to compare the degree of resistance to the silverleaf whitefly of tomato plant lines rich in acyl sugars (AS), zingiberene (ZGB), and 2-tridecanone (2-TD) and to establish whether selection for strains with higher densities of glandular trichomes promotes sufficient resistance to this insect pest. The investigated lines were developed by performing back-crossings in tomato (Solanum lycopersicum) from the interspecific crossing of S. lycopersicum x S. habrochaites var. glabratum 'PI 134417'. Lines rich in AS, ZGB, and 2-TD were tested for their levels of resistance to B. tabaci biotype B. Two tomato plant lines (TOM-584 and TOM-679) with normal AS levels and one wild specimen (PI 134417) with high 2-TD content were used as controls. TOM-687, ZGB-703, and TOM-622 were less preferred by B. tabaci for oviposition, and nymphs exhibited a poorer survival rate on those plant lines than on the susceptible controls, TOM-584 and TOM-679. Allelochemical-rich lines exhibited pest resistance, whereas the controls did not, and the allelochemical-rich lines did not differ significantly from each other in the level of resistance. The results show that the development of tomato plant lines rich in 2-TD, ZGB and AS is an effective option for indirect selection for resistance to B. tabaci biotype B. All lines selected based on high trichome density except for BPX-365F-751-05-01-03 exhibited fewer nymphs than the susceptible controls, indicating that selection for more glandular trichomes was generally effective in promoting increased resistance to the silverleaf white flay.

Response of Bemisia tabaci Genn. (Hemiptera: Aleyrodidae) Biotype B to Genotypes of Pepper Capsicum annuum (Solanales: Solanaceae)

Bemisia tabaci Genn. biotype B is a widely distributed plant pest that represents one of the major constraints for horticultural crop production. The purpose of the present work was to evaluate the oviposition preference, survivorship, and development of B. tabaci biotype B on semi-cultivated genotypes of Capsicum annuum from southeast Mexico. In free-choice experiments to evaluate the oviposition preference, lower number of eggs laid by B. tabaci biotype B was observed in the genotypes Maax and Xcat´ik relative to that in the commercial genotype Parado. Egg hatchability was significantly lower in Pico Paloma, Bolita, Blanco, Chawa, Payaso, and Xcat´ik than in the rest of the genotypes, including the commercial genotype Jalapeño. Likewise, survivorship of nymphs was significantly lower in Pico Paloma, Bolita, and Blanco than in the remaining genotypes. Nymph developmental time and the period of development from egg to adult were the shortest in Amaxito. Therefore, sources of resistance to B. tabaci biotype B by antibiosis (accumulation of plant defense compounds) might be found in the semi-cultivated genotypes Pico Paloma, Bolita, and Blanco.

Current Scenario ofTomato Yellow Leaf Curl Virus(TYLCV) and its Possible Management: A Review

Tomato yellow leaf curl virus is a major limiting threat to tomato agriculture in many parts of the world especially tropical and sub-tropical regions. The severe outbreak of the disease is associated with whitefly B. tabaci biotypes especially biotype B. The severity and high disease incidence reduce yield to zero leading to catastrophic losses in tomato production. TYLCV was first reported from Israel in 1939 but currently it has rapidly spread in most parts of the world and damage to tomato crops attributed to virus species of the TYLCV group has been reported from the Middle and Far East, Africa, Europe, Caribbean Islands, Central America and South America. Typical symptoms of the disease in tomato are yellow (chlorotic) leaf edges, upward leaf cupping, leaf mottling, reduced leaf size, and flower drop. TYLCV can have a severe impact on tomato production. Plants infected at an early stage won't bear fruit and their growth will be severely stunted. Identification of TYLCV based only on symptomatology is unreliable, because similar symptoms can be caused by other viruses or different growing conditions. Sanitation is very important for preventing the migration of whitefly adults and the spread of TYLCV from one localized place to other places. Rogue tomato or other infected plants with early symptoms of TYLCV can be removed from fields by placing infected-looking plants in plastic bags immediately at the beginning season. Maintenance good weed control in the field and surrounding areas are quite helpful to minimize the incidence and severity of disease. Tomato fields should be cleaned up immediately after harvest and the residues should be destroyed after harvest to reduce whitefly migration. Foliar systemic insecticide sprays at an interval of 2-3 weeks could help in the prevention of whitefly population which could ultimately reduce the high disease incidence.

The effects of some botanical insecticides and pymetrozine on life table parameters of silver leaf whitefly Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae)

The objective of this research was to assess the effects of extracts of two medicinal plant species: Allium sativum (Linn) and Calotropis procera (Aiton), and a formulation containing azadirachtin on life table parameters of silver leaf whitefly (SLW), Bemisia tabaci biotype B (Gennadius) (Hemiptera: Aleyrodidae), grown on greenhouse tomato plants. The effects were compared to that of pymetrozine, a synthetic insecticide. Bioassays were carried out in a greenhouse under controlled conditions of 27 ? 2?C, R.H. of 55 ? 5% and 16:8 h (L:D) photo period. All treatments significantly affected the survivorship and fertility of SLW female adults, reducing the net reproduction rate, mean generation time and intrinsic rate of increase of this insect. The net reproductive rate [R0] values for the populations treated with garlic extract, milkweed extract, pymetrozine, azadirachtin, control for extracts (ethanol + distilled water) and control for pesticides (distilled water) were 23.58, 19.32, 10.78, 8.23, 49.66, 57.55; the intrinsic rate of increases [rm] were 0.134, 0.139, 0.110, 0.090, 0.177, 0.178; the mean generation times [T] were 23.49, 21.23, 21.66, 23.50, 22.06, 22.69; the doubling times [DT] were 5.14, 4.95, 6.27, 7.56, 3.91, 3.87, and the finite rates of increase [?] were 1.144, 1.149, 1.116, 1.094, 1.193, 1.195, respectively. Azadirachtin had the highest effect on the life table parameters of SLW. Our findings indicated that, although herbal extracts were not effective as much as the chemical insecticides, they can be effective in pest control. Therefore, they are suitable choices for replacing chemical insecticides and for alternative use with azadirachtin in SLW IPM program.

Isaria poprawskii sp. nov. (Hypocreales: Cordycipitaceae), a new entomopathogenic fungus from Texas affecting sweet potato whitefly

Isaria poprawskii is described as a new entomopathogenic species similar to Isaria javanica (= Paecilomyces javanicus). It was discovered on the sweet potato whitefly, Bemisia tabaci biotype B in the Lower Rio Grande Valley of Texas (LRGV), USA. Morphological and DNA examinations indicated the distinctness of I. poprawskii from the ex-type isolate of I. javanica. I. poprawskii produced light yellow young colonies to darker yellow with a grayish-violet center to a taupe or a brownish-gray mature conidial mass; conidia hyaline, one-celled, 3.9 (2.9–4.6) μm long × 1.6 (1.4–2.1) μm wide; colored synnemata, but I. javanica ex-type produced white colony, hyaline conidia and no synnemata. A phylogenetic position of I. poprawskii was inferred by a nucleotide sequence analysis of β-tubulin along with standard β-tubulin sequences from GenBank. Fifteen unsequenced isolates, including eight from the LRGV, were investigated. The analysis confirmed that I. poprawskii could be recovered from LRGV fields, and that both I. javanica and I. poprawskii are present in the LRGV in sympatry. I. poprawskii was shown to be closely related to I. javanica; however, it formed its own unique clade, thus confirming its status as a new fungal species.

Resistance of melon cultivars to Bemisia tabaci biotype B

The silverleaf whitefly, Bemisia tabaci biotype B, is currently one of the most important pests of melon, causing direct and indirect damage to plants, and significantly reducing production in the field. Due to the need for alternative methods of chemical control in melon crops, the melon cultivars AF-646, AF-682, Don Luis, Frevo, Jangada, Nilo, Vereda, Amarelo Ouro and Hales Best were assessed at field, greenhouse, and laboratory trials for resistance to whitefly B. tabaci biotype B. In general, 'Hales Best' and 'Amarelo Ouro' were the most resistant, showing oviposition non-preference against whitefly. The trichome density is associated with the variation in oviposition on the cultivars and should be further investigated in future work. These results may be helpful in melon breeding programs, focusing on plant resistance to B. tabaci biotype B.

Multi-Generation Life Tables of <I>Bemisia tabaci</I> (Gennadius) Biotype B (Hemiptera: Aleyrodidae) Under High-Temperature Stress

Much attention has been focused on insects' ability to survive long-term high-temperature stress and on their resulting population distributions under global warming. In this study, life tables of the whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) biotype B, were collected over five consecutive generations at 27, 31, and 35°C and for one generation at 37°C. At 37°C, the intrinsic rate of increase (r) and the net reproductive rate (r(0)) of the whitefly were 0.0383 d(-1) and 2.8 offspring, respectively. These results demonstrate that the lethal high temperature for B. tabaci is >37°C. At 27°C, neither r(0) nor r decreased over the generations studied. However, both of these values decreased over time at 31 and 35°C, and the decrease was more evident at 35°C. Our results on the ability of B. tabaci biotype B to survive long-term high-temperature stress are important for understanding its population distribution under global warming.

Reduction in the Fitness of <I>Bemisia tabaci</I> Fed on Three Previously Infested Tomato Genotypes Differing in the Jasmonic Acid Pathway

The effect of previous infestation (preconditioning) by the whitefly Bemisia tabaci (Gennadius) biotype B on the population fitness of subsequent infestations that fed on three isogenic tomato genotypes (wild-type [Wt], a jasmonic acid [JA] defense-enhanced genotype [35S], and a JA-deficient genotype [spr2]) was examined. We tested the hypotheses that whiteflies fed on preconditioned tomatoes (Solanum lycopersicum L.) would have reduced fitness and that the effect would be mediated via the JA-dependent systemic plant defense pathway. Preconditioning by the whitefly resulted in decreased levels of soluble sugars and free amino acids and increased salicylic acid (SA), total phenolics, and condensed tannins for all three genotypes. The durations of the larval and pupal stages were prolonged in whiteflies fed on the preconditioned plants compared with those that fed on control plants. Furthermore, preconditioning resulted in reduced fecundity and intrinsic rate of increase (r(m)) of the whiteflies that subsequently fed on the three tomato genotypes. Whiteflies were more likely to feed and deposit eggs on control plants than on preconditioned plants. Our results indicate that preconditioning induced decreases in leaf nutrients and increased induction of an SA based defense that degraded the quality of the substrate as evidenced by an increased developmental time and reduced fecundity of whiteflies that subsequently fed on them.

New experimental tools for bioassays with whitefly in laboratory

The objective of this work was to develop an experimental kit for assessments of repellency, deterrence for oviposition, and insecticidal activity on adults of the whitefly Bemisia tabaci biotype B. The kit, which consisted of arenas and nebulizer, was effective for conducting bioassays, and the application of aqueous extracts by inhaler was adequate. The techniques are simple, cheap, and may contribute to research on this insect.

Evaluation of Tomato Hybrids Carrying Ty‐1 and Ty‐2 Loci to Japanese Monopartite Begomovirus Species

AbstractTobacco leaf curl Japan virus, Honeysuckle yellow vein mosaic virus and Tomato yellow leaf curl virus are three begomoviruses that infect tomato crops in Japan. Tomato infection by begomoviruses has increased in Japan after the development of a high level of resistance to certain insecticides in some populations of the vector B. tabaci biotypes ‘B and Q’. Ty‐1 and Ty‐2 homozygous tomato hybrids were evaluated for reaction to monopartite begomovirus species in Japan by Agrobacterium‐mediated inoculation. Test plants were evaluated by a disease assessment scale (DAS), varying from 1 = no symptoms to 4 = severe symptoms, and systemic infection was evaluated by polymerase chain reaction (PCR), using specific begomovirus primers for each virus. Ty‐1 hybrids showed tolerance to HYVMV and with a large number of plants being neither virus‐free nor symptom‐free. The response of Ty‐1 hybrids was also resistant to moderately resistant against TbLCJV. The response of Ty‐2 hybrids was resistant to highly resistant against the three monopartite begomoviruses, when compared with susceptible plants.