A Tomato-Free Period Delays and Reduces Begomovirus Disease in Processing Tomato Fields in a Complex Agroecosystem in Central Brazil.

A mandatory tomato-free period (TFP) was implemented in the state of Goiás, Brazil, in 2007 to help manage diseases caused by whitefly-transmitted begomoviruses. The impact of the TFP was examined in five locations across three states in Central Brazil from 2013 to 2016. Surveys revealed significant differences in begomovirus disease incidence among locations, i.e., low in Guaíra-TFP and Patos de Minas-TFP; moderate-high in Itaberaí-TFP and Morrinhos-TFP; and high in the non-TFP (NTFP) control, Cristalina-NTFP. PCR tests and DNA sequencing were used to validate the symptoms and showed that all collected symptomatic plant samples were infected with tomato severe rugose virus (ToSRV), a common indigenous bipartite begomovirus. Early season surveys (20 to 40 days after transplants [DAT]) in Itaberaí-TFP and Morrinhos-TFP revealed significantly less begomovirus disease in fields established sooner after the TFP (0 to 2 months) compared with incidences in (i) equivalent early planted fields in the Cristalina-NTFP control and (ii) fields established longer after the end of the TFP (>2 to 5 months). Whitefly infestation of crops was detected year-round in all locations and years, and all tested adults were classified in the Bemisia tabaci MEAM1 cryptic species. Infestation levels were significantly higher during the summer but did not vary significantly among locations. Results of monthly monitoring of adult whiteflies for general begomovirus and ToSRV were positively correlated and were indicators of disease incidence in the field. Notably, ToSRV was not detected in whiteflies collected from nontomato plants during the TFP, and there was a longer lag period before detection in whiteflies collected from processing tomatoes for Itaberaí-TFP and Morrinhos-TFP compared with Cristalina-NTFP. Taken together with the low levels of ToSRV infection detected in potential nontomato reservoir hosts at all locations, our results revealed low levels of primary inoculum during the TFP. Thus, even in a complex agroecosystem with year-round whitefly infestation of crops, the TFP was beneficial due to delayed and reduced begomovirus disease pressure during a critical stage of plant development (first month) and for favoring low levels of primary inoculum. Thus, we concluded that the TFP should be part of a regional integrated pest management (IPM) program targeting ToSRV in Brazil.

Differences in gene expression in whitefly associated with CYSDV-infected and virus-free melon, and comparison with expression in whiteflies fed on ToCV- and TYLCV-infected tomato.

BACKGROUND: Cucurbit yellow stunting disorder virus (CYSDV; genus Crinivirus, Closteroviridae) is transmitted in a semipersistent manner by the whitefly, Bemisia tabaci, and is efficiently transmitted by the widely prevalent B. tabaci cryptic species, MEAM1. In this study, we compared transcriptome profiles of B. tabaci MEAM1, after 24 h, 72 h and 7 days of acquisition feeding on melon plants infected with CYSDV (CYSDV-whiteflies) with those fed on virus-free melon, using RNA-Seq technology. We also compared transcriptome profiles with whiteflies fed on tomato plants separately infected with Tomato chlorosis virus (ToCV), a crinivirus closely related to CYSDV, and Tomato yellow leaf curl virus (TYLCV), a member of the genus Begomovirus, which has a distinctly different mode of transmission and their respective virus-free controls, to find common gene expression changes among viruliferous whiteflies feeding on different host plants infected with distinct (TYLCV) and related (CYSDV and ToCV) viruses. RESULTS: A total of 275 differentially expressed genes (DEGs) were identified in CYSDV-whiteflies, with 3 DEGs at 24 h, 221 DEGs at 72 h, and 51 DEGs at 7 days of virus acquisition. Changes in genes encoding orphan genes (54 genes), phosphatidylethanolamine-binding proteins (PEBP) (20 genes), and AAA-ATPase domain containing proteins (10 genes) were associated with the 72 h time point. Several more orphan genes (20 genes) were differentially expressed at 7 days. A total of 59 common DEGs were found between CYSDV-whiteflies and ToCV-whiteflies, which included 20 orphan genes and 6 lysosomal genes. A comparison of DEGs across the three different virus-host systems revealed 14 common DEGs, among which, eight showed similar and significant up-regulation in CYSDV-whiteflies at 72 h and TYLCV-whiteflies at 24 h, while down-regulation of the same genes was observed in ToCV-whiteflies at 72 h. CONCLUSIONS: Dynamic gene expression changes occurred in CYSDV-whiteflies after 72 h feeding, with decreased gene expression changes associated with 7 days of CYSDV acquisition. Similarities in gene expression changes among CYSDV-whiteflies, ToCV-whiteflies and TYLCV-whiteflies suggest the possible involvement of common genes or pathways for virus acquisition and transmission by whiteflies, even for viruses with distinctly different modes of transmission.

Transcriptome analysis of the whitefly, Bemisia tabaci MEAM1 during feeding on tomato infected with the crinivirus, Tomato chlorosis virus, identifies a temporal shift in gene expression and differential regulation of novel orphan genes.

BACKGROUND: Whiteflies threaten agricultural crop production worldwide, are polyphagous in nature, and transmit hundreds of plant viruses. Little is known how whitefly gene expression is altered due to feeding on plants infected with a semipersistently transmitted virus. Tomato chlorosis virus (ToCV; genus Crinivirus, family Closteroviridae) is transmitted by the whitefly (Bemisia tabaci) in a semipersistent manner and infects several globally important agricultural and ornamental crops, including tomato. RESULTS: To determine changes in global gene regulation in whiteflies after feeding on tomato plants infected with a crinivirus (ToCV), comparative transcriptomic analysis was performed using RNA-Seq on whitefly (Bemisia tabaci MEAM1) populations after 24, 48, and 72 h acquisition access periods on either ToCV-infected or uninfected tomatoes. Significant differences in gene expression were detected between whiteflies fed on ToCV-infected tomato and those fed on uninfected tomato among the three feeding time periods: 447 up-regulated and 542 down-regulated at 24 h, 4 up-regulated and 7 down-regulated at 48 h, and 50 up-regulated and 160 down-regulated at 72 h. Analysis revealed differential regulation of genes associated with metabolic pathways, signal transduction, transport and catabolism, receptors, glucose transporters, α-glucosidases, and the uric acid pathway in whiteflies fed on ToCV-infected tomatoes, as well as an abundance of differentially regulated novel orphan genes. Results demonstrate for the first time, a specific and temporally regulated response by the whitefly to feeding on a host plant infected with a semipersistently transmitted virus, and advance the understanding of the whitefly vector-virus interactions that facilitate virus transmission. CONCLUSION: Whitefly transmission of semipersistent viruses is believed to require specific interactions between the virus and its vector that allow binding of virus particles to factors within whitefly mouthparts. Results provide a broader understanding of the potential mechanism of crinivirus transmission by whitefly, aid in discerning genes or loci in whitefly that influence virus interactions or transmission, and subsequently facilitate development of novel, genetics-based control methods against whitefly and whitefly-transmitted viruses.

Differential expression patterns among heat-shock protein genes and thermal responses in the whitefly Bemisia tabaci (MEAM 1).

There is convincing evidence that heat-shock proteins (HSP) are upregulated by stress conditions in insects; however, the relative contribution of each HSP gene to the heat-shock response remains unclear. Here we considered the whitefly Bemisia tabaci (MEAM 1), a phloem feeder and invasive species whose molecular stress response is an important mechanism for overcoming heat stress. We assessed the expression of the hsp23, 40, 70 and 90 genes at the mRNA level when submitted to heat shocks of 40 and 44°C/1h (control at 25°C). For this, we evaluated a set of available and suitable reference genes in order to perform data normalization using the real-time polymerase chain reaction (qRT-PCR) technique, and then confirmed the production of HSP70 protein based on Western blot. Results were compared with the hardening capacity of B. tabaci, measured by fitness components as a response to heat shocks, using 40°C as the induction temperature. Three of the four genes (hsp23, 70 and 90) were upregulated by heat stress at mRNA, showing differential expression patterns. Hsp70 expression was confirmed at the protein level. Hardening significantly increased fitness following heat stress, suggesting that HSPs may contribute to hardening capacity in B. tabaci. Potential role of each gene in the heat-shock response for whiteflies is discussed.

Monitoring the susceptibility of Bemisia tabaci Middle East-Asia Minor 1 (Hemiptera: Aleyrodidae) to afidopyropen, cyantraniliprole, dinotefuran, and flupyradifurone in south Florida vegetable fields.

Bemisia tabaci Middle East-Asia Minor 1 (MEAM1) is a significant pest that damages a wide range of high-value vegetable crops in south Florida. This pest has demonstrated the ability to develop resistance to various insecticide groups worldwide. Monitoring the resistance levels of MEAM1 populations and maintaining baseline susceptibility data are crucial for the long-term effectiveness of insecticide management strategies. We conducted serial dilution bioassays on 15 field populations of MEAM1 collected in south Florida to assess their resistance to 4 key insecticides: afidopyropen, cyantraniliprole, dinotefuran, and flupyradifurone. To quantify resistance levels, resistance ratios (RR) were generated by comparing the LC50 values of field populations to those of a known susceptible MEAM1 colony reared in the laboratory. Our findings reveal that all field-collected populations were susceptible to dinotefuran (RR 1-8) and flupyradifurone (RR 2-8). While over 80% of the populations tested were susceptible to afidopyropen (RR 1-9), 2 populations exhibited low (RR 38) and moderate resistance (RR 51), respectively. In contrast, most of the populations (57%) showed low to moderate resistance to cyantraniliprole (RR 21-78), and the remaining populations were susceptible (RR 3-10). The 2 populations with resistance to afidopyropen also exhibited moderate resistance to cyantraniliprole. Further research in this direction can aid in refining insecticide resistance management programs in Florida and other regions where B. tabaci MEAM1 is a major pest. Exploring the implications of these findings will be essential for insecticide use and integrated pest management strategies in south Florida.

A Maximum Dose Bioassay to Assess Efficacy of Key Insecticides Against Bemisia tabaci MEAM1 (Hemiptera: Aleyrodidae).

The whitefly, Bemisia tabaci MEAM1 Gennadius causes serious losses to Florida vegetable and ornamental production. In 2019, a maximum dose bioassay was administered to 20 field populations of B. tabaci MEAM1 collected from various economic and weed hosts across south Florida to assess insecticide efficacy. The maximum dose bioassay tests the top labeled rate of the insecticide against B. tabaci adults on treated cotton leaves in a Petri dish over a 72-h period. A susceptible laboratory colony of B. tabaci MEAM1 and a colony of B. tabaci MED were also tested. Survival over 72 h was used to produce an area under the maximum dose curve, which was used to compare insecticide effects on different populations. Overall, imidacloprid demonstrated the poorest efficacy, dinotefuran and flupyradifurone were the most effective, and bifenthrin, cyantraniliprole, and thiamethoxam tended to group together, providing intermediate control. Across populations tested, survival in whitefly adults treated with dinotefuran was 50% lower than whiteflies treated with imidacloprid, about 33% lower than whiteflies treated with thiamethoxam, bifenthrin, and cyantraniliprole, and 10% lower than whiteflies treated with flupyradifurone. Efficacy of bifenthrin was less than imidacloprid on some populations, particularly from the Homestead area. Imidacloprid and thiamethoxam had no effect on mortality of the MED population when it was tested after 22 mo in culture without exposure to insecticides, although 7 mo later, these materials resulted in some mortality for the MED population.

Identification of a Sulfatase that Detoxifies Glucosinolates in the Phloem-Feeding Insect Bemisia tabaci and Prefers Indolic Glucosinolates.

Cruciferous plants in the order Brassicales defend themselves from herbivory using glucosinolates: sulfur-containing pro-toxic metabolites that are activated by hydrolysis to form compounds, such as isothiocyanates, which are toxic to insects and other organisms. Some herbivores are known to circumvent glucosinolate activation with glucosinolate sulfatases (GSSs), enzymes that convert glucosinolates into inactive desulfoglucosinolates. This strategy is a major glucosinolate detoxification pathway in a phloem-feeding insect, the silverleaf whitefly Bemisia tabaci, a serious agricultural pest of cruciferous vegetables. In this study, we identified and characterized an enzyme responsible for glucosinolate desulfation in the globally distributed B. tabaci species MEAM1. In in vitro assays, this sulfatase showed a clear preference for indolic glucosinolates compared with aliphatic glucosinolates, consistent with the greater representation of desulfated indolic glucosinolates in honeydew. B. tabaci might use this detoxification strategy specifically against indolic glucosinolates since plants may preferentially deploy indolic glucosinolates against phloem-feeding insects. In vivo silencing of the expression of the B. tabaci GSS gene via RNA interference led to lower levels of desulfoglucosinolates in honeydew. Our findings expand the knowledge on the biochemistry of glucosinolate detoxification in phloem-feeding insects and suggest how detoxification pathways might facilitate plant colonization in a generalist herbivore.

Modelling the potential distribution of Bemisia tabaci in Europe in light of the climate change scenario.

BACKGROUND: Bemisia tabaci is a serious pest of agricultural and horticultural crops in greenhouses and fields around the world. This paper deals with the distribution of the pest under field conditions. In Europe, the insect is currently found in coastal regions of Mediterranean countries where it is subject to quarantine regulations. To assess the risk presented by B. tabaci to Europe, the area of potential establishment of this insect, in light of the climate change scenario, was assessed by a temperature-dependent physiologically based demographic model (PBDM). RESULTS: The simulated potential distribution under current climate conditions has been successfully validated with the available field records of B. tabaci in Europe. Considering climate change scenarios of +1 and +2 °C, range expansion by B. tabaci is predicted, particularly in Spain, France, Italy, Greece and along the Adriatic coast of the Balkans. Nonetheless, even under the scenario of +2 °C, northern European countries are not likely to be at risk of B. tabaci establishment because of climatic limitations. CONCLUSION: Model validation with field observations and evaluation of uncertainties associated with model parameter variability support the reliability of model results. The PBDM developed here can be applied to other organisms and offers significant advantages for assessing the potential distribution of invasive species.