Tabaci Nymphs Research Articles

Short-term temperature changes affected the predation ability of Orius similis on Bemisia tabaci nymphs

Abstract Bemisia tabaci (Gennadius), a major pest that can adversely affect economies and agriculture globally, is particularly sensitive to climate change-induced temperature fluctuations, which can intensify its outbreaks. Orius similis Zheng, a primary natural predator of B. tabaci, also experiences temperature-related effects that influence its biocontrol efficacy. Thus, understanding the response of O. similis to temperature changes is pivotal for optimizing its biocontrol potential. Herein, our investigations showed that the functional response of O. similis to both high- and low-instar nymphs of B. tabaci adheres to the type II model at temperatures of 19, 22, 25, 28, and 31 °C. At 28 °C, O. similis exhibits the highest instantaneous attack rate (high-instar: 1.1580, low-instar: 1.2112), and the shortest handling time per prey (high-instar: 0.0218, low-instar: 0.0191). The efficacy of O. similis in controlling B. tabaci nymphs follows the sequence: 28 °C > 25 °C > 31 °C > 22 °C > 19 °C. Additionally, search efficiency inversely correlates with prey density. Simulations using the Hessell–Varley interference model indicate that increased density of O. similis under any temperature condition leads to reduced predation rates. Moreover, O. similis shows a predation preference for low-instar nymphs of B. tabaci, with higher predation level observed at the same temperature. In conclusion, for effective control of B. tabaci in field releases, O. similis should be optimally released at temperatures between 25 and 28 °C to preferably target the egg or early nymph stages of B. tabaci and determining the appropriate number of O. similis is important to minimize interference among individuals and enhance biocontrol efficacy.

Bioactivity of andiroba oil on whitefly, Bemisia tabaci (Gennadius, 1889) (Hemiptera: Aleyrodidae)

The whitefly, Bemisia tabaci (Gennadius, 1889) (Hemiptera: Aleyrodidae) is a phytophagous insect that is difficult to control and can cause great damage to several crops of economic importance, as it can use more than 600 botanical species as hosts. This study aimed to evaluate the insecticidal and deterrent effect of andiroba (Carapa guianensis Aubl., Meliaceae) fixed oil on B. tabaci biotype B in kale (Brassica oleracea var. acephala). The andiroba oil samples, Manaus and Silves were diluted in acetone P.A. at concentrations of 0.5%, 1%, and 1.5%, and compared with the commercial insecticide Evidence® 700WG (imidacloprid). For the deterrence test, the concentrations were applied on healthy seedlings and placed in a cage with adult insects. Then the oviposition of whiteflies on the leaves was counted. For the mortality test, applications were performed on seedlings with leaves infested with B. tabaci nymphs to evaluate the nymphicidal effect. Analysis of variance was performed using the F test, and comparison of means using the Tukey test (p<0.05), using the statistical program R®. Concentrations of 1% and 1.5% reached a deterrent effect of 82.13% and 88.55%, respectively. All concentrations caused mortality greater than 60%. These results attest to the potential of andiroba oil as an alternative control for the whitefly.

Diversity study of Beauveria bassiana species for finding the most virulent strain to manage Bemisia tabaci in cotton

Beauveria bassiana (Bal.-Criv.) is an important entomopathogenic fungus being used for the management of various agricultural pests worldwide. However, all strains of B. bassiana may not be effective against whitefly, Bemisia tabaci, or other pests, and strains show diversity in their growth, sporulation, virulence features, and overall bioefficacy. Thus, to select the most effective strain, a comprehensive way needs to be devised. We studied the diversity among the 102 strains of B. bassiana isolated from 19 insect species based on their physiological features, virulence, and molecular phylogeny, to identify promising ones for the management of B. tabaci. Strains showed diversity in mycelial growth, conidial production, and their virulence against B. tabaci nymphs. The highest nymphal mortality (2nd and 3rd instar) was recorded with MTCC-4511 (95.1%), MTCC-6289 (93.8%), and MTCC-4565 (89.9%) at a concentration of 1 × 106 conidia ml−1 under polyhouse conditions. The highest bioefficacy index (BI) was in MTCC-4511 (78.3%), MTCC-4565 (68.2%), and MTCC-4543 (62.1%). MTCC-4511, MTCC-4565, and MTCC-4543 clustered with positive loading of eigenvalues for the first two principal components and the cluster analysis also corresponded well with PCA (principal component analysis) (nymphal mortality and BI). The molecular phylogeny could not draw any distinct relationship between physiological features, the virulence of B. bassiana strains with the host and location. The BI, PCA, and square Euclidean distance cluster were found the most useful tools for selecting potential entomopathogenic strains. The selected strains could be utilized for the management of the B. tabaci nymphal population in the field through the development of effective formulations.Key points• 102 B. bassiana strains showed diversity in growth and virulence against B. tabaci.• Bioefficacy index, PCA, and SED group are efficient tools for selecting potential strains.• MTCC-4511, 4565, and 4543 chosen as the most virulent strains to kill whitefly nymphs.

Field effectiveness of some essential oil emulsions against the whitefly Bemisia tabaci (GENN.) that infest potato plants in Egypt

AbstractWhitefly, Bemisia tabaci, nymphs and sucking sap adults, is one of the most damaging pests of potato, Solanum tuberosum. Excessive use of pesticides causes environmental pollution and the death of beneficial insects, so it is necessary to search for safer controlling alternatives. An experiment was carried out during seasons 2020–2021 and 2021–2022, under field conditions in Egypt. The objective of this study was to identify the main constituent compounds of peppermint and eucalyptus essential oils prepare coarse emulsion (CE) and nanoemulsion (NE) of both peppermint and eucalyptus essential oils and evaluate their efficiency against the whitefly, B. tabaci, in potato cultivars and the effect of these emulsions on the chemical components of potato leaves. The results revealed that the toxicity of the emulsions decreased with increasing time after spraying. The second spray which took place at a 10-day interval was more effective than the first spray. During the season of 2021, three days following the second spray, the tested emulsions' toxicity was highly effective. The reduction percentages of nymph for peppermint coarse emulsion (PCE), peppermint nanoemulsion (PNE), eucalyptus coarse emulsion (ECE), eucalyptus nanoemulsion (ENE) and imidacloprid were 82.64, 84.14, 73.26, 72.72 and 89.03, but they were 78.58, 83.27, 77.85, 69.97 and 89.26 compared with 2022. A moderately positive correlation was identified between temperature, specific humidity, wind speed and the effectiveness of the emulsions. This indicates that higher levels of temperature, humidity and wind speed were associated with increased efficacy of the emulsions. The study of the phytochemicals (total soluble protein, total carbohydrate, total phenolic contents and peroxidase activity). PCE and ECE achieved a slight decrease in protein levels. Also, ECE increased total plant carbohydrates. All treatments did not affect the phenolic compounds of potato leaf plants except ENE, which caused an increase in phenolic compounds. All treatments decreased the nitrogen plants' contents, while PCE, PNE, and ENE increased the potassium content. All treatments increase the activity of peroxidase (POX) compared with untreated plants. The formulations PNE and ENE might be an interesting alternative for integrated pest management of B. tabaci nymphs.

Host-feeding capacity and parasitism performance of heteronomous hyperparasitoid Encarsia lutea Masi (Hym.: Aphelinidae) on different host plant species

Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) is one of the most economically significant and widely distributed whitefly species. Encarsia lutea Masi (Hymenoptera: Aphelinidae) is a heteronomous hyperparasitoid and is reported to be one of the key factors in the management of B. tabaci populations in Mediterranean countries. This study aimed to evaluate the interactions among E. lutea, B. tabaci, and the host plant, obtaining comprehensive data to enhance its application in biological control programmes. Therefore, laboratory studies were carried out to determine the host-feeding capacity and parasitism of E. lutea at six B. tabaci nymph densities (10, 20, 40, 60, 80, and 100) on three host plant species: bean, cotton, and eggplant. The number of nymphs killed by the parasitoid through feeding and parasitism increased with increasing nymph densities for all host plants. The lowest (4.06) and the highest (27.5) mean numbers of parasitised nymphs were observed at host densities of 10 and 100 nymphs, respectively. The feeding behaviour of E. lutea was affected by the host plant, and the mean number of nymphs killed by feeding was found to be statistically significant and higher in cotton (6.7) than in bean (4.6) and eggplant (4.3), when pooled over all nymph densities. In conclusion, although the results showed that E. lutea can act as a density-dependent parasitoid, and its performance varies depending on the host plant, further studies on its hyperparasitism behaviour should be conducted before evaluating it as a potential candidate for the biological control agent of B. tabaci.

Functional response of Franklinothrips vespiformis (Thysanoptera: Aeolothripidae) to eggs and nymphs of Bemisia tabaci (Hemiptera: Aleyrodidae).

The Middle East Asia Minor 1 biotype of Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae) is a greenhouse and field crop pest of global significance. The objective of this study was to assess the potential of the generalist predatory thrips, Franklinothrips vespiformis Crawford (Thysanoptera: Aeolothripidae), as a biological control agent for B. tabaci. This was achieved by determining the functional responses of F. vespiformis larvae and adults to the egg and nymphal stages of B. tabaci under laboratory conditions. Analyses consisted of 10 replicates of each predator and prey stage combination on bean leaf discs for a 24-h period. Following logistic regression analyses to determine the functional response type exhibited, response parameters were estimated with nonlinear least squares regression using Roger's equation. Results showed that F. vespiformis larvae and adults exhibited a Type II functional response when feeding on immature B. tabaci. The handling times (Th) of F. vespiformis larvae and adults were magnitudes higher for B. tabaci nymphs than they were for eggs, which were in part driven by the higher attack rates (a) observed on eggs. The maximum attack rate (T/Th) for B. tabaci eggs and nymphs exhibited by first-stage larvae, second-stage larvae, and adult F. vespiformis increased with increasing predator age. Results from this study suggest that F. vespiformis larvae and particularly adults are promising biological control agents for B. tabaci and are efficient predators at both low and high prey densities.

Synergistic of Trichoderma virede and Beauveria bassiana to Biocontrol Tomata Against and Bemisia tabaci

In Iraq, Bemisia tabaci is a major Tomato pest that causes significant crop losses, which lowers farmers’ revenue. The purpose of this study was to detect entomopathogenic fungus from dead whiteflies and to assess their relative frequency and different structural characteristics. Only two fungal species, Trichodrema virede and Beauveria bassiana, with relative frequencies of 15.07 and 10.94%, respectively, were validated microscopically as recognised entomopathogenic species out of the 11 fungal species isolated from the whitefly cadavers. The 7th day following inoculation was when T. virede and B. bassiana had the largest mortality impact on B. tabaci nymphs and adults, with an average mortality of more than 60% (with a concentration of 106 conidia/ml). In comparison to nymphs, suspension T.virede and B.bassiana. were significantly twice as pathogenic.

Population Density of Bemisia tabaci on Sweet Pepper (Capsicum annuum) Varieties in the Greenhouse

We conducted an experiment in a greenhouse at the research station belonging to the Department of Plant Protection / Ministry of Agriculture, in Abu Ghraib area during the spring and autumn season 2022-2023, to study the population density of the whitefly on two varieties of sweet pepper plant (Charisma and Sierra Nevada). The experiment was laid out in a randomized complete block design “RCBD” with three replicates for each variety. The results showed that in spring season the population density of B. tabaci eggs and nymphs reached the peak in the last week of May, which where 2.667 and 4.444 individual / leaf, respectively while the population density peak of the adults was in the first week of June, where it reached 3.33 individual / leaf for Charisma variety, while in Sierra Nevada variety the population density of eggs reached its peak at the first week of May 2.889 individual / leaf, while the nymphs reached its peak at the last week of May 4.44 individual / leaf, also the adults reached its peak the in the second week of June 2.667 individual / leaf. In autumn season the population density of the eggs, nymphs and adults on Charisma variety reached its peak in the third week of November, where it were 3.556, 2.778 and 3.444 individual / leaf respectively, while the population density of the eggs, nymphs and adults recorded on the Sierra Nevada variety reached its peak in the third week of November with 3.889, 3.778 and 3.778 individual / leaf respectively. These results clearly showed that B. tabaci had nearly the same preference to infest the two varieties of sweet pepper, Charisma and Sierra Nevada through the abundance of their stages on the plants.

Effect of Sowing dates in Cucumber on Incidence of <i>thrips tabaci</i> (Lindeman)

Experiments were conducted in Fayoum Governorate, Egypt to evaluate the impact of sowing dates on onion thrips Thrips tabaci (Lindeman) that attack cucumber (Cucumis sativus L.). The study spanned two consecutive years (2018 and 2019) and involved three planting dates: March, August, and October. Weekly thrips counts were recorded and compared across the different planting dates. According to the results, T. tabaci nymphs recorded maximum incidence in March sowing date and amounted to 118.5± 19.79 and 79.6± 18.99 individuals/ sample. While cucumber crop in October sowing date hosted the lowest number of T. tabaci nymphs amounted to 34.1± 7.38 and 29.5± 7.57 individuals/sample. Temperature and population of T. tabaci nymphs correlated significantly in August and October cucumber plantations.

Akanthomyces diversity in Brazil and their pathogenicity to plant-sucking insects

Currently, species within the genus Akanthomyces are poorly studied and explored compared to other hypocrealean entomopathogenic fungi employed as commercial biocontrol agents. This study aimed to molecularly identify 23 Brazilian Akanthomyces strains, most originally isolated from aphids and scales (n = 22), and one from the coffee leaf rust, and further investigate their pathogenicity to six plant-sucking insects as a means to better understand their host spectra. We also explored the capacity of A. muscarius CG935 for blastospore production via liquid fermentation. Akanthomyces dipterigenus, A. muscarius, A. lecanii, and two unidentified species were recognized as naturally occurring in Brazil. Akanthomyces dipterigenus CG829 and A. muscarius CG935 were highly virulent to nymphs of Bemisia tabaci (67.5–85.4% confirmed mortality) and the aphid Aphis fabae (74.6–75.3%), but only the first strain was virulent to the mealybug Planococcus sp. (80.9%). Akanthomyces lecanii CG824 was weakly virulent to all tested insects. None of the strains were pathogenic to the thrips Caliothrips phaseoli, and all strains showed low virulence to the wooly whitefly Aleurothrixus floccosus and the scale Duplachionaspis divergens. Submerged liquid fermentation yields varied from 1.72 × 109 (day 2) to 3.90 × 109 (day 5) blastospores mL−1. Blastospores or aerial conidia from A. muscarius CG935, at a single concentration of 1 × 107 viable propagules mL−1, resulted in 67.5–83.1% mortality of B. tabaci nymphs within 8 days post-treatment. Overall, these results encourage additional studies that could lead to the development of new mycopesticides based on Akanthomyces strains.

Technique to deliver dsRNA in Bemisia tabaci nymphs and its validation through silencing of juvenile hormone esterase gene

AbstractRNA interference (RNAi) is a technique employed to investigate the functions of various genes in whitefly and other insects. The effectiveness of the RNAi technique depends upon the delivery of dsRNA into the insects and it has been achieved through microinjection, oral feeding, egg soaking, transfection, topical application, spraying with nanoparticles, leaf‐mediated dsRNA feeding or plant‐mediated/ transgenic plants. In Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae), most of the studies on RNAi were conducted on the adult through either injection or oral feeding. There is a need to develop a system to deliver dsRNA in whitefly nymphs because the first instar nymphs after hatching find a suitable place on the leaf and feed on the same place till adult emergence. So, we evaluated nine different techniques using different sponges, tubes, and, Petri plates for feeding nymphs. The detached leaf survived for maximum number of days (8.25 days) with minimum nymphal mortality (12.01%) in the Whitefly Nymphal Feeding System‐1 (WNFS‐1) treatment; therefore, WNFS‐1 was selected for the delivery of dsRNA to B. tabaci nymphs. In WNFS‐1, blue food dye was used to confirm that nymphs were being fed, and the results were evidenced by blue‐coloured bodies. The juvenile hormone esterase (jhe) gene was silenced in order to successfully deliver dsRNA to nymphs using WNFS‐1 and resulting in much higher nymphal mortality (68.36%). Therefore, WNFS‐1 is a reliable method of delivering dsRNA for the purpose of silencing the genes in the nymphal stages of whiteflies. The WNFS system may also be used extensively to evaluate any chemistry (insecticides, hormones, biopesticides, etc.) in nymphs of whitefly.

Translaminar activity of different insecticides against Bemisia tabaci

One of the main mechanisms of action for many insecticides is translaminar redistribution or local systemic. The present study was carried out at Chaudhary Charan Singh Haryana Agricultural University, Hisar, Haryana during 2019 and 2020 to investigate the translaminar activity of different insecticides having different doses and sprays on treated brinjal plant having Bemisia tabaci (Gennadius) nymphs. Different treatments, i.e. diafenthiuron 50% WP (150, 210, and 300 g a.i./ha), fenpropathrin 30% EC (50, 70, and 100 g a.i./ha), thiamethoxam 25% WG (25, 35, and 50 g a.i./ha), and deltamethrin 2.8% EC (7.5, 10.5 and 15 g a.i./ha) were frequently sprayed on brinjal plants (var. Hisar Shyamal) growing in pots. Insecticides effectiveness was measured through nymphal mortality of B. tabaci (whitefly). Similar study was conducted in 2020 to ensure reliability of results. The results revealed that, almost similar trendswere obtained during 2019 and 2020, hence proving reliability. Among all tested insecticides, maximum translaminar effect was observed in thiamethoxam 25% WG treated plant at 50 g a.i./ha (50.72% nymphal mortality). Whereas, deltamethrin 2.8% EC treated plant at 15 g a.i./ha showed minimum translaminar effect (0.63% nymphal mortality) as compared to other treatments. Translaminar effect of leaves treated with diafenthiuron 50% WP and fenpropathrin 30% EC was found at par with each other. Nymphal mortality is low in sub-lethal doses of insecticides as compared to lethal doses. It can be concluded that resistance may develop due to sub-lethal doses of insecticides. Farmers and agricultural experts would benefit from this study's findings.

Insecticidal activity of isolated Purpureocillium lilacinum PL1 against whitefly, Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae) on cassava plantations in southern Viet Nam

BackgroundWhitefly Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae) is a plant-damaging insect in tropical and subtropical regions that causes agricultural damage worldwide, including in Viet Nam. The abuse of pesticides derived from chemicals has resulted in the evolution of insect-resistant strains, polluting the environment and threatening human health. Using entomopathogenic fungi (EPF) for biological control is an alternative strategy in integrated pest management. Hence, an attempt was conducted to isolate, characterize and evaluate the efficacy of EPF, Purpureocillium lilacinum against whitefly B. tabaci under laboratory and field conditions.ResultsPurpureocillium lilacinum PL1 (PL1) was isolated from the whitefly B. tabaci cadavers and subsequently identified using morphological study and internal transcribed spacer sequencing. Purpureocillium lilacinum PL1 had effectively grown and sporulated at temperatures ranging from 25 to 35 °C and throughout a broad pH range, which is particularly advantageous against the harsh tropical monsoon climate. Bioassay study indicated that 1 × 107 conidia/ml of P. lilacinum PL1 had a high lethality against the whitefly B. tabaci nymphs in vitro with efficiency was 88.24% after 7 days of treatment. The median lethal concentration (LC50) of P. lilacinum PL1 to B. tabaci after 7 days of treatment was 1.24 × 105 conidia/ml. In field conditions, 1 × 107 conidia/ml of P. lilacinum PL1 lowered the population of B. tabaci nymphs with efficacy was 78.86% after 2 batches, 7 days after treatments.ConclusionThe findings indicated that P. lilacinum PL1 was effective in the biological control of B. tabaci nymphs, which could be a potential alternative to chemical pesticides for pest management.

Parasitism of the whitefly Bemisia tabaci by aphelinid parasitoids on cassava across five agro-ecological zones of Cameroon

The whitefly Bemisia tabaci (Gennadius) is the vector of cassava mosaic viruses causing cassava viral diseases, which are the most important biotic constraints of cassava production in sub-Saharan Africa (SSA). Presently, B. tabaci management in cassava fields calls for the development of an integrated approach that relies on host plant resistance and biological control. Data on B. tabaci's natural enemies, particularly parasitoids, in Central Africa are limited. Field surveys were conducted from 2015 to 2017 to identify parasitoids associated with B. tabaci in 5 Cameroon agro-ecological zones. Additionally, population dynamics studies were conducted in replicated fields experiments were conducted from 2016 to 2018 to identify cassava genotypes that can best promote B. tabaci parasitism. Two parasitoids, Encarsia sophia (Girault & Dodd) and Encarsia lutea (Masi) were found parasitizing B. tabaci nymphs with higher parasitism by E. lutea compared with E. sophia. The average parasitism rate during the survey was 33.4% for E. lutea and 8.4% for E. Sophia, regardless of AEZ. The highest parasitism rates by E. lutea (48.2% and 24.2% from field trials and surveys, respectively) were observed in the Western Highlands (AEZ 3) while parasitism by E. sophia was less than 12.4%. Four cassava genotypes (I090590, I011797, I090574, and I070593) promoted higher parasitism rates of B. tabaci by E. lutea and E sophia. The contributions of the two parasitoids and their integration with cassava genotypes for the management of B. tabaci in cassava fields are discussed.

LABORATORY EVALUATION OF THE ADULTICIDAL AND NYMPHICIDAL ACTIVITY OF Aspergillus niger In Bemisia tabaci (HEMIPTERA: ALEYRODIDAE)

Whitefly, Bemisia tabaci (Gennadius), is a widespread polyphagous insect pest and a dangerous vector for many viruses that cause plant diseases. Farmers urgently need safe pesticides to protect their crops and plants, making biopesticide a good alternative to chemicals. Biopesticides are part of an integrated pest management program and offer a safer, more natural alternative to chemical pesticides. Since biocides were introduced, several pest management products have been released, some of which dominate the market. The current laboratory study tested the biological agent Aspergillus niger at three concentrations (0.25, 0.50, and 1.00 con/ml) to manage and reduce Bemisia tabaci population density in greenhouses and field crops. Laboratory tests showed that the two isolates were highly virulent against Bemisia tabaci nymphs and adults. Mortality was significantly different from controls in relation to isolate concentrations and time. Culture filtrate concentration and duration affected nymph and adult mortality. The 100% concentrations of both An1 and An2 were superior to the remaining concentrations, giving mortality in nymphs of B.tabaci 48.88 and 45.55 for isolates (An1 and An2) respectively, 42.21 and 36.66 for isolates (An1 and An2) respectively in adults stage. Effect of duration on post treatment mortality, highest mortality in nymphs and adults occurred 9 days after treatment, 74.44 , 56.66% in nymph and 53.33, 45.55 in adults for isolates (An1and An2) respectively. Concerning the interaction between concentration and duration, as is clear from Tables (1) and (2), the mortality was highest at 1.00% concentration. After 9 days of treatment, the isolates (An1, An2) achieved mortality 86.66, 80.0 in nymphs and 73.33%, 63.33% in adults, respectively. These findings demonstrate A. niger's biopesticide potential.

Relationship between viruliferous Bemisia tabaci population and disease incidence of Pepper yellow leaf curl Indonesia virus in chili pepper

Abstract. Temaja IGRM, Selangga DGW, Phabiola TA, Khalimi K, Listihani L. 2022. Relationship between viruliferous Bemisia tabaci population and disease incidence of Pepper yellow leaf curl Indonesia virus in chili pepper. Biodiversitas 23: 5360-5366. Bemisia tabaci Genn is an important pest in horticulture crops. Until today, B. tabaci has always been found in chili pepper and causes damage. In addition to a direct injury to the chili pepper, it is also the vector of Begomovirus. There is no research till date regarding the relationship between B. tabaci with Begomovirus which caused damage to chili pepper crops. Thus, the aim of this research was to analyze the interaction between B. tabaci population with the disease incidence of Begomovirus on chili peppers crops, as well as the percentage of viruliferous B. tabaci. This research noted B. tabaci population dynamics, disease incidence of pepper yellow leaf curl disease, and the percentage of viruliferous B. tabaci via PCR by using Begomovirus universal primer and DNA analysis confirmation. The highest imago population occurred at 6 WAP with the average density 27.21 imago/yellow sticky card, while the highest nymph population occurred at 8 WAP with the average density of 4.26 nymph/leaf. The high population of B. tabaci nymph and imago caused the incidence of Begomovirus disease to reach 83.07% at 12 WAP. Result showed that high population of B. tabaci accelerated the speed of virus in the field. The confirmation result of Begomovirus in B. tabaci body showed that the virus was Pepper yellow leaf curl Indonesia virus (PYLCIV). The highest homology obtained was between PYLCIV isolates from Sekaan, Bangli with isolates from Bayung Gede, Bangli which ranged from 99.6 to 99.8%. Further phylogenetic analysis showed that PYLCIV isolates from Sekaan, Bali formed a group with the isolate from Bayung Gede, Bangli, which was from a different group with other isolates. This proved that B. tabaci carries and transmits PYLCIV to chili peppers in Bali.

The Toxicity, Sublethal Effects, and Biochemical Mechanism of β-Asarone, a Potential Plant-Derived Insecticide, against Bemisia tabaci.

Bemisia tabaci is a threat to agriculture worldwide because of its potential to cause devastating damage to various crops. β-asarone is a bioactive pesticidal chemical originating from Acorus calamus (or “Sweet Flag”) plants, and it displays significant lethal effects against insect pests. In this study, we established a baseline of susceptibility to β-asarone from China and patterns of cross-resistance to other popular insecticides. We found that all the 12 field-collected B. tabaci populations exhibited high susceptibility to β-asarone, and there was no cross-resistance detected for other tested insecticides. We subsequently evaluated the sublethal effects of β-asarone on physiology and biochemistry via LC25 treatment (4.7 mg/L). LC25 of β-asarone resulted in prolonged developmental duration and decreased survival rates in B. tabaci nymphs, pseudopupae, and adults. Significant reductions in oviposition duration, fecundity, and hatchability were also observed. Additionally, the metabolic enzyme activity and expression profiles of selected cytochrome P450 monooxygenase (P450) genes following the LC25 treatment of β-asarone suggest that enhanced detoxification via P450s could be involved in the observed sublethal effects. These findings demonstrate the strong toxicity and significant sublethal effects of β-asarone on B. tabaci and suggest that the induced overexpression of P450 genes could be associated with the response to β-asarone.

Effect of Feeding Stage and Density of Whiteflies on Subsequent Aphid Performance on Tobacco Plants

Bemisia tabaci Middle East-Asia Minor 1 (MEAM1) is a cosmopolitan, highly polyphagous agricultural pest, which has the capacity to displace other native insect herbivores. Here, equipped with an integrated approach, the effect of developmental stages and feeding density of whiteflies on Myzus persicae performance in tobacco plants are investigated. Bioassay results showed that B. tabaci nymphs, but not adult, pre-infestation significantly reduced survival and fecundity of M. persicae, and the strongest resistance to M. persicae was detected at the medium density (9–10 nymphs/cm2). Neither low nor high feeding density of B. tabaci nymphs triggered visible resistance to aphids. However, no significant results were detected in salicylate-deficient NahG plants after B. tabaci nymph infestation. In addition to performance distinctions, hormone quantification and qPCR results revealed very different effects for nymph and adult whitefly stages on the defense responses in tobacco. B. tabaci nymph infestation significantly increased SA accumulation and SA-responsive genes (PR-1a, PR-2a) expression but suppressed JA-regulated responses. In contrast, tobacco plants responded to adult infestation by slightly increasing in both SA- and JA-regulated defenses. Furthermore, higher transcription level of Bt56, coding gene of a secretory salivary effector, was recorded in nymphs vs. adults, while silencing of Bt56 by virus-induced gene silencing (VIGS) partly impaired the aphid resistance induced by B. tabaci nymphs. These results proved that the induction of tobacco defense responses varied with the feeding stages of whiteflies: nymphs of B. tabaci, but not adults, induced a defense response against aphids, with a density threshold for this induced resistance.

Efficacy of buprofezin, pyriproxyfen and spirotetramat against Bemisia tabaci MEAM1 nymphal field populations in Florida

The whitefly, Bemisia tabaci MEAM1 (Gennadius) (Hemiptera: Aleyrodidae) is a major pest of vegetable crops in the USA, causing yield losses through transmission of plant viruses and induction of plant disorders. Irregular ripening of tomato and silvering of squash leaves are whitefly-induced plant disorders associated with B. tabaci nymphal feeding. Insecticides applied to manage B. tabaci nymphs and these plant disorders include insect growth regulators (IGRs) and lipid biosynthesis inhibitors. Eleven B. tabaci MEAM1 field populations were collected from vegetables and weeds in south Florida in 2019–2020 to assess the efficacy of nymphal insecticides using a maximum dose bioassay. A susceptible laboratory colony of B. tabaci MEAM1 and a colony of B. tabaci MED were also tested. Among the field populations, spirotetramat was the least efficient product for reducing adult emergence and pyriproxyfen and buprofezin were both highly effective. In contrast to the field populations, the lab MED colony was highly susceptible to spirotetramat while pyriproxyfen and buprofezin demonstrated low efficacy for reducing adult emergence. The results indicate that tolerance to spirotetramat may be present in field populations of B. tabaci.

Influence of Cassava Morphological Traits and Environmental Conditions on Field Populations of Bemisia tabaci.

High populations of species in the whitefly complex Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae) were reported to cause severe damage to cassava in East and Central Africa. However, reasons for B. tabaci population increases are not well understood. We investigated the effect of cassava morphological traits, temperature, rainfall and relative humidity (RH) on the abundance of B. tabaci. Five cassava genotypes with varying levels of resistance to cassava mosaic disease, cassava brown streak disease, and B. tabaci infestation were planted in three Ugandan agro-ecological zones. The experiment was conducted in 2016 and 2017 in a randomized complete block design. Across all locations, the tallest genotype Alado alado supported the lowest number of B. tabaci adults. In areas with high B. tabaci prevalence, leaf area, leaf lobe width, and leaf lobe number exhibited significant positive effects (p < 0.001) on B. tabaci adult count. Positive effects of relative humidity and negative effects of temperature and rainfall on B. tabaci adult and nymph counts were observed in 2016 and 2017, resulting in low populations in Lira. Evidently, temperatures of 28-30 °C, rainfall of 30-150 mm and RH of 55-70%, and deployment of cassava genotypes of low plant height, large leaf area, and lobe width significantly enhanced B. tabaci population growth.