Tabaci Populations Research Articles

Population fluctuation of the whitefly Bemisia tabaci Gennadius, 1889 (Homoptera - Aleyrodidae) on vegetable crops and effect of two entomopathogenic fungi Verticillium sp. and Paecilomyces sp.

The cotton or sweet potato whitefly, Bemisia tabaci, is a major pest in Algeria, affecting various greenhouse-grown crops. This study aimed to monitor B. tabaci population dynamics on tomatoes, peppers, zucchinis, and strawberries to understand its infestation patterns. The methodology involved regular monitoring of pest activity on these crops and a laboratory bioassay to assess the efficacy of two entomopathogenic fungi, Verticillium sp. and Paecilomyces sp., in controlling the whitefly. Results revealed that B. tabaci was most prevalent on tomatoes, with a 43.73% infestation rate, followed by peppers at 24%, zucchinis at 19.14%, and strawberries at 13.11%. In addition, laboratory trials were conducted to evaluate the efficacy of two entomopathogenic fungi, Verticillium sp. and Paecilomyces sp., in controlling the whitefly. Verticillium sp. showed higher efficacy, achieving a 73% mortality rate, while Paecilomyces sp. resulted in a significantly lower mortality of 23%. These findings suggest that Verticillium sp. holds promise as a biological control agent for managing B. tabaci in Algeria, particularly on tomato crops.

Susceptibility of Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae) Mediterranean Populations Found in São Paulo, Brazil to 11 Insecticides and Characterization of Their Endosymbionts.

The silverleaf whitefly, Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae), is a significant agricultural pest worldwide, impacting a variety of crop yields. Since the introduction of B. tabaci Mediterranean (MED) species in Brazil, limited research has measured the relative efficacy of the primary insecticides used in whitefly management. This study evaluated the susceptibility of three distinct B. tabaci MED populations to 11 insecticide active ingredients and characterized the bacterial endosymbionts within each population. The insecticides tested were acetamiprid, bifenthrin, cyantraniliprole, diafenthiuron, spiromesifen, imidacloprid, pymetrozine, pyriproxyfen, sulfoxaflor, and thiamethoxam. Results showed varying LC50 and LC90 values among tested insecticides and populations. Notably, populations varied in response to imidacloprid and thiamethoxam with some populations having a 6× higher tolerance. Sequencing data of endosymbionts revealed that individuals from the most susceptible B. tabaci population harbored Rickettsia and Arsenophonus, whereas these bacteria were not detected in the resistant populations. These findings highlight the need for frequent insecticide toxicity bioassays of distinct B. tabaci populations and the adoption of integrated pest management strategies to preserve the efficacy of insecticides for B. tabaci control. Additionally, the role of infection by endosymbionts to alter susceptibility should be further explored.

Population Dynamics of Major Insect Pests and Natural Enemies in Tomato

An experiment on major insect pests and natural enemies of tomato was conducted during rabi, 2022-23 at the experimental farm for PG research, Biswanath College of Agriculture, Sonitpur. Results revealed eleven insect pests; whitefly, Bemisia tabaci (Gennadius); aphid, Aphis craccivora Koch; leafminer, Lyriomyza trifolii (Burgess); fruitborer, Helicoverpa armigera (Hubner); jassid, Amrasca biguttula biguttula (Ishida); semilooper, Trichoplusia ni (Hubner) were found to be the most dominant species. Two coccinellid predators viz., Micraspis discolor(F) and Cheilomenes sexmaculata (F) and two spiders Lycosa tista Tikader, Anyphaena accentuata (Walckenaer) were recorded as natural enemies. It was observed that the incidence of B. tabaci, A. craccivora and A. biguttula biguttula showed significant negative correlation with both maximum and minimum temperature. B. tabaci population registered a positive significant correlation with morning relative humidity. Both L. trifolii and H. armigera exhibited significant negative correlation with bright sunshine hour. Furthermore, T. ni showed significant negative correlation with maximum temperature and bright sunshine hour. As regards coccinellids, a significant negative correlation existed with maximum and minimum temperature, and rainfall and significant positive correlation with morning relative humidity. A significant positive correlation of aphids was also observed with coccinellids.

Population of Bemisia tabaci and Incidence of Yellow Disease in Chili Intercropped with Corn

Bemisia tabaci is one of the limiting factors in chili farming, because it can cause damage both directly and indirectly as a vector for the Pepper yellow leaf curl virus (PepYLCV). Intercropping chili with corn is one of the efforts to control B. tabaci. Physically, corn plants are able to withstand the presence of B. tabaci, in addition to producing volatile compounds that are repellent to B. tabaci. This research was conducted to determine the optimal age of corn plants to be intercropped with chili plants. The research was conducted in Pleret District, Bantul Regency by testing five different ages of corn: 2 weeks after planting, 6 weeks after planting, 8 weeks after planting, 10 weeks after planting and control (without intercropping with corn). Weeks after planting are counted from the first day the corn seeds were planted. Yellow sticky trap (YST) was used to determine the presence of B. tabaci population in each treatment plot. YST was tied to bamboo sticks and placed on treatment beds with as many as 2 (two) traps per treatment plot. The distance between the yellow sticky trap and the plant was 30 cm, so the height of the trap was always adjusted according to the height of the plant. Observation of B. tabaci population was carried out every 5 days by counting the number of B. tabaci caught in yellow sticky traps. The results showed that the population of B. tabaci in the chili plots intercropped with corn was lower than that in the control plot, especially at the age of 6 weeks after planting (WAP). However, the intercropping of chilies and corn had no significant effect on the incidence of yellow disease in chilies.

Development of a sequential sampling plan for classifying Thrips tabaci (Thysanoptera: Thripidae) populations in onion fields.

Onion thrips, Thrips tabaci Lindeman, is a global pest of onion crops, causing substantial economic damage by diminishing bulb yields and transmitting plant pathogens. Insecticides are used to manage T. tabaci infestations with control decisions traditionally based on action thresholds that require visually counting thrips on a fixed, predetermined number of onion plants per field. However, this approach for treatment decisions is inefficient when thrips populations are well above or below the action threshold. The aim of this research was to develop a sequential sampling plan that would provide a rapid and reliable classification of thrips populations in commercial onion fields above or below prespecified management thresholds. The study was conducted in a total of 24 commercial onion fields in New York in 2021 and 2022. Taylor's power law and Wald's Sequential Probability Ratio Test were used in concert to develop each sampling plan. Simulated and historical field data of thrips populations were used to further validate the efficacy of each sampling plan. Results demonstrated the sequential sampling plan required an average of 78% fewer samples to make a control decision compared with the traditional fixed-sampling approach. Treatment decisions were reached in 72% of cases after inspecting only 10 plants, while only 6% of the cases required examining more than 25 plants. Comparisons with fixed-sample sizes ranging from 23 to 68 plants revealed a 96% agreement in decision-making and a 78% reduction in sampling effort when using the sequential sampling plans.

Efficiency of three indigenous species of coccinellid predators for controlling aphids and whiteflies on cucumbers in greenhouses

Cucumber plants can be infested with many insect pests such as aphids, whiteflies, and thrips, especially in greenhouses, resulting in significant damage to the crops. This study investigated the efficacy of three species of coccinellids (Coccinella undecimpunctata, Coccinella septempunctata, and Hippodamia variegata), indigenous to the Taif region of Saudi Arabia, to control Bemisia tabaci whiteflies and Aphis gossypii aphids on cucumbers in greenhouses. The study was conducted with a release rate of five second-instar larvae of each coccinellid species per plant. One week after the first release of coccinellids, there were no significant differences among the treatment groups in terms of infestation rate, but all three groups differed significantly from the control group. After the first week, the B. tabaci and A. gossypii infestation rates decreased significantly in the H. variegata group compared with the other two coccinellid species, a trend that continued until the end of the experiment. These results suggested that H. variegata was the most effective of the three species at decreasing the B. tabaci population. After the second release of each coccinellid species, the reduction rates were >90% in all three groups, being significantly higher in the H. variegata group. Thus, these results suggest that second-instar larvae of all three coccinellid species would be effective predators of B. tabaci and A. gossypii on cucumbers in greenhouses, with those of H. variegata showing the greatest efficacy. Future research should focus on the effects of these predators on outdoor cucumber fields and on other crops grown in the Taif region.

Biochemical and molecular analyses of insecticide resistance in greenhouse populations of Bemisia tabaci (Hemiptera: Aleyrodidae) in Türkiye

The sweet potato/cotton whitefly Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) is one of the most destructive vegetable pests in greenhouses in Türkiye. While the preferred method of control primarily relies on insecticides such as neonicotinoids, organophosphates and pyrethroids, their intensive use has caused whiteflies to rapidly become resistant. Samples were collected from 13 Turkish B. tabaci greenhouse populations. Bioassays from the Marmara Region identified as high as a 53-fold increase in resistance to chlorpyrifos-ethyl, a 303-fold increase to imidacloprid and a 282-fold increase to acetamiprid. Bioassays in the Central Anatolia Region reported a 76-fold increase in resistance to deltamethrin and—15-fold increase to thiamethoxam. Most of the populations showed cross-resistance for neonicotinoids. All collected B. tabaci populations were determined to be MEAM 1 (also referred to as biotype B) for diagnostic band E0.14. The E0.14 esterase variant that helps to diagnose biotype B insects was found in all individuals from field populations. Almost all populations showed higher non-specific esterase, glutathione-S-transferase (GST) and monooxygenase activity when compared to susceptible SUD-S population. AChE insensitivity assays for individual B. tabaci suggest a target-site modification as a mechanism of resistance to chlorpyrifos-ethyl. This is the first report of AChE variants identified based on their sensitivities to chlorpyrifos ethyl-oxon and pirimicarb in Turkish B. tabaci populations. Fixed ace mutations in the target-site of organophosphates and pyrethroids were identified in six populations. Resistance to organophosphates and neonicotinoids were at least partially related to both ace mutations and insensitive AChE and monooxygenase activities, respectively. The results will help develop effective resistance management programs of B. tabaci in Türkiye.Graphical

Susceptibility of Bemisia tabaci (Hemiptera: Aleyrodidae) Adult Populations to Imidacloprid in Georgia, USA

Abstract Imidacloprid has been one of the most widely used insecticides for managing the sweetpotato whitefly Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) in the United States since the U.S. Environmental Protection Agency first registered it in 1994. A major whitefly control failure occurred in the state of Georgia in 2017 when B. tabaci–induced economic losses in horticultural and field crops surpassed approximately US$160 million. Vegetable growers have historically used imidacloprid for whitefly management, which likely led to the insecticide control failures of whiteflies in spring vegetables. Despite this, only a single site documentation of imidacloprid resistance in adults from 2007 in Georgia exists, making the current status unknown. Thus, it is likely that Georgia has an ongoing risk of imidacloprid-resistant B. tabaci infestations. No multicounty, extensive survey for imidacloprid dose response in whitefly exists for the state of Georgia. Therefore, an adult mortality bioassay of a range of imidacloprid concentrations was used to evaluate B. tabaci populations from several counties in South Georgia, where most of these economic losses occurred. This included a maximum dose concentration representing the current highest labeled rate. Dose response to the insecticide was not uniform across locations, with whiteflies in several areas displaying unexpected susceptibility to imidacloprid. Median lethal concentrations (LC50s) ranging from 0.02 to 196.05 mg of active ingredient per liter in Georgia whitefly populations were substantially lower than the reference Florida whitefly population. This baseline information for the state is critical to future evaluations of this insecticide in resistance management programs.

Effectiveness and Biochemical Impact of Flubendiamide and Flonicamid Insecticides against Bemisia tabaci (Hemiptera: Aleyrodidae) and Residue Dissipation in Cherry Tomato Plants and Soil under Greenhouse Conditions

Abstract We investigated the effectiveness and biochemical impact of the insecticides flubendiamide and flonicamid compared with azadirachtin and acetamiprid against the whitefly Bemisia tabaci (Grennadius) (Hemiptera: Aleyrodidae) infesting cherry tomato (Solanum lycopersicum var. cerasiforme L.) grown under greenhouse conditions. The dissipation of both insecticides in the plants and in the soil also was determined using the QuEChERS (quick, easy, cheap, effective, rugged, and safe) and liquid chromatography–electrospray ionization–mass spectrometry methods. Both insecticides were more effective for reducing B. tabaci populations than were either acetamiprid or azadirachtin. Biochemical analysis revealed that esterase may play an important role in whitefly adaptation to flubendiamide and flonicamid. The QuEChERS method was determined suitable for quickly detecting residues of flubendiamide and flonicamid in complex matrices. The recovery rates on tomato fruit samples were 92.8–106.0%, with a relative standard deviation (RSD) range of 0.46–2.65%. For soil samples, the recovery rates were 81.3–95.7% with RSDs of 1.20–3.86%. We further determined that flubendiamide had dissipation half-lives of 3.13, 3.63, and 3.68 d in tomato fruit, tomato leaves, and soil, respectively. Flonicamid had half-lives of 4.25, 3.54, and 2.60 d in fruit, leaves, and soil, respectively. These results suggest that preharvest intervals of 3 and 7 d are appropriate for flubendiamide and flonicamid, respectively, in cherry tomato production. The risk quotient was >1 by the day 5 after application; however, that value declined to <1 on day 7 after application, indicating little long-term risk to human health.

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.

Can Capsicum spp. genotypes resist simultaneous damage by both Phytophthora capsici and Bemisia tabaci? Can natural enemies of Bemisia complement plant resistance?

Capsicum (Solanaceae) includes peppers and chilies. Phytophthora capsici (Peronosporaceae) and Bemisia tabaci (Hemiptera: Aleyrodidae) are two relevant problems in the production of this genus. Among the sustainable alternatives for disease and pest control, plant resistance and biological control stand out. The main objective of this research was to evaluate the resistance of Capsicum genotypes to damage by P. capsici and infestation by B. tabaci, as well as to diagnose whether the action of predators and parasitoids against B. tabaci could complement the resistance of the plants. The progression of disease caused by P. capsici and infestation by B. tabaci was estimated in 23 Capsicum genotypes, corresponding to the species: Capsicum annuum, Capsicum baccatum, Capsicum chinense, Capsicum frutescens and Capsicum. pubescens, from the GenBank of the National Institute of Agricultural Research (INIAP-Ecuador). Three genotypes: ECU-11993 (C. baccatum), ECU-11991 and ECU-2244 (C. pubescens) showed high susceptibility to both P. capsici damage and B. tabaci infestation. C. baccatum, C. chinense and C. frutescens genotypes showed the highest resistance to both pests, suggesting multiple resistance. Six taxa of predators and parasitoids reduced B. tabaci populations that developed in the most infested genotypes. Plant resistance is a control alternative that could allow the use of biological control, making it environmentally friendly. These results provide the basis for breeding programs in Capsicum.

Phylogenetic and population genetic analyses of Thrips tabaci Lindeman (Thysanoptera: Thripidae) on Allium host in India.

Onion thrips (Thrips tabaci) is a complex of cryptic species with subtle morphological differences and distinct genetic backgrounds; thus, species identification using traditional methods remains challenging. The existence of different haplotypes and genotypes within a species can significantly influence various aspects of its biology, including host preference, reproductive capacity, resistance to pesticides, and vector competence for plant viruses. Understanding the genetic diversity and population structure of cryptic species within T. tabaci will not only aid in the development of more effective control strategies tailored to specific genetic variants but also in monitoring population dynamics, tracking invasive species, and implementing quarantine measures to prevent the spread of economically damaging thrips biotypes. This study aims to explore intraspecies genetic diversity and molecular evolutionary relationships of the mitochondrial cytochrome oxidase gene subunit I (mtCOI) in T. tabaci populations from India. To capture diversity within the Indian T. tabaci populations, amplicon sequencing was performed for the thrips mtCOI gene from eight diverse localities in India. A total of 48 sequences retrieved for the mtCOI gene from the NCBI Nucleotide database were analysed. Multiple insertions and deletions were detected at various genomic positions across the populations from different localities, with the highest variation observed in the 300-400 genome position range. Molecular diversity analyses identified 30 haplotypes within the population, with certain subpopulations exhibiting higher gene flow. Analysis of single nucleotide polymorphism patterns within the mtCOI gene across diverse Indian locales revealed significant intrapopulation genetic heterogeneity and its potential repercussions on gene functionality. Elevated F statistics (Fst) values in the northern-western subpopulations suggested high genetic variability, particularly evident in haplotype networks originating mainly from the northern region, notably Delhi. While most populations displayed stable and ancient evolutionary histories, thrips populations from northern, western, and north-eastern regions indicated rapid growth.

Bemisia tabaci MEAM1 still remains the dominant species in open field crops in Brazil.

Among Bemisia tabaci species, the invasive MEAM1 and MED species are key agricultural pests for many crops. In Brazil, most part of B. tabaci population outbreaks were associated with MEAM1, which, since 1990s quickly spread across the entire country. Later in 2014, the MED was identified in Brazil, initially more restricted to greenhouses, but suddenly reaching new areas in the South and Southeast open regions. Thus, our objective was to investigate the geographical distribution of MEAM1 and MED on open field crops in Brazil. MEAM1 is still the predominant species on open field crops such as soybean, cotton, and tomato. The sequencing of a cytochrome c oxidase subunit I (COI) gene fragment revealed a single haplotype of MEAM1, suggesting the establishment of a single MEAM1 strain in the country. The haplotypes found for MEAM1 and MED are genetically related to the globally dispersed strains, Jap1 and Mch1, respectively. Continuous monitoring of B. tabaci species is crucial because landscape alterations, climatic changes, and pest management methods may shift the B. tabaci species distribution and dominance in Brazilian crop areas.

Natural habitat connectivity and organic management modulate pest dispersal, gene flow, and natural enemy communities.

The simplification and fragmentation of agricultural landscapes generate effects on insects at multiple spatial scales. As each functional group perceives and uses the habitat differently, the response of pest insects and their associated natural enemies to environmental changes varies. Therefore, landscape structure may have consequences on gene flow among pest populations in space. This study aimed to evaluate the effects of local and landscape factors, at multiple scales, on the local infestation, gene flow and broad dispersion dynamics of the pest insect Bemisia tabaci (Genn.) Middle East-Asia Minor 1 (MEAM-1, former biotype B) (Hemiptera: Aleyrodidae) and its associated natural enemies in a tropical agroecosystem. We evaluated the abundance of B. tabaci populations and their natural enemy community in 20 tomato farms in Brazil and the gene flow between farms from 2019 to 2021. Landscapes dominated by agriculture resulted in larger B. tabaci populations and higher gene flow, especially in conventional farms. A higher density of native vegetation patches disfavored pest populations, regardless of the management system. The results revealed that whitefly responds to intermediate spatial scales and that landscape factors interact with management systems to modulate whitefly populations on focal farms. Conversely, whitefly natural enemies benefited from higher amounts of natural vegetation at small spatial scales, while the connectivity between natural habitat patches was beneficial for natural enemies regardless of the distance from the focal farm. The resulting dispersion model predicts that the movement of whiteflies between farms increases as the amount of natural vegetation decreases. Our findings demonstrate that landscape features, notably landscape configuration, can mediate infestation episodes, as they affect pest insects and natural enemies in opposite ways. We also showed that landscape features interact with farm traits, which highlights the need for management strategies at multiple spatial scales. In conclusion, we demonstrated the importance of the conservation of natural areas as a key strategy for area-wide ecological pest management and the relevance of organic farming to benefit natural enemy communities in tropical agroecosystems.

Status of population genetic structure and distribution of Bemisia tabaci genetic groups in vegetable crops and others in India

Whitefly, Bemisia tabaci is one of the polyphagous pests infesting wide variety of crop plants and is vectors of plant viruses belonging to begomivruses whose transmission efficiencies have been reported to be varying. Therefore, we have conducted a series of extensive surveys during 2019-21 to monitor and collect B. tabaci populations across the country and studied the distribution of its genetic groups. Further, PCR amplification, purification, cycle sequencing and partial CO-I gene sequencing has been done to understand population genetic structure and the distribution of genetic groups B. tabaci in India. Data analysis revealed a total of 11 genetic groups of which Asia II-3, Asia II-6 & Asia III were new to India reported for the first time from Chhattisgarh, Andhra Pradesh and Maharashtra for the first time in India. These studies will help farmers and other stakeholders to effectively manage whitefly and whitefly borne begomoviruses for increased vegetables and in turn vegetable oil production.

The first standardized sampling plan designed to scout Bemisia tabaci (Hemiptera: Aleyrodidae) adults in neotropical soybean crops

Glycinemax (L) soybean (Merr) is the world's most widely produced and consumed oilseed. Since its establishment in Brazilian fields, the sweetpotato whitefly Bemisia tabaci (Gennadius 1899) Hemiptera: Aleyrodidae became a notorious pest in soybean fields. However, there is not a sampling plan specifically designed to scout B. tabaci adults in tropical soybean crops. Hence, this study aimed to develop a standardized sampling plan for scouting B. tabaci adults in tropical agriculture. This study was conducted in commercial soybean fields in the Brazilian Savanah from 2017 to 2021, encompassing the vegetative, flowering, and fruiting stages. B. tabaci adults were evaluated to establish a conventional sampling plan, following a five-step approach: (i) determination of the appropriate sample unit, (ii) sampling technique evaluation, (iii) analysis of the frequency distribution of B. tabaci were evaluated to establish a conventional sampling plan, following a five-step approach density, (iv) calculation of the optimal number of samples, and (v) assessment of costs and sampling time. The apical part of the soybean canopy was the ideal sampling unit for assessing B. tabaci populations throughout the plant cycle. Beating the apical part of the plant against a plastic tray proved to be the most suitable sampling technique. A total of 49 samples per field were required to effectively scout this pest. The sample process lasted no more than 5 min per hectare, and the associated costs did not exceed US$ 0.74 per hectare. These results provide the first precise and representative standardized sampling plan to scout B. tabaci adults in tropical soybean fields.

Control of Pepper yellow leaf curl Indonesia virus and Its Vector (Bemisia tabaci Genn.) on Chili Plants (Capsicum annum L.) Using Resistant Variety and Insecticide Application

PepYLCIV, the cause of chili yellow leaf curl disease, is currently widespread in Indonesia and cause up to 100% yield loss, transmitted by whitefly, namely Bemisia tabaci. The purpose of the current study was to determine the effect of using chili varieties with different resistance to Geminivirus and different frequencies of insecticides application on B. tabaci population, PepYLCIV incidence and severity on two chili varieties with different resistance to Geminivirus. The experimental design used was a Split Plot Design. The main plots were chili varieties consisting of Baja MC F1 and Pilar F1. Sub-plots were the frequency of insecticides application which consisted of three levels, those are: not applied, applied once a week, and applied twice a week. Parameters observed were B. tabaci population, disease incidence and severity which carried out every week (starting 23 days after planting). The results showed, the use of insecticides and varieties with different resistance to Geminivirus had no effect on suppressing B. tabaci populations during the rainy season. Thus, chili plants didn’t need insecticides application during the rainy season. The use of resistant varieties can reduce the incidence and severity of chili yellow leaf curl disease, but both varieties reacted similarly to B. tabaci.

Akanthomyces dipterigenus acts as a potential biocontrol agent by causing mortality and inhibiting population growth of Bemisia tabaci

Bemisia tabaci is a worldwide pest, and has developed severe resistance to many insecticide. Therefore, it is great significance to find new substitute for chemical insecticide to control B. tabaci. In this study, selected efficient strains by comparing the virulence of Akanthomyces dipterigenus, Cordyceps javanica, Purpureocillium lilacinum, Penicillium camemberti, Metarhizium anisopliae, and Beauveria bassiana against 2nd-instar nymphs of B. tabaci and bioassays were conducted on various developmental stages of B. tabaci using highly pathogenic strain. Additionally, the effects of medium lethal concentration of high-efficiency strains on the biological parameters of B. tabaci were also studied. The bioassay showed that six entomopathogenic fungi have significant effects on the 2nd-instar nymphs of B. tabaci, the median lethal concentration (LC50) of A. dipterigenus against 2nd-instar nymphs of B. tabaci was only 6.54 × 103 (3.35 × 103–1.13 × 104) conidia mL−1, which was lower than that of the other five fungi, and the median lethal time (LT50) was the shortest. In addition, A. dipterigenus also had lethal effects on eggs, nymphs and adults of B. tabaci, among which the mortality rate of 2nd-instar nymphs was the highest. The fungal treatment affected the population parameters of B. tabaci, R0, r, and λ were significantly reduced, T was significantly prolonged, and had higher preadult mortality and shorter adult longevity, but had no significant effect on the total fecundity. These findings highlight the potential of using A. dipterigenus as a sustainable and eco-friendly alternative to chemical insecticides for controlling B. tabaci populations in agricultural settings.

Genetic diversity of thrips populations on Allium species around the world.

Thrips are a serious pest in many crops. In onion cultivation, Thrips tabaci is the most important, but not the only thrips species causing damage. We investigated which thrips species affects onion and related species worldwide, how much genetic variation there is within T. tabaci populations, and how this evolves. Furthermore, we determined the reproductive mode and the correlation between the genetic and geographic distances. Thrips samples from infested onions or related species were obtained from 14 different locations worldwide. Species and haplotypes were determined through DNA barcoding with the mitochondrial Cytochrome Oxidase subunit I (COI) gene. Thrips tabaci was the most commonly observed species, but Scirtothrips dorsalis, Thrips palmi, Frankliniella intonsa, Frankliniella occidentalis and Frankliniella tenuicornis were also found, especially at the beginning of the growing seasons and depending on the location. The Nei's genetic distance within T. tabaci was less than 5% and the haplotypes were clustered into two phylogenetic groups, each linked to a specific mode of reproduction, thelytokous or arrhenotokous. Thelytokous thrips were more common and more widely distributed than arrhenotokous thrips. A high percentage of heteroplasmy was detected in the arrhenotokous group. Heteroplasmic thrips were only found in populations where thelytokous and arrhenotokous were present in sympatry. Some T. tabaci haplotypes were present in high frequency at several sampled locations. No correlation was found between the genetic and geographic distances, which points to anthropic activities spreading thrips haplotypes throughout the world.

Flavonoid production in tomato mediates both direct and indirect plant defences against whiteflies in tritrophic interactions.

The role of plant flavonoids in direct defences against chewing and sap-sucking herbivorous insects has been extensively characterized. However, little is known about flavonoid-mediated tritrophic interactions between plants, herbivorous insects and natural enemies. In this study, we investigated how flavonoids modulate plant-insect interactions in a tritrophic system involving near-isogenic lines (NILs) of cultivated tomato (Solanum lycopersicum) with high (line NIL-purple hypocotyl [PH]) and low (line NIL-green hypocotyl [GH]) flavonoid levels, with a generalist herbivore whitefly (Bemisia tabaci) and its predatory bug (Orius sauteri). By contrasting levels of tomato flavonoids (direct defence) while manipulating the presence of predators (indirect defence), we found that high production of flavonoids in tomato was associated with a higher inducibility of direct defences and a stronger plant resistance to whitefly infestation and stimulated the emissions of induced volatile organic compounds, thereby increasing the attractiveness of B. tabaci-infested plants to the predator O. sauteri. Furthermore, suppression of B. tabaci population growth and enhancement of plant growth were mediated directly by the high production of flavonoids and indirectly by the attraction of O. sauteri, and the combined effects were larger than each effect individually. Our results conclude that high flavonoid production in tomato enhances herbivore-induced direct and indirect defences to better defend against herbivores in tritrophic interactions. Thus, the development of transgenic plants may present an opportunity to utilize the beneficial role of flavonoids in integrated pest management, while simultaneously maintaining or improving resistance against other pests and pathogens. This article is protected by copyright. All rights reserved.