Distribution of Bemisia tabaci Genetic Groups in India

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.

Bottle gourd IC-0262269, a super-susceptible genotype to tomato leaf curl Palampur virus

While conducting field trial of 82 genotypes of bottle gourd at Delhi during 2020-2021, a particular genotype, IC-0262269 was found to be affected by chlorotic curly stunt disease (CCSD). The affected plants were severely stunted and bearing very small chlorotic and crinkle leaves. The disease incidence in the said genotype was as high as 80% among different replicated trial blocks. The application of PCR using a generic primers specific to begomoviruses, as well as species-specific PCR diagnostics to six tomato-infecting begomoviruses: tomato leaf curl New Delhi virus (ToLCNDV), tomato leaf curl Palampur virus (ToLCPalV), tomato leaf curl Joydebpur virus (ToLCJoV), tomato leaf curl Gujrat virus (ToLCGuV), tomato leaf curl Bangalore virus (ToLCBV), and chilli leaf curl virus (ChiLCV) showed that, only ToLCPalV could be detected in the genotype IC-0262269. Following, rolling circle amplification, cloning and sequencing of full-length DNA-A and DNA-B genome of an isolate BoG1-ND from the genotype IC-0262269 revealed association of ToLCPalV with the disease. The successful agro-infection of the cloned genome of BoG1-ND (DNA-A and DNA-B) in the plants of Nicotiana benthamiana and bottle gourd demonstrated that ToLCPalV is the causal begomovirus of CCSD. The study provides the first evidence of the natural occurrence of ToLCPalV in bottle gourd crop and also showed that the bottle gourd genotype IC-0262269 is super-susceptible to ToLCPalV.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03838-y.

Geographical distribution of tomato-infecting begomoviruses in major cucurbits in India: a diagnostic analysis using begomovirus species specific PCR

Cucurbits are an essential summer-season vegetable crops, but they are highly vulnerable from a range of abiotic and biotic factors. One of the significant biotic factors posing a growing menace to the production of major cucurbits in India is the emergence of tomato-infecting begomoviruses. In this study, we utilized PCR-based species-specific primers, developed earlier in our laboratory for the detection of begomoviruses infecting tomato and chilli plants, to identify begomoviruses in cucurbits across various regions of India. Leaf samples from major cucurbits were collected from different regions of Haryana, Delhi, Uttar Pradesh, Chhattisgarh, Maharashtra, Telangana and Karnataka, during the year 2020-2021. Total nucleic acid (TNA) was extracted from the samples and subjected to PCR using a generic primer specific to begomoviruses. The samples that exhibited positive amplification were further tested using six different species-specific primers targeting specific begomovirus species, namely Tomato leaf curl New Delhi virus (ToLCNDV), Tomato leaf curl Palampur virus (ToLCPalV), Tomato leaf curl Bangalore virus (ToLCBV), Tomato leaf curl Joydebpur virus (ToLCJoV), Tomato leaf curl Gujarat virus (ToLCGuV), and Chilli leaf curl virus (ChiLCV). The PCR analysis revealed that among the 551 plant samples tested, a total of 124 samples exhibited positive amplification using the universal begomovirus PCR. Specifically, 47 samples tested positive for ToLCNDV, 73 samples were positive for ToLCPalV and only one sample showed positive amplification for ChiLCV. However, none of the samples tested positive for ToLCJoV, ToLCGuV and ToLCBV. These findings from our study indicate the prevalence of ToLCNDV and ToLCPalV in major cucurbits across India. Furthermore, the study highlights the varied distribution of begomoviruses in major cucurbits between northern and southern regions of India.

Native and Non-Native Bemisia tabaci NAFME Haplotypes Can Be Implicated in Dispersal of Endemic and Introduced Begomoviruses in Oman

Irrigated agriculture and global trade expansion have facilitated diversification and spread of begomoviruses (Geminiviridae), transmitted by the Bemisia tabaci (Gennadius) cryptic species. Oman is situated on major crossroads between Africa and South Asia, where endemic/native and introduced/exotic begomoviruses occur in agroecosystems. The B. tabaci 'B mitotype' belongs to the North Africa-Middle East (NAFME) cryptic species, comprising at least eight endemic haplotypes, of which haplotypes 6 and/or 8 are recognized invasives. Prevalence and associations among native and exotic begomoviruses and NAFME haplotypes in Oman were investigated. Nine begomoviral species were identified from B. tabaci infesting crop or wild plant species, with 67% and 33% representing native and exotic species, respectively. Haplotypes 2, 3, and 5 represented 31%, 3%, and 66% of the B. tabaci population, respectively. Logistic regression and correspondence analyses predicted 'strong'- and 'close' virus-vector associations involving haplotypes 5 and 2 and the exotic chili leaf curl virus (ChiLCV) and endemic tomato yellow leaf curl virus-OM, respectively. Patterns favor a hypothesis of relaxed virus-vector specificity between an endemic haplotype and the introduced ChiLCV, whereas the endemic co-evolved TYLCV-OM and haplotype 2 virus-vector relationship was reinforced. Thus, in Oman, at least one native haplotype can facilitate the spread of endemic and introduced begomoviruses.

Ecological Factors Associated with the Distribution of Bemisia tabaci Cryptic Species and Their Facultative Endosymbionts

The sweetpotato whitefly, Bemisia tabaci species complex, comprises at least 44 morphologically indistinguishable cryptic species, whose endosymbiont infection patterns often varied at the spatial and temporal dimension. However, the effects of ecological factors (e.g., climatic or geographical factors) on the distribution of whitefly and the infection frequencies of their endosymbionts have not been fully elucidated. We, here, analyzed the associations between ecological factors and the distribution of whitefly and their three facultative endosymbionts (Candidatus Cardinium hertigii, Candidatus Hamiltonella defensa, and Rickettsia sp.) by screening 665 individuals collected from 29 geographical localities across China. The study identified eight B. tabaci species via mitochondrial cytochrome oxidase I (mtCOI) gene sequence alignment: two invasive species, MED (66.9%) and MEAM1 (12.2%), and six native cryptic species (20.9%), which differed in distribution patterns, ecological niches, and high suitability areas. The infection frequencies of the three endosymbionts in different cryptic species were distinct and multiple infections were relatively common in B. tabaci MED populations. Furthermore, the annual mean temperature positively affected Cardinium sp. and Rickettsia sp. infection frequencies in B. tabaci MED but negatively affected the quantitative distribution of B. tabaci MED, which indicates that Cardinium sp. and Rickettsia sp. maybe play a crucial role in the thermotolerance of B. tabaci MED, although the host whitefly per se exhibits no resistance to high temperature. Our findings revealed the complex effects of ecological factors on the expansion of the invasive whitefly.

Genetic diversity of cryptic species of Bemisia tabaci in Asia

Bemisia tabaci is a species complex consisting of various genetically different cryptic species worldwide. To understand the genetic characteristics and geographic distribution of cryptic species of B. tabaci in Asia, we conducted an extensive collection of B. tabaci samples in ten Asian countries (Bangladesh, Indonesia, Japan, Korea, Myanmar, Nepal, Philippines, Singapore, Taiwan, and Vietnam) from 2013 to 2020 and determined 56 different partial sequences of mitochondrial cytochrome oxidase subunit I (COI) DNA. In addition, information on 129 COI sequences of B. tabaci identified from 16 Asian countries was downloaded from the GenBank database. Among the total 185 COI sequences of B. tabaci, the sequence variation reached to 19.68%. In addition, there were 31 cryptic species updated from 16 countries in Asia, that is, Asia I, Asia I India, Asia II (1-13), Asia III, Asia IV, Asia V, China 1-6, MEAM (1, 2, K), MED, Australia/Indonesia, Japan (1 and 2). Further, MED cryptic species consisted of 2 clades, Q1 and Q2. This study provides updated information to understand the genetic variation and geographic diversity of B. tabaci in Asia.

Mitochondrial Genetic Diversity of Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) Associated with Cassava in Lao PDR

Cassava Mosaic Disease (CMD) caused by Sri Lankan cassava mosaic virus (SLCMV), has rapidly spread in Southeast Asia (SEA) since 2016. Recently it has been documented in Lao PDR. Previous reports have identified whitefly species of B. tabaci as potential vectors of CMD in SEA, but their occurrence and distribution in cassava fields is not well known. We conducted a countrywide survey in Lao PDR for adult whiteflies in cassava fields, and determined the abundance and genetic diversity of the B. tabaci species complex using mitochondrial cytochrome oxidase I (mtCOI) sequencing. In order to expedite the process, PCR amplifications were performed directly on whitefly adults without DNA extraction, and mtCOI sequences obtained using nanopore portable-sequencing technology. Low whitefly abundances and two cryptic species of the B. tabaci complex, Asia II 1 and Asia II 6, were identified. This is the first work on abundance and genetic identification of whiteflies associated with cassava in Lao PDR. This study indicates currently only a secondary role for Asia II in spreading CMD or as a pest. Routine monitoring and transmission studies on Asia II 6 should be carried out to establish its potential role as a vector of SLCMV in this region.

Evaluation of the Bioefficacy and Insecticide Compatibility of Entomopathogens for Management of Whitefly (Hemiptera: Aleyrodidae) on Upland Cotton Under Laboratory and Polyhouse Conditions

Entomopathogens (EPFs) are potential alternatives to chemical insecticides for managing Bemisia tabaci (Genn.), an invasive pest of the cotton crop. EPFs alone may not always provide enough insect pest control, but combining EPFs with pesticides, provided both components are compatible, can make an integrated pest management program considerably more effective. Hence, the bioefficacy of EPFs against whitefly, their compatibility with pesticides, and the factors responsible for determining compatibility were studied. The highest nymphal mortality was recorded with the Beauveria bassiana strains Bb-4511 (95.1%) and Bb-4565 (89.9%), and Metarhizium anisopliae Ma-1299 (86.7%) at 1 × 10⁶ conidia ml^-1. Lower LC₅₀ values were observed for Cordyceps javanica Cj-089 and Bb-4511, 0.2 × 10⁴ and 0.5 × 10⁴ conidia ml^-1, respectively. The toxicity index values in insecticide sensitivity assays ranged from 19.4 to 119.6% among all the EPFs. Comparatively, all the EPFs except Bb-4543 and Bb-4565 showed compatible to moderately toxic reactions to neonicotinoids and spinosyns. Organophosphates (ethion) and pyrethrins (bifenthrin) were toxic to very toxic to all the EPFs except Bb-4511, Fv-083, and Ma-1299. Cj-102 and Cj-089 were compatible with 50% of the average recommended dose of bifenthrin and ethion, and the average recommended dose for the field application of neonicotinoids and spinosyns. Principal component analysis showed that spore production and toxicity index values correlate with each other and are responsible for determining the EPF compatibility with insecticides. The EPF spore production and toxicity index are important factors for determining chemical compatibility. Compatible EPFs can be used individually or in combination as promising and compatible biological alternatives to insecticides in the management of whitefly in cotton.

Unraveling the Basis of Neonicotinoid Resistance in Whitefly Species Complex: Role of Endosymbiotic Bacteria and Insecticide Resistance Genes

Bemisia tabaci (whitefly) is one of the most detrimental agricultural insect pests and vectors of many plant viruses distributed worldwide. Knowledge of the distribution patterns and insecticide resistance of this cryptic species is crucial for its management. In this study, genetic variation of mitochondrial cytochrome oxidase subunit 1 (MtCoI) gene of B. tabaci was analyzed followed by a study of the infection profile of various endosymbionts in 26 whitefly populations collected from West Bengal, India. Phylogenetic analysis revealed Asia I as the major cryptic species (65.38%), followed by Asia II 5, China 3, and Asia II 7, which were diversified into 20 different haplotypes. In addition to the primary endosymbiont (C. poriera), each of the four whitefly species showed a variable population of three secondary endosymbionts, majorly Arsenophonus with the highest infection rate (73.07%), followed by Wolbachia and Rickettsia. Further phylogenetic analyses revealed the presence of two subgroups of Arsenophonus, viz., A1 and A2, and one each in Wolbachia (W1) and Rickettsia (R3). Resistance to thiamethoxam, imidacloprid, and acetamiprid insecticides was analyzed for a clear picture of pesticide resistance status. The highest susceptibility was noted toward thiamethoxam (LC₅₀ = 5.36 mg/L), followed by imidacloprid and acetamiprid. The whitefly population from Purulia and Hooghly districts bearing Asia II 7 and Asia II 5 cryptic species, respectively, shows maximum resistance. The differences in mean relative titer of four symbiotic bacteria among field populations varied considerably; however, a significant positive linear correlation was observed between the resistance level and relative titer of Arsenophonus and Wolbachia in the case of imidacloprid and thiamethoxam, while only Wolbachia was found in case of acetamiprid. Expression analysis demonstrated differential upregulation of insecticide resistance genes with Purulia and Hooghly populations showing maximally upregulated P450 genes. Moreover, thiamethoxam and imidacloprid resistance ratio (RR) showed a significant correlation with CYP6CM1, CYP6DZ7, and CYP4C64 genes, while acetamiprid RR correlated with CYP6CX1, CYP6DW2, CYP6DZ7, and CYP4C64 genes. Taken together, these findings suggested that P450 mono-oxygenase and symbiotic bacteria together affected whitefly resistance to neonicotinoids. Hence, a symbiont-oriented management programme could be a better alternative to control or delay resistance development in whitefly and can be used for pesticide clean-up in an agricultural field.

Pervasive Endosymbiont Arsenophonus Plays a Key Role in the Transmission of Cotton Leaf Curl Virus Vectored by Asia II-1 Genetic Group of Bemisia tabaci

Insects often coevolved with their mutualistic partners such as gut endosymbionts, which play a key in the physiology of host. Studies on such interactions between Bemisia tabaci and its primary and secondary endosymbionts have gained importance due to their indispensable roles in the biology of this insect. Present study reports the predominance of two secondary endosymbionts, Arsenophonus and Cardinium in the Asia II-1 genetic group of whitefly and elucidates their role in the transmission of its vectored Cotton leaf curl virus. Selective elimination of endosymbionts was optimized using serial concentration of ampicillin, chloramphenicol, kanamycin, tetracycline, and rifampicin administered to viruliferous whiteflies through sucrose diet. Primary endosymbiont, Portiera was unresponsive to all the antibiotics, however, rifampicin and tetracycline at 90 μg/ml selectively eliminated Arsenophonus from the whitefly. Elimination of Arsenophonus resulted in significant decrease in virus titer from viruliferous whitefly, further the CLCuV transmission efficiency of these whiteflies was significantly reduced compared to the control flies. Secondary endosymbiont, Cardinium could not be eliminated completely even with higher concentrations of antibiotics. Based on the findings, Arsenophonus plays a key role in the retention and transmission of CLCuV in the Asia II-1 genetic group of B. tabaci, while the role of Cardinium could not be established due to its unresponsiveness to antibiotics.

A new record of Asia II 5 genetic group of Bemisia tabaci (Gennadius) in the major potato growing areas of India and its relationship with tomato leaf curl New Delhi virus infecting potato

The whitefly, Bemisia tabaci (Gennadius), is responsible for significant yield losses in many crops, including potato, by sucking the phloem sap and transmitting a number of plant viruses. B. tabaci is a complex of cryptic species which is commonly designated as genetic groups. The B. tabaci genetic groups differ biologically with respect to host plant preference, insecticidal resistance, reproduction capacity, and ability to transmit begomoviruses. Therefore, understanding genetic variation among populations is important for establishing crop-specific distribution profile and management. We sequenced the mitochondrial cytochrome oxidase I (mtCOI) gene of B. tabaci collected from major potato growing areas of India. BLAST analysis of the 24 mtCOI sequences with reference Gene Bank sequences revealed four B. tabaci genetic groups prevailing in this region. mtCOI analysis exhibited the presence of Asia II 1, Asia II 5, Asia 1, and MEAM1 B. tabaci genetic groups. Our study highlighted that a new genetic group Asia II 5 has been detected in Indo-Gangetic Plains. Further virus-vector relationship study of ToLCNDV with Asia II 5 B. tabaci revealed that females are efficient vector of this virus as compared to males. This behavior of females might be due to their ability to acquire more virus titer than males. This study will help in better understanding of whitefly genetic group mediated virus diseases.

Capsicum-infecting begomoviruses as global pathogens: host-virus interplay, pathogenesis, and management

Whitefly-transmitted begomoviruses are among the major threats to the cultivation of Capsicum spp. (Family: Solanaceae) worldwide. Capsicum-infecting begomoviruses (CIBs) have a broad host range and are commonly found in mixed infections, which, in turn, fuels the emergence of better-adapted species through intraspecies and interspecies recombination. Virus-encoded proteins hijack host factors to breach the well-coordinated antiviral response of plants. Epigenetic modifications of histones associated with viral minichromosomes play a critical role in this molecular arms race. Moreover, the association of DNA satellites further enhances the virulence of CIBs as the subviral agents aid the helper viruses to circumvent plant antiviral defense and facilitate expansion of their host range and disease development. The objective of this review is to provide a comprehensive overview on various aspects of CIBs such as their emergence, epidemiology, mechanism of pathogenesis, and the management protocols being employed for combating them.

Evaluation of bioefficacy potential of entomopathogenic fungi against the whitefly (Bemisia tabaci Genn.) on cotton under polyhouse and field conditions

The whitefly, Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae), is becoming a serious problem on Bt cotton. It causes enormous crop loss through its direct feeding and as a vector of cotton leaf curl virus. Chemical-dependent management is harming the environment and increased insecticide resistance is often observed in the fields. Identification of most virulent strains of entomopathogenic fungi (EPF) is essential to serve as an important component of an IPM program for management of B. tabaci. Compared to B. tabaci adults, the nymphal stage is reported to be more susceptible to entomopathogens, and targeting nymphs also helps vector management. We evaluated the bioefficacy of EPF and chemical pesticides against nymphs of B. tabaci on Bt cotton under polyhouse and field conditions. The bioefficacy index (BI) was considered as a mechanism to select the most effective EPF strains for field evaluation. The highest nymphal mortality under polyhouse conditions was recorded for Metarhizium anisopliae NA-01299 (86.7%), Beauveria bassiana MT-4511 (85.1%), Cordyceps javanica IT-10498 (81.1%), IT-10499 (81%), and B. bassiana NA-0409 (78.2%) relative to other EPF strains, spiromesifen (69.6%), buprofezin (62.2%) and pyriproxyfen (52.7%) at 7-days-post-spray treatment (DAS). However, among all the EPF, the highest BI was recorded in C. javanica IT-10499 (77%), IT-10495 (75.4%), Fusarium verticillioides IT-10493 (74.6%), and B. bassiana MT-4511 (73.1%). The pooled data of two-year field trials (2017-18 & 2018-19) revealed that the highest nymphal mortality was recorded for MT-4511 (85%), IT-10499 (83.2%), and pyriproxyfen 10% EC (78.6%) at 7-DAS. The BI-based selection of EPF proved to be a useful predictor of field efficacy. A sequential spray of the selected EPF would be a vital approach for resilient and sustainable integrated management of the B. tabaci nymphal population under field conditions.

Within-Season Changes in Land-Use Impact Pest Abundance in Smallholder African Cassava Production Systems

Cassava (Manihot esculenta Crantz), an important commercial and food security crop in East and Central Africa, continues to be adversely affected by the whitefly Bemisia tabaci. In Uganda, changes in smallholder farming landscapes due to crop rotations can impact pest populations but how these changes affect pest outbreak risk is unknown. We investigated how seasonal changes in land-use have affected B. tabaci population dynamics and its parasitoids. We used a large-scale field experiment to standardize the focal field in terms of cassava age and cultivar, then measured how Bemisia populations responded to surrounding land-use change. Bemisia tabaci Sub-Saharan Africa 1 (SSA1) was identified using molecular diagnostics as the most prevalent species and the same species was also found on surrounding soybean, groundnut, and sesame crops. We found that an increase in the area of cassava in the 3-7-month age range in the landscape resulted in an increase in the abundance of the B. tabaci SSA1 on cassava. There was a negative relationship between the extent of non-crop vegetation in the landscape and parasitism of nymphs suggesting that these parasitoids do not rely on resources in the non-crop patches. The highest abundance of B. tabaci SSA1 nymphs in cassava fields occurred at times when landscapes had large areas of weeds, low to moderate areas of maize, and low areas of banana. Our results can guide the development of land-use strategies that smallholder farmers can employ to manage these pests.

Simulation of leaf curl disease dynamics in chili for strategic management options

Leaf curl, a whitefly-borne begomovirus disease, is the cause of frequent epidemic in chili. In the present study, transmission parameters involved in tripartite interaction are estimated to simulate disease dynamics in a population dynamics model framework. Epidemic is characterized by a rapid conversion rate of healthy host population into infectious type. Infection rate as basic reproduction number, R₀ = 13.54, has indicated a high rate of virus transmission. Equilibrium population of infectious host and viruliferous vector are observed to be sensitive to the immigration parameter. A small increase in immigration rate of viruliferous vector increased the population of both infectious host and viruliferous vector. Migrant viruliferous vectors, acquisition, and transmission rates as major parameters in the model indicate leaf curl epidemic is predominantly a vector -mediated process. Based on underlying principles of temperature influence on vector population abundance and transmission parameters, spatio-temporal pattern of disease risk predicted is noted to correspond with leaf curl distribution pattern in India. Temperature in the range of 15–35 °C plays an important role in epidemic as both vector population and virus transmission are influenced by temperature. Assessment of leaf curl dynamics would be a useful guide to crop planning and evolution of efficient management strategies.

Inaccessibility to double-stranded RNAs in plastids restricts RNA interference in Bemisia tabaci (whitefly)

BACKGROUND

RNA interference (RNAi) has emerged as a promising technology for insect pest control. Because of the accumulation of high levels of long double-stranded RNAs (dsRNAs) in plastids, it was previously shown that expression of dsRNAs from plastid genome led to higher mortality of some insect pests with chewing mouthparts than dsRNAs expression from nuclear genome. However, whether plastid-expressed dsRNAs have effects on phloem sap-sucking pests is unknown. In this study, we compared the RNAi effects of nuclear transgenic and transplastomic plants on the whitefly Bemisia tabaci, a serious sap-sucking pest.

RESULTS

Nuclear transgenic and transplastomic tobacco plants were developed for the expression of dsRNA against BtACTB gene of Bemisia tabaci, respectively. Feeding nuclear transgenic plants to Bemisia tabaci resulted in reduced gene expression of BtACTB and survival rate, and impaired fecundity of Bemisia tabaci. We did not observe any effects of transplastomic plants on Bemisia tabaci fitness. Furthermore, we found that the inability of B. tabaci to obtain dsRNAs from plastids might restrict its RNAi responses.

CONCLUSION

Our study indicated that the expression of dsRNAs in nuclear transgenic plants was more effective than that in transplastomic plants for the control of Bemisia tabaci. The inaccessibility of Bemisia tabaci to plastids contributes to the inefficiency of plastid-mediated RNAi. Our findings are of great significance to future optimization of transgenically delivered RNAi approaches for efficient controlling of sap-sucking pests. © 2020 Society of Chemical Industry.

Dominance of recombinant cotton leaf curl Multan-Rajasthan virus associated with cotton leaf curl disease outbreak in northwest India

Cotton leaf curl disease (CLCuD), caused by whitefly (Bemisiatabaci) transmitted single-stranded DNA viruses belonging to the Genus, Begomovirus (family, Geminiviridae) in association with satellite molecules; is responsible for major economic losses in cotton in three northwest (NW) Indian states Haryana, Punjab, and Rajasthan. Annual CLCuD incidences during 2012 to 2014 were estimated to be 37.5%, 63.6%, and 38.8% respectively. Cotton leaves were collected from symptomatic plants annually for three years and subjected to DNA isolation, followed by rolling circle amplification (RCA), cloning, and DNA sequencing of apparently full-length begomoviral genomes and associated betasatellites and alphasatellites. Among the thirteen CLCuD-begomoviral genomes recovered, eight were identified as Cotton leaf curl Multan virus-Rajasthan (CLCuMuV-Ra), one as -Pakistan (PK) and another as -Faisalabad (Fai), whereas, three were as Cotton leaf curl Kokhran virus-Burewala (CLCuKoV-Bu), indicating that CLCuMuV-Ra was the most prevalent begomovirus species. Five of the eight CLCuMuV-Ra sequences were found to be recombinants. The CLCuMuV-Ra- associated satellites consisted of Cotton leaf curl Multan betasatellite (CLCuMB), and Gossypium darwinii symptomless alphasatellite (GDarSLA), and Croton yellow vein mosaic alphasatellite (CrYVMoA). The second most abundant helper virus species, CLCuKoV-Bu, was associated with CLCuMB and GDarSLA.

Transmission efficiency of Cotton leaf curl Multan virus by three cryptic species of Bemisia tabaci complex in cotton cultivars

Cotton leaf curl Multan virus (CLCuMuV) is a serious and economically important viral disease agent in cotton and ornamental plants like Hibiscus in many regions of the world, especially in South Asia. CLCuMuV is transmitted exclusively by Bemisia tabaci cryptic species complex. This virus was recently recorded in southern China, presumably an invasion from South Asia. This study was performed to estimate the efficiency of three species of the B. tabaci whitefly complex (tentatively named as MEAM1, MED and Asia II 7, respectively) to transmit CLCuMuV and Cotton leaf curl multan virus betasatelite (CLCuMuB). Transmission assays and real-time quantitative PCR were conducted using three cultivars of cotton, Gossypium hirsutum, including 112-2, Xinhai-21 and Zhongmian-40. The results indicated that Asia II 7 was able to transmit the virus to two of the cotton cultivars, i.e. 112-2 and Xinhai-21, with the highest transmission efficiencies of 40% and 30%, respectively, but was unable to transmit the virus to the cotton cultivar Zhongmian-40. MEAM1 and MED failed to transmit CLCuMuV and CLCuMuB to any of the three cotton cultivars. After the three cryptic species of whiteflies had fed on virus-infected cotton plants for 48 h, the relative quantity of CLCuMuV in Asia II 7 was detected to be significantly higher than that in both MEAM1 and MED (P < 0.05). These results indicate that among the three species of whiteflies Asia II 7 is likely the most efficient vector for CLCuMuV and CLCuMuB in Malvaceae crops in China. Our findings provide valuable information to the control of viral diseases caused by CLCuMuV in the field.

Genetic Status and Endosymbionts Diversity of Bemisia tabaci (Gennadius) on Hosts Belonging to Family Malvaceae in India

A study was instigated to examine the genetic status and distribution of known endosymbionts namely Portiera, Rickettsia, Wolbachia, Cardinium, and Arsenophonus in the populations of Bemisia tabaci (Gennadius) from three host plants: cotton (Gossypium herbaceum), okra (Abelmoschus esculentus L.), and China rose (Hibiscus rosa-sinensis) belonging to the family Malvaceae. The presence of four secondary endosymbionts Rickettsia, Wolbachia, Cardinium, and Arsenophonus was checked in Bemisia tabaci populations. Phylogenetic analyses grounded on the mitochondrial cytochrome oxidase I gene (mtCO1) unveiled the presence of Asia 1, Asia II 1, and Asia II 7 genetic groups for Bemisia tabaci on abovementioned crops. Individuals were examined for symbiotic bacterial infection with specific primers amplifying the 16S rRNA gene for Portiera, Rickettsia, Cardinium, and Wolbachia, and the 23S rRNA gene for Arsenophonus. The results show that Portiera was present in all the Bemisia tabaci samples. However, variations were noted in the circulation frequencies of secondary endosymbionts among the Bemisia tabaci populations. A significant difference was noticed in the distribution frequency of Rickettsia between cotton and China rose or okra with their p values as 0.016 and 0.033 respectively. The uneven incidence of secondary endosymbionts ropes the assumption that each endosymbiotic bacterium not only has a role in the endurance but may contribute to the polyphagous nature of Bemisia tabaci. It also brings an uncomplicated evidence for progressive studies on control measures of this notorious insect pest.

Genetic Diversity of Bemisia tabaci (Hemiptera: Aleyrodidae) Species Complex Across Malaysia

The tobacco whitefly Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) is a cryptic species complex with members capable of inducing huge economic losses. Precise identification of members of this complex proves essential in managing existing populations and preventing new incursions. Despite records of serious outbreaks of this pest in Malaysia little is known about species status of B. tabaci in this region. To address this, a comprehensive sampling of B. tabaci from different host plants was conducted in 10 states of Malaysia from 2010 to 2012. Members of the complex were identified by sequencing partial mitochondrial cytochrome oxidase subunit I (mtCOI) gene and constructing a Bayesian phylogenetic tree. Seven putative species were identified including Asia I, Mediterranean (MED), China 1, China 2, Asia II 6, Asia II 7, and Asia II 10. The most important finding of the study is the identification of the invasive MED species from locations without previous records of this species. All putative species except Asia I and MED are recorded from Malaysia for the first time. This study provided the first introductory map of B. tabaci species composition in Malaysia and emphasizes the urgent need for further studies to assess the status of MED invasion in this country.

Genetic diversity and geographic distribution of the Bemisia tabaci species complex in Bangladesh

Bemisia tabaci (Gennadius) is a species complex consisting of at least 40 cryptic species. Although the genetic diversity of B. tabaci has been studied in various regions, little is known about distribution in Bangladesh, which is covered by the Bengal delta, the largest delta on Earth. We conducted an extensive survey throughout the country and determined the nucleotide sequence of mitochondrial cytochrome c oxidase subunit 1 (COI) from 110 individuals. We then examined phylogenetic relationships. The results identified four cryptic species that expressed distinct interspecific variation but low intraspecific variation. Asia I was the most abundant, both Asia II 1 and Asia II 5 were moderately abundant, and Asia II 10 was found only in the central region. COI sequences of each cryptic species were distinctive and differentiated into many haplotypes. Our study provides important information to better understand the genetic diversity and geographic distribution of cryptic species in Bangladesh and nearby countries.

Species-complex diversification and host-plant associations in Bemisia tabaci: A plant-defence, detoxification perspective revealed by RNA-Seq analyses

Insect–plant associations and their role in diversification are mostly studied in specialists. Here, we aimed to identify macroevolution patterns in the relationships between generalists and their host plants that have the potential to promote diversification. We focused on the Bemisia tabaci species complex containing more than 35 cryptic species. Mechanisms for explaining this impressive diversification have focused so far on allopatric forces that assume a common, broad, host range. We conducted a literature survey which indicated that species in the complex differ in their host range, with only few showing a truly broad one. We then selected six species, representing different phylogenetic groups and documented host ranges. We tested whether differences in the species expression profiles of detoxification genes are shaped more by their phylogenetic relationships or by their ability to successfully utilize multiple hosts, including novel ones. Performance assays divided the six species into two groups of three, one showing higher performance on various hosts than the other (the lower performance group). The same grouping pattern appeared when the species were clustered according to their expression profiles. Only species placed in the lower performance group showed a tendency to lower the expression of multiple genes. Taken together, these findings bring evidence for the existence of a common detoxification “machinery,” shared between species that can perform well on multiple hosts. We raise the possibility that this “machinery” might have played a passive role in the diversification of the complex, by allowing successful migration to new/novel environments, leading, in some cases, to fragmentation and speciation.

A nation-wide genetic survey revealed a complex population structure of Bemisia tabaci in Pakistan

The whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) is a cryptic species complex distributed worldwide. In Pakistan, B. tabaci poses a serious threat to agriculture production. To understand its diversity in Pakistan, a large-scale sampling was conducted from various locations of all four provinces of the country and Mitochondrial cytochrome oxidase I (mtCOI) gene sequencing was used to determine the whiteflies genetically. The study revealed the presence of five different cryptic species in Pakistan namely Asia II-1, Asia II-5, Asia II-7, Asia II-8 and MEAM-1, respectively. Among them, Asia II-1, which was previously reported from a few areas in the country, had been found now to be prevalent all over the country covering 88.7% of all the sequenced samples. Based on the mtCOI sequences and genetic distance analyses, the diversity of Asia II-1 was much greater than all other cryptic species, which exist only in small patches.

Assessment of bacterial endosymbionts and the host, Bemisia tabaci (Hemiptera: Aleyrodidae), using rRNA and mitochondrial cytochrome oxidase I gene sequences

Endosymbionts are vital factor for arthropod ecology. The whitefly Bemisia tabaci (Hemiptera: Aleyrodidae) is a cryptic species complex composed of more than 34 putative species. Moreover to the primary endosymbiont Portiera aleyrodidarum, six secondary endosymbionts Cardinium, Arsenophonus, Rickettsia, Wolbachia, Hamiltonella and Fritschea are known in B. tabaci. Here, we tested four of the six secondary endosymbiont lineages (excluding Fritschea and Hamiltonella) from 180 whitely individuals collected from six host plants belonging to families Solanaceae (Brinjal, Tomato and Potato) and Fabaceae (Soyabean, Mungbean and Subabool). Phylogenetic studies grounded on the mitochondrial cytochrome I gene revealed the presence of Asia 1, Asia II 1 and Asia II 7 genetic groups for B. tabaci. Specific primers targeting 16S rRNA and 23S rRNA gene were used for estimating the bacterial endosymbionts. As a primary endosymbiont Portiera aleyrodidarum was present in all the studied samples; whereas, an uneven distribution of secondary endosymbionts were recorded. Overall our finding exposes the variation and diversity of endosymbionts within the B. tabaci collected from different host plants and outlines the genetic groups of the insect pest. The study delivers a significant information concerning the circulation of secondary endosymbionts with host preferences of B. tabaci and provides suggestion for progressive studies on targeting the specific endosymbionts with respect to host for the control measures.

African ancestry of New World, Bemisia tabaci-whitefly species

Bemisia tabaci whitefly species are some of the world’s most devastating agricultural pests and plant-virus disease vectors. Elucidation of the phylogenetic relationships in the group is the basis for understanding their evolution, biogeography, gene-functions and development of novel control technologies. We report here the discovery of five new Sub-Saharan Africa (SSA) B. tabaci putative species, using the partial mitochondrial cytochrome oxidase 1 gene: SSA9, SSA10, SSA11, SSA12 and SSA13. Two of them, SSA10 and SSA11 clustered with the New World species and shared 84.8‒86.5% sequence identities. SSA10 and SSA11 provide new evidence for a close evolutionary link between the Old and New World species. Re-analysis of the evolutionary history of B. tabaci species group indicates that the new African species (SSA10 and SSA11) diverged from the New World clade c. 25 million years ago. The new putative species enable us to: (i) re-evaluate current models of B. tabaci evolution, (ii) recognise increased diversity within this cryptic species group and (iii) re-estimate divergence dates in evolutionary time.

Diversity and Distribution of Cryptic Species of the Bemisia tabaci (Hemiptera: Aleyrodidae) complex in Pakistan

Bemisia tabaci (Gennadius; Hempitera: Aleyrodidae) is considered to be a cryptic (sibling) species complex, the members of which exhibit morphological invariability while being genetically and behaviorally distinct. Members of the complex are agricultural pests that cause direct damage by feeding on plants, and indirectly by transmitting viruses that cause diseases leading to reduced crop yield and quality. In Pakistan, cotton leaf curl disease, caused by multiple begomovirus species, is the most economically important viral disease of cotton. In the study outlined here, the diversity and geographic distribution of B. tabaci cryptic species was investigated by analyzing a taxonomically informative fragment of the mitochondrial cytochrome c oxidase 1 gene (mtCOI-3'). The mtCOI-3' sequence was determined for 285 adult whiteflies and found to represent six cryptic species, the most numerous being Asia II-1 and Middle East Asia Minor 1 (MEAM-1), the later also referred to as the B-biotype, which was previously thought to be confined to Sindh province but herein, was also found to be present in the Punjab province. The endemic Asia I was restricted to Sindh province, while an individual in the Asia II-8 was identified in Pakistan for the first time. Also for the first time, samples were collected from northwestern Pakistan and Asia II-1 was identified. Results indicate that in Pakistan the overall diversity of B. tabaci cryptic species is high and, based on comparisons with findings from previous studies, the distribution is dynamic.

New putative cryptic species detection and genetic network analysis of Bemisia tabaci (Hempitera: Aleyrodidae) in China based on mitochondrial COI sequences

The whitefly Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) is a cryptic species complex and widely distributed throughout tropical and subtropical regions. To understand the B. tabaci cryptic species diversity in China more comprehensively, in the year 2014 and 2016, a large-scale sampling was conducted from the famous biodiversity hotspot of China, Yunnan province. Mitochondrial cytochrome oxidase I gene sequences were used to identify new putative cryptic species. Phylogenetic analyses were performed using Bayesian methods to evaluate the position of new cryptic species in the context of the B. tabaci diversity in Asia. Two new cryptic species, China 5 and Asia V were identified. In total, 19 B. tabaci cryptic species are present in China, two invasive (MED and MEAM1) and 17 indigenous. A new sibling species of B. tabaci was first defined and reported. Based on the mtCOI sequences and haplotype network analyses, the genetic diversity of MED was far higher than MEAM1. We confirmed the exotic MED was originated from the western Mediterranean regions and first invaded into Yunnan, China. The genetic structures of other four indigenous species (Asia I, Asia II 1, Asia II 6, and China 1) with relatively wide distribution ranges in China were also discussed.

Insecticide resistance status in the whitefly, Bemisia tabaci genetic groups Asia-I, Asia-II-1 and Asia-II-7 on the Indian subcontinent

The present study is a summary of the current level of the insecticide resistance to selected organophosphates, pyrethroids, and neonicotinoids in seven Indian field populations of Bemisia tabaci genetic groups Asia-I, Asia-II-1, and Asia-II-7. Susceptibility of these populations was varied with Asia-II-7 being the most susceptible, while Asia-I and Asia-II-1 populations were showing significant resistance to these insecticides. The variability of the LC₅₀ values was 7x for imidacloprid and thiamethoxam, 5x for monocrotophos and 3x for cypermethrin among the Asia-I, while, they were 7x for cypermethrin, 6x for deltamethrin and 5x for imidacloprid within the Asia-II-1 populations. When compared with the most susceptible, PUSA population (Asia-II-7), a substantial increase in resistant ratios was observed in both the populations of Asia-I and Asia-II-1. Comparative analysis during 2010-13 revealed a decline in susceptibility in Asia-I and Asia-II-1 populations of B. tabaci to the tested organophosphate, pyrethroid, and neonicotinoid insecticides. Evidence of potential control failure was detected using probit analysis estimates for cypermethrin, deltamethrin, monocrotophos and imidacloprid. Our results update resistance status of B. tabaci in India. The implications of insecticide resistance management of B. tabaci on Indian subcontinent are discussed.