Phylo‐biogeographical distribution of whitefly Bemisia tabaci (Insecta: Aleyrodidae) mitotypes in Ecuador

Sentinel plot surveillance of cotton leaf curl disease in Pakistan- a case study at the cultivated cotton-wild host plant interface

A sentinel plot case study was carried out to identify and map the distribution of begomovirus-betasatellite complexes in sentinel plots and commercial cotton fields over a four-year period using molecular and high-throughput DNA 'discovery' sequencing approaches. Samples were collected from 15 study sites in the two major cotton-producing areas of Pakistan. Whitefly- and leafhopper-transmitted geminiviruses were detected in previously unreported host plant species and locations. The most prevalent begomovirus was cotton leaf curl Kokhran virus-Burewala (CLCuKoV-Bu). Unexpectedly, a recently recognized recombinant, cotton leaf curl Multan virus-Rajasthan (CLCuMuV-Ra) was prevalent in five of 15 sites. cotton leaf curl Alabad virus (CLCuAlV) and cotton leaf curl Kokhran virus-Kokhran, 'core' members of CLCuD-begomoviruses that co-occurred with CLCuMuV in the 'Multan' epidemic were detected in one of 15 sentinel plots. Also identified were chickpea chlorotic dwarf virus and 'non-core' CLCuD-begomoviruses, okra enation leaf curl virus, squash leaf curl virus, and tomato leaf curl New Delhi virus. Cotton leaf curl Multan betasatellite (CLCuMuB) was the most prevalent CLCuD-betasatellite, and less commonly, two 'non-core' betasatellites. Recombination analysis revealed previously uncharacterized recombinants among helper virus-betasatellite complexes consisting of CLCuKoV, CLCuMuV, CLCuAlV and CLCuMuB. Population analyses provided early evidence for CLCuMuV-Ra expansion and displacement of CLCuKoV-Bu in India and Pakistan from 2012-2017. Identification of 'core' and non-core CLCuD-species/strains in cotton and other potential reservoirs, and presence of the now predominant CLCuMuV-Ra strain are indicative of ongoing diversification. Investigating the phylodynamics of geminivirus emergence in cotton-vegetable cropping systems offers an opportunity to understand the driving forces underlying disease outbreaks and reconcile viral evolution with epidemiological relationships that also capture pathogen population shifts.

The Bemisia tabaci cryptic (sibling) species group - imperative for a taxonomic reassessment

The taxonomy of the Bemisia tabaci cryptic species group remains a challenge due to the lack of morphological differentiation and porous species boundaries among its members. Additionally, it is unclear whether B. tabaci consists of several species in evolutionary stasis with limited morphological change or is the result of a recent adaptive radiation characterized by great ecological diversity but little morphological divergence. Here, a historical overview of the development of the nomenclature used to classify B. tabaci is provided covering changes after synonymizing several species in 1957 until recent insights gained from whole-genome sequencing data. The article discusses the limitations of using a 3.5% mtCOI threshold and argues that a 1% nuclear divergence cutoff better reflects ecological and biogeographic species boundaries. Finally, a plan of action is outlined for naming B. tabaci species using a Latin binomial system in accordance with the International Comission on Zoological Nomenclature (ICZN) regulations.

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.

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.

Predicting Climate Change Effects on the Potential Distribution of Two Invasive Cryptic Species of the Bemisia tabaci Species Complex in China

Middle East-Asia Minor 1 (MEAM1) and Mediterranean (MED) are two invasive cryptic species of the Bemisia tabaci species complex (Hemiptera: Aleyrodidae) that cause serious damage to agricultural and horticultural crops worldwide. To explore the possible impact of climate change on their distribution, the maximum entropy (MaxEnt) model was used to predict the potential distribution ranges of MEAM1 and MED in China under current and four future climate scenarios, using shared socioeconomic pathways (SSPs), namely SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5, over four time periods (2021-2040, 2041-2060, 2061-2080, and 2081-2100). The distribution ranges of MEAM1 and MED were extensive and similar in China under current climatic conditions, while their moderately and highly suitable habitat ranges differed. Under future climate scenarios, the areas of suitable habitat of different levels for MEAM1 and MED were predicted to increase to different degrees. However, the predicted expansion of suitable habitats varied between them, suggesting that these invasive cryptic species respond differently to climate change. Our results illustrate the difference in the effects of climate change on the geographical distribution of different cryptic species of B. tabaci and provide insightful information for further forecasting and managing the two invasive cryptic species in China.

Earlier than expected introductions of the Bemisia tabaci B mitotype in Brazil reveal an unprecedented, rapid invasion history

During 1991, in Brazil, the presence of the exotic Bemisia tabaci B mitotype was reported in São Paulo state. However, the duration from the time of initial introduction to population upsurges is not known. To investigate whether the 1991 B mitotype outbreaks in Brazil originated in São Paulo or from migrating populations from neighboring introduction sites, country-wide field samples of B. tabaci archived from 1989-2005 collections were subjected to analysis of mitochondrial cytochrome oxidase I (mtCOI) and nuclear RNA-binding protein 15 (RP-15) sequences. The results of mtCOI sequence analysis identified all B. tabaci as the NAFME 8 haplotype of the B mitotype. Phylogenetic analyses of RP-15 sequences revealed that the B mitotype was likely a hybrid between a B type parent related to a haplotype Ethiopian endemism (NAFME 1-3), and an unidentified parent from the North Africa-Middle East (NAF-ME) region. Results provide the first evidence that this widely invasive B mitotype has evolved from a previously undocumented hybridization event. Samples from Rio de Janeiro (1989) and Ceará state (1990), respectively, are the earliest known B mitotype records in Brazil. A simulated migration for the 1989 introduction predicted a dispersal rate of 200-500 km/year, indicating that the population was unlikely to have reached Ceará by 1990. Results implicated two independent introductions of the B mitotype in Brazil in 1989 and 1990, that together were predicted to have contributed to the complete invasion of Brazil in only 30 generations.

Phylogeographic and SNPs Analyses of Bemisia tabaci B Mitotype Populations Reveal Only Two of Eight Haplotypes Are Invasive

Simple Summary

The whitefly Bemisia tabaci taxon consists of an undefined number of morphologically identical genetic variants of which only a few, including the B, harbor invasive haplotypes. These haplotypes have potential to upsurge and become important pests and plant virus vectors in irrigated agroecosystems worldwide. In the 1980s, unprecedented outbreaks associated with the B variant were reported worldwide, however, the precise origin(s) of the invasive haplotypes has not been determined. In this study, available B. tabaci mitochondrial gene sequences were examined for patterns of conserved single nucleotide changes (SNPs). The whitefly sequence records represented North Africa-Middle Eastern habitats, the proposed B variant center of origin, and distant locales recently invaded by haplotype(s) of the B variant. Unexpectedly, the analysis revealed eight SNPs groups (haplotypes) demonstrating that the genetic architecture of the B mitoype is more complex than previously recognized. Also, the distribution patterns of the eight B haplotypes were tightly linked to well-defined eco-geographic regions, suggesting the different groups have diversified by geographic isolation. Contrary to claims that collectively, the B variant is invasive, only two of the eight haplotypic groups have established in geographical locations outside of their zone of endemism.

Abstract

The Bemisia tabaci cryptic species contains 39 known mitotypes of which the B and Q are best recognized for having established outside their extant endemic range. In the 1980s, previously uncharacterized haplotype(s) of the B mitotype rapidly established in tropical and subtropical locales distant from their presumed center of origin, leading to displacement of several native mitotypes and extreme damage to crops and other vegetation particularly in irrigated agroecosystems. To trace the natural and evolutionary history of the invasive B haplotypes, a phylo-biogeographic study was undertaken. Patterns of single nucleotide polymorphisms (SNPs) and signatures potentially indicative of geographic isolation were investigated using a globally representative mitochondrial cytochrome oxidase I gene (mtCOI) sequence database. Eight haplotype groups within the North Africa-Middle East (NAFME) region were differentiated, NAFME 1–8. The NAFME 1–3 haplotypes were members of the same population that is associated with warm desert climate niches of the Arabian Peninsula and east coastal Africa-Ethiopia. The NAFME 4 and 5 haplotypes are endemic to warm and cold semi-arid niches delimited by the Irano-Turanian floristic region, itself harboring extensive biodiversity. Haplotypes 6 and 7 co-occurred in the Middle East along eastern Mediterranean Sea landmasses, while NAFME 8 was found to be endemic to Cyprus, Turkey, and desert micro-niches throughout Egypt and Israel. Contrary to claims that collectively, the B mitotype is invasive, NAFME 6 and 8 are the only haplotypes to have established in geographical locations outside of their zone of endemism.

Why are there not more herbivorous insect species?

Insect species richness is estimated to exceed three million species, of which roughly half is herbivorous. Despite the vast number of species and varied life histories, the proportion of herbivorous species among plant-consuming organisms is lower than it could be due to constraints that impose limits to their diversification. These include ecological factors, such as vague interspecific competition; anatomical and physiological limits, such as neural limits and inability of handling a wide range of plant allelochemicals; phylogenetic constraints, like niche conservatism; and most importantly, a low level of concerted genetic variation necessary to a phyletic conversion. It is suggested that diversification ultimately depends on what we call the intrinsic trend of diversification of the insect genome. In support of the above, we survey the major types of host-specificity, the mechanisms and constraints of host specialization, possible pathways of speciation, and hypotheses concerning insect diversification.

Low virus diversity and spread in wild Capsicum spp. accessions from Ecuador under natural inoculum pressure

Challenging wild plant accessions with pathogens is an initial approach for finding resistance genes for breeding programs. Viruses can be transmitted artificially by mechanical or arthropod-borne inoculation, but these experimental assays do not always reproduce natural conditions in the field. In this study, 56 wild Capsicum spp. accessions from Ecuador that were under natural inoculum pressure for six months were screened for virus infections by RNA sequencing. These plants exhibited low virus diversity in comparison to a commercial pepper cultivar that was used as a susceptible host. Subjecting numerous plants to natural infection prior to artificial assays may indicate promising accessions to track within virus/vector resistance breeding programs.