Plasticity in mating behaviour drives asymmetric reproductive interference in whiteflies

Synthesis and Scope of the Role of Postmating Prezygotic Isolation in Speciation

How barriers to gene flow arise and are maintained are key questions in evolutionary biology. Speciation research has mainly focused on barriers that occur either before mating or after zygote formation. In comparison, postmating prezygotic (PMPZ) isolation-a barrier that acts after gamete release but before zygote formation-is less frequently investigated but may hold a unique role in generating biodiversity. Here we discuss the distinctive features of PMPZ isolation, including the primary drivers and molecular mechanisms underpinning PMPZ isolation. We then present the first comprehensive survey of PMPZ isolation research, revealing that it is a widespread form of prezygotic isolation across eukaryotes. The survey also exposes obstacles in studying PMPZ isolation, in part attributable to the challenges involved in directly measuring PMPZ isolation and uncovering its causal mechanisms. Finally, we identify outstanding knowledge gaps and provide recommendations for improving future research on PMPZ isolation. This will allow us to better understand the nature of this often-neglected reproductive barrier and its contribution to speciation.

Polyandry may mitigate the negative impact of reproductive interference among bumblebees in Japan

In social hymenopterans, monandry of the queen is an ancestral trait, and polyandry is a derived trait. Polyandry of the queen is the norm in a limited number of lineages, such as honeybees, leaf-cutting ants, Pogonomyrmex ants, and Vespula wasps, which presumably provide fitness advantages for the whole colony. The queen of the introduced bumblebee, Bombus terrestris, is polyandrous in Japan, whereas it is monandrous in native regions. We hypothesize that polyandry can evolve in a process that avoids the negative impacts of reproductive interference caused by interspecific mating and conducted genetic studies of the invasive species B. terrestris and two native subspecies, Bombus hypocrita sapporoensis and Bombus hypocrita hypocrita, in Japan. Our results revealed that although the native queens of B. hypocrita hypocrita allopatric with B. terrestris were strictly monandrous, the native queens of B. hypocrita sapporoensis sympatric with B. terrestris were polyandrous. These results suggested that the queens of native B. hypocrita sapporoensis do not experience negative impacts on interspecific mating from the invasive B. terrestris. We discuss the possibility that reproductive interference is a driving force in selection for multiple mating through an arms race between sympatric species.

Sensory perception of rivals has trait-dependent effects on plasticity in Drosophila melanogaster

The social environment has myriad effects on individuals, altering reproduction, immune function, cognition, and aging. Phenotypic plasticity enables animals to respond to heterogeneous environments such as the social environment but requires that they assess those environments accurately. It has been suggested that combinations of sensory cues allow animals to respond rapidly and accurately to changeable environments, but it is unclear whether the same sensory inputs are required in all traits that respond to a particular environmental cue. Drosophila melanogaster males, in the presence of rival males, exhibit a consistent behavioral response by extending mating duration. However, exposure to a rival also results in a reduction in their lifespan, a phenomenon interpreted as a trade-off associated with sperm competition strategies. D. melanogaster perceive their rivals by using multiple sensory cues; interfering with at least two olfactory, auditory, or tactile cues eliminates the extension of mating duration. Here, we assessed whether these same cues were implicated in the lifespan reduction. Removal of combinations of auditory and olfactory cues removed the extended mating duration response to a rival, as previously found. However, we found that these manipulations did not alter the reduction in lifespan of males exposed to rivals or induce any changes in activity patterns, grooming, or male-male aggression. Therefore, our analysis suggests that lifespan reduction is not a cost associated with the behavioral responses to sperm competition. Moreover, this highlights the trait-specific nature of the mechanisms underlying plasticity in response to the same environmental conditions.

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

Abstract 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.

Reproductive interference and Satyrisation: mechanisms, outcomes and potential use for insect control

Reproductive Interference occurs when interactions between individuals from different species disrupt reproductive processes, resulting in a fitness cost to one or both parties involved. It is typically observed between individuals of closely related species, often upon secondary contact. In both vertebrates and invertebrates, Reproductive Interference is frequently referred to as 'Satyrisation'. It can manifest in various ways, ranging from blocking or reducing the efficacy of mating signals, through to negative effects of heterospecific copulations and the production of sterile or infertile hybrid offspring. The negative fitness effects of Satyrisation in reciprocal matings between species are often asymmetric and it is this aspect, which is most relevant to, and can offer utility in, pest management. In this review, we focus on Satyrisation and outline the mechanisms through which it can operate. We illustrate this by using test cases, and we consider the underlying reasons why the reproductive interactions that comprise Satyrisation occur. We synthesise the key factors affecting the expression of Satyrisation and explore how they have potential utility in developing new routes for the management and control of harmful insects. We consider how Satyrisation might interact with other control mechanisms, and conclude by outlining a framework for its use in control, highlighting some of the important next steps.

Distribution and Genetic Variability of Bemisia tabaci Cryptic Species (Hemiptera: Aleyrodidae) in Italy

Bemisia tabaci is a key pest of horticultural, fibre and ornamental crops worldwide, primarily as a vector of plant viruses. In Italy, B. tabaci has established since the 1980s-1990s in southern regions as well as in Sicily and Sardinia. Recent reports of infestations in some areas of central Italy prompted a new survey to assess the whitefly distribution in the country as well as to update the species and haplotype composition of the populations present in southern Italy and in the main islands. The survey confirmed that B. tabaci is nowadays established in central Italy even at more northern latitudes than those noticed before. Most of the specimens collected throughout the country belonged to the Mediterranean (MED) species. The MEDQ1 and Q2 haplogroups were prevailing in open-field and greenhouse cultivations, respectively, except in Sardinia where only Q1 specimens were found on a wide range of crops and weeds. Population genetics analyses showed that several MEDQ1 haplotypes currently occur in Italy and their distribution is unrelated to evident temporal and geographic trends, except for a new genetic variant which seems to have originated in Sardinia. The MED species is known to better adapt to insecticide treatments and high temperatures, and its northward spread in Italy may have been favoured by the intensive agricultural practices and steady increase in both winter and summer temperatures occurring in the last few decades. The extensive presence of B. tabaci in Italy proves that a strict surveillance for possible new outbreaks of whitefly-transmitted viruses should be addressed to a range of sites that are expanding northwards.

Feeding behavior explains the different effects of cabbage on MEAM1 and MED cryptic species of Bemisia tabaci

MEAM1 (Middle East-Asia Minor 1, "B" biotype) and MED (Mediterranean, "Q" biotype) are the two most destructive cryptic species of the Bemisia tabaci complex on the planet. Our previous studies have shown that MEAM1 outcompetes MED on cabbage; the underlying mechanism is unknown. In the Brassicaceae family, the glucosinolate-myrosinase defense system plays a crucial role in deterring feeding, inhibiting growth, and causing acute toxicity against a wide range of generalist herbivores. In the present study, we first compared the survival of MEAM1 and MED exposed to sinigrin (a glucosinolate) and myrosinase (an enzyme that degrades glucosinolates); we found that survival of both species was high in response to sinigrin alone but was near zero in response to sinigrin + myrosinase. We then used electropenetrography (electrical penetration graphs, EPG) to assess the feeding behaviors of MEAM1 and MED whiteflies on cabbage. The EPG results revealed that the mean duration of each potential drop (pd, indicating an intracellular puncture) was substantially longer for MED than MEAM1 on cabbage, indicating that the exposure to the toxic hydrolysates of glucosinolate and myrosinase is greater for MED than for MEAM1. We therefore conclude that differences in penetrating behaviors may help explain the different effects of cabbage on MEAM1 and MED whitefly species.

Positive density dependence acting on mortality can help maintain species-rich communities

Conspecific negative density dependence is ubiquitous and has long been recognized as an important factor favoring the coexistence of competing species at local scale. By contrast, a positive density-dependent growth rate is thought to favor species exclusion by inhibiting the growth of less competitive species. Yet, such conspecific positive density dependence often reduces extrinsic mortality (e.g. reduced predation), which favors species exclusion in the first place. Here, using a combination of analytical derivations and numerical simulations, I show that this form of positive density dependence can favor the existence of equilibrium points characterized by species coexistence. Those equilibria are not globally stable, but allow the maintenance of species-rich communities in multispecies simulations. Therefore, conspecific positive density dependence does not necessarily favor species exclusion. On the contrary, some forms of conspecific positive density dependence may even help maintain species richness in natural communities. These results should stimulate further investigations into the precise mechanisms underlying density dependence.

Reproductive Interference in an Introduced Bumblebee: Polyandry may Mitigate Negative Reproductive Impact

As a signature of reproductive interference (RI), we reviewed hybrid production in eusocial bumblebees in Japan, by comparing introduced Bombus terrestris with native B. ignitus in Honshu (main island of Japan) and with native B. hypocrita sapporoensis in Hokkaido (northern island of Japan). In this review, we present additional new data showing hybrid production between introduced B. terrestris and native B. ignitus in Honshu. Interspecific mating with introduced B. terrestris disrupts the reproduction of native B. h. sapporoensis and B. ignitus, which belong to the same subgenus of Bombus, through inviable egg production. This interference appears to facilitate species replacement on Hokkaido. Simultaneously, the mating frequencies for queens of B. terrestris have increased, suggesting that polyandry might evolve in response to the extent of RI between B. terrestris and B. h. sapporoensis. To suppress the population size of B. terrestris in Hokkaido, two methods have been proposed: the mass release of B. h. sapporoensis males to induce RI between the two species and the spraying of insecticides against foraging workers so that the workers will carry the insecticides back to their colonies, killing the immature bees within the colonies. A candidate insecticide type is insect growth regulator, which may disrupt larval development without any apparent effect on foraging workers.

Comparative studies of stenogamous behaviour in the mosquito Culex pipiens complex

Understanding the processes of reproductive behaviour in mosquitoes is crucial for improving mating competitiveness and mating specificity for sterile insect release programmes. The Culex pipiens (Linneaus) (Diptera: Culicidae) forms pipiens and molestus (Forskål), two biotypes of the Cx. pipiens complex, are vectors for West Nile virus, St Louis encephalitis virus and lymphatic filariases. Hybridization of these biotypes is known to occur in nature, although form pipiens mates above ground in large spaces (eurygamy) and form molestus preferentially mates in small spaces (stenogamy) such as sewage tunnels. Hybridization may allow gene flow of biotype-specific characteristics that are crucial in the disease transmission cycle. The present study examined and compared mating behaviours, insemination rates, fecundity and fertility in parental and F1 hybrids between Cx. pipiens f. pipiens and Cx. pipiens f. molestus in conditions of stenogamy. Unique mating behaviour sequences were identified in Cx. pipiens f. molestus, including tapping, mounting, co-flying and copulation. Despite the considerably high insemination rates in hybrid crosses, fertility and fecundity rates were varied. This observation could suggest reproductive isolation in the hybrid zone. The study also documents a failure of heterospecific males to produce fertile eggs in Cx. pipiens f. pipiens females, which may be attributable to gametic incompatibilities and may represent an additional barrier to gene exchange.

Previous Interspecific Courtship Impairs Female Receptivity to Conspecifics in the Parasitoid Wasp Nasonia longicornis But Not in N. vitripennis

Interspecific sexual interactions are not uncommon in animals. In sympatry, females often face the risk of accidentally mating with a heterospecific male. Based on the actual risks imposed by the environment at a given time and place, females should be able to adjust their mate acceptance in order to avoid interspecific copulations as well as accidentally refusing to mate with a conspecific. We investigate the ability of females of the two parasitoid wasp species Nasonia vitripennis (Nv) and N. longicornis (Nl) to adjust their mate acceptance in response to previous unsuccessful courtship by heterospecific males. We show that Nl females are more reluctant to mate with a conspecific male when having been courted previously by a heterospecific male, but Nv females are not. We argue that this strategy is reasonable for Nl females but not for Nv females, which follow a different strategy to avoid the fitness costs imposed by heterospecific copulations.

Reproductive Plasticity of an Invasive Insect Pest, Rice Water Weevil (Coleoptera: Curculionidae)

Reproductive plasticity is a key determinant of species invasiveness. However, there are a limited number of studies addressing this issue in exotic insects. The rice water weevil Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae), which is native to North America, is one of the most invasive insect pests in east Asia. In this study, we investigated the reproductive status of first-generation females (progeny of overwintered weevils) from five geographic regions in southern and northern China in the field, and reproductive status and ovipositional features of females provided with suitable host plants in the laboratory after collection. Under field conditions, a proportion of females oviposited, while the rest remained in diapause from all three southern regions investigated, but reproductive development did not take place in females from the two northern regions, where the weevil produces only one generation per year. However, when fed host plants in the laboratory, females from all regions laid eggs. They typically had a very short ovipositional period (3-6 d on average on rice at a temperature of 27°C), laid a low number of eggs, and did not die soon after oviposition; this was different from common reproductive females. We concluded that first-generation L. oryzophilus females, which largely enter diapause after emergence, are highly plastic in their reproductive performance and are ready to reproduce under favorable conditions. Our results indicate the significance of their reproductive plasticity for geographic spread and population development.

Cryptic Species Identification and Composition of Bemisia tabaci (Hemiptera: Aleyrodidae) Complex in Henan Province, China

Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) is a cryptic species complex, causing significant crop losses in China during the last decade. Although knowledge of cryptic species composition and dynamics within B. tabaci complex is critical for developing sustainable pest management strategies, limited information is available on this pest in the Henan province of China. A systematic survey of the cryptic species composition and distribution of B. tabaci complex in different locations of Henan province was conducted in 2012. The results of RAPD-PCR and the gene for the mitochondrial cytochrome oxidase subunit-1 (mtCOI) based phylogenetic relationships established using Bayesian method indicated there were four known cryptic species MEAM1, MED, Asia II 3, Asia II 9 and a new cryptic species named China 6 in Henan province. In the survey, the invasive cryptic species MED and MEAM1 were found to be predominant with wide spread distribution across the surveyed regions. On the contrary, the indigenous B. tabaci cryptic species including Asia II 3, Asia II 9 and China 6 remained with low prevalence in some surveyed regions. Cryptic species MEAM1 and MED have not completely displaced the native B. tabaci in Henan province. This current study for the first time unifies our knowledge of the diversity and distribution of B. tabaci across Henan province of China.

Natal Host Plants Can Alter Herbivore Competition

Interspecific competition between herbivores is widely recognized as an important determinant of community structure. Although researchers have identified a number of factors capable of altering competitive interactions, few studies have addressed the influence of neighboring plant species. If adaptation to/ epigenetic effects of an herbivore’s natal host plant alter its performance on other host plants, then interspecific herbivore interactions may play out differently in heterogeneous and homogenous plant communities. We tested wether the natal host plant of a whitefly population affected interactions between the Middle-east Asia Minor 1 (MEAM1) and Mediterranean (MED) cryptic species of the whitefly Bemisia tabaci by rearing the offspring of a cabbage-derived MEAM1 population and a poinsettia-derived MED population together on three different host plants: cotton, poinsettia, and cabbage. We found that MED dominated on poinsettia and that MEAM1 dominated on cabbage, results consistent with previous research. MED also dominated when reared with MEAM1 on cotton, however, a result at odds with multiple otherwise-similar studies that reared both species on the same natal plant. Our work provides evidence that natal plants affect competitive interactions on another plant species, and highlights the potential importance of neighboring plant species on herbivore community composition in agricultral systems.

Asymmetrical reproductive interference between two sibling species of tea looper: Ectropis grisescens and Ectropis obliqua

Ectropis grisescens Warren and Ectropis obliqua (Prout) are two morphologically similar sibling species with overlapping ranges. In this study, manipulative laboratory experiments were conducted to examine the possibility of reproductive interference in sympatric populations of E. grisescens and E. obliqua and the potential consequences of the mating interaction. Our results showed that the presence of males or females of different species could incur mating interference and significant reduction of F 1 offspring. The reduction was not significant relevant to the initial relative abundance of E. grisescens and E. obliqua. Detailed observations of mating opportunity showed that female mating frequencies of both species were not significantly affected by the absolute species density, but the mating success of E. obliqua females with conspecific males depended on species ratio. In addition, adding males to the other species resulted in lower number of offspring suggesting that the males' behaviour might be linked with mating interference. Males of both E. grisescens and E. obliqua could interfere the intraspecific mating of the other species, but the impact of the mating interference differed. These combined data indicated that asymmetric reproductive interference existed in E. grisescens and E. obliqua under laboratory conditions, and the offspring of the mixed species were significantly reduced. The long term outcome of this effect is yet to be determined since additional reproductive factors such as oviposition rate and progeny survival to adulthood may reduce the probability of demographic displacement of one species by the other in overlapping niches.

Satyrization and satyrization-resistance in competitive displacements of invasive mosquito species

Competitive displacements or reductions of resident populations of insects, often effected by a related species, may be caused by a variety of mechanisms. Satyrization is a form of mating interference in which males of one species mate with females of another species, significantly decreasing their fitness and not generating hybrids. Satyrization has been established to be the probable cause of competitive displacements of resident mosquitoes by invasive species, especially of Aedes aegypti by Aedes albopictus, two important vectors of dengue and chikungunya viruses. Mathematical models predict that even low levels of asymmetric mating interference are capable of producing competitive displacements or reductions. Couplings of virgin Ae. aegypti females with Ae. albopictus males effectively sterilize these females through the monogamizing actions of male accessory gland products, but the converse interspecific mating does not impact the future reproduction of Ae. albopictus females. Populations of Ae. aegypti exposed to satyrization quickly evolve resistance to interspecific mating, which is believed to ameliorate reproductive interference from, and promote co-existence with, Ae. albopictus. The evolution of satyrization resistance among Ae. aegypti in laboratory cages is accompanied by fitness costs, such as reduced fecundity and slower receptivity to conspecific males. Cage experiments and field observations indicate that Ae. albopictus males are capable of satyrizing females of other species of the Stegomyia subgenus, potentially leading to competitive displacements, and possible extinctions, especially of endemic species on islands. Examination of other examples of reproductive interference in insects reveals few parallels to the mechanism and outcomes of satyrization by Ae. albopictus. We conclude by posing the hypothesis that satyrization may favor the ecological success of Ae. albopictus, and suggest many lines for future research on this phenomenon.

Insecticides promote viral outbreaks by altering herbivore competition

While the management of biological invasions is often characterized by a series of single-specieg decisions, invasive species exist within larger food webs. These biotic interactions can alter the impact of control/eradication programs and may cause suppression efforts to inadvertently facilitate invasion spread and impact. We document the rapid replacement of the invasive Bemisia Middle East-Asia Minor I (MEAM1) cryptic biotype by the cryptic Mediterranean (MED) biotype throughout China and demonstrate that MED is more tolerant of insecticides and a better vector of tomato yellow leaf curl virus (TYLCV) than MEAMJ. While MEAM1 usually excludes MED under natural conditions, insecticide application reverses the MEAM1-MED competitive hierarchy and allows MED to exclude MEAMI. The insecticide-mediated success of MED has led to TYLCV outbreaks throughout China. Our work strongly supports the hypothesis that insecticide use in China reverses the MEAMl-MED competitive hierarchy and allows MED to displace MEAM1 in managed landscapes. By promoting the dominance of a Bemisia species that is a competent viral vector, insecticides thus increase the spread and impact of TYLCV in heterogeneous agroecosystems.

Widespread evidence for interspecific mating between Aedes aegypti and Aedes albopictus (Diptera: Culicidae) in nature

Aedes aegypti and Aedes albopictus, two important vectors of the dengue and chikungunya viruses to humans, often come in contact in their invasive ranges. In these circumstances, a number of factors are thought to influence their population dynamics, including resource competition among the larval stages, prevailing environmental conditions and reproductive interference in the form of satyrization. As the distribution and abundance of Ae. aegypti and Ae. albopictus have profound epidemiological implications, understanding the competitive interactions that influence these patterns in nature is important. While evidence for resource competition and environmental factors had been gathered from the field, the evidence for reproductive interference, though strongly inferred through laboratory trials, remained sparse (one small-scale field trial). In this paper we demonstrate that low rates (1.12-3.73%) of interspecific mating occur in nature among populations of these species that have co-existed sympatrically from 3 to 150yrs. Finally this report contributes a new species-specific primer set for identifying the paternity of sperm extracted from field collected specimens.

Invasion of the Q2 mitochondrial variant of Mediterranean Bemisia tabaci in southern Italy: possible role of bacterial endosymbionts

BACKGROUND

The whitefly Bemisia tabaci (Gennadius) is a complex of cryptic species, some of which, namely the Mediterranean (MED) and the Middle East-Asia Minor 1 (MEAM1), are highly invasive and injurious crop pests worldwide and able to displace local genotypes. Invasiveness of B. tabaci may depend on the phenotype of inherited bacterial endosymbionts. Here, the B. tabaci genetic diversity variation that has occurred in recent years in southern Italy was examined. Whitefly was genotyped by restriction fragment length polymorphism analysis of polymerase-chain-reaction-amplified fragments (PCR-RFLP) of the COI gene and molecular identification of endosymbionts. Possible factors leading to the observed genetic diversity were examined.

RESULTS

Q1 and Q2 mitochondrial types of MED, the only species found, coexisted in the field, while MEAM1 disappeared. A large spreading of Q2 (70% of individuals) was observed for the first time in Italy. Q2 showed a significant female-biased sex ratio and largely outnumbered Q1 on solanaceous hosts, in greenhouses and on insecticide-treated plants. Q1, with an even sex ratio, slightly prevailed on non-solanaceous hosts, especially on wild and untreated plants. Endosymbiont composition was associated with the mitochondrial type. Hamiltonella and Rickettsia were found at near fixation in Q1 and Q2 respectively; Arsenophonus, Cardinium and Wolbachia were found in both types, although at different frequencies.

CONCLUSIONS

Q2 invasion seems to have been favoured by the agroecological conditions of southern Italy and by the female-biased sex ratio. Endosymbionts may have a role in Q2 invasiveness, acting as sex-ratio manipulators (e.g. Rickettsia) and possibly by benefiting the host fitness.

Effects of reproductive interference on the competitive displacement between two invasive whiteflies

Reproductive interference is one of the major factors mediating species exclusion among insects. The cryptic species Middle East-Asia Minor 1 (MEAM1) and Mediterranean (MED) of the whitefly Bemisia tabaci complex have invaded many parts of the world and often exhibit niche overlap and reproductive interference. However, contrasting patterns of competitive displacement between the two invaders have been observed between regions such as those in USA and China. Understanding the roles of reproductive interference in competitive interactions between populations of the two species in different regions will help unravel other factors related to their invasion. We integrated laboratory population experiments, behavioural observations and simulation modelling to investigate the role of reproductive interference on species exclusion between MEAM1 and MED in China. In mixed cohorts of the two species MEAM1 always excluded MED in a few generations when the initial proportion of MEAM1 was ⩾0.25. Even when the initial proportion of MEAM1 was only 0.10, however, MEAM1 still had a higher probability of excluding MED than that for MED to exclude MEAM1. Importantly, we show that as MEAM1 increased in relative abundance, MED populations became increasingly male-biased. Detailed behavioural observations confirmed that MEAM1 showed a stronger reproductive interference than MED, leading to reduced frequency of copulation and female progeny production in MED. Using simulation modelling, we linked our behavioural observations with exclusion experiments to show that interspecific asymmetric reproductive interference predicts the rate of species exclusion of MED by MEAM1. These findings not only reveal the importance of reproductive interference in the competitive interactions between the two invasive whiteflies as well as the detailed behavioural mechanisms, but also provide a valuable framework against which the effects of other factors mediating species exclusion can be explored.

Members of Bemisia tabaci (Hemiptera: Aleyrodidae) cryptic species and the status of two invasive alien species in the Yunnan Province (China)

Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) is a cryptic species complex that includes some of the most significant pests of agriculture and horticulture worldwide. To understand the diversity and distribution of B. tabaci cryptic species in Yunnan, a famous biodiversity hotspot in China, a large-scale sampling was conducted from year 2010 to 2013 in 10 prefectures. Mitochondrial cytochrome oxidase I gene sequences were used to identify different cryptic species. Phylogenetic analyses were performed using Bayesian methods to assess the position of a new B. tabaci cryptic species in the context of the B. tabaci diversity in Asia. The survey indicates at least eight B. tabaci cryptic species are present in Yunnan, two invasive (MEAM1 and MED) and six indigenous (China 2, China3, China 4, Asia I, Asia II 1, and Asia II 6), MEAM1, MED, and Asia I being the three predominant cryptic species in Yunnan. Compared with MEAM1, MED has a wider distribution. Based on molecular data, a new cryptic species, here named China 4, was identified that appears to be related to China 1, China 2, and China 3. Future efforts should focus on the interactions between predominant B. tabaci cryptic species and begomoviruses and on the development of effective control strategies.

Competitive displacement between two invasive whiteflies: insecticide application and host plant effects

The cryptic species Middle East-Asia Minor 1 (MEAM1), formerly referred to as 'B biotype', of the whitefly Bemisia tabaci complex entered China in the mid 1990s, and the Mediterranean (MED) cryptic species, formerly referred to as 'Q biotype', of the same whitefly complex entered China around 2003. Field surveys in China after 2003 indicate that in many regions MED has been replacing the earlier invader MEAM1. The factors underlying this displacement are unclear. We conducted laboratory experiments and field sampling to examine the effects of insecticide application on the competitive interactions between MEAM1 and MED. In the laboratory, on cotton, a plant showing similar levels of suitability to both whitefly species, MEAM1 displaced MED in five generations when initial populations of the two species were equal and no insecticide was applied. In contrast, MED displaced MEAM1 in seven and two generations, respectively, when 12.5 and 50.0 mg l⁻¹ imidacloprid was applied to the plants via soil drench. Field sampling indicated that in a single season MED displaced MEAM1 on crops heavily sprayed with neonicotinoid insecticides but the relative abundance of the two species changed little on crops without insecticide spray. We also examined the effects of host plants on the competitive interactions between the two species in the laboratory. When cohorts with equal abundance of MEAM1 and MED were set up on different host plants, MEAM1 displaced MED on cabbage and tomato in five and seven generations, respectively, but MED displaced MEAM1 on pepper in two generations. As field populations of MED have lower susceptibility than those of MEAM1 to nearly all commonly used insecticides including imidacloprid, insecticide application seems to have played a major role in shifting the species competitive interaction effects in favour of MED in the field across China. Host plants may also shape competition between the two species depending on the relative levels of plant suitability.

Analysis of the transcriptional differences between indigenous and invasive whiteflies reveals possible mechanisms of whitefly invasion

BACKGROUND

The whitefly Bemisa tabaci is a species complex of more than 31 cryptic species which include some of the most destructive invasive pests of crops worldwide. Among them, Middle East-Asia Minor 1 (MEAM1) and Mediterranean have invaded many countries and displaced the native whitefly species. The successful invasion of the two species is largely due to their wide range of host plants, high resistance to insecticides and remarkable tolerance to environmental stresses. However, the molecular differences between invasive and indigenous whiteflies remain largely unknown.

METHODOLOGY/PRINCIPAL FINDINGS

Here the global transcriptional difference between the two invasive whitefly species (MEAM1, MED) and one indigenous whitefly species (Asia II 3) were analyzed using the Illumina sequencing. Our analysis indicated that 2,422 genes between MEAM1 and MED; 3,073 genes between MEAM1 and Asia II 3; and 3,644 genes between MED and Asia II 3 were differentially expressed. Gene Ontology enrichment analysis revealed that the differently expressed genes between the invasive and indigenous whiteflies were significantly enriched in the term of 'oxidoreductase activity'. Pathway enrichment analysis showed that carbohydrate, amino acid and glycerolipid metabolisms were more active in MEAM1 and MED than in Asia II 3, which may contribute to their differences in biological characteristics. Our analysis also illustrated that the majority of genes involved in 'drug metabolic pathway' were expressed at a higher level in MEAM1 and MED than in Asia II 3. Taken together, these results revealed that the genes related to basic metabolism and detoxification were expressed at an elevated level in the invasive whiteflies, which might be responsible for their higher resistance to insecticides and environmental stresses.

CONCLUSIONS/SIGNIFICANCE

The extensive comparison of MEAM1, MED and Asia II 3 gene expression may serve as an invaluable resource for revealing the molecular mechanisms underlying their biological differences and the whitefly invasion.

Differential effects of an exotic plant virus on its two closely related vectors

Concurrent spread of Tomato yellow leaf curl virus (TYLCV) with invasion of Bemisia tabaci Q rather than B in China suggests a more mutualistic relationship between TYLCV and Q than B. To assess this hypothesis, we quantified the impacts of TYLCV on the performance and competitiveness of B and Q in the laboratory. The results showed that relative to their non-infected counterparts feeding on cotton (a non-host for TYLCV), infected B exhibited significant reductions in life-history traits, whereas infected Q only showed marginal reductions. While Q performed better on TYLCV-infected tomato plants than on uninfected ones, the reverse was observed in B. Q displacement by B took one more generation on TYLCV-infected tomato plants than on healthy ones. These results demonstrate that TYLCV was indirectly mutualistic to Q but directly and indirectly parasitic to B.

Roles of mating behavioural interactions and life history traits in the competition between alien and indigenous whiteflies

Interference competition between closely related alien and indigenous species often influences the outcome of biological invasions. The whitefly Bemisia tabaci species complex contains ≥28 putative species and two of them, Mediterranean (MED, formally referred to as the 'Q biotype') and Middle East-Asia Minor 1 (MEAM1, formally referred to as the 'B biotype'), have recently spread to much of the world. In many invaded regions, these species have displaced closely related indigenous whitefly species. In this study, we integrated laboratory population experiments, behavioural observations and simulation modelling to investigate the capacity of MED to displace Asia II 1 (AII1, formally referred to as the 'ZHJ2 biotype'), an indigenous whitefly widely distributed in Asia. Our results show that intensive mating interactions occur between MED and AII1, leading to reduced fecundity and progeny female ratio in AII1, as well as an increase in progeny female ratio in MED. In turn, our population cage experiments demonstrated that MED has the capacity to displace AII1 in a few generations. Using simulation models, we then show that both asymmetric mating interactions and differences in life history traits between the two species contribute substantially to the process of displacement. These findings would help explain the displacement of AII1 by MED in the field and, together with earlier studies on mating interactions between other species of the B. tabaci complex, indicate the widespread significance of asymmetric mating interactions in whitefly species exclusions.

Influence of plant combinations on population characteristics of Bemisia tabaci biotypes B and Q

In recent years, the dominant biotype of Bemisia tabaci (Gennadius) has shifted from biotype B to Q in many locations of China. Our field monitoring showed that B. tabaci biotype Q could be found on pepper Capsicum frutescens L. while biotype B could not be found on the plant. To study the role of the host plant in the displacement of biotype B by Q, the adult mortality, female fecundity, and adult emergence of both biotypes B and Q on different host combinations were studied using a model system involving pepper and eggplant. The results showed that pepper is not a preferred host for either biotype B or Q adults in comparison with eggplant. The negative impact of pepper to biotype B is, however, much greater than that to biotype Q. Because both the survival rates of the adult whitefly and the average number of emerged adults per female of biotype Q on pepper are higher than that of biotype B, biotype Q showed higher fitness in comparison with biotype B. Our results suggest that the existence and differential impact of a nonpreferred host might affect the population fitness and therefore could play a role in the displacement of biotype B in some regions.

Asymmetric reproductive interference between specialist and generalist predatory ladybirds

1. Closely related species often differ greatly in the quality and breadth of resources exploited, but the actual mechanisms causing these differences are poorly understood. Because in the laboratory specialized species often survive and perform as well or better on host species that are never utilized in nature, negative ecological interactions restricting host range must exist. Here, we focused on reproductive interference, which has been theoretically predicted to drive niche separation between closely related species with overlapping mating signals. 2. We examined the interspecific sexual interactions in relation to ecological specialization and generalization in two sibling ladybird species, Harmonia yedoensis and Harmonia axyridis. Harmonia yedoensis is a specialist predator that preys only on pine aphids, which are highly elusive prey for ladybird hatchlings, whereas H. axyridis is a generalist predator with a broad prey and habitat range. 3. We experimentally showed that conspecific sperm fertilized the vast majority of eggs regardless of mating order (i.e. conspecific sperm precedence) when a female of H. yedoensis or H. axyridis mated with both a conspecific and a heterospecific male. Moreover, we demonstrated that mating opportunities of H. yedoensis females strongly decreased as heterospecific density increased relative to conspecific density. In contrast, in H. axyridis, female mating success was high regardless of conspecific or heterospecific density. 4. Our results suggest that the generalist H. axyridis should be dominant to the specialist H. yedoensis in terms of reproductive interference. Our results support the hypothesis that asymmetric reproductive interference from the dominant species may force the non-dominant species to become a specialist predator that exclusively utilizes less preferred prey in nature.

Genetic networking of the Bemisia tabaci cryptic species complex reveals pattern of biological invasions

BACKGROUND

A challenge within the context of cryptic species is the delimitation of individual species within the complex. Statistical parsimony network analytics offers the opportunity to explore limits in situations where there are insufficient species-specific morphological characters to separate taxa. The results also enable us to explore the spread in taxa that have invaded globally.

METHODOLOGY/PRINCIPAL FINDINGS

Using a 657 bp portion of mitochondrial cytochrome oxidase 1 from 352 unique haplotypes belonging to the Bemisia tabaci cryptic species complex, the analysis revealed 28 networks plus 7 unconnected individual haplotypes. Of the networks, 24 corresponded to the putative species identified using the rule set devised by Dinsdale et al. (2010). Only two species proposed in Dinsdale et al. (2010) departed substantially from the structure suggested by the analysis. The analysis of the two invasive members of the complex, Mediterranean (MED) and Middle East - Asia Minor 1 (MEAM1), showed that in both cases only a small number of haplotypes represent the majority that have spread beyond the home range; one MEAM1 and three MED haplotypes account for >80% of the GenBank records. Israel is a possible source of the globally invasive MEAM1 whereas MED has two possible sources. The first is the eastern Mediterranean which has invaded only the USA, primarily Florida and to a lesser extent California. The second are western Mediterranean haplotypes that have spread to the USA, Asia and South America. The structure for MED supports two home range distributions, a Sub-Saharan range and a Mediterranean range. The MEAM1 network supports the Middle East - Asia Minor region.

CONCLUSION/SIGNIFICANCE

The network analyses show a high level of congruence with the species identified in a previous phylogenetic analysis. The analysis of the two globally invasive members of the complex support the view that global invasion often involve very small portions of the available genetic diversity.

Further spread of and domination by Bemisia tabaci (Hemiptera: Aleyrodidae) biotype Q on field crops in China

The sweetpotato whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), causes severe crop losses to many crops. The worst of these losses are often associated with the invasion and establishment of biotypes B and Q of this pest. Previous research in 2007 showed that biotype Q occurred with other biotypes in most field populations in China. To determine the current status of the biotype composition in the field, an extensive survey covering mainly eastern parts of China was conducted in 2009. Using polymerase chain reaction primers specific for the mitochondrial cytochrome oxidase I of biotypes B and Q and gene sequencing, we determined the biotypes composition in 61 whitefly populations and their distribution across 19 provinces in China. Our research revealed that only biotypes B and Q have been found in the field in 2009 in China. Among them, biotype Q was dominant in 44 locations (100.0%) and biotype B was dominant in 17 locations (100.0%). The current survey indicates that biotype Q has rapidly displaced biotype B in most locations in China.

Reproductive incompatibility between the B and Q biotypes of the whitefly Bemisia tabaci in China: genetic and behavioural evidence

The B and Q 'biotypes' of Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) have been invading many parts of the world and causing severe damage to a range of crops. Recent phylogenetic analyses indicate that B and Q are cryptic species within the B. tabaci species complex. Although various attempts have been made to examine the reproductive compatibility between B and Q, few studies have tested the fertility of the F1 females and so the extent of possible gene flow remains unclear. In this study, we conducted a series of crossing experiments and behavioural observations to examine in detail the reproductive compatibility between the B and Q biotypes collected from Zhejiang, China, a region recently invaded by these whiteflies. Crossing experiments between the two biotypes using either single-pairs or small groups demonstrated that proportions of females in the F1 progeny were only 0-2% in the inter-biotype crosses compared to 58-68% in the intra-biotype treatments. Furthermore, all inter-biotype F1 females were sterile. Continuous video observations showed that B and Q adults very rarely copulated, and copulation occurred only when adults of opposite sex from different biotypes were enclosed in dense cohorts for a relatively long period of time. These data show that the B and Q biotypes examined in this study are completely isolated in reproduction. The isolation was due to mainly a copulation barrier, but post-copulation barriers were also involved.

Avoidance of interspecific mating in female Syrian hamsters is stronger toward familiar than toward unfamiliar heterospecific males

Adult Syrian hamster females (Mesocricetus auratus) learn to discriminate against familiar heterospecific males (Turkish hamster, M. brandti). We investigated whether females learn to avoid any heterospecific male after exposure to just one heterospecific male. We predicted that, after being exposed to one heterospecific male, a female would avoid mating not only with that familiar male but also with any unfamiliar heterospecific male. We exposed females to a heterospecific male across a wire-mesh barrier for 8 days and then paired the female with (a) that same heterospecific male or (b) an unfamiliar heterospecific male. Females exhibited lordosis faster and for a longer duration toward the unfamiliar than toward the familiar heterospecific male. However, females were similarly aggressive toward familiar and unfamiliar heterospecific males. Perhaps exposure to stimuli from several heterospecific males (a likely scenario in the wild) would result in females behaving similarly toward familiar and unfamiliar heterospecific males.

An extensive field survey combined with a phylogenetic analysis reveals rapid and widespread invasion of two alien whiteflies in China

BACKGROUND

To understand the processes of invasions by alien insects is a pre-requisite for improving management. The whitefly Bemisia tabaci is a cryptic species complex that contains some of the most invasive pests worldwide. However, extensive field data to show the geographic distribution of the members of this species complex as well as the invasion by some of its members are scarce.

METHODOLOGY/PRINCIPAL FINDINGS

We used field surveys and published data to assess the current diversity and distribution of B. tabaci cryptic species in China and relate the indigenous members to other Asian and Australian members of the complex. The survey covered the 16 provinces where indigenous B. tabaci occur and extends this with published data for the whole of China. We used molecular markers to identify cryptic species. The evolutionary relationships between the different Asian B. tabaci were reconstructed using Bayesian methods. We show that whereas in the past the exotic invader Middle East-Asia Minor 1 was predominant across China, another newer invader Mediterranean is now the dominant species in the Yangtze River Valley and eastern coastal areas, and Middle East-Asia Minor 1 is now predominant only in the south and south eastern coastal areas. Based on mtCO1 we identified four new cryptic species, and in total we have recorded 13 indigenous and two invasive species from China. Diversity was highest in the southern and southeastern provinces and declined to north and west. Only the two invasive species were found in the northern part of the country where they occur primarily in protected cropping. By 2009, indigenous species were mainly found in remote mountainous areas and were mostly absent from extensive agricultural areas.

CONCLUSIONS/SIGNIFICANCE

Invasions by some members of the whitefly B. tabaci species complex can be rapid and widespread, and indigenous species closely related to the invaders are replaced.

Mating behaviour, life history and adaptation to insecticides determine species exclusion between whiteflies

1. Negative interspecific interactions, such as resource competition or reproductive interference, can lead to the displacement of species (species exclusion). 2. Here, we investigated the effect of life history, mating behaviour and adaptation to insecticides on species exclusion between cryptic whitefly species that make up the Bemisia tabaci species complex. We conducted population cage experiments independently in China, Australia, the United States and Israel to observe patterns of species exclusion between an invasive species commonly referred to as the B biotype and three other species commonly known as biotypes ZHJ1, AN and Q. 3. Although experimental conditions and species varied between regions, we were able to predict the observed patterns of exclusion in each region using a stochastic model that incorporated data on development time, mating behaviour and resistance to insecticides. 4. Between-species variation in mating behaviour was a more significant factor affecting species exclusion than variation in development time. Specifically, the ability of B to copulate more effectively than other species resulted in a faster rate of population increase for B, as well as a reduced rate of population growth for other species, leading to species exclusion. The greater ability of B to evolve resistance to insecticides also contributed to exclusion of other species in some cases. 5. Results indicate that an integrative analysis of the consequences of variation in life-history traits, mating behaviours and adaption to insecticides could provide a robust framework for predicting species exclusion following whitefly invasions.