Host Plant Preference Research Articles

When different contact zones tell different stories: putative ring species in the Megachile concinna species complex (Hymenoptera: Megachilidae)

We examine the genetics, morphology and ecology of the widely distributed Megachile concinna species complex (Hymenoptera: Megachilidae), which is composed of numerous taxa of unclear taxonomic status in Africa and the Palearctic. In the Western Palearctic, three genetically distinct operational taxonomic units (OTUs) are found around the Mediterranean Sea: the western Mediterranean OTU M. pusilla, the eastern Mediterranean OTU M. anatolica and the predominantly Arabian OTU M. leucostoma. A morphological cline is present between anatolica and leucostoma in the Near East, despite a lack of mitochondrial introgression between the two; one nuclear marker suggests some gene flow between these OTUs. The contact zone between pusilla and leucostoma could not be sampled but phenotypic intergradation is also observed between these OTUs in northern Africa. In contrast, study of the contact zone between pusilla and anatolica indicates that both OTUs retain phenotypic and genomic integrity in sympatry over a contact zone spanning 1000 km. The arrangement of these three OTUs suggests a ring of interconnected populations around the Mediterranean Sea and sympatry between pusilla and anatolica at both ends of the ring in southeastern Europe. The latter two OTUs exhibit ecological differences, including phenology and host-plant preferences, which may contribute to their isolation. In addition, our results suggest that two OTUs, M. venusta and M. concinna, maintain genetic and phenotypic integrity in sympatry in parts of Africa; the latter is recognized as a valid species here. Lastly, our results indicate that two OTUs have been introduced independently into the New World, pusilla in North America and Argentina, and concinna in the Antilles.

Microhabitat selection of Aporia crataegi (Lepidoptera: Pieridae) larvae in a traditionally managed landscape

In this study we assessed microhabitat and host plant preferences of Aporia crataegi (Linne 1758) larvae in the field. The study was conducted in the submediterranean part of Slovenia, at the edge of the limestone region Kraski rob, where this species is widespread. The larvae were most abundant on blackthorn (Prunus spinosa L.) and the common hawthorn (Crataegus monogyna Jacq.), and infrequent on the rosehip (Rosa sp.) and rock cherry (Prunus mahaleb L.). Smaller shrubs with greater exposure to sun appeared to be preferred and larvae constructed their nests on outer branches of plants. The thermophilic nature of larvae was evident by the low and sheltered position of the nests, although in P. spinosa, which is more thermophilic than C. monogyna, they were positioned somewhat higher. As the nests and larvae occur mostly on plants growing in warmer microhabitats, larvae that had overwintered can take advantage of the quicker development of buds and leaves in early spring. The rocky ground below and around the occupied plants was often covered with grass, suggesting the need for cooler and warmer microclimate during hot summers and cold winters with strong winds, respectively. Densities of larvae and nests were positively but non-significantly correlated to density of host plants; however, in later successional stages, where host plants are most abundant, open and sunny microhabitats that can provide opportunities for larvae to warm up are lacking. The revival of the traditional management practices with extensive grazing with late and only occasional mowing may slow down the overgrowing process, leaving spiny host plants abundant and in close proximity to the nectaring sources for the adults.

A new subspecies in a Heliconius butterfly adaptive radiation (Lepidoptera: Nymphalidae)

A fundamental goal in evolutionary biology is to understand how evolutionary patterns and processes shape natural diversity. This, however, requires a complete characterization of the phenotypic and genetic variation between and within species. Here, we used molecular, morphological and behavioural data to describe a new and stable subspecies of Heliconius timareta, named Heliconius timareta linaresisubsp.nov. This race differs phenotypically from other red-coloured H. timareta and instead exhibits a black and yellow wing pattern more similar to Heliconius cydno. However, mtDNA, microsatellite and amplified-fragment length polymorphism data indicate a closer relationship with H. timareta than H. cydno and Heliconius melpomene. Larval morphology and host plant preferences are similar to other H. timareta and H. cydno races. Thus, our combined data indicate that this taxon is a novel subspecies of H. timareta, clearly differentiated from H. cydno and H. melpomene.

Spatial turnover in host-plant availability drives host-associated divergence in a South African leafhopper (Cephalelus uncinatus)

BackgroundThe evolution of reproductive isolation between herbivorous insect populations is often initiated by shifts to novel host-plants, a process that underlies some of the best examples of ecological speciation. However, it is not well understood why host-shifts occur. Arguably the most common hypothesis is that host-shifts occur in response to competition, while a less frequently invoked hypothesis is that herbivores adapt locally to geographic differences in potential host-plant communities. Here we investigate whether geographic variation in host-plant availability is likely to have driven host-shifts in restio leafhoppers. We studied local adaptation of a camouflaged restio leafhopper species, Cephalelus uncinatus, to host-plants in the Restionaceae (restios); a family of plants with exceptional diversity in the anomalously species-rich Cape Floristic Region (CFR). To determine whether C. uncinatus experiences heterogeneous host communities across its range, we first quantified the degree of geographic overlap between C. uncinatus and each of its associated host-plant species. Then we quantified trait divergence (host preference, body size and colour) for three pairs of C. uncinatus populations found on different host-plant species differing in their degree of spatial overlap. Spectral reflectance was modelled in bird visual space to investigate whether body colour divergence in C. uncinatus corresponds to leaf sheath colour differences between restio species as perceived by potential predators.ResultsWe demonstrate that C. uncinatus is forced to use different restio species in different regions because of turnover in available host species across its range. Comparisons between geographically separated populations were consistent with local adaptation: restio leafhoppers had preferences for local host-plants over alternative host-plants and matched local plants better in terms of size and colour.ConclusionsSpatial turnover in host-plant availability has likely facilitated host-shifts in C. uncinatus. Spatial turnover in host-plant availability may be an important driver of insect diversification in the CFR and globally.

Bitki Sekonder Maddelerinin Herbivor Böceklere Etkileri

Plants have developed mechanical and chemical defense strategies that are effective against herbivores. Plants contain chemicals that are known as secondary metabolites (allelochemical) and these chemicals do not directly involve in organisms’ reproduction and growth, on the other hand, they affect survival, growth and behavior of species. These compounds usually take ecological tasks and plants use these compounds against diseases, parasites, and predators for interspecies competition. It is known through the observations on feeding of herbivorous insects that these compounds act as deterrent chemicals or they are toxic against them. Feeding is one of the most fundamental and the most important behaviors for herbivorous insects. Even though host plant preference of herbivores is partially depend on nutrients, this behavior greatly depends on secondary chemistry of plants. Effects of secondary compounds on herbivorous insects can be positive or negative.

Mitogenome evolution in Cephini (Hymenoptera: Cephidae): Evidence for parallel adaptive evolution

Two mitogenomes of remarkable size of the stem-boring sawflies, Trachelus tabidus (18539 bp) and T. iudaicus (20730 bp), were characterized and compared with previously known mitogenomes of Cephini. A rearrangement in the IQM gene cluster, an unusual elongation in rrnS gene and supposedly functional tandem repeat sequences in the A+T-rich region are synapomorphies of Cephini. Mitogenome evolution of the Cephini was investigated in a dataset of seven species representing all genera. The noticeably divergent mitogenomes of the Cephini both at nucleotide and amino acid level, and the variable rates of ω values, indicate the effects of different selective forces, rather than neutral evolution. The effect of positive selection is revealed by radical amino acid changes with ten physicochemical properties (Pα, Br, pK′, h, El, Hnc, αc, αn, Ra and Hp) throughout each branch of the tree. The radical changes in the ND and ATP complexes are mostly related to chemical and energetic properties due to different energy requirements among species. The phenology of Cephini species and their host plants, together with habitat structure, rather than host plant preferences or phylogenetic constraint, are suggested to explain the role of adaptive evolution in shaping Cephini mitogenomes.

Female fecundity variation affects reproducibility of experiments on host plant preference and acceptance in a phytophagous insect.

Reproducibility is a scientific cornerstone. Many recent studies, however, describe a reproducibility crisis and call for assessments of reproducibility across scientific domains. Here, we explore the reproducibility of a classic ecological experiment-that of assessing female host plant preference and acceptance in phytophagous insects, a group in which host specialization is a key driver of diversification. We exposed multiple cohorts of Pieris napi butterflies from the same population to traditional host acceptance and preference tests on three Brassicaceae host species. Whereas the host plant rank order was highly reproducible, the propensity to oviposit on low-ranked hosts varied significantly even among cohorts exposed to similar conditions. Much variation could be attributed to among-cohort variation in female fecundity, a trait strongly correlated both to female size and to the size of the nuptial gift a female receives during mating. Small males provide small spermatophores, and in our experiment small females that mated with small males had a disproportionally low propensity to oviposit on low-ranked hosts. Hence, our results provide empirical support to the theoretical prediction that female host utilization is strongly affected by non-genetic, environmental variation, and that such variation can affect the reproducibility of ecological experiments even under seemingly identical conditions.

Do the mechanisms modulating host preference in holometabolous phytophagous insects depend on their host plant specialization? A quantitative literature analysis

In holometabolous phytophagous insects, adult females and larvae determine host plant selection through oviposition and feeding preferences. Pre-imaginal and/or imaginal experiences with plant chemical cues can modulate these preferences. Various studies found evidence, or not, of host preference modulation through previous experience but they appear to contradict each other. Most probably, modulation of host preference depends on the degree of specialization of the insects. Our literature analysis revealed that the positive influence of experience in the modulation of host plant preference occurred equally in polyphagous, oligophagous and monophagous species, but was significantly more influenced by the phylogeny of the insect and the developmental stage involved in plant cue experience. Identification of phylogenic and developmental stage factors of “host learning” abilities appeared to be key information for predicting the response of species to habitat modifications rather than the insect’s degree of host plant specialization. The signification of this output on the fact that some insect species or populations shifted from the wild to cultivated habitats to become important pests is discussed.

Genetic variation in light vision and light-dependent movement behaviour in the eyeless Collembola Folsomia candida

Animals can cope with spatiotemporal variation in their environment through mobility and selective habitat choice. Intra-specific variation in habitat choice has been documented especially for host plant preferences and cryptic habitat selection in insects. Here, we investigated the genetic variation in light sensitivity and light-dependent habitat choice in the eyeless Collembola Folsomia candida with a choice test under four different lighting conditions (control dark condition, two simulations of undergrowth natural light conditions and red light). We tested twelve clonal strains from diverse geographical origins that are clustered in two evolutionary clades with contrasting fast or slow life-history strategies. The clones differed in their mean movement probabilities in the dark treatment. These differences were related to the two different phylogenetic clades, where fast-life history clones are on average more mobile than slow-life history counterparts as predicted by the ‘colonizer syndrome’ hypothesis. We found behavioural avoidance of light in the three light conditions. Moreover, photophobia was stronger when the simulated light spectrum was brighter and included non-red light. Photophobia was similar among all clonal lineages and between the two clades, which suggests that this behaviour is a shared behavioural trait in this species. We discuss the use of light as an environmental cue for orientation, displacement and habitat choice under natural conditions.

Determination of Oviposition Preference and Infestation Level of Tuta absoluta on Major Solanaceae Crops Under Glasshouse Conditions in Ethiopia

Tuta absoluta (Meyrick) is a very destructive insect pest with a strong preference for tomato plants. It originates from South America where it has been considered a key pest since the 1980s. It can also attack the aerial parts of tomato, potato, tobacco and some solanaceous weeds. Based on the leaf and fruit-infestation data, four genotypes of tomato (Coshoro, Roman-VF, Galila and Local var.), showed susceptible responses; four genotypes of potato (Jalane, Menagesha, Tolcha and Local var.) showed a tolerant trend and four pepper genotypes (M. Awaze, M. Fana, M. Zala and Local var.), with non-infestation and high resistant, were resulted during 2015-2017. Significant differences were observed, among the genotypes, regarding to the oviposition, in number of eggs/plant. Tomato, showed a maximum oviposition of 62.38%/plant on upper leaf followed by lower leaf 35.72%/plant; while minimum oviposition was recorded to be on flower 0.37% and stem 0.53% per plant, respectively. In contrast, on potato genotypes the maximum ovipostion was recorded on lower leaf as an average 79.63%/plant and 15.11% was recorded on upper leaf; while minimum oviposition were recorded on stem of potato genotypes as an average 1.93%/plant and on all pepper genotype no oviposition was recorded in both years. Variations were found to be significant among dates of observation, regarding to the larval-population and infestation-percentage of the leaf and fruits, during both the study years. There were no significant (P>0.05) differences among each crop varieties. Hence, these present findings are suggest that T. absoluta oviposition behavior is dependent on the host plant preferences among major solanaceae crops and not on varieties of each crop.

Egg laying behaviour, host plants and larval survival of Euphydryas aurinia provincialis (Lepidoptera Nymphalidae) in a Mediterranean population (central Italy)

In this paper, we show the results of research that can inform conservation measures elsewhere in Europe for the endangered butterfly Euphydryas aurinia. A five year field study was undertaken to identify the host plant preference of larvae of Euphydryas aurinia provincialis in the Mediterranean and which signals are used by females to lay their eggs. The females oviposit on Gentiana cruciata, Scabiosa columbaria and Cephalaria leucantha; the larvae feed on all these plants and additionally on Lonicera caprifoliumin the wild and on Gentiana lutea in the laboratory. The females do not show any preference for a specific host plant and the larvae move from one species of plant to another without any difficulty. The most important factors in determining the female oviposition are the visibility, accessibility and sun-exposure of the host plants. The vegetative state of host plants is the key factor in larval use of plants during the pre- and post-diapause period. The large-sized host plants, G. cruciata and C. leucantha, are optimal for the growth and survival of the pre-diapause I-III larval instar, while they are unavailable to the larvae in Spring because of their delayed vegetative growth. The post-diapause larvae preferentially feed on plants of S. columbaria, and to lesser degree L. caprifolium, as they provide and abundant food source compared with G. cruciata and C. leucantha. The results also suggest that, there is an evolutionary advantage in large numbers of caterpillars feeding together, with the females of E. aurinia provincialis preferring to lay their eggs nearby or above egg batches laid previously by another female, and selecting large plants for oviposition. Despite the competition for food among caterpillars, the oviposition behaviour of females is advantageous and increases the larval survival rate on large plants. The gregarious larval behaviour provides several benefits during both pre-diapause period (avoiding starvation) and post-diapause period (efficiency in thermoregulation).

Performance of Western Tent Caterpillar (Malacosoma californicum) on Two Common Host Plants, Including a New Host Plant Record

ABSTRACT. Tent caterpillars are generalists across their full host range, but display local host plant preferences. We present evidence for a new host plant record, wax currant (Ribes cereum), for western tent caterpillars (Malacosoma californicum) along the Colorado Front Range. We tested the suitability of wax currant as a host plant for western tent caterpillars as compared to chokecherry (Prunus virginiana), an abundant and commonly used host plant. We measured the density of tent caterpillar tents in areas where both host plants occur to assess host plant use. We reared tent caterpillar larvae on both host plants and measured fitness effects due to host plant quality (survival, pupal mass) and natural enemies (parasitism). We did not find a relationship between host plant abundance and use by tent caterpillars and found no evidence for a preference for either host plant. We found that western tent caterpillars do not differ in pupal mass when reared on chokecherry and on wax currant in a laboratory s...

Comparative transcriptome analysis of chemosensory genes in two sister leaf beetles provides insights into chemosensory speciation

Divergence in chemosensory traits has been posited as an important component of chemosensory speciation in insects. In particular, chemosensory genes expressed in the peripheral sensory neurons are likely to influence insect behaviors such as preference for food, oviposition sites, and mates. Despite their key role in insect behavior and potentially speciation, the underlying genetic basis for divergence in chemosensory traits remains largely unexplored. One way to ascertain the role of chemosensory genes in speciation is to make comparisons of these genes across closely related species to detect the genetic signatures of divergence. Here, we used high throughput transcriptome analysis to compare chemosensory genes of the sister leaf beetles species Pyrrhalta maculicollis and P. aenescens, whose sexual isolation and host plant preference are mediated by divergent chemical signals. Although there was low overall divergence between transcriptome profiles, there were a number of genes that were differentially expressed between the species. Furthermore, we also detected two chemosensory genes under positive selection, one of which that was also differentially expressed between the species, suggesting a possible role for these genes in chemical-based premating reproductive isolation and host use. Combined with the available chemical and ecological work in this system, further studies of the divergent chemosensory genes presented here will provide insight into the process of chemosensory speciation among Pyrrhalta beetles.

Horizontal gene transfer is more frequent with increased heterotrophy and contributes to parasite adaptation.

Horizontal gene transfer (HGT) is the transfer of genetic material across species boundaries and has been a driving force in prokaryotic evolution. HGT involving eukaryotes appears to be much less frequent, and the functional implications of HGT in eukaryotes are poorly understood. We test the hypothesis that parasitic plants, because of their intimate feeding contacts with host plant tissues, are especially prone to horizontal gene acquisition. We sought evidence of HGTs in transcriptomes of three parasitic members of Orobanchaceae, a plant family containing species spanning the full spectrum of parasitic capabilities, plus the free-living Lindenbergia Following initial phylogenetic detection and an extensive validation procedure, 52 high-confidence horizontal transfer events were detected, often from lineages of known host plants and with an increasing number of HGT events in species with the greatest parasitic dependence. Analyses of intron sequences in putative donor and recipient lineages provide evidence for integration of genomic fragments far more often than retro-processed RNA sequences. Purifying selection predominates in functionally transferred sequences, with a small fraction of adaptively evolving sites. HGT-acquired genes are preferentially expressed in the haustorium-the organ of parasitic plants-and are strongly biased in predicted gene functions, suggesting that expression products of horizontally acquired genes are contributing to the unique adaptive feeding structure of parasitic plants.

The role of leaf cellulose content in determining host plant preferences of three defoliating insects present in the Andean‐Patagonian forest

AbstractPhytophagous insects choose their feeding resources according to their own requirements in addition to properties of the host plants, such as biomechanical defences. The feeding preferences of the native folivorous insects of the Andean‐Patagonian forest (Argentina) have rarely been studied. These environments present a wide diversity and abundance of insects associated with trees of the Nothofagus and Lophozonia (Nothofagaceae) genera, which represent the main tree species of the forests of the southern hemisphere. In particular, Lophozonia alpina and Lophozonia obliqua are of great interest because they have a wide distribution, a high capacity for hybridization and exhibit great phenotypic plasticity. This versatility causes substantial variation in the biomechanical properties of leaves, affecting the feeding preferences of insects. The purpose of this work was to study the food selection behaviour of three leaf‐chewing insects (Polydrusus nothofagii, Polydrusus roseaus (Coleoptera: Curculionidae) and Perzelia arda (Lepidoptera: Oecophoridae)) associated with L. alpina and L. obliqua as host plants. Based on their choices, our aim was to determine a preference scale for each insect species and the variables on which these preferences were based. Therefore, we selected trees of L. alpina and L. obliqua, measured several properties such as cellulose content and recorded which leaves were eaten. As a result, we determined that the three species of insects feed on both host plants but prefer the leaves of L. obliqua, with cellulose content being the main determining factor for their decisions. However, in the case of P. arda, there was a positive relationship between cellulose and host plant preference, whereas there was an opposite relationship for the weevils. We conclude that during feeding selection, there are some properties of the leaves that have a more important role than others and that the same property does not exert the same behavioural response in all folivorous insects.

Development of defoliating insects and their preferences for host plants under varying temperatures in a subtropical evergreen forest in eastern China

The aim of this work was to understand the development of defoliating insects and their preferences for host plants under varying temperatures in a subtropical evergreen broad-leaved forest in China. We measured the main developmental parameters of three typical defoliating insects (i.e., Ourapteryx ebuleata szechuana, Biston marginata, and Euproctis angulata) and their preferences for five host plants at temperatures from 16°C to 31°C at 3°C intervals in the Tiantong National Forest Research station in eastern China. The results showed the following. 1) An appropriate rise in temperature increases the survival rate with an increase in the number of offspring. The developmental durations for these three insects were shortened, and pupal weight increased with an increase in temperature. 2) A shift in the preference for host plants for these three insects was observedat elevated temperatures. They all preferred to feed on Schima superba and Castanopsis sclerophylla at elevated temperatures, showing an opposite response to the other three plants. The daily leaf consumption of the three insects was positively correlated with their feeding preference, with more leaves being consumed from the plants they preferred. 3) For O. ebuleata szechuana larvae, daily leaf consumption initially increased and then decreased with increasing temperatures. In contrast, Biston marginata and Euproctis angulata larvae consumed more leaves at elevated temperatures. The feeding preferences of O. ebuleata szechuana and Biston marginata were more sensitive to changing temperatures than that of Euproctis angulata laevae. We concluded that increased numbers of offspring and generations, pupal weights, and a shift in preference to two plants for these three defoliating insects might lead to severe damage to these two plants which would enhance the fragmentation and decrease the stability of the forest communities under changing temperatures. Meanwhile, the variations in the responses of defoliating insects to the changing temperatures should be taken into consideration for the pest management of forests to adapt to the changing climate.

The effects of soil eutrophication propagate to higher trophic levels

AbstractAimNitrogen deposition is a major global driver of change in plant communities, but its impacts on higher trophic levels are insufficiently understood. Here, we introduce and test a novel conceptual trait‐based model describing how the effects of soil eutrophication cascade to higher trophic levels across differential plant–herbivore interactions.LocationNorthern Europe.MethodsWe synthesize previous literature on the effects of nitrogen on plants and herbivorous insects as well as relevant multispecies patterns of insect communities concerning species dietary breadth, body size, dispersal propensity and voltinism in order to derive the model. We empirically evaluate the proposed, hitherto untested, four main model pathways using statistical modelling and data on 1064 northern European butterfly and moth species, their life‐history traits, phylogeny and population trends.ResultsWe show that across all species: (1) larval dietary breadth and host plant foliar nitrogen content are positively and equally strongly related to insect body size, and that (2) multivoltinism, host plant preferences for soil nitrogen, body size and larval dietary breadth are positively related to population trends of butterflies and moths as predicted by the model. Positive relationships between plant foliar nitrogen content and body size as well as multivoltinism and population trends are the first multispecies demonstrations for these patterns.Main conclusionsSoil nitrogen enrichment amplifies the diverging trends of herbivorous insects feeding on nitrophilous versus nitrophobous plants through differential plant–herbivore interactions, causing predictable changes in community composition at higher trophic levels. A positive foliar nitrogen–insect body size relationship, now empirically supported, is the integrating link within this cascade. As nitrogen deposition is a global driver, our model suggests that a major future trend may be an increased dominance of insects that are large, dispersive, multivoltine, dietary generalists or specialized on nitrophilous plant species at the expense of species preferring oligotrophic environments.

Host plant preference in the protected myrmecophilous Transylvanian Blue (Pseudophilotes bavius hungarica) butterfly (Lepidoptera: Lycaenidae) and its relationship with potential ant partners

When selecting specific host plants, caterpillars of many lycaenid butterflies, such as the protected Pseudophilotes bavius hungarica, are known to engage in various interactions with ants, which help them survive. Although P. bavius is a protected species, data about its host plant selection is very scarce, and little information is available on its myrmecophilous relationships. Our aim was to identify the host plant characteristics that determine the occurrence of the caterpillar and to clarify the specificity of its myrmecophily. We conducted a series of field surveys regarding host plant characteristics. Laboratory experiments were carried out to investigate the nature of interactions between the caterpillar and its potential ant partners. Control experiments involving non-visiting ants were also performed. On the basis of our findings, the physical characteristics of host plants do not seem to influence host plant choice, but the absence of aphids and the presence of different ant species proved important. According to the results of behavioural assays, neutral reactions to the caterpillars were recorded in the case of ant species that regularly visited the host plant (Lasius paralienus, Camponotus aethiops), in contrast to Tapinoma subboreale, which was not observed at all on the host plants and which behaved aggressively towards the larvae. Therefore, the caterpillar is expected to show a certain ant host selectivity. The study constitutes an essential contribution to our knowledge of the natural history of a protected butterfly species, which can be used as a basis for more appropriate management strategies, while also shedding light on aspects of myrmecophilous relationships in Lycaenidae in general.

Effects of Soybean Vein Necrosis Virus on Life History and Host Preference of Its Vector, Neohydatothrips variabilis, and Evaluation of Vector Status of Frankliniella tritici and Frankliniella fusca.

Soybean vein necrosis virus (SVNV) is an emerging Tospovirus that is now considered to be the most widespread soybean virus in the United States. SVNV is transmitted from plant-to-plant by soybean thrips, Neohydatothrips variabilis (Beach). We hypothesized that a positive interaction between the host plant, SVNV, and the vector may have resulted in the widespread distribution of the virus in a short span of time. Our study found that SVNV-infected N. variabilis females produced significantly more offspring compared with non-infected females. No other life-history trait varied between SVNV-infected and non-infected thrips. There was considerable variation in SVNV copy number in infected thrips ranging from 10(2) -10(6) Moreover, there was a significant negative correlation between SVNV copy number and fecundity in infected N. variabilis This suggests that excessive virus accumulation may result in lower viability of N. variabilis In choice tests, SVNV-infected N. variabilis preferred to feed on non-infected leaflets compared with infected leaflets. Vector competence assays indicated that Frankliniella tritici and Frankliniella fusca can transmit SVNV, but at a lower efficiency than N. variabilis Comparison of life history of between the primary and secondary vectors showed that N. variabilis had the highest fecundity, but F. tritici had the shortest development time and greatest larval survival. Taken together, the increased fecundity of SVNV-infected N. variabilis, their apparent preference for non-infected host plants, in conjunction with the ability of secondary vectors to survive and reproduce on soybean may, in part, explain the rapid spread of SVNV in the United States.

Resolving the taxonomic status of Frankliniella schultzei (Thysanoptera: Thripidae) colour forms in Kenya – a morphological-, biological-, molecular- and ecological-based approach

AbstractFrankliniella schultzeiTrybom is a polyphagous pest and vector of tospoviruses worldwide. It occurs in dark and pale colour forms that are morphologically similar but differ in vector competency and geographic spread. In Kenya and other tropical regions, mixed populations of both colour forms are observed in similar habitats, so are considered as one species. To ascertain the taxonomic status of the two colour forms, they were characterized using morphological, molecular, biological and ecological approaches. Morphological characterization revealed differences between the colour forms on eight features and they separated into distinct clusters through principal component analysis. Restriction fragment length polymorphism of the internal transcribed spacer region (ITS-RFLP) analysis revealed differences between the two colour forms and was confirmed by differences in ITS2 sequences. Virgin pale females had female offspring (thelytoky), while virgin dark females had male offspring (arrhenotoky). Interbreeding of dark males with pale females resulted in pale females, indicating absence of interbreeding between the two colour forms. Laboratory colonies of pale forms lacked males and further analysis ofF. schultzeimales fromIpomoea setosaflowers in the field indicated the presence of dark males and the absence of pale males. Field surveys in Kenya indicated differences in distribution and host plant preferences among the colour forms. Lack of interbreeding, distinct host preferences and distribution, and morphological and molecular differences indicate that the two colour forms ofF. schultzeicould be different species. The results highlight the need for combining morphological, biological, molecular and ecological characteristics for resolving taxonomic status of closely related insects.