Generalized host‐plant feeding can hide sterol‐specialized foraging behaviors in bee–plant interactions

Host‐plant selection is a key factor driving the ecology and evolution of insects. While the majority of phytophagous insects is highly host specific, generalist behavior is quite widespread among bees and presumably involves physiological adaptations that remain largely unexplored. However, floral visitation patterns suggest that generalist bees do not forage randomly on all available resources. While resource availability and accessibility as well as nectar composition have been widely explored, pollen chemistry could also have an impact on the range of suitable host‐plants. This study focuses on particular pollen nutrients that cannot be synthesized de novo by insects but are key compounds of cell membranes and the precursor for molting process: the sterols. We compared the sterol composition of pollen from the main host‐plants of three generalist bees: Anthophora plumipes, Colletes cunicularius, and Osmia cornuta, as well as one specialist bee Andrena vaga. We also analyzed the sterols of their brood cell provisions, the tissues of larvae and nonemerged females to determine which sterols are used by the different species. Our results show that sterols are not used accordingly to foraging strategy: Both the specialist species A. vaga and the generalist species C. cunicularius might metabolize a rare C₂₇ sterol, while the two generalist species A. plumipes and O. cornuta might rather use a very common C₂₈ sterol. Our results suggest that shared sterolic compounds among plant species could facilitate the exploitation of multiple host‐plants by A. plumipes and O. cornuta whereas the generalist C. cunicularius might be more constrained due to its physiological requirements of a more uncommon dietary sterol. Our findings suggest that a bee displaying a generalist foraging behavior may sometimes hide a sterol‐specialized species. This evidence challenges the hypothesis that all generalist free‐living bee species are all able to develop on a wide range of different pollen types.     

Comparative demography of a specialist and generalist fruit fly: Implications for host use and pest management

Host plants used by phytophagous insects can have significant consequences on demography parameters, overall lifetime fitness and their subsequent population dynamics. Here, we conduct a comparative demographic study between the specialist Zeugodacus cucumis (French) and generalist Bactrocera tryoni (Froggatt) (Diptera: Tephritidae) to determine whether the host plants used by these fly species play any role in their overall lifetime fitness and explains current host use patterns. These two fly species are pests within the north-eastern region of Australia and we further aimed to use complete life-history data to determine the population parameters and models that would help identify the sensitive life-history stage that could be targeted for effective field management. Eggs collected from laboratory-reared flies were inoculated into organically grown fruits of both the primary and alternate host plant cultivars of both fly species. The proportion surviving each life stage from egg through to adult and fecundity were monitored for all cohorts from the different plant cultivars. Complete stage-base life-tables for cohorts of each fly species developing from each fruit cultivar were constructed, and the key demographic parameters and population models were analysed using PopTools matrix model programme. Our results showed that the host used by each fly species had significant consequences on fly demographic parameters and hence their overall lifetime fitness. The generalist B. tryoni was able to compensate for the fitness loss experienced at the pre-adult stage by having adults with higher fecundity, but this was not the case for the specialist Z. cucumis. Stage-base population models revealed that the population growth rate of both species was highly sensitive at the adult reproductive stage, indicating that manipulating probability of survival at this life stage would effectively manage populations of these pest species. This study provides the empirical evidence of undertaking complete life history demography studies of phytophagous insects to accurately understand their lifetime fitness consequences of using a certain host, their observed host use patterns, and overall population dynamics. We suggest that any efforts to manage dacine fruit fly pest population should consider life-history consequences of host use.     

Geographic and between-generation variation in the parasitoid communities associated with an invading gallwasp,Andricus quercuscalicis (Hymenoptera: Cynipidae)

The knopper gallwasp Andricus quercuscalicis Burgsdorf 1783 (Hymenoptera: Cynipidae) has invaded western and northern Europe from southern and eastern Europe over the last 400 years. A. quercuscalicis has two alternating generations, which differ in phenology, structure, and host oak species. This study describes geographic variation in the community in the tiny catkin galls of the sexual generation on Turkey oak, Quercus cerris, and compares the patterns obtained with those in the community attacking the alternate agamic generation. As predicted from considerations of parasitoid recruitment to the communities of invading phytophagous insects (Cornell and Hawkins 1993), in its native range the sexual generation shows (1) higher parasitoid community species richness, (2) higher total mortality due to parasitoid attack and (3) a higher ratio of specialist to generalist parasitoid species than is evident in the invaded range. Counter to predictions, there is no indication that parasitoid community richness in the invaded range has increased with time since the arrival of the new host. Higher host mortality in the native range is due principally to a single specialist, Aulogymnus obscuripes Mayr 1877 (Hymenoptera: Eulophidae), and is not distributed evenly among parasitoid species which attack the gall-former only in this area. This contrasts with the community in Britain, where three principal generalist parasitoids cause approximately equal mortalities. The agamic gall contains a taxonomically and structurally diverse guild of parasitoid and inquiline species, associated with the changing resource provided by a large, long-lived, complex gall. In contrast, the sexual community includes a taxonomically and structurally narrow guild, associated with a resource which is structurally simple, small in size and short-lived. No parasitoid species attacks the gall-former in both generations. Surprisingly, in spite of these differences in the nature of the gall resource in the two generations, over their entire range (native and invaded) the parasitoid guilds of the two are equally species rich.     

You stay,but I Hop: Host shifting near and far co‐dominated the evolution of Enchenopa treehoppers

The importance and prevalence of phylogenetic tracking between hosts and dependent organisms caused by co‐evolution and shifting between closely related host species have been debated for decades. Most studies of phylogenetic tracking among phytophagous insects and their host plants have been limited to insects feeding on a narrow range of host species. However, narrow host ranges can confound phylogenetic tracking (phylogenetic tracking hypothesis) with host shifting between hosts of intermediate relationship (intermediate hypothesis). Here, we investigated the evolutionary history of the Enchenopa binotata complex of treehoppers. Each species in this complex has high host fidelity, but the entire complex uses hosts across eight plant orders. The phylogenies of E. binotata were reconstructed to evaluate whether (1) tracking host phylogeny; or (2) shifting between intermediately related host plants better explains the evolutionary history of E. binotata. Our results suggest that E. binotata primarily shifted between both distant and intermediate host plants regardless of host phylogeny and less frequently tracked the phylogeny of their hosts. These findings indicate that phytophagous insects with high host fidelity, such as E. binotata, are capable of adaptation not only to closely related host plants but also to novel hosts, likely with diverse phenology and defense mechanisms.     

Interactions between phytophagous insects and their Opuntia hosts

Abstract.

• 1 The cactophagous insect community on opuntias is analysed to show the number of insect species in different taxa. An extension of this analysis gives the average species complement on large and small opuntias.
• 2 A highly significant positive correlation is found between the total number of phytophagous insect species on individual Opuntia species and a measure of the overall ‘architecture’ of their host plants.
• 3 The specificity of the phytophagous insects on opuntias is briefly considered and the community as a whole analysed by guilds. The co-evolution of the Opuntia-feeding insects and their hosts has culminated in a community of specialist insects to the exclusion of nearly all generalist phytophages.
• 4 The life history strategies of the Opuntia-feeding insects are reviewed. Common to all developmental stages are morphological and behavioural adaptations that reduce the risk of attack by natural enemies. This is clearly the consequence of living on structurally simple host plants where there is little place to hide.
• 5 The possible influence of insect herbivores on Opuntia evolution is discussed.
• 6 An understanding of the interactions between the phytophagous insect community and opuntias has clear implications for the biological control of alien Opuntia weeds.

     

Preference and performance of generalist and specialist herbivores on chemically defended host plants

1. Both the physiological efficiency (PE) hypothesis and the preference–performance (PP) hypothesis address the complex interactions between herbivores and host plants, albeit from different perspectives. The PE hypothesis contends that specialists are better physiologically adapted to their host plants than generalists. The PP hypothesis predicts that larvae perform best on the host plant preferred by ovipositing females. 2. This study tests components of both hypotheses using the specialist checkerspot, Euphydryas anicia, the generalist salt marsh caterpillar, Estigmene acrea, and host plants in the genus Penstemon, which are defended by iridoid glycosides. 3. In laboratory experiments, the generalist preferred and performed significantly better on the less well defended host plant species. This is consistent with results from a common garden experiment where the less well defended Penstemon species received more damage from the local community of generalists. Larvae of the specialist checkerspot preferred the more chemically defended species in the laboratory, but performed equally well on both hosts. However, field experiments demonstrated that adult checkerspot females preferred to oviposit on the less well defended host plant. 4. Components of the physiological efficiency hypothesis were supported in this system, as the specialist outperformed the generalist on the more iridoid glycoside‐rich host plant species. There was no support for the PP hypothesis, however, as there was no clear relationship between female preference in the field and offspring performance in the laboratory.     

Host specificity of the egg pupal parasitoid Fopius arisanus (Hymenoptera: Braconidae) in La Reunion

Fopius arisanus is a polyphagous parasitoid of Tephritidae, which has been recently introduced to La Réunion Island as part of a classical biological control programme. We carried out laboratory experiments to assess the host specificity of this parasitoid, initially reared on Bactrocera zonata, and then offered for parasitization the eight local tephritid pest species. Naive or experienced parasitoid females were given tephritid eggs in no choice tests. Fopius arisanus females parasitize all fly species but parasitism varies with host species. No adult wasps emerge from Bactrocera cucurbitae and the survival of this species is only slightly affected by parasitism. Dissections show that the late instars of this fly may eliminate the parasitoid by encapsulation. When developing on Ceratitis capitata, Ceratitis rosa, Dacus ciliatus, Dacus demmerezi, and Neoceratitis cyanescens, parasitoid survival rate ranges from 10 to 25%. Bactrocera zonata and Ceratitis catoirii are the best hosts, yielding parasitoid survival rates of more than 70% with no premature mortality. The egg-larval mortality of C. capitata, C. rosa, D. ciliatus, and N. cyanescens, and the pupal mortality of D. demmerezi, are significantly increased by parasitism. The size of emerging adults is affected by host species and is correlated to pupal weight. Bactrocera zonata would be a favorable host to support routine colonization of F. arisanus for mass production of this parasitoid.     

Genetic divergence with ongoing gene flow is maintained by the use of different hosts in phytophagous ladybird beetles genus Henosepilachna

Adaptation to different environments can promote population divergence via natural selection even in the presence of gene flow – a phenomenon that typically occurs during ecological speciation. To elucidate how natural selection promotes and maintains population divergence during speciation, we investigated the population genetic structure, degree of gene flow and heterogeneous genomic divergence in three closely related Japanese phytophagous ladybird beetles: Henosepilachna pustulosa, H. niponica and H. yasutomii. These species act as a generalist, a wild thistle (Cirsium spp.) specialist and a blue cohosh (Caulophyllum robustum) specialist, respectively, and their ranges differ accordingly. The two specialist species widely co‐occur but are reproductively isolated solely due to their high specialization to a particular host plant. Genomewide amplified fragment‐length polymorphism (AFLP) markers and mitochondrial cytochrome c oxidase subunit I (COI) gene sequences demonstrated obvious genomewide divergence associated with both geographic distance and ecological divergence. However, a hybridization assessment for both AFLP loci and the mitochondrial sequences revealed a certain degree of unidirectional gene flow between the two sympatric specialist species. Principal coordinates analysis (PCoA) based on all of the variable AFLP loci demonstrated that there are genetic similarities between populations from adjacent localities irrespective of the species (i.e. host range). However, a further comparative genome scan identified a few fractions of loci representing approximately 1% of all loci as different host‐associated outliers. These results suggest that these three species had a complex origin, which could be obscured by current gene flow, and that ecological divergence can be maintained with only a small fraction of the genome is related to different host use even when there is a certain degree of gene flow between sympatric species pairs.     

An omics evolutionary perspective on phytophagous insect–host plant interactions in Anastrepha obliqua: a review

Phytophagous insects have a close relationship with their host plants. For this reason, their interactions can lead to important changes in insect population dynamics and evolutionary trajectories. Next generation sequencing (NGS) has provided an opportunity to analyze omics data on a large scale, facilitating the change from a classical genetics approach to a more holistic understanding of the underlying molecular mechanisms of host plant use by insects. Most studies have been carried out on model species in Holarctic and temperate zones. In tropical zones, however, the effects of use of various host plants on evolutionary insect history is less understood. In the current review, we describe how omics methodologies help us to understand phytophagous insect–host plant interactions from an evolutionary perspective, using as example the Neotropical phytophagous insect West Indian fruit fly, Anastrepha obliqua (Macquart) (Diptera: Tephritidae), an economically important fruit crop pest in the Americas. Anastrepha obliqua could adopt a generalist or a specialist lifestyle. We first review the adaptive molecular mechanisms of phytophagous insects to host plants, and then describe the main tools to study phytophagous insect–host plant interactions in the era of omics sciences. The omics approaches will advance the understanding of insect molecular mechanisms and their influence on diversification and evolution. Finally, we discuss the importance of a multidisciplinary approach that integrates the use of omics tools and other, more classical methodologies in evolutionary studies.     

Host plant preference and performance of the sibling species of butterflies <Emphasis Type="Italic">Leptidea sinapis</Emphasis> and <Emphasis Type="Italic">Leptidea reali</Emphasis>: a test of the trade-off hypothesis for food specialisation

A large proportion of phytophagous insect species are specialised on one or a few host plants, and female host plant preference is predicted to be tightly linked to high larval survival and performance on the preferred plant(s). Specialisation is likely favoured by selection under stable circumstances, since different host plant species are likely to differ in suitability—a pattern usually explained by the “trade-off hypothesis”, which posits that increased performance on a given plant comes at a cost of decreased performance on other plants. Host plant specialisation is also ascribed an important role in host shift speciation, where different incipient species specialise on different host plants. Hence, it is important to determine the role of host plants when studying species divergence and niche partitioning between closely related species, such as the butterfly species pair Leptidea sinapis and Leptidea reali. In Sweden, Leptidea sinapis is a habitat generalist, appearing in both forests and meadows, whereas Leptidea reali is specialised on meadows. Here, we study the female preference and larval survival and performance in terms of growth rate, pupal weight and development time on the seven most-utilised host plants. Both species showed similar host plant rank orders, and larvae survived and performed equally well on most plants with the exceptions of two rarely utilised forest plants. We therefore conclude that differences in preference or performance on plants from the two habitats do not drive, or maintain, niche separation, and we argue that the results of this study do not support the trade-off hypothesis for host plant specialisation, since the host plant generalist Leptidea sinapis survived and performed as well on the most preferred meadow host plant Lathyrus pratensis as did Leptidea reali although the generalist species also includes other plants in its host range. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Trade-offs of host use between generalist and specialist <Emphasis Type="Italic">Helicoverpa</Emphasis> sibling species: adult oviposition and larval performance

Much attention has been paid to the question of the relative importance of female behaviour versus larval feeding capacities in determining the host range of herbivorous insects. Host-use trade-offs displayed by generalist and specialist sister species of the genus Helicoverpa were evaluated to examine the relationship between maternal choice and offspring performance. The prediction of optimal oviposition theory, that females will choose to lay eggs on plants on which their offspring perform best as larvae, was tested by measuring oviposition preference and larval performance of Helicoverpa armigera and H. assulta on tobacco, sunflower, and hot pepper. These two measures were more highly correlated in the specialist H. assulta. Both species exhibited the same oviposition preference ranking: tobacco > sunflower > hot pepper. H. armigera larvae preferred sunflower, followed by tobacco and hot pepper; while H. assulta larvae preferred tobacco to sunflower and hot pepper, consistent with their mothers’ oviposition preference. Duration of the total period from egg to adult emergence for each species was significantly shorter on the host plant preferred by the larvae. H. assulta had shorter larval duration and higher relative growth rate than H. armigera on tobacco and hot pepper, and vice versa for sunflower, indicating species differences in host utilization. Thus, while only the specialist H. assulta displayed the predicted optimal oviposition pattern, females of both species show the least preference for the plant on which their offspring perform worst. Selection for optimal oviposition may be stronger on the specialist, which has fewer choices and lower lifetime fecundity than the generalist.     

Can monophagous specialists mediate host plant choices in generalist planthoppers (Hemiptera: Delphacidae)?

1. A preference experiment was set up with two planthopper species (Hemiptera: Delphacidae) to test the influence of competition on host plant choice.
2. The delphacid Javesella pellucida was chosen as a generalist and the rarer Ribautodelphax imitans as a monophagous specialist, which feeds on the grass, tall fescue Schedonorus arundinaceus.
3. In the absence of the specialist, the generalist showed a marked preference for tall fescue. In some experiments, however, the introduction of the specialist resulted in a shift of preference to an alternative plant if the specialist was established prior to the introduction of the generalist.
4. This experiment supports the hypothesis that specialist herbivores can potentially alter the host plant choices of generalists, which may lead to differing host plant use patterns in insect communities.

     

Diversity and assemblage structure of phytophagous Hemiptera along a latitudinal gradient: predicting the potential impacts of climate change

Aims The aims were (1) to assess the species richness and structure of phytophagous Hemiptera communities along a latitudinal gradient, (2) to identify the importance of rare species in structuring these patterns, and (3) to hypothesize about how phytophagous Hemiptera communities may respond to future climate change. Location East coast of Australia. Methods Four latitudes within the 1150 km coastal distribution of Acacia falcata were selected. The insect assemblage on the host plant Acacia falcata was sampled seasonally over two years. Congeneric plant species were also sampled at the sites. Results Ninety‐eight species of phytophagous Hemiptera were collected from A. falcata. Total species richness was significantly lower at the most temperate latitude compared to the three more tropical latitudes. We classified species into four climate change response groups depending on their latitudinal range and apparent host specificity. Pairwise comparisons between groups showed that the cosmopolitan, generalist feeders and specialists had a similar community structure to each other, but the climate generalists had a significantly different structure. Fifty‐seven species were identified as rare. Most of these rare species were phloem hoppers and their removal from the dataset led to changes in the proportional representation of all guilds in two groups: the specialist and generalist feeders. Main conclusions We found no directional increase in phytophagous Hemiptera species richness. This indicates that, at least in the short term, species richness patterns of these communities may be similar to that found today. As the climate continues to change, however, we might expect some increases in species richness at the more temperate latitudes as species migrate in response to shifting climate zones. In the longer term, more substantial changes in community composition will be expected because the rare species, which comprise a large fraction of these communities, will be vulnerable to both direct climatic changes, and indirect effects via changes to their host's distribution.     

Larval feeding induced defensive responses in tobacco: comparison of two sibling species of <Emphasis Type="Italic">Helicoverpa</Emphasis> with different diet breadths

Plants respond differently to damage by different herbivorous insects. We speculated that sibling herbivorous species with different host ranges might also influence plant responses differently. Such differences may be associated with the diet breadth (specialization) of herbivores within a feeding guild, and the specialist may cause less intensive plant responses than the generalist. The tobacco Nicotinana tabacum L. is the common host plant of a generalist Helicoverpa armigera (Hübner) and a specialist H. assulta Guenée (Lepidoptera, Noctuidae). The induced responses of tobacco to feeding of these two noctuid herbivores and mechanical wounding were compared. The results showed that the feeding of the specialist H. assulta and the generalist H. armigera resulted in the same inducible defensive system, but response intensity of plants was different to these two species. Inductions of jasmonic acid (JA), lipoxygenase (LOX), and proteinase inhibitors (PIs) were not significantly different concerning these two species, but H. assulta caused the less intensive foliar polyphenol oxidase (PPO) increase, more intensive nicotine and peroxidase (POD) increases in tobacco than H. armigera. The defensive response of plant to herbivores with different diet breadth seems to be more complicated than we expected, and the specialist does not necessarily cause less intensive plant responses than the generalist.     

The invertebrate fauna on broom,Cytisus scoparius,in two native and two exotic habitats

This study quantifies the invertebrate fauna found on broom, Cytisus scoparius, L. (Link), in two countries where it grows as a native plant (France and England) and two countries where it grows as an alien plant (New Zealand and Australia). The data are used to test three hypotheses concerning the predicted differences in invertebrate community structure in native versus exotic habitats: (1) Are generalist phytophages dominant in exotic habitats and specialist phytophages dominant in native habitats? (2) Are there empty phytophage niches in exotic habitats? (3) As a plant species accumulates phytophages, do these in turn accumulate natural enemies? The broom fauna was sampled at five sites in each country by beating five broom bushes per site. The sampling efficiency of beating was quantified at one field site and it was shown to collect 87 % of invertebrate abundance, 95 % of invertebrate biomass and 100 % of phytophagous species found on the branches. Generalist phytophages were dominant on broom in exotic habitats and specialists dominant on broom in the native habitats. Thus, the two countries where broom grows as a native plant had higher numbers of total phytophage species and a higher abundance of specialist phytophages per bush. There was no significant difference in the average abundance of generalist phytophage species found per bush in native and alien habitats. Phytophages were assigned to seven feeding niches: suckers, root feeders, external chewers, flower feeders, seed feeders, miners and pollen feeders. Empty niches were found in the exotic habitats; species exploiting structurally specific parts of the host plant, such as flowers and seeds, were absent in the countries where broom grows as an alien plant. The pattern of niche occupancy was similar between native and exotic habitats when just the generalist phytophages were considered. As phytophage abundance and biomass increased, there were concomitant increases in natural enemy abundance and biomass. Thus, it appears that as plants accumulate phytophages, the phytophages in turn accumulate natural enemies and a food web develops around the plant. Moreover, in the native countries, the history of association between the natural enemies and their prey has been sufficient for specialist predators and parasitoids, feeding on the specialist phytophages, to have evolved.     

The role of host plant species in the phenotypic differentiation of sympatric populations of Aleiodes nolophanae and Cotesia marginiventris

The ecology of parasitoids is strongly influenced by their host plant species. Parasitoid fitness can be affected by a variety of plant traits that could promote phenotypic differentiation among populations of parasitoids. Generalist parasitoids are expected to be more affected by plant traits (e.g., plant defensive traits) than specialist parasitoids. Data are presented on phenotypic differences of two braconid parasitoid wasps ovipositing on the same insect host species on two different host plant species. Adult mass, adult longevity, and percent parasitism are compared for the generalist parasitoid Cotesia marginiventris Cresson and the specialist parasitoid Aleiodes nolophanae Ashmead (both Hymenoptera: Braconidae) emerging from green cloverworms, Hypena scabra Fabricius (Lepidoptera: Noctuidae), feeding on two host plant species, alfalfa (Medicago sativa L.) and soybean (Glycine max L. Merr.) (both Fabaceae), at three locations. Specialist wasps that parasitized the green cloverworm on alfalfa had a significantly larger mass than the ones that parasitized the green cloverworm on soybean at the three study sites. Generalist wasps that parasitized green cloverworms on alfalfa had a larger mass than wasps parasitizing green cloverworms on soybean only at one of the study sites (i.e., Prince George's County, MD, USA). Similarly, both specialist and generalist wasps lived longer when parasitizing green cloverworms on alfalfa than when parasitizing them on soybean at only one of the study sites (i.e., Prince George's County). In Prince George's County, percent parasitism on alfalfa by the specialist parasitoid was higher than on soybean for three consecutive years and percent parasitism by the generalist parasitoid was the same on alfalfa and soybean every year. Thus, phenotypic differences among populations associated with different host plant species vary geographically (i.e., parasitoid phenotype associated with different host plant species differ at some sites while it is the same at other sites). The implications of geographic variation for biological control are discussed.     

Advancements in management of major fruit flies (Diptera: Tephritidae) in North Africa and future challenges: A review

Fruit flies are one of the most economically damaging pests of fleshy fruits worldwide. Two species of highest concern for fruit production in North Africa are the Mediterranean fruit fly (Medfly) Ceratitis capitata (Wied.) and the peach fruit fly (PFF) Bactrocera zonata (Saunders) (in Egypt and Libya only). Currently, both fruit fly species are mainly targeted by chemical applications of broad-spectrum contact insecticides. Despite the disparities in control efforts among North African countries, government and research are focused on reducing chemical reliance and adopt more environmentally friendly technologies. In this review, advances in integrated pest management (IPM) implementation against fruit flies are outlined for each country. In addition, challenges for future efforts are identified with emphasis on the efficacy of trapping for monitoring and control.     

Host specialization is ancestral in Torymus (Hymenoptera,Chalcidoidea) cynipid gall parasitoids

The host range of parasitoids varies greatly among species: Some only parasitize one to a few hosts (specialists), while others parasitize multiple species or a variety of host types (generalists). The direction of most host range shifts in parasitoid groups, that is from generalist to specialist or, alternatively, from specialist to generalist, is unknown. To explore the origin of host range shifts, we studied a clade within the genus Torymus (Hymenoptera, Chalcidoidea) that includes both generalist and specialist parasitoids of Cynipidae (Hymenoptera). We analysed the phylogenetic relationships of the species of Torymus on the basis of two gene fragments (cox1 and ITS2) of 246 specimens and performed an ancestral state reconstruction of the specialist/generalist trait. Our results revealed the following: (a) The ancestral state of this group of Torymus is specialist, with the generalist state evolving through a loss of specialization. (b) The species Torymus cyaneus and Torymus flavipes both have a strong genetic structure, suggesting the existence of different biological identities. (c) There has been a host plant shift in the lineage(s) leading to Torymus rubi and Torymus bedeguaris from galls on Quercus to those on Rosaceae. (d) The alien species Torymus sinensis and the native European species Torymus notatus are phylogenetically closely related. (e) Speciation within Torymus was likely associated with the diversification of their cynipid hosts, which itself was driven by the dramatic changes in climate and vegetation that occurred during the Miocene.     

Phytophagous insect oviposition shifts in response to probability of flower abortion owing to the presence of basal fruits

Phytophagous insects use a wide range of indicators or associated cues to avoid laying eggs in sites where offspring survival is low. For insects that lay eggs in flowers, these unsuitable sites may be created by the host plant's resource allocation to flowers. In the sequentially flowering host plant, Yucca glauca, late‐opening distal flowers are more likely to be aborted in the presence of already‐initiated basal fruits because they are strong resource sinks. If flowers are aborted, all eggs of the phytophagous insect, Tegeticula yuccasella, within the flower die. We used the phytophagous insect T. yuccasella that lays eggs in and pollinates host plant Y. glauca flowers to test the hypothesis that phytophagous insect females are less likely to invest eggs in host plant flowers if basal fruits are present because they are more likely to be aborted. We also investigated potential predictors of arrival of T. yuccasella at inflorescences at the onset of flowering. These factors may influence a phytophagous insect's decisions to select oviposition sites. We carried out a behavioral experiment using wild‐caught T. yuccasella females on manipulated inflorescences with distal flowers with basal fruits and without fruits. As potential predictors of T. yuccasella arriving at inflorescences, we used floral display size and day of onset of flowering. In support of our hypothesis, our experimental results showed that T. yuccasella was significantly less likely to oviposit in distal flowers on inflorescences with basal fruits. We also found that T. yuccasella arrival was higher at inflorescences with larger floral display size and earlier in the flowering season. These findings uncover a novel indicator of unsuitable oviposition sites—the presence of basal fruits, that phytophagous insects use to make oviposition decisions. Further, our study contributes to the growing body of evidence that shows that females prefer sites that increase the probability of survival of their offspring.