Skewed sex ratios and multiple founding in galls of the oak apple gall wasp Biorhiza pallida

Abstract. 1. The gall wasp Biorhiza pallida (Hymenoptera: Cynipidae) reproduces by cyclical parthenogenesis. The adults of the sexual generation develop within galls (oak apples) that contain many larval cells.
2. Folliot [(1964) Annales Des Sciences Naturelles: Zoologie, 12, 407–564] found asexual generation females to be of three reproductive types. Androphores produce only sons, gynophores produce only daughters, and gynandrophores produce both sons and daughters. In nature, most oak apples give rise to either only males or only females but a proportion produces both sexes. These mixed‐sex galls could result either from eggs laid by one or more gynandrophores or from eggs laid by androphores and gynophores developing within a single gall (multiple founding).
3. Here the frequency of mixed‐ and single‐sex galls was quantified, and morphological and genetic analyses were carried out on the adults emerging from 10 galls to determine the frequency of multiple founding in B. pallida .
4. Seventy-five per cent of 627 galls yielded only one sex. The majority of the remaining 25% had a highly skewed sex ratio. Low genetic variation in B. pallida limited the application of allozyme-based genetic techniques, however seven of the 10 galls analysed in detail, including mixed-sex galls, appeared to have been multiply founded. Contributions by the different foundresses in multiply founded galls were highly skewed.
5. The significance of multiple founding is discussed in the light of possible adaptive scenarios (reduction of parasitoid-induced mortality, avoidance of local stochastic extinction and inbreeding) and possible competition for oviposition sites.     

The structure of cynipid oak galls: patterns in the evolution of an extended phenotype

Galls are highly specialized plant tissues whose development is induced by another organism. The most complex and diverse galls are those induced on oak trees by gallwasps (Hymenoptera: Cynipidae: Cynipini), each species inducing a characteristic gall structure. Debate continues over the possible adaptive significance of gall structural traits; some protect the gall inducer from attack by natural enemies, although the adaptive significance of others remains undemonstrated. Several gall traits are shared by groups of oak gallwasp species. It remains unknown whether shared traits represent (i) limited divergence from a shared ancestral gall form, or (ii) multiple cases of independent evolution. Here we map gall character states onto a molecular phylogeny of the oak cynipid genus Andricus, and demonstrate three features of the evolution of gall structure: (i) closely related species generally induce galls of similar structure; (ii) despite this general pattern, closely related species can induce markedly different galls; and (iii) several gall traits (the presence of many larval chambers in a single gall structure, surface resins, surface spines and internal air spaces) of demonstrated or suggested adaptive value to the gallwasp have evolved repeatedly. We discuss these results in the light of existing hypotheses on the adaptive significance of gall structure.     

Longitudinal range expansion and cryptic eastern species in the western Palaearctic oak gallwasp, Andricus coriarius

The oak gallwasp Andricus coriarius is distributed across the Western Palaearctic from Morocco to Iran. It belongs to a clade of host-alternating Andricus species that requires host oaks in two sections of Quercus subgenus Quercus to complete its lifecycle, a requirement that has restricted the historic distribution and dispersal of members of this clade. Here we present nuclear and mitochondrial sequence evidence from the entire geographic range of A. coriarius to investigate the genetic legacy of longitudinal range expansion. We show A. coriarius as currently understood to be para- or polyphyletic, with three evolutionarily independent (but partially sympatric) lineages that diverged c. 10 million years ago (mya). The similarities in gall structure that have justified recognition of single species to date thus represent either strong conservation of an ancestral state or striking convergence. All three lineages originated in areas to the east of Europe, underlining the significance of Turkey, Iran and the Levant as 'cradles' of gallwasp evolution. One of the three lineages gave rise to all European populations, and range expansion from a putative Eastern origin to the present distribution is predicted to have occurred around 1.6 mya.     

Lifecycle closure, lineage sorting, and hybridization revealed in a phylogenetic analysis of European oak gallwasps (Hymenoptera: Cynipidae: Cynipini) using mitochondrial sequence data

Oak gallwasps are cyclically parthenogenetic insects that induce a wide diversity of highly complex species- and generation-specific galls on oaks and other Fagaceae. Phylogenetic relationships within oak gallwasps remain to be established, while sexual and parthenogenetic generations of many species remain unpaired. Previous work on oak gallwasps has revealed substantial intra-specific variation, particularly between regions known to represent discrete Pleistocene glacial refuges. Here we use statistical phylogenetic inference methods on sequence data for a fragment of the mitochondrial cytochrome b gene to reconstruct the relationships among 62 oak gallwasp species. For 16 of these we also include 23 additional cytochrome b haplotype sequences from different Pleistocene refuge areas to test the effect of intra-specific variation on inter-specific phylogeny reconstruction. The reconstructed phylogenies show good intra-generic resolution and identify several conserved clades, but fail to reconstruct either very recent or very ancient divergences. Nine of the 16 species represented by multiple haplotypes are not monophyletic. The apparent discordance between the recovered gene tree and the current taxonomic classification can be explained through: (a) collapsing of some species currently known only from either a sexual or a parthenogenetic generation into a single cyclically parthenogenetic entity; (b) sorting of ancestral polymorphism in diverging lineages, and (c) horizontal transfer of haplotypes, perhaps due to hybridization within glacial refuges. Our conclusions emphasise the need for careful intra-specific sampling when reconstructing phylogenies for radiations of closely related species and imply that for certain taxonomic groups full phylogenetic resolution (using molecular markers) may not be attainable.     

Discovery of an oak gall wasp (Hymenoptera: Cynipidae) inducing galls on deciduous oak trees in India

We report for the first time the occurrence of an oak gall wasp Andricus mukaigawae (Mukaigawa) (Hymenoptera: Cynipidae) on the deciduous oak Quercus griffithii Hook. F & Thomson ex Miq. in India. Andricus mukaigawae is the only cynipid species that has been observed to induce galls on deciduous oak species in India to date. In addition, this is the first record of a gall wasp species with a distribution extending all the way from the eastern Palearctic region to the Indian subcontinent, suggesting the existence of a close relationship between cynipid faunas on deciduous oak trees in the two regions.     

Parasitoid and inquiline attack in the galls of four alien, cynipid gall wasps: host switches and the effect on parasitoid sex ratios

1. Four alien cynipid gall wasps of the genus Andricus are established and still spreading in the British Isles. The order, according to the northerliness of their distribution boundary, is: A. corruptrix→A. quercuscalicis→A. lignicola→A. kollari. All four aliens have a sexual generation in spring on Quercus cerris (introduced to Britain) and an agamic generation in autumn on native oak species. 2. For 2 years 1994 and 1995, galls of both generations of the four alien species were sampled at eight sites from the south of England to the north of Scotland to determine the parasitoid and inquiline species that attack the new galls. The spring generations of the invading species shared a parasitoid complex of four pteromalid species. Five species of inquilines and 11 species of parasitoids emerged from the autumn galls. 3. Two colonisation events were recorded for A. lignicola and A. corruptrix. On both occasions, the spring generations were found first at the new sites, indicating that the agamic generation provides the colonisers for these invading species. After colonisation, the galls of both species were attacked by parasitoids in their first season. 4. In spring, the invading species were among the most abundant cynipids at all eight sites. By sampling the whole local community of cynipid galls, it was found that the parasitoid species attacking the spring galls of the invaders seemed to have shifted their attack to the new hosts. 5. The secondary sex ratios of the parasitoid species emerging from the sexual galls of A. quercuscalicis (the smallest of the four) showed a strong and significant male bias at all sites and in both years. Parasitoid emergence from the galls of the sexual generations of the other three species (all about equal in size) was between 60 and 70% male, and variable among sites and between years.     

Partitioning of herbivore hosts across time and food plants promotes diversification in the Megastigmus dorsalis oak gall parasitoid complex

Communities of insect herbivores and their natural enemies are rich and ecologically crucial components of terrestrial biodiversity. Understanding the processes that promote their origin and maintenance is thus of considerable interest. One major proposed mechanism is ecological speciation through host‐associated differentiation (HAD), the divergence of a polyphagous species first into ecological host races and eventually into more specialized daughter species. The rich chalcid parasitoid communities attacking cynipid oak gall wasp hosts are structured by multiple host traits, including food plant taxon, host gall phenology, and gall structure. Here, we ask whether the same traits structure genetic diversity within supposedly generalist parasitoid morphospecies. We use mitochondrial DNA sequences and microsatellite genotypes to quantify HAD for Megastigmus (Bootanomyia) dorsalis, a complex of two apparently generalist cryptic parasitoid species attacking oak galls. Ancient Balkan refugial populations showed phenological separation between the cryptic species, one primarily attacking spring galls, and the other mainly attacking autumn galls. The spring species also contained host races specializing on galls developing on different host‐plant lineages (sections Cerris vs. Quercus) within the oak genus Quercus. These results indicate more significant host‐associated structuring within oak gall parasitoid communities than previously thought and support ecological theory predicting the evolution of specialist lineages within generalist parasitoids. In contrast, UK populations of the autumn cryptic species associated with both native and recently invading oak gall wasps showed no evidence of population differentiation, implying rapid recruitment of native parasitoid populations onto invading hosts, and hence potential for natural biological control. This is of significance given recent rapid range expansion of the economically damaging chestnut gall wasp, Dryocosmus kuriphilus, in Europe.     

A new Andricus Hartig oak gallwasp species from China (Hymenoptera: Cynipidae: Cynipini)

A new species of oak gallwasp, Andricus xishuangbannaus is described from China. The species induces leaf galls on Quercus griffithii (Fagaceae). Diagnosis, distribution, and biology of the new species are included.     

Gall morpho-type corresponds to separate species of gall-inducing thrips (Thysanoptera: Phlaeothripidae)

Kladothrips rugosus Froggatt has previously been considered a single polyphagous species that, in Australia, induces galls on several species of Acacia , with the gall structure varying both within and between hosts. On Acacia papyrocarpa , two types of gall are induced by this species, one with the surface ridged but the other with the surface smooth. Using sequence data from cytochrome oxidase subunit I (CO I ) and elongation factor-1 alpha gene fragments, we show that the thrips inducing these two gall-types are genetically distinct and comprise separate lineages. Uncorrected ' p ' distances calculated from CO I gene fragments were 0.000 and 0.006 within lineages and 0.074 and 0.078 between lineages. The between-lineage distances are comparable with distances between morphologically distinct species of other Acacia gall-thrips. Re-examination of adult thrips from the two gall types revealed consistent differences in body colour, as well as in body sculpture. Together with observations on gall founding behaviour, these data indicate that the thrips populations in the two gall types on A. papyrocarpa are reproductively isolated and should be considered as separate species. The form from smooth galls on A. papyrocarpa is therefore described as Kladothrips nicolsoni sp. nov. , although the form from ridged galls can be considered only as ' K. rugosus agg.'. These inconsistencies in the taxonomic status of the various units within the K. rugosus species complex are discussed, although most of them cannot be distinguished morphologically at present.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 88 , 555–563.     

The parasitoid community of <Emphasis Type="Italic">Andricus quercuscalifornicus</Emphasis> and its association with gall size,phenology, and location

Plant galls are preyed upon by a diverse group of parasitoids and inquilines, which utilize the gall, often at the cost of the gall inducer. This community of insects has been poorly described for most cynipid-induced galls on oaks in North America, despite the diversity of these galls. This study describes the natural history of a common oak apple gall (Andricus quercuscalifornicus [Cynipidae]) and its parasitoid and inquiline community. We surveyed the abundance and phenology of members of the insect community emerging from 1234 oak apple galls collected in California’s Central Valley and found that composition of the insect community varied with galls of different size, phenology, and location. The gall maker, A. quercuscalifornicus, most often reached maturity in larger galls that developed later in the season. The parasitoid Torymus californicus [Torymidae] was associated with smaller galls, and galls that developed late in the summer. The most common parasitoid, Baryscapus gigas [Eulophidae], was more abundant in galls that developed late in the summer, though the percentage of galls attacked remained constant throughout the season. A lepidopteran inquiline of the gall (Cydia latiferreana [Tortricidae] and its hymenopteran parasitoid (Bassus nucicola [Braconidae]) were associated with galls that developed early in the summer. Parasitoids and inquilines, in general, had a longer emergence period and diapause within the gall than the gall-inducer. The association of different parasite species with galls of different size and phenology suggests that different parasite species utilize galls with slight differences in traits.     

Taxonomic contribution to the Aleiodes melanopterus (Erichson) species-group (Hymenoptera, Braconidae, Rogadinae) from Brazil

The Aleiodes melanopterus (Erichson, 1848) species-group includes 21 species, of which seven are known from the Neotropical region: Aleiodes flavistigma Shaw, 1993, Aleiodes lucidus (Szépligeti, 1906), Aleiodes melanopterus, Aleiodes mexicanus Cresson, 1869, Aleiodes politiceps (Gahan, 1917), and the new species Aleiodes shaworumsp. n. and Aleiodes vassunungasp. n. Distribution ranges of Aleiodes melanopterus, Aleoides flavistigma and Aleiodes lucidus are extended and the female of Aleiodes lucidus is described. A key to the Neotropical species of this species-group is presented.     

A new Asphondylia species (Diptera: Cecidomyiidae) and a eulophid wasp (Hymenoptera) inducing similar galls on leaf buds of Schoepfia jasminodora (Schoepfiaceae), with reference to their ecological traits and a description of the new gall midge

Different gall inducers belonging to distinct insect orders are rarely known to induce similarly shaped galls on the same host plant organs. We report that Asphondylia tojoi Elsayed & Tokuda sp. nov. (Diptera: Cecidomyiidae) and Ceratoneura sp. (Hymenoptera: Eulophidae) induce galls on leaf buds of Schoepfia jasminodora Sieb. et Zucc. (Schoepfiaceae). We describe the gall midge species as new to science and report a phylogenetic analysis for known Japanese Asphondylia species. We also describe life histories of the two species, based on monthly surveys during 2015–2017: although both species are multivoltine, A. tojoi overwinters as first instars in galls, whereas Ceratoneura sp. possibly does so as adults outside the galls. In addition, the internal structure of galls differed between the two species. Galls containing A. tojoi consist of a single chamber with inner walls clearly covered with whitish fungal mycelia after the gall midges develop into second instars. Those containing the Ceratoneura sp. have multiple chambers with hard black inner walls. Although some eulophids are known to be inquilines of galls induced by Asphondylia species, we consider that the Ceratoneura sp. is probably a true gall inducer because of the different gall structure and absence of fungal mycelia in their galls. This is the first report detailing the annual life history of a Ceratoneura species. Asphondylia tojoi represents the first example of monophagous Asphondylia species with a multivoltine life history on a deciduous tree.     

Interactions between oak tannins and parasite community structure: Unexpected benefits of tannins to cynipid gall-wasps

Plant species vary tremendously in the number of phytophagous species they support. May (1979) and Price (1980) proposed that some of this variation may be due to variation in biochemical defenses. We find that variation between oak species in leaf tannin levels is positively correlated with 1) variation in the numbers of species of leaf-galling cynipid wasps those trees host; and 2) the density of individual galls per oak leaf. We hypothesize that leaf and gall tannins serve a protective function for cynipids, decreasing the amount of cynipid larval mortality due to fungal infestation. This defensive function would explain the observed positive relationships between oak tannin levels and cynipid diversity as well as cynipid abundance.     

A new genus of oak gallwasp, Coffeikokkos Pujade-Villar & Melika, gen. n., with a description of a new species from Costa Rica (Hymenoptera, Cynipidae)

A new genus of oak gallwasp, Coffeikokkos Pujade-Villar & Melika, gen. n., is described from Costa Rica. Diagnostic characters and generic limits of the new genus are discussed in detail. The new genus includes Coffeikokkos copeyensis Pujade-Villar & Melika, sp. n., which induces galls on stems of Quercus bumelioides, an endemic oak to Costa Rica, Honduras and Panama. The new species and galls are described and illustrated.     

Fungal endophytes which invade insect galls: insect pathogens,benign saprophytes,or fungal inquilines?

Fungi are frequently found within insect galls. However, the origin of these fungi, whether they are acting as pathogens, saprophytes invading already dead galls, or fungal inquilines which invade the gall but kill the gall maker by indirect means, is rarely investigated. A pathogenic role for these fungi is usually inferred but never tested. I chose the following leaf-galling-insect/host-plant pairs (1) a cynipid which forms two-chambered galls on the veins of Oregon white oak, (2) a cynipid which forms single-chambered galls on California coast live oak, and (3) an aphid which forms galls on narrowleaf cottonwood leaves. All pairs were reported to have fungi associated with dead insects inside the gall. These fungi were cultured and identified. For the two cynipids, all fungi found inside the galls were also present in the leaves as fungal endophytes. The cottonwood leaves examined did not harbor fungal endophytes. For the cynipid on Oregon white oak, the fungal endophyte grows from the leaf into the gall and infects all gall tissue but does not directly kill the gall maker. The insect dies as a result of the gall tissue dying from fungal infection. Therefore, the fungus acts as an inquiline. Approximately 12.5% of these galls die as a result of invasion by the fungal endophyte.     

Sex ratio in relation to season and host plant quality in a monogenous stem-galling midge (Diptera: Cecidomyiidae)

Abstract.  1. The sex determination mechanism in gall midges is little understood, although it is known that the females of several species primarily or exclusively produce unisexual broods throughout their lifetime.
2. The gall midge Izeniola obesula Dorchin is a multivoltine species, inducing multi-chambered stem galls on the salt-marsh plant Suaeda monoica . Each gall contains 5–70 individuals, all being the progeny of a single female. Sampling of more than 450 galls, from which adult midges were reared, suggested that I .  obesula exhibits strict monogeny, resulting in galls that contain either all female or all male progeny.
3. Characterisation of the growth pattern of young S .  monoica shoots revealed that shoots in apical positions grew more rapidly than shoots in more basal positions. Galls that were induced on such shoots were larger and yielded more adult midges.
4. No difference in the site of gall induction was found between male and female galls, with galls of either sex being mainly induced on more rapidly growing shoots. It is concluded that I .  obesula females cannot control the sex of their progeny, and that both female-producers and male-producers strive to maximise their reproductive success by choosing the faster-growing shoots for gall induction.
5. Female galls were larger and more abundant than male galls at almost all times. The sex ratio among galls fluctuated throughout the year, ranging from 4:1 in spring to 1:1 in winter. The skewed sex ratio among galls possibly results from greater mortality rates among male galls than among female galls, due to either primary or secondary factors. Alternatively, it is possible that the number or fitness of male-producers in the population is reduced relative to female-producers.     

Finding hidden females in a crowd: Mate recognition in fig wasps

Multi-species mating aggregations are crowded environments within which mate recognition must occur. Mating aggregations of fig wasps can consist of thousands of individuals of many species that attain sexual maturity simultaneously and mate in the same microenvironment, i.e, in syntopy, within the close confines of an enclosed globular inflorescence called a syconium – a system that has many signalling constraints such as darkness and crowding. All wasps develop within individual galled flowers. Since mating mostly occurs when females are still confined within their galls, male wasps have the additional burden of detecting conspecific females that are “hidden” behind barriers consisting of gall walls. In Ficus racemosa, we investigated signals used by pollinating fig wasp males to differentiate conspecific females from females of other syntopic fig wasp species. Male Ceratosolen fusciceps could detect conspecific females using cues from galls containing females, empty galls, as well as cues from gall volatiles and gall surface hydrocarbons.In many figs, syconia are pollinated by single foundress wasps, leading to high levels of wasp inbreeding due to sibmating. In F. racemosa, as most syconia contain many foundresses, we expected male pollinators to prefer non-sib females to female siblings to reduce inbreeding. We used galls containing females from non-natal figs as a proxy for non-sibs and those from natal figs as a proxy for sibling females. We found that males preferred galls of female pollinators from natal figs. However, males were undecided when given a choice between galls containing non-pollinator females from natal syconia and pollinator females from non-natal syconia, suggesting olfactory imprinting by the natal syconial environment.     

Apiomorpha gullanae sp. n., an unusual new species of gall-inducing scale insect (Hemiptera: Eriococcidae)

Abstract An unusual new species of the gall-inducing scale insect genus Apiomorpha Rübsaamen is described from Queensland. The adult female, its gall, and the first-instar nymph (crawler) are illustrated, and relationships of the new species are estimated using mitochondrial COII data. Adult females induce cigar-shaped galls on leaves of several eucalypts in section Adnataria of subgenus Symphyomyrtus . The bilobed anal lobes of the adult female differ from those of all other Apiomorpha species (single lobe) and the first-instar nymph possesses features, such as broad frontal tubercles and dorsal stripes, that are not present in crawlers of other Apiomorpha species. However, DNA sequence data confirm that the new species falls within Apiomorpha , rather than representing a sister group, and indicate that the new species is not closely related to the A. pharetrata (Schrader) species-group, the only other group within Apiomorpha that induces cigar-shaped galls on leaves. The systematic affiliations of A. gullanae sp. n. are currently not known. Females only are known and there is some indication that reproduction in the new taxon is parthenogenetic. This represents the first putative case of parthenogenesis in Apiomorpha .     

Systematic re‐appraisal of the gall‐usurping wasp genus Synophrus Hartig, 1843 (Hymenoptera: Cynipidae: Synergini)

Several unanswered questions remain regarding the taxonomy and phylogeny of inquiline gallwasps (Cynipidae: Synergini), obligate inhabitants of plant galls induced primarily by other gallwasps (Cynipidae: Cynipini and Diplolepidini). Here we use morphological and molecular data to revise the inquiline genus Synophrus, members of which are notable for extensively modifying the structure of galls induced by oak gallwasp hosts on oaks in the section Cerris of Quercus subgenus Quercus in the Western Palaearctic. Previous taxonomic treatments have recognized three Western Palaearctic species of Synophrus: S. pilulae, S. politus and S. olivieri. Our results support the establishment of four additional Western Palaearctic species: Synophrus hungaricus sp.n. , S. libani sp.n. , S. syriacus sp.n. and S. hispanicus sp.n. We describe and diagnose these new taxa, analyse their phylogenetic relationships, and show that Synophrus inquilines are able to impose their own gall phenotypes on those of their hosts. We provide an updated key to Synophrus.     

Phylogeny,Evolution and Classification of Gall Wasps: The Plot Thickens

Gall wasps (Cynipidae) represent the most spectacular radiation of gall-inducing insects. In addition to true gall formers, gall wasps also include phytophagous inquilines, which live inside the galls induced by gall wasps or other insects. Here we present the first comprehensive molecular and total-evidence analyses of higher-level gall wasp relationships. We studied more than 100 taxa representing a rich selection of outgroups and the majority of described cynipid genera outside the diverse oak gall wasps (Cynipini), which were more sparsely sampled. About 5 kb of nucleotide data from one mitochondrial (COI) and four nuclear (28S, LWRh, EF1alpha F1, and EF1alpha F2) markers were analyzed separately and in combination with morphological and life-history data. According to previous morphology-based studies, gall wasps evolved in the Northern Hemisphere and were initially herb gallers. Inquilines originated once from gall inducers that lost the ability to initiate galls. Our results, albeit not conclusive, suggest a different scenario. The first gall wasps were more likely associated with woody host plants, and there must have been multiple origins of gall inducers, inquilines or both. One possibility is that gall inducers arose independently from inquilines in several lineages. Except for these surprising results, our analyses are largely consistent with previous studies. They confirm that gall wasps are conservative in their host-plant preferences, and that herb-galling lineages have radiated repeatedly onto the same set of unrelated host plants. We propose a revised classification of the family into twelve tribes, which are strongly supported as monophyletic across independent datasets. Four are new: Aulacideini, Phanacidini, Diastrophini and Ceroptresini. We present a key to the tribes and discuss their morphological and biological diversity. Until the relationships among the tribes are resolved, the origin and early evolution of gall wasps will remain elusive.