The effect of hosptlant and parasitoids on the reproductive success of the parthenogenetic gall wasp Diplolepis rosae (Hymenoptera, Cynipidae)

Population Genomics of the Mostly Thelytokous Diplolepis rosae (Linnaeus, 1758) (Hymenoptera: Cynipidae) Reveals Population-specific Selection for Sex

In Hymenoptera, arrhenotokous parthenogenesis (arrhenotoky) is a common reproductive mode. Thelytokous parthenogenesis (thelytoky), when virgin females produce only females, is less common and is found in several taxa. In our study, we assessed the efficacy of recombination and the effect of thelytoky on the genome structure of Diplolepis rosae, a gall wasp-producing bedeguars in dog roses. We assembled a high-quality reference genome using Oxford Nanopore long-read technology and sequenced 17 samples collected in France with high-coverage Illumina reads. We found two D. rosae peripatric lineages that differed in the level of recombination and homozygosity. One of the D. rosae lineages showed a recombination rate that was 13.2 times higher and per-individual heterozygosity that was 1.6 times higher. In the more recombining lineage, the genes enriched in functions related to male traits ('sperm competition", "insemination", and "copulation" gene ontology terms) showed signals of purifying selection, whereas in the less recombining lineage, the same genes showed traces pointing towards balancing or relaxed selection. Thus, although D. rosae reproduces mainly by thelytoky, selection may act to maintain sexual reproduction.

Extinction Threat to a Previously Undescribed Species of Gall Wasp (Hymenoptera: Cynipidae) and Two Associated Parasitoid Species (Hymenoptera: Braconidae and Eulophidae) on a Threatened Rose

Diplolepis ogawai Abe and Ide sp. nov. (Hymenoptera: Cynipidae) induces galls on Rosa hirtula (Regel) Nakai (Rosales: Rosaceae), which is endemic to a restricted area of Honshu, the main island of Japan. The gall is induced mainly on the leaf of R. hirtula in spring and the mature gall falls to the ground in early summer. The gall-inducing wasp emerges from the gall on the ground in the following spring, suggesting that D. ogawai is univoltine. From spring to summer, the braconid Syntomernus flavus Samartsev and Ku and the eulophid Aprostocetus sp. are parasitic on the larva of D. ogawai in the gall, and the adult wasp of both parasitoid species emerges from the gall on the ground in summer. For S. flavus, this is the first distribution record in Japan and the first host record. Since R. hirtula is threatened with extinction by succession and deforestation, D. ogawai and its two parasitoid wasp species are considered to be at risk of coextinction with the threatened rose. In the event that the population size of this rose species is further reduced, D. ogawai and its parasitoids may -become extinct prior to the extinction of R. hirtula. To conserve these three wasp species associated with R. hirtula, protection of remnant vegetation where individuals of this threatened rose species grow is necessary.

Predation on rose galls: parasitoids and predators determine gall size through directional selection

Both predators and parasitoids can have significant effects on species’ life history traits, such as longevity or clutch size. In the case of gall inducers, sporadically there is evidence to suggest that both vertebrate predation and insect parasitoid attack may shape the optimal gall size. While the effects of parasitoids have been studied in detail, the influence of vertebrate predation is less well-investigated. To better understand this aspect of gall size evolution, we studied vertebrate predation on galls of Diplolepis rosae on rose (Rosa canina) shrubs. We measured predation frequency, predation incidence, and predation rate in a large-scale observational field study, as well as an experimental field study. Our combined results suggest that, similarly to parasitoids, vertebrate predation makes a considerable contribution to mortality of gall inducer larvae. On the other hand, its influence on gall size is in direct contrast to the effect of parasitoids, as frequency of vertebrate predation increases with gall size. This suggests that the balance between predation and parasitoid attack shapes the optimal size of D. rosae galls.

The enemy hypothesis: correlates of gall morphology with parasitoid attack rates in two closely related rose cynipid galls

We tested the enemy hypothesis for gall morphology on a model system comprising two Diplolepis rose gall wasp species and their associated parasitoids. The enemy hypothesis predicts both that gall traits will influence parasitoid attack rates within species, and that galls with contrasting morphologies will support different parasitoid communities. This hypothesis is supported by studies at both intraspecific and broader taxonomic levels (i.e. between genera), but patterns remain to be explored in closely related species. Our aims were to explore the relationships between aspects of gall morphology (number of larval chambers, overall gall size and thickness of the gall wall) in each of Diplolepis mayri and D. rosae, and to explore correlations between these traits and both the presence/absence (=incidence) and attack rates imposed by parasitoids. We found in both galls that chamber number is positively correlated with gall size. In galls of D. mayri, parasitoid incidence was negatively correlated with thickness of the wall of the larval chamber, but there was no significant correlation between parasitoid attack rates and overall gall size. In D. rosae galls, parasitoid incidence was positively correlated with chamber wall thickness, but parasitoid attack rates were negatively correlated with gall size, suggesting that selection may favour the induction of galls containing more larval chambers. These results confirm that gall extended phenotypes can significantly influence enemy attack rates, consistent with the 'enemy hypothesis'. Further, differences in gall morphology between the two Diplolepis species may underlie differences in their associated parasitoid communities--further research is required to test this hypothesis.

No concordant phylogeographies of the rose gall wasp Diplolepis rosae (Hymenoptera, Cynipidae) and two associated parasitoids across Europe

According to the Host-tracking Hypothesis, species of higher trophic levels with a close relationship to their hosts, such as parasites or parasitoids, are expected to show spatio-temporal phylogeographic patterns similar to those of their host. Alternatively, with ecological sorting, a subset of the local species pools might shift to a related host species, thereby disengaging common phylogeographic patterns. Here, we compare the phylogeographic structures of the cynipid rose gall wasp Diplolepis rosae across Europe and of two of its most common parasitoids, the wasps Orthopelma mediator and Glyphomerus stigma, by analysing the sequences of two gene fragments (COI and ITS 2). The phylogeographic structures of the three species associated with roses were incongruent. D. rosae had the lowest genetic diversity with one major clade, O. mediator showed the classical phylogeographic structure for Europe with one eastern and one western clade, and G. stigma had the highest diversity but no geographical structuring. This discordance of geographical patterns may be explained by 1) the dispersal propensity of adult parasitoids or 2) the parasitoids having the ability to switch to another host, while the primary host becomes rare or is even not available. Furthermore there was no indication that phylogenetic patterns were affected by Wolbachia infections. Our results document that communities of closely interacting species may be the result of idiosyncratic biogeographic histories.

ADAPTATIONS OF GALL WASPS OF THE GENUS DIPLOLEPIS (HYMENOPTERA: CYNIPIDAE) AND THE ROLE OF GALL ANATOMY IN CYNIPID SYSTEMATICS

Adaptations and attributes of gall-inducing cynipid wasps are reviewed to emphasize that differences in life cycles and anatomical features of their galls are just as useful for systematic purposes as are structural differences in the adult insects themselves. The extent to which cynipid wasps have specialized is illustrated by the genus Diplolepis, all species of which are restricted to native and introduced roses and induce structurally distinct galls. Various aspects of Diplolepis biology including life cycles, host specificity, and gall development and anatomy are reviewed. The biologies of two species of Diplolepis that commonly co-exist in the same habitat in central Ontario are then examined in detail. Diplolepis polita (Ashmead) induces a single-chambered gall on the leaves of Rosa acicularis Lindl. whereas Diplolepis spinosa (Ashmead) induces a multi-chambered gall on the stems of Rosa blanda Ait. Differences in life cycles, distribution, host and organ specificity, oviposition, gall initiation and development, along with differences in the communities of parasitoids and inquilines attracted to the galls, confirm the existence of distinct species and allow some speculation on their ecological and phylogenetic relationships.

Use of population genetic data to infer oviposition behaviour: species-specific patterns in four oak gallwasps (Hymenoptera: Cynipidae)

Many species of oak gallwasp (Hymenoptera: Cynipidae: Cynipini) induce galls containing more than one larva (multilocular galls) on their host plant. To date, it has remained unclear whether multilocular galls result solely from clustered oviposition by a single female, or include the aggregated offspring of several females (multiple founding). We have developed a novel maximum-likelihood approach for use with population genetic data that estimates the number and genotypes of parents contributing to offspring from each gall. We apply this method to allozyme data from multiple populations of four oak gallwasps whose asexual generations develop in multilocular galls (Andricus coriarius, A. lucidus, A. panteli and A. seckendorffi). We find strong evidence for multiple founding in all four species, and show the data to be compatible with multiple founding rather than founding by a single foundress mated with multiple males. The extent of multiple founding differs among species: in A. lucidus and A. seckendorffi most galls are induced by a single female, whereas in A. coriarius and A. panteli over half of the galls sampled were multiple founded. We suggest that variation in levels of multiple founding may be due to consistent ecological differences between the four species.

The population biology of oak gall wasps (Hymenoptera: Cynipidae)

Oak gall wasps (Hymenoptera: Cynipidae, Cynipini) are characterized by possession of complex cyclically parthenogenetic life cycles and the ability to induce a wide diversity of highly complex species- and generation-specific galls on oaks and other Fagaceae. The galls support species-rich, closed communities of inquilines and parasitoids that have become a model system in community ecology. We review recent advances in the ecology of oak cynipids, with particular emphasis on life cycle characteristics and the dynamics of the interactions between host plants, gall wasps, and natural enemies. We assess the importance of gall traits in structuring oak cynipid communities and summarize the evidence for bottom-up and top-down effects across trophic levels. We identify major unanswered questions and suggest approaches for the future.

Insect herbivores as potential causes of mortality and adaptation in gallforming insects

Recent studies have suggested that plant galls benefit only the insects living in them and not the host plants, and that galls are induced by insects primarily to improve the plant as a microenvironment or a food source. The potential advantage to insects of protection from their predators and parasitoids has been considered unclear and perhaps minor in importance. However, the potential threat to gallforming insects from other insect herbivores has usually been relatively neglected. This paper notes literature and observations which suggest that herbivores may either consume or be deterred by galls. Even soft leaf galls produced by Hormaphis and Phylloxera aphids appeared to deter some herbivores in the field. The threat of herbivory to galls might help explain general patterns of gall ecology and morphology, and deserves closer attention.

Variability of the grass Phragmites australis in relation to the behaviour and mortality of the gall-inducing midge Giraudiella inclusa (Diptera, Cecidomyiidae)

Variability within and between shoots of the grass Phragmites australis proved to be important for both survival (successful gall induction) and reproduction (larval weight) of the gall-inducing midge Giraudiella inclusa. The ovipositing females and the migrating first instar larvae chose a predictable microhabitat within shoots and within internodes characterized by a high nutritional quality (nitrogen, mineral content, sugar, water) and reduced palnt defense properties (silicate). Clutch size increased with the shoot diameter, larval scramble competition could not be detected. Female shoot selection was random, although the chances of successful gall induction greatly differed between shoots. Thick and intact shoots (≥6 mm) led to a high larval mortality. But thick shoots destroyed apically by stem-mining caterpillars (of the noctuid moth Archanara geminipuncta) had on average large gall clusters. Accordingly, the adjustment of the clutch size to the shoot diameter resulted in an advantage for the gall midge females only when shoots were thin and short (i.e. stressed by water and nutrient deficiency) or heavily damage (i.e. stressed) by caterpillars. Thus, the monophagous gall maker G. inclusa did not compensate for all features of intershoot variation of P. australis, although grasses are well-known for their simple plant architecture and their low diversity and low concentration of secondary compounds.