Gall Size Research Articles

Putative role of IAA during the early response of Brassica napus L. to Plasmodiophora brassicae

This study examined the role of indole-3-acetic acid (IAA) during the early stage of infection of rapeseed (Brassica napus L.) by the obligate biotrophic protist Plasmodiophora brassicae Woron., which causes clubroot disease. Treatment of infected B. napus seedlings with exogenous IAA promoted the development of clubroot disease, including an increase in the number and size of galls, whereas treatment with N-1-naphthylphthalamic acid (NPA) attenuated the disease and altered the location and size of the root nodules, resulting in a reduced disease index. An increased level of free IAA was detected in the roots at 3 and 7 days after inoculation (DAI) compared with the control, suggesting the activation of IAA signaling in the early stage of P. brassicae infection. Moreover, IAA treatment caused no significant change in the germination rate of the resting spores but resulted in enhanced root hair infection. RT–PCR and quantitative real-time PCR (qPCR) were used to analyze the expression of IAA homeostasis-related genes (3, 7, and 10 DAI) to identify gene expression patterns in the roots and leaves of B. napus after inoculation. Five IAA biosynthesis-related genes examined in this study were induced in the roots after inoculation with P. brassicae but not in the leaves. The rapid induction of BnAAO4 expression at 3 DAI may be responsible for the overproduction of IAA during the early stages of infection. This study suggests that IAA acts as a signaling molecule that putatively stimulates root hair infection in the early response of B. napus to P. brassicae infection.

Comparisons of Pathological Responses in Carrot to Root-knot Nematodes.

Carrot (Dacus carota var. sativus) is one of the top-ten most economically important vegetable crops produced worldwide, and the root-knot nematodes, Meloidogyne spp., are one of the most important pests in the carrot. In Korea, M. hapla and M. incognita are presumed to be the major root-knot nematodes distributing mostly in open carrot fields and greenhouses, respectively. In our study, currently-developed and commercial carrot cultivars and the parental lines were examined for their pathological responses to M. incognita and M. hapla 7 weeks after inoculation with about 1,000 second-stage juveniles (J2) of the nematodes. All the carrot cultivars and lines showed susceptible responses to both nematodes with the gall index (GI) of 2.4–4.4, which were always higher on the carrot plants infected with M. incognita than M. hapla. Gall sizes were remarkably larger with more serious reduction of the root growths in the plants infected with M. incognita than M. hapla, suggesting the carrot lines examined in our study were more susceptible to the former than the latter. In the infection sites of the root tissues, giant cells were more extensively formed, occupying larger stellar regions with the prominent destruction of adjacent xylem vessels by M. incognita than M. hapla. All of these results suggest M. incognita affect more seriously on the carrot plants that are grown in greenhouses, compared to M. hapla that has a major distribution in open carrot fields, which would be used for determining cropping systems based on target nematode species, their damage and pathological characteristics.

Relationship between gall-midge parasitism, plant vigor, and developmental instability in Ouratea polygyna Engl (Ochnaceae) in a patch of a Brazilian Atlantic Forest

We tested the preference prediction of plant vigor hypothesis by examining the relationship between gall occurrence and leaf size. We also examined the effect of galls on leaf asymmetry, which is a measure of developmental instability. Gall occurrence did not increase with leaf size, thereby providing no support to the preference prediction. Galled leaves were significantly more asymmetric than ungalled leaves. Moreover, leaf asymmetry increased with both gall occurrence and gall size, indicating that galls boosted the stress levels in Ouratea polygyna.

Spring phenology and the response to global warming in gall-inducing sawflies

The phenological window of opportunity for mating, oviposition and larval development is an important part in the life cycle of gall-inducing sawflies. Spring temperatures play an essential role in the timing of eclosion and host plant leaf flush, which are evolutionarily synchronized. This study investigates important events in spring phenology and timing of eclosion for three sympatric gall-inducing sawfly species (Symphyta: Tenthredinidae: Pontania nivalis, P. glabrifrons and P. arcticornis) at two sites in northern Norway. The rate of development was established by monitoring the time to eclosion at constant temperatures of 9, 15, 23 and 28 °C. There was no significant difference in the lower developmental threshold (2.36 °C) and hour-degree requirement for eclosion (6909 hour-degrees) for the three Pontania species. These two values were used with field and historical temperature data to estimating eclosion over 21 years (1993–2013). The results showed later eclosion dates at the arctic than at subarctic site (mean difference 16 days, range 2–30). There was a highly significant advance of eclosion from 1993 to 2013 in both sites, an evidence of global warming. Adult presence in the subarctic site (field trapping, 2012 and 2013) supported the simulated model used. Measurements of gall size showed continuous gall growth until late August, well ahead of winter hibernation. To conclude, gall-inducing sawflies show large phenological plasticity in timing of eclosion, largely regulated by spring temperature, indicating that they are highly adapted to unpredictable subarctic and arctic climates.

Factors associated with the distribution and size of Adelges abietis (Homoptera: Adelgidae) galls on a sev- eral years old spruce (Picea abies) plantation

The eastern spruce gall adelgid (Adelges abietis) is a homopteran insect related to aphids. It forms pineapple-like pseudocone galls on Norway spruce (Picea abies) shoots, which are often deformed by them. The factors responsible for gall distribution within a tree crown are not clear. We investigated the distribution of galls in crowns on a spruce plantation. We assumed that the number and size of galls is dependent on the size of the tree, position on the crown, the type of shoot and its placement relative to the compass points. We also counted the larval chambers and related their number with gall size. We demonstrated that the largest galls are in the upper part of the crown and on the lateral shoots, and the number of chambers is closely related to the size of the galls. The level of shoot embrace has a significant impact on shoot deformation.

Elucidating the determination of the rosette galls induced by Pisphondylia brasiliensis Couri and Maia 1992 (Cecidomyiidae) on Guapira opposita (Nyctaginaceae)

The modulation of plant development has been the focus of research on insect galls because galling insects induce distinct shapes to acquire the same necessities, shelter and food. Due to the variety of gall morphotypes, it can be assumed that the key processes for their development rely on plant cells’ morphogenetical potentialities. In the present study we investigated the rosette bud galls induced by Pisphondylia brasiliensis on Guapira opposita to check whether two morphogenetical pathways – the shortening of the internodes and the over differentiation of axillary buds – are independent or whether they are concomitant events towards the morphogenesis of the galls. Biometrical measures were made to test whether the final size of the galls is correlated with the number of inducers per gall. We noted that two patterns of activity were observed in gall meristems: the first differentiated pairs of leaves with opposite phyllotaxy, and the other differentiated new buds at the base of each leafy projection, with the development of sequential leafy projections, in a disorganised phyllotaxy. This second pattern repeated until gall maturation, when a master cambium, typical of the Nyctaginaceae, differentiated in larger galls. The two morphogenetical pathways occurred concomitantly, leading to the overproduction of leafy projections. Cell responses at gall development site produce mechanical protection to P. brasiliensis individuals. The larger galls have the higher number of inducers, and the coalescence of galls allows an increase in gall size by precociously triggering the master cambium activity, a developmental peculiarity of G. opposita uncommon for Cecidomyiidae galls.

Indirect competitive effects of stemborers on a gall community

AbstractInterspecific competition between phytophagous insects using the same host plant occurs frequently and can strongly affect population densities of competing species. Competition between gallmakers and stemborers could be especially intense because both types of herbivore are unable to avoid competition by relocation during their immature stages. For apical meristem gallmakers the main result of competition is likely to be the interruption of resources to the gall by the stemborers' devouring of stem contents. The proximate effect of such competition could be to reduce gall size, thereby increasing the number of chambers per gall unit volume, and reducing the size and potential reproductive output of the gallformer. In addition, smaller galls may be more susceptible to attack from size‐limited parasitoids, resulting in a second indirect effect of competition. Using a community of galling and stemboring insects on the saltmarsh shrubIva frutescensL. (Asteraceae), we measured for indirect effects of competition. We examined the primary indirect effect of competition on gall midge crowding and the secondary effects on parasitism rates and parasitoid guild composition. Results indicated that galls co‐occurring with stemborers were smaller, crowding of gall inhabitants was 22% greater, and the composition of the parasitoid guild was altered relative to galls on unbored stems. The overall parasitism rate was not different between galls on bored vs. unbored stems. These results show that competition resulting from the presence of stemborers has the potential to affect the gall midgeAsphondylia borrichiaeRossi &Strong (Diptera:Cecidomyiidae) and secondarily to affect its guild of hymenopteran parasitoids.

Výskyt, vývoj a hálkový polymorfismus Harmandiola cavernosa (Rübs.) (Diptera, Cecidomyiidae)

A gall midge Harmandiola cavernosa (Rübs.) is the second most frequent Cecidomyiidae species on Po­pu­lus tremula in the CR. In 2007 and 2008, it occurred very abundantly in Forest District Bílovice nad Svitavou, Training Forest Enterprise Masaryk Forest in Křtiny (former Brno-venkov District). Imagoes occurred there at the end of April and at the beginning of May. Galls grew up as early as at the end the first week in May. The formation of galls is mainly indicated by larvae of the first instar and partly larvae of the second instar. Larvae of the third instar did not participate in the creation of galls. Mature galls were on average 5.4 mm long, 4.8 mm wide and 4.7 mm high showing an inner chamber of an ave­ra­ge length 2.4 mm and width 1.4 mm. Larvae abandoned galls from the end of May until mid-July. On average, 44% larvae completed successfully their development in galls. About 26% larvae were killed by insect parasitoids (mainly Torymus quercinus Boh.) and then same proportion of larvae died without any apparent exogenous causes). Insect predators and birds killed 4% larvae on average. It has been found that mortality factors markedly participated in the size, morphological, anatomical and physiognomic differentiation of galls. Gall polymorphism was analysed in detail in the paper. Galls significantly unfavourably affected the size of leaves and thus also photosynthesis.1

Biology and field host range of Ceutorhynchus cardariae, a potential biological control agent for Lepidium draba

AbstractLepidium draba (Brassicaceae) is a clonal herb, originating from Eurasia, which is invasive in North America. A classical biological control project was initiated in 2001, and the gall‐forming weevil Ceutorhynchus cardariae was prioritized as a candidate agent. We studied its biology and field host range between 2003 and 2014 in the laboratory and a common garden in Switzerland and in the field in Romania. Ceutorhynchus cardariae is a univoltine to bivoltine species. In Switzerland, oviposition usually started at the beginning of March and can occur at temperatures as low as 2.5°C. Galls are formed on stems, leaf stalks and midribs of L. draba rosettes and bolting plants. Gall size increased with an increasing number of larvae per gall. The three larval instars feed inside the galls and leave the plant to pupate in the soil once mature. In Switzerland, development from egg to adult took about 12 weeks in spring. Adults emerged from May to July. After a brief feeding period, adults aestivate. From late summer, feeding recommenced and females may oviposit, forming a partial second generation. Eggs and all larval instars can be found in galls throughout winter. The rate of larval ectoparasitism reached 78%, while endoparasitism was low with a maximum of 2.3%. Lepidium draba populations differed in their suitability for development (number of C. cardariae produced), indicating that effectiveness of C. cardariae – in case released – may be variable. In the field, we observed that gall formation by C. cardariae can severely stunt or even kill shoots. Investigations on the field host range of C. cardariae indicated that only the closely related Lepidium campestre may act as an alternative host for the weevil in Europe. Host‐specificity tests are underway to determine its environmental safety before field release in North America is being considered.

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.

Interspecific patterns of phenotypic selection do not predict intraspecific patterns

We estimated linear (β) and nonlinear (γ) selection gradients to quantify host plant-mediated selection on the trait gall size in each of 22 unequally sampled subpopulations of the cynipid gall wasp Belonocnema treatae. We characterized the relationship between variation in subpopulation sample size and the magnitude of and the variance among selection gradients. We then tested the hypothesis that the intraspecific patterns we observed would follow two patterns that have emerged from published estimates of linear and nonlinear selection gradients compiled across species, namely that the average magnitude of β and γ and the variance among estimated β and γ decrease with increasing sample size. For both β and γ, intraspecific patterns of phenotypic selection in relation to sample size were not predicted by interspecific patterns. Thus, our results suggest that when selection is heterogeneous among subpopulations, variation in the biological basis for selection is more important in influencing estimates of selection than is variation in study size. Our study highlights the value of inspecting selection in relation to sampling effort at the level at which understanding the sources of variation in selection is most important, among populations within species.

Gall Development and Clone Dynamics of the Galling Aphid <I>Schlechtendalia chinensis</I> (Hemiptera: Pemphigidae)

The aphid Schlechtendalia chinensis (Bell) induces galls on its primary host, Rhus chinensis Mill. We studied temporal changes in gall and aphid clonal population size throughout the period of gall development. Gall-size changes occurred in four stages: a first slow growth period, a fast growth period, a second slow growth period, and a growth reduction period. Gall volume and surface area increased abruptly toward the end of July, peaking during October, in parallel with an increase in aphid clonal population size, from one individual to > 10,000 aphids per gall. Clear changes were seen in the clone dynamics of S. chinensis. Fundatrix began to produce first-generation apterous fundatrigenia during late May to early June. Second-generation apterous fundatrigenia appeared at the start of July. Alate fundatrigeniae with wing pads first appeared at the end of August, but accounted for < 1% of the individuals in the galls. Adult alate fundatrigeniae first appeared at the start of October. Abrupt changes in aphid density and crowding might trigger the induction of alate morphs in the galls. Of the eight gall properties that we recorded, gall volume was the most accurate measure of gall fitness.

Interactions of Ralstonia solanacearum and Pectobacterium carotovorum with Meloidogyne incognita on potato

Effect of interactions of Meloidogyne incognita with Ralstonia solanacearum and interaction of M. incognita with Pectobacterium carotovorum were studied in sequential and simultaneous inoculations on potato (Solanum tuberosum). Inoculation of M. incognita caused a lesser reduction in plant growth than caused by R. solanacearum. Inoculation of M. incognita plus R. solanacearum caused a greater reduction in plant growth than the damage caused by either pathogen. Inoculation of M. incognita prior to R. solanacearum resulted in a greater reduction in plant growth than R. solanacearum was inoculated prior to M. incognita. However, inoculation of M. incognita or P. carotovorum caused similar reduction in plant growth. Inoculation of P. carotovorum prior to M. incognita caused lesser reduction in plant growth than simultaneous inoculation of both pathogens. Inoculation of M. incognita caused galling in potato roots but the size of galls was small. Inoculation of P. carotovorum or R. solanacearum with M. incognita had adverse effect on galling and nematode multiplication. Wilting or soft rot index was 3 when R. solanacearum or P. carotovorum was inoculated alone. In other treatments, where R. solanacearum or P. carotovorum was inoculated with M. incognita, wilting or soft rot indices were 5.

Local and latitudinal variation in abundance: the mechanisms shaping the distribution of an ecosystem engineer

Ecological processes that determine the abundance of species within ecological communities vary across space and time. These scale-dependent processes are especially important when they affect key members of a community, such as ecosystem engineers that create shelter and food resources for other species. Yet, few studies have examined the suite of processes that shape the abundance of ecosystem engineers. Here, we evaluated the relative influence of temporal variation, local processes, and latitude on the abundance of an engineering insect—a rosette-galling midge, Rhopalomyia solidaginis (Diptera: Cecidomyiidae). Over a period of 3–5 years, we studied the density and size of galls across a suite of local experiments that manipulated genetic variation, soil nutrient availability, and the removal of other insects from the host plant, Solidago altissima (tall goldenrod). We also surveyed gall density within a single growing season across a 2,300 km latitudinal transect of goldenrod populations in the eastern United States. At the local scale, we found that host-plant genotypic variation was the best predictor of rosette gall density and size within a single year. We found that the removal of other insect herbivores resulted in an increase in gall density and size. The amendment of soil nutrients for four years had no effect on gall density, but galls were smaller in carbon-added plots compared to control and nitrogen additions. Finally, we observed that gall density varied several fold across years. At the biogeographic scale, we observed that the density of rosette gallers peaked at mid-latitudes. Using meta-analytic approaches, we found that the effect size of time, followed by host-plant genetic variation and latitude were the best predictors of gall density. Taken together, our study provides a unique comparison of multiple factors across different spatial and temporal scales that govern engineering insect herbivore density.

ECOLOGY OF THE GALL-FORMING APHID, SLAVUM WERTHEIMAE, ON PISTACIA ATLANTICA: POPULATION DYNAMICS AND DIFFERENTIAL HERBIVORY

ABSTRACT The aphid Slavum wertheimae HRL (Homoptera; Pemphigidae, Fordinae) is monoecious on its host tree, Pistacia atlantica (Anacardiaceae). S. wertheimae induces large, conspicuous, coral-shaped “cauliflower” galls and is very abundant on some trees, while rare or absent on others nearby. It is the only species among Israeli Fordinae which does not alternate between host plants. We investigated the changes in gall size, and in clone size of their aphid inhabitants, from 1994 to 1996, in order to understand the causes of differential herbivory. Gall abundance on male and female trees was similar, but galls on male trees were larger and contained twice as many aphids as those on female trees, suggesting sex-dependent resource allocation in the host plant. Trees heavily galled in 1994 were recolonized in 1995 and 1996, while other trees nearby remained uncolonized. Similarly, within galled trees, shoots on branches carrying old galls were more likely to be freshly galled than shoots on previously ungalle...

Ectopic expression of Kip‐related proteins restrains root‐knot nematode‐feeding site expansion

The development of nematode feeding sites induced by root-knot nematodes involves the synchronized activation of cell cycle processes such as acytokinetic mitoses and DNA amplification. A number of key cell cycle genes are reported to be critical for nematode feeding site development. However, it remains unknown whether plant cyclin-dependent kinase (CDK) inhibitors such as the Arabidopsis interactor/inhibitor of CDK (ICK)/Kip-related protein (KRP) family are involved in nematode feeding site development. This study demonstrates the involvement of Arabidopsis ICK2/KRP2 and ICK1/KRP1 in the control of mitosis to endoreduplication in galls induced by the root-knot nematode Meloidogyne incognita. Using ICK/KRP promoter-GUS fusions and mRNA in situ hybridizations, we showed that ICK2/KRP2, ICK3/KRP5 and ICK4/KRP6 are expressed in galls after nematode infection. Loss-of-function mutants have minor effects on gall development and nematode reproduction. Conversely, overexpression of both ICK1/KRP1 and ICK2/KRP2 impaired mitosis in giant cells and blocked neighboring cell proliferation, resulting in a drastic reduction of gall size. Studying the dynamics of protein expression demonstrated that protein levels of ICK2/KRP2 are tightly regulated during giant cell development and reliant on the presence of the nematode. This work demonstrates that impeding cell cycle progression by means of ICK1/KRP1 and ICK2/KRP2 overexpression severely restricts gall development, leading to a marked limitation of root-knot nematode development and reduced numbers of offspring.

Reduction of clubroot (Plasmodiophora brassicae) formation in Arabidopsis thaliana after treatment with prohexadione‐calcium, an inhibitor of oxoglutaric acid‐dependent dioxygenases

Recently, flavonoids were shown to modulate the outcome of clubroot development in Arabidopsis thaliana after infection with the obligate biotrophic pathogen Plasmodiophora brassicae. Therefore, the development of clubroot disease was investigated in Arabidopsis after treatment with prohexadione‐calcium (ProCa), an inhibitor of ascorbic acid/2‐oxoglutaric acid‐dependent dioxygenases such as flavanone‐3‐hydroxylase. The treatment resulted in a reduction of the flavonols quercetin and kaempferol in clubroots, whereas the precursor naringenin highly accumulated. The root system of ProCa‐treated plants was better developed although galls were still visible. Thus, ProCa treatment resulted in reduced gall size. Flavonoids are thought to inhibit polar auxin transport by modulating auxin efflux carriers. It was investigated whether the auxin response might change as a consequence of the accumulation of naringenin in ProCa‐treated plants. In the areas of gall development an auxin response was indicated by the auxin‐responsive promoter DR5 coupled to the reporter β‐glucuronidase (GUS), whereas very little staining was found in healthy root parts. No differences in GUS activity were found between P. brassicae‐infected and ProCa‐treated plants, and plants only infected with P. brassicae, indicating that the effect of ProCa treatment on clubroot reduction is not via changes in auxin responses. As ProCa is also an inhibitor of late steps in gibberellin biosynthesis, a specific gibberellin biosynthesis inhibitor, chlormequatchloride (CCC), was tested on club development. However, CCC did not reduce disease symptoms, indicating that the observed reduced gall development was not because of gibberellin biosynthesis inhibition by ProCa.

Biology and systematics of gall-inducing triozids (Hemiptera: Psylloidea) associated with Psidium spp. (Myrtaceae).

Psidium myrtoides (Myrtaceae) shelters the gall inducer Nothotrioza myrtoidis gen. et sp. n. (Hemiptera: Psylloidea) which is described and illustrated here. Nothotrioza belongs to the family Triozidae and is probably most closely related to Neolithus, a monotypic Neotropical genus associated with Sapiun (Euphorbiaceae). Three species are recognized within Nothotrioza: the type species N. myrtoidis sp. n. associated with Psidium myrtoides, N. cattleiani sp. n. (misidentified by Butignol & Pedrosa-Macedo as Neotrioza tavaresi) with Psidium cattleianum, and N. tavaresi (Crawford) comb. n. (from Neotrioza) with an unidentified species of Malpighiaceae, respectively. A lectotype is designated here for Neotrioza tavaresi. Also, the diversity of insect galls associated with P. myrtoides and the biology of N. myrtoidis were examined. N. myrtoidis presents five instars and an annual life cycle synchronised with the phenology of P. myrtoides. Gall size was proportional to the insect developmental stages, and rates of parasitism and mortality were 15.7 % and 29.8 %, respectively. The red colour is an important macroscopic diagnostic feature of the gall that could be associated with parasite-free condition of the galling insect. The biological features presented by the system Psidium myrtoides--Nothotrioza myrtoidis are in accordance with other systems involving sucking galling insects, however, it is exceptional by its univoltine life cycle associated with a perennial plant in the Neotropics. The galls induced by the three known Nothotrioza spp. are morphologically similar, i.e. closed, globoid and unilocular, as well as the opening mechanism for releasing the adults.

Efficacy of native antagonistic bacterial isolates in biological control of crown gall disease in Egypt

In vitro analyzing the antagonistic activity of seventy native bacterial isolates towards plant tumorigenic Agrobacterium tumefaciens resulted in a selection of eight potential biocontrol agents. These isolates were screened for their antagonistic effect in vitro as well as their efficacy in reducing gall formation in planta. They were identified using Biolog microplates system as Bacillus megaterium, Paenibacillus polymyxa, Pseudomonas fragi (two isolates), Pseudomonas viridilivd, Pseudomonas asplenii, Curtobacterium flaccumfaciens and Curtobacterum sp.All antagonists tested exhibited considerable inhibitory activity in vitro and significantly reduced incidence and size of galls in rose shoots, kalanchoe leaves and squash fruits with variable degrees on the tested hosts. C. flaccumfaciens reduced the incidence of crown gall up to 100% in the case of rose shoots and kalanchoe leaves whereas the same antagonist reduced galling of squash fruits to 75%. Likewise, P. asplenii, P. viridilivd and P. polymyxa reduced the incidence of crown gall up to 100% in the case of kalanchoe leaves and squash fruits, whereas they reduced galling of rose shoots to 66.7%, 55.6% and 44.5% respectively. In the same manner, the two isolates of P. fragi reduced galling up to 100% in squash fruits, while it was 88.9% in rose shoots and kalanchoe leaves. Interestingly, B. megaterium isolate completely suppressed the gall development in rose shoots, whereas the gall incidence was 100% in kalanchoe leaves and 25% in squash fruits. Bacterial isolates characterized in this study may be considered as potential sources of novel bioactive metabolites as well as promising candidates to develop new biocontrol agents for controlling crown gall disease.

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.