Do aphid galls provide good nutrients for the aphids?: Comparisons of amino acid concentrations in galls among Tetraneura species (Aphididae: Eriosomatinae)

Some aphid species induce leaf galls, in which the fundatrix parthenogenetically produces many nymphs. In order to ensure high performance, galls have to provide the aphids with sufficient nutrients, in particular, amino acids as a nitrogen source. We tested this hypothesis using six Tetraneura aphid species that induce closed galls. We extracted free amino acids from the whole gall tissues of unit weight and quantified the concentration of each amino acid. There were large differences in the total amino acid concentrations among galls of the Tetraneura species. Tetraneura species in which higher concentrations of total amino acids were found in the gall tended to produce larger numbers of offspring. Of the amino acids found, asparagine was predominant in the gall. The asparagine concentration in T. yezoensis galls was several hundred times as high as in control leaves. We discussed why such a high level of asparagine accumulates in aphid galls.     

PEMPHIGUS REVISITED: CHANGES IN GEOGRAPHIC VARIATION BUT CONSTANCY IN VARIABILITY AND COVARIATION

Samples of the gall-forming aphids Pemphigus populicaulis and P. populitransversus (both elongate and globular morphs) were re-collected at sites in eastern North America after 13 to 16 years. Twenty-three morphometric characters of the galls, stem mothers, and alate fundatrigeniae were analyzed by univariate and multivariate methods. Varying proportions of the variance of each character are attributable to the four levels of variation—locality, year, year by locality interaction, and among galls (within one year and locality). The year by locality interaction level generally has the greatest variation and is highly significant. Year and locality effects tend to be lower and not significant. The variance components do not exhibit trends with time. Geographic variation patterns of single variables or factor scores in the original and revisited populations show significant spatial structure overall but lack clear-cut spatial patterns, especially clines. Observable patterns of variation match results of the spatial analyses: most characters lack clear trends; patterns in the revisited data do not resemble patterns for the same variables in the original data. Variability profiles for characters change little over the time span and are comparable among and within localities. Covariation among characters over localities is largely maintained during the time interval despite the changes in patterns. Fluctuating interclonal competition among aphids on secondary hosts is believed to cause the marked heterogeneity in space and time among the aphids in the galls.     

An aphidiine parasitoid Monoctonia vesicarii (Hymenoptera: Braconidae) and three chalcidoid hyperparasitoids of Pemphigus matsumurai (Homoptera: Aphididae) forming leaf galls on Populus maximowiczii in Japan

More than 300 unopened leaf galls formed by the pemphigine aphid Pemphigus matsumurai on Populus maximowiczii were collected at Nakasatsunai, Hokkaido, Japan, in July and September 2007 and kept in cold conditions during winter. From mummified fundatrices in the galls an aphidiine parasitoid Monoctonia vesicarii and three species of hyperparasitoids belonging to Pteromalidae, Eupelmidae and Eulophidae emerged from March to May 2008. Monoctonia vesicarii, which is new to Japan, is redescribed. The eulophid hyperparasitoid is described as a new species, Aprostocetus (Aprostocetus) doronokianus, and the pteromalid and eupelmid hyperparasitoids are identified as Pachyneuron sp. and Eupelmus sp., respectively. Approximately 180 unopened mummies of P. matsumurai were dissected in August and November 2008 and a living larva of M. vesicarii was found in each of 17 of them. These observations suggest that some individuals of M. vesicarii pass through two‐year cycles. The implications of the three species of hyperparasitoids to P. matsumurai galls are discussed.     

Molecular identification and population dynamics of two species of Pemphigus (Homoptera: Pemphidae) on cabbage

The poplar petiole gall aphid, Pemphigus populitransversus Riley, has been one of the major pests on cruciferous vegetable in the Rio Grande Valley (LRGV) of Texas since the late 1940s. It normally migrates from poplar trees to cruciferous vegetables in the fall, and migrates back to the trees in early spring of the coming year. Some root‐feeding aphids were found on cruciferous vegetables in late spring and early summer in 1998 and the following years. Those aphids have been identified as Pemphigus obesinymphae Moran. This discovery completely changed the current knowledge about the root‐feeding aphids on cruciferous vegetables in the LRGV. Due to their small size, morphological and feeding similarities between P. populitransversus and P. obesinymphae, their identification and distinction are difficult. In this study, random amplification of polymorphic DNA (RAPD) and amplified fragment length polymorphism (AFLP) were used to distinguish these two species over a period of time when the two species occurred together, or separately, in cabbage fields. The two species occurred on cabbage at different times of the year, and overlapped from October to June. From May to October, both species migrated to their primary hosts. The apterous aphids found on cabbage in winter contained mainly P. obesinymphae, whereas in early spring more apterous P. populitransversus were recovered. The root‐feeding aphids would feed on cabbage plants as long as this host was available even during the hot, dry summer in the LRGV, although their populations were generally low. Both RAPD and AFLP techniques were efficient in discriminating the two species that showed obviously genetic variability. These molecular techniques confirmed the existence of the two aphid species in apterous samples collected from the soil in cabbage fields in the LRGV, and the results performed by RAPD were confirmed by AFLP. Furthermore, the results suggest that RAPD technique was a better choice despite its reproducibility problem, as it was less time‐consuming and required less technology, labor and expense than AFLP.     

To be suspended or to be cut off? Differences in the performance of two types of leaf-rolls constructed by the attelabid beetle Cycnotrachelus roelofsi

The attelabid beetle Cycnotrachelus roelofsi constructs two types of leaf-rolls (cradles): one is suspended from leaves (suspended type), and the other is severed from the leaves (cut-off type). To evaluate differences in performance between these two cradle types, we monitored densities, survival rates, and mortality factors throughout the active season, from April to June. The proportions of the two cradle types changed over time; the suspended type was dominant early in the season but was gradually replaced by the cut-off type. Irrespective of differences in mortality factors between the two cradle types, the survival rate was always higher in the cut-off type than in the suspended type. Beetle mortality tended to be highest at the egg stage, and the predominant cause of mortality was parasitism by two minute trichogrammatid wasp species, Poropoea morimotoi and P. sp.1. Parasitism by P. morimotoi was significantly higher in cut-off cradles than in suspended cradles, when cut-off cradles were abundant, whereas parasitism by P. sp.1 tended to be higher in suspended cradles when suspended cradles were abundant. These results suggest opposed frequency-dependent attacks by P. morimotoi and P. sp.1. We discuss how these egg parasitoids maintain coexistence of these two cradle types.     

Tuberaphis owadai (Homoptera), a new aphid species forming a large gall on Styrax tonkinensis in northern Vietnam

Tuberaphis owadai sp. nov., an aphid species forming coral‐shaped galls on Styrax tonkinensis in northern Vietnam, is described. We found that the species produces many sterile second‐instar soldiers in the gall. The colony size of a large gall was estimated to be 178 000, approximately half of which were soldiers. Alates emerging from galls contained sexual embryos, indicating that the life cycle is monoecious (non‐host‐alternating). Predaceous larvae of the pyralid moth Assara seminivalis were found in several galls.     

Ant effects on three-trophic level interactions: plant, galls, and parasitoids

1. Ants have evolved mutualistic relationships with a diverse array of plant and animal species. Usually, the predatory/aggressive behaviour of ants near food sources can limit herbivore damage. 2. Galls of Disholcaspis edura on Quercus turbinella produce a secretion that is harvested by three species of ants (Formica neorufibarbis, Liometopium apiculatum, and Monomorium cyaneum) in the chaparral vegetation of Arizona, U.S.A. The study reported here provides evidence of a mutualistic relationship between these species of ants and the gall-forming wasp Disholcaspis edura. 3. An ant exclusion experiment showed that when ants tended galls, the rate of parasitism by Platygaster sp. on Disholcaspis edura was nearly halved in comparison to a treatment in which ants were excluded. 4. In the presence of ants, galls with the largest diameter suffered a lower mortality rate due to parasitoid attack than when ants were excluded. Thus, ant presence reduced the selective pressure imposed by Platygaster sp. on the galls with larger diameter.     

Astegopteryx spinocephala (Hemiptera: Aphididae), a new aphid species producing sterile soldiers that guard eggs laid in their gall

Astegopteryx spinocephala sp. nov., a soldier‐producing aphid species forming banana‐bunch shaped galls on Styrax benzoides in northern Thailand, is described. We found that galls of the species are formed in approximately June and last for almost 1 year, and that the aphid completes its life cycle without migrating to secondary hosts. Many alate sexuparae appeared in March/April, when many sexuals (arostrate males and rostrate females) and eggs were found in live subgalls guarded by soldiers that plugged the ostiole with their sclerotized, spiny heads. Two healthy galls sampled in April contained 2799 and 2659 eggs, respectively. Many live galls were still found in May, and some at the beginning of June. These galls contained both active soldiers and eggs, some of which had already hatched. This indicates that soldiers of A. spinocephala guard eggs until they hatch in at least some galls.     

Differential response of trees and shrubs to browsing and pruning: the effects on Pistacia growth and gall-inducing aphids

The effects of long term browsing on growth and morphology of P. atlantica trees and P. palaestina shrubs, and on the colonization of these hosts by their respective gall-inducing aphid guilds, were studied in natural vegetation pastures in Israel. To simulate apical dominance release by browsing, trees and shrubs were pruned and observed one year later. P. atlantica responded strongly to browsing, producing a crown of dense and sharp dry branches and thorn-like shoots, and pruning, compensating or overcompensating for the lost biomass in the studied morphological variables. Morphological responses of P. palaestina were less evident: we found no compensation in most variables. Three species of aphids produced more galls on browsed than on control shoots of P. atlantica. Two species induced more galls on pruned shoots. The five aphid species on P. palaestina colonized browsed and unbrowsed shoots equally, and produced fewer galls on pruned shoots. The role of apical dominance in architectural responses of trees and shrubs to browsing and pruning, as related to resource availability and timing, is discussed. This revised version was published online in June 2006 with corrections to the Cover Date.     

Geographic covariation of hosts und parasites: Evidence from Populus und Pemphigus1

The geographic covariation of the eastern cottonwood Populus deltoides with three different gallforming aphids in the genus Pemphigus is studied over eastern North America. Ten vegetative Populus characters were analyzed together with 32 stem mother, slate und gall dimension characters in Pemphigus populicaulis und in two morphs of P. populitransversus. The number of locality samples studied ranges from 56 to 157. The covariation between host und parasite characters was examined by correlation analysis und canonical correlations und shown to be slight. Multiple regressions of factor scores of Pemphigus variables on Populus characters show relatively low percentages of explained variance und few significant partial regression coefficients. Spatial autocorrelation analyses of Pemphigus factor scores und of their residuals on Populus variables demonstrated largely independent spatial structure of the two sets of variables. These findings were confirmed by multiple Mantel tests of distance matrices based on cottonwood und aphid phenetics und on geography. The undoubtedly close Pemphigus-Populus coevolution over geological time is not reflected in the microevolutionary variation over geographic space. Possible esplanations for these surprising findings are discussed.     

Host range and host preference of a flea weevil, Orchestes hustachei, parasitizing aphid galls

Although larvae of flea weevils (Curculioninae: Rhamphini) have been known to be leaf miners, larvae of the rhamphine weevil Orchestes hustachei have been found in aphid galls of four Tetraneura species on Ulmus davidiana and in galls of Paracolopha morissoni on Zelkova serrata. This study clarified the feeding habits of O. hustachei larvae and evaluated gall selection by ovipositing females to test the hypothesis of host race formation on their hosts, Tetraneura and Paracolopha galls. When weevil larvae were placed in half‐cut galls, they always fed on aphids rather than on gall tissue. When given gall tissue only, all larvae failed to reach adulthood. The number of aphids surviving in a parasitized gall decreased significantly with the development of the weevil larvae. These results suggest that O. hustachei larvae use aphids as their major food source. In the field, ovipositing females did not discern between four Tetraneura species on U. davidiana, in spite of a large difference in suitability as food. Paracolopha morrisoni was introduced into Hokkaido approximately 100 years ago, together with the host plant Z. serrata. It is probable that P. morrisoni has recently come to be used as a host by O. hustachei in Hokkaido. Host choice experiments using Tetraneura sp. O and P. morrisoni galls indicated that female weevils from Z. serrata preferred P. morrisoni to Tetraneura sp. O galls, while females from U. davidiana selected the two types of gall randomly. On Z. serrata, female weevils selected larger P. morrisoni galls, while on U. davidiana, females did not show a preference for gall size. These results suggest that a host shift to P. morrisoni galls may have led to an initial stage of host race formation between the weevil population using Tetraneura galls on U. davidiana, and that using P. morrisoni galls on Z. serrata.     

Sampling Bias in Roadsides: The Case of Galling Aphids on Pistacia Trees

Sampling along roadsides is convenient and is widely practiced in insect population researches. Ecological conditions in road verges are very different than those prevailing in natural habitats and they affect the annual growth of plants in semi-arid and arid regions. This in turn may improve development, survival and abundance of insects feeding on plants growing in roadsides. These trends may bias the results of sampling. To verify this assertion, we quantified the effects of growing in roadside on annual growth of Pistacia atlantica trees and Pistacia palaestina shrubs and compare two demographic indexes of nine gall-inducing aphid species on trees growing along roads with trees in the open landscape, in Israel. The annual growth of the two host plants was significantly more vigorous in roadsides than away from roads. Tests of Combined Probabilities showed that the likelihood of P. atlantica and P. palaestina to be parasitized by more galls of Fordini species is higher in roadsides than away from roads. Moreover, in the semi-dry regions of Israel, three aphid species on P. atlantica and five species on P. palaestina induced more galls in plants growing along roads than away from roads, while in the rainy Northern region, the difference was not significant between the two habitats. These results indicate a biased evaluation of population size in roadside habitat, which has to be accounted in insect–plant relation researches.     

Introduced ants reduce interaction diversity in a multi‐species,ant–aphid mutualism

Mutualisms contribute in fundamental ways to the origin, maintenance and organization of biological diversity. Introduced species commonly participate in mutualisms, but how this phenomenon affects patterns of interactions among native mutualists remains incompletely understood. Here we examine how networks of interactions among aphid‐tending ants, ant‐tended aphids, and aphid‐attacking parasitoid wasps differ between 12 spatially paired riparian study sites with and without the introduced Argentine ant Linepithema humile in southern California. To resolve challenges in species identification, we used DNA barcoding to identify aphids and screen for parasitoid wasps (developing inside their aphid hosts) from 170 aphid aggregations sampled on arroyo willow Salix lasiolepis. Compared to uninvaded sites, invaded sites supported significantly fewer species of aphid‐tending ants and ant‐tended aphids. At invaded sites, for example, we found only two species of ant‐tended aphids, which were exclusively tended by L. humile, whereas at uninvaded sites we found 20 unique ant–aphid interactions involving eight species of ant‐tended aphids and nine species of aphid‐tending ants. Ant–aphid linkage density was thus significantly lower at invaded sites compared to uninvaded sites. We detected aphid parasitoids in 14% (28/198) of all aphid aggregations. Although the level of parasitism did not differ between invaded and uninvaded sites, more species of wasps were detected within uninvaded sites compared to invaded sites. These results provide a striking example of how the assimilation of introduced species into multi‐species mutualisms can reduce interaction diversity with potential consequences for species persistence.     

The aphid Ceratovacuna nekoashi (Hemiptera: Aphididae: Hormaphidinae) and its allied species in Korea,Japan and Taiwan

The aphid Ceratovacuna nekoashi and its allied species have been a taxonomically difficult group. They form peculiar “cat's‐paw” galls (called “Nekoashi” in Japanese) on Styrax trees and also use Microstegium grasses as their secondary hosts. Through sampling aphids from both Styrax galls and Microstegium grasses in South Korea, Japan and Taiwan, and sequencing their DNA, we made it clear that four distinct species occur in these regions: C. nekoashi (Sasaki), C. oplismeni (Takahashi), C. orientalis (Takahashi) and C. subtropicana sp. nov. In Korea, C. nekoashi forms galls on both S. japonicus and S. obassia, whereas in Japan the species forms galls on the former but not on the latter; our molecular analyses unequivocally indicated the occurrence of a single species in South Korea and mainland Japan. Aphids of the four species on the secondary host were morphologically discriminated from one another. The identity of the primary‐ and secondary‐host generations was also clarified for each species. All four species were found to produce second‐instar sterile soldiers in their Styrax galls, and first‐instar soldiers were found in colonies of C. subtropicana on the secondary host.     

Geographic variation in Pemphigus populicaulis (Insecta: Aphididae) in Eastern North America*,†

The geographic variation of 33 morphological characters of the gall-forming aphid Pemphigus populicaulis is studied for 118 localities east of 100^oW longitude. Variation can be partitioned into within-gall, among-gall and among-locality components. Among localities variation ranges from 26 to 54%, being significant for all characters. Variation among galls within localities ranges from 24 to. 56%, that within-galls from 8 to 4796. The design of the study permits computation of character correlation matrices within and among localities. Gall size is correlated with tnorphometric characters only on an interlocality but not on an intralocality basis. Interlocalily correlations are a function of intralocality correlations, confirming earlier predictions. There is little correlation between characters of stem mother and alate morphotypes within localities, whereas among localities such correlation is appreciable. This phenomenon may be caused by aspects ol the environment that vary among localities but remain reasonably constant through the earlv life cycle of the aphid. When subjected to factor analysis both correlation matrices yield four factors. Multiple discriminant analysis of the data set results in five interpretable significant axes. Maps are furnished for characters representing the independent dimensions of variation and for discriminant function scores. The patterns of variation can be shown to be significantly nonrandom by Mantel's test and by spatial autocorrelation analysis. All variables are significantly positively autocorrelated at 200 km, many at 400 km and a few at 600 km; few general statements can be made about significant autocorrelations at higher distances. The positive autocorrelation at relatively short distances may be related to the pool of clones from which the genotypes of any one locality sample are taken. There are three correlogram patterns that can be associated with four clusters of variation patterns of characters. The separate patterns presumably cannot be explained by a single microevolutionary process.     

Impact of a gall-inducing aphid on Pistacia atlantica Desf. trees

The impact of gall-inducing aphids on shoot development was analyzed in 900 shoots from 20 pistachio trees, Pistacia atlantica Desf. (Anacardiaceae): 600 in which the axillary—lateral buds were galled by Slavum wertheimae HRL during the previous growth season, and 300 ungalled shoots. Although P. atlantica is a compensating tree, and the aphids do not attack the apical buds, further development of shoots from the apical buds was stopped in 62% of the galled shoots, while only 8.7% of nongalled shoots stopped their growth. Further development was stopped more often on shoots carrying two or more galls than on shoots supporting only one gall. To assess the hypothesis that bud destruction by the aphids explains this pattern, a field experiment was conducted in 140 shoots, distributed across seven trees. One, two or three axillary buds from five shoots of each tree were removed for each treatment, and five other shoots were marked as controls. Only 14 shoots (10%) of the 140 did not develop. The growth of the other shoots was not very different among the treatments. The colonization of the apical shoots, which developed on previously treated shoots, by three other galling aphid species was monitored. Removing lateral buds considerably reduced the establishment of Geoica sp. galls (70% of them colonized control shoots), but weakly influenced Forda riccobonii (Stefani). It also contributed only 5% of the total variance of the distribution of Smynthurodes betae West. The different results of the survey and the experiment show that the impact of S. wertheimae galls on the future growth of shoots from apical buds is more complex than the simple physical destruction of the axillary buds. Handling editor: Graham Stone     

Host plant effects on the development and survivorship of the galling insect Neopelma baccharidis (Homoptera: Psyllidae)

In this study, the mortality factors acting upon the galling psyllid Neopelma baccharidis Burckhardt (Homoptera) caused by its host plant, Baccharis dracunculifolia De Candole (Asteraceae) were analysed. In March 1999, 982 galls of the same cohort were randomly marked on 109 individuals of B. dracunculifolia in the field. Galls were censused each month during their development, from April to August, and dead galls were collected and analysed for mortality factors. Gall dehiscence rates were calculated for each month. The major mortality source of N. baccharidis was gall dropping (13.2% of the original cohort), which is probably a normal outcome of previous mortality caused by the other factors observed in this study. Unknown factors killed 11.7% of this gall population and were ascribed to plant resistance during gall development. Empty galls represented 7.7% of the observed mortality and may be a consequence of egg retention or egg mortality/abortion related to variations in plant quality. Shoot mortality was high during the dry season and killed 7.5% of the galls, but this impact was minimized after the third month from gall formation due to the ability of nymphs to accelerate development and emerge from galls on dying shoots. However, the size of dehisced galls on dead shoots tended to be smaller, possibly affecting adult performance. Mortality of N. baccharidis attributed to B. dracunculifolia strongly controlled the galling insect population, killing 40.7% of the original cohort of galls. Plant‐mediated mortality was caused by often neglected factors acting predominantly during the first 3 months of development, which are critical to gall survivorship. These results reinforce the importance of bottom‐up forces in plant‐insect systems.     

Drastic changes in host preference in a gall‐parasitic flea weevil,Orchestes hustachei,during the last decade

1. Factors affecting host preference in herbivorous insects are actively discussed. Larval performance, competition and predation on each host, and host abundance are reportedly factors affecting the host preference of ovipositing females. In the present study, chronological changes in female host preference were examined by employing a flea weevil species that uses the original host and a newly introduced host simultaneously. 2. Orchestes hustachei Klima (Coleoptera: Curclionidae) is an aphidophagous flea weevil that oviposits on aphid galls, and the larvae feed on aphids inside. The weevil's native hosts are galls of the Tetraneura species on Ulmus davidiana, while the novel hosts are galls of an introduced species, Paracolopha morrisoni on Zelkova serrata, an introduced hardwood. Choice experiments were conducted using Tetraneura galls and Paracolopha galls and the results were compared with experiments conducted 10 years ago. 3. More than 90% of ovipositing females selected Paracolopha galls. This result is in marked contrast with the result of the 2002 experiment, in which 66.3% of females selected Paracolopha galls. To explore driving forces of the preference change, mortality factors, pupal mass on the two hosts, and temporal changes in the abundance of the host galls were examined. 4. Abundance of Tetraneura galls decreased gradually throughout the last 26 years. By contrast, weevil survival and performance did not vary significantly between the two hosts. Therefore, it is concluded that temporal changes in the relative abundance of two hosts are main factors of the change in host preference.     

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.     

Aphid galls accumulate high concentrations of amino acids: a support for the nutrition hypothesis for gall formation

The nutrition hypothesis for the adaptive significance of insect gall formation postulates that galls accumulate higher concentrations of nutritive compounds than uninfested plant tissue, resulting in a high performance of the gall former. This hypothesis has been supported by some taxa of gall insects, but not by taxa such as cynipid wasps. Aphid galls are expected to require higher levels of nitrogen than other insects’ galls with a single inhabitant, because aphid galls are required to sustain a number of aphids reproducing parthenogenetically over two generations. The present study tested this hypothesis by evaluating aphid performance and amino acid concentration in phloem sap, using the aphid Rhopalosiphum insertum (Walker) (Homoptera: Aphididae), which establishes colonies on leaves of Sorbus commixta Hedlund or in galls of the aphid Sorbaphis chaetosiphon Shaposhnikov (Homoptera: Aphididae). We prepared the gall and non‐gall treatments on trees of S. commixta, in which R. insertum fundatrices were reared and allowed to reproduce. In S. chaetosiphon galls, R. insertum colonies propagated more rapidly, and the second generation grew larger and more fecund than on ungalled leaves. The amount of amino acids exuding from cut galled leaves was fivefold that in ungalled leaves; however, there was no significant difference in the amino acid composition between galled and ungalled leaves. In the intact leaves, total amino acid concentration in the phloem sap declined rapidly from late April to late May; however, the galls retained this high amino acid concentration in developing leaves for 1 month. These results indicate that the improved performance in R. insertum is ascribed to the increased concentration of amino acids in galled leaves. We suggest that S. chaetosiphon galls function to promote the breakdown of leaf protein, leading to an increased performance of gall‐inhabiting aphids.