Cytological and histochemical gradients on two <Emphasis Type="BoldItalic">Copaifera langsdorffii</Emphasis> Desf. (Fabaceae)—Cecidomyiidae gall systems

Previous ultrastructural and histochemical analysis proposed patterns in the accumulation of substances in galls of Diptera: Cecidomyiidae in some plant species of the temperate region. Similar analyses were done to verify the conservativeness of these patterns in the Neotropical region, where a great number of species of Cecidomyiidae is responsible for a wide diversity of morphotypes. Two gall morphotypes induced by Cecidomyiidae in a unique host plant, Copaifera langsdorffii, were studied. The gradients of carbohydrates and the activity of invertases and acid phosphatases were similar, but the cytological gradients and distribution of proteins evidenced that the sites of the induction as well as the amount of neoformed tissues may be peculiar to each gall system. The production of lipids just in the secretory cavities either in the non-galled or galled tissues indicated a potentiality of the host plant which could not be manipulated by the galling insects. Further, the absence of nucleus in the nutritive tissue, an exclusive feature of the horn-shaped galls, indicates cell death attributed to the feeding habit of the galling herbivore.     

Indirect competitive effects of stemborers on a gall community

Interspecific 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 shrub Iva frutescens L. (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 midge Asphondylia borrichiae Rossi & Strong (Diptera: Cecidomyiidae) and secondarily to affect its guild of hymenopteran parasitoids.     

Phenotypic plasticity and similarity among gall morphotypes on a superhost,Baccharis reticularia (Asteraceae)

Understanding factors that modulate plant development is still a challenging task in plant biology. Although research has highlighted the role of abiotic and biotic factors in determining final plant structure, we know little of how these factors combine to produce specific developmental patterns. Here, we studied patterns of cell and tissue organisation in galled and non‐galled organs of Baccharis reticularia, a Neotropical shrub that hosts over ten species of galling insects. We employed qualitative and quantitative approaches to understand patterns of growth and differentiation in its four most abundant gall morphotypes. We compared two leaf galls induced by sap‐sucking Hemiptera and stem galls induced by a Lepidopteran and a Dipteran, Cecidomyiidae. The hypotheses tested were: (i) the more complex the galls, the more distinct they are from their non‐galled host; (ii) galls induced on less plastic host organs, e.g. stems, develop under more morphogenetic constraints and, therefore, should be more similar among themselves than galls induced on more plastic organs. We also evaluated the plant sex preference of gall‐inducing insects for oviposition. Simple galls were qualitative and quantitatively more similar to non‐galled organs than complex galls, thereby supporting the first hypothesis. Unexpectedly, stem galls had more similarities between them than to their host organ, hence only partially supporting the second hypothesis. Similarity among stem galls may be caused by the restrictive pattern of host stems. The opposite trend was observed for host leaves, which generate either similar or distinct gall morphotypes due to their higher phenotypic plasticity. The Relative Distance of Plasticity Index for non‐galled stems and stem galls ranged from 0.02 to 0.42. Our results strongly suggest that both tissue plasticity and gall inducer identity interact to determine plant developmental patterns, and therefore, final gall structure.     

Direct and indirect interactions involving ants, insect herbivores, parasitoids, and the host plant Baccharis dracunculifolia (Asteraceae)

Abstract.  1. The relative importance of direct and indirect interactions in controlling organism abundance is still an unresolved question. This study investigated the role of the direct and indirect interactions involving ants, aphids, parasitoids, and the host plant Baccharis dracunculifolia (Asteraceae) on a galling herbivore Baccharopelma dracunculifoliae (Homoptera: Psyllidae).
2. The effects of these interactions on the galling herbivore's performance were evaluated by an exclusion experiment during two consecutive generations of the galling insect.
3. Ants had a direct negative effect on the performance of the galling herbivore by reducing the number of nymphs per gall. In contrast, ants had no indirect effects on gall mortality through the associated parasitoids.
4. Aphids negatively affected gall development, suggesting that galls and aphids might be partitioning photoassimilates and nutrients moving throughout host-plant tissues.
5. In addition, galls that developed during the rainy season were heavier, indicating that variation in the host plant, due to weather changes, can affect the development of B. dracunculifoliae galls. However, variation in the development of B. dracunculifoliae galls due to presence of aphids or the weather changes did not affect parasitoid attack.
6. These results suggest that direct interactions between ants and galls influenced galling insect abundance, whereas numerical indirect effects involving galling insects, ants, aphids, and host plants were less conspicuous.     

Galling: the prevalent form of insect folivory in the latest Neogene monsoon-influenced tropical forests of the Chotanagpur Plateau,eastern India

Indian Cenozoic deposits contain well-preserved diverse angiosperm leaf assemblages, but galling, a common form of angiosperm leaf damage in modern tropical forests, has not been well-documented. Here we report insect herbivory on diverse angiosperm fossil leaf specimens from Pliocene (Rajdanda Formation) sediments of the Chotanagpur Plateau, eastern India, revealing that galling was the most common form of folivory in the latest Neogene monsoon-adapted tropical forests of eastern India. Diverse well-preserved galls are described on the basis of their size, shape and position on the host angiosperm leaf remains. Nine gall damage types (DT 32, DT 33, DT 34, DT 80, DT 83, DT 85, DT 110, DT 120, and DT 144) are identified. They are compared with extant galls and the probable gall inducers making morphologically similar galls on related host tropical plant species of Ficus, Mangifera, Albizia, Galactia, Ziziphus, Hylodesmum, Adina, and Psidium. The gall producers belong to the insect orders Orthoptera, Hemiptera, Hymenoptera, Coleoptera, Lepidoptera, and Diptera (Cecidomyiidae). Although the detailed morphology of the phytophagous insects associated with the recovered fossil leaves is unknown, our findings indicate that many modern plant-insect relationships were likely established by the Pliocene. The reconstructed warm, humid Pliocene climate with a weak monsoon seasonality was conducive to extensive galling activity during this time.     

The interplay between plant traits and herbivore attack: a study of a stem galling midge in the neotropics

1. The relationship between plant traits and the frequency of attack by a stem galling midge, Neolasioptera sp. (Diptera: Cecidomyiidae), on Eremanthus erythropappus (Asteraceae) was studied. The morphological changes of the host after a galler attack and the potential effects of these changes on attacks by the next generation of gallers were analysed. The study was conducted in the Serra do Japi, São Paulo, south-eastern Brazil. 2. Galled branches were significantly longer, thicker, and had more leaves than ungalled branches. Accordingly, gall establishment was higher in the longer and more foliose branches. Hence, it is suggested that ovipositing females are maximizing their performance by selecting larger branches. 3. Galled branches were larger than ungalled branches of the same age. Two hypotheses, not necessarily exclusive, can explain this pattern: (1) the plant vigour hypothesis that the females are choosing the more vigorous, fast-growing branches, which still remain more vigorous after galling; or (2) the resource regulation hypothesis that galling increases branch growth rates, thus increasing resource quality for forthcoming conspecifics. 4. Co-occurrence frequencies of current and past generation galls showed that the likelihood of a branch being galled increased when it, or the branch from which it stemmed, had been galled before. The data indicated that this preference was conditioned by the number of previous attacks. Heavier attack intensities, such as one gall in the same branch and another in the branch from which it stemmed, decreased the probability of further galling. 5. The suggested links between herbivore attack and plant traits indicate that studies on host selection by phytophagous insects must take into account that herbivory itself may change the plant traits that are postulated to be selected by the insects.     

Western Palaearctic phylogeography of an inquiline oak gall wasp,Synergus umbraculus

Insect‐induced galls on plants comprise species‐rich but self‐contained communities of herbivores and natural enemies. In the present study, we focus on galls induced by cynipid gall wasps on oaks, and on the least‐known trophic level that these galls contain: inquilines. These insects, also cynipids, feed on gall tissue and are an abundant but taxonomically poorly understood part of an otherwise well‐studied system. We used DNA sequence data to examine spatial patterns in the genetic diversity of Synergus umbraculus Olivier 1791 (Hymenoptera: Cynipidae: Synergini), a widespread species attacking many host galls across the Western Palaearctic. Analysis of 239 cytochrome b sequences revealed eight haplogroups showing significant phylogeographic pattern across the Western Palaearctic, corresponding to putative glacial refugia in Iberia, Central Europe, Turkey, and Iran. There were significant genetic discontinuities across the Pyrenees and the Anatolian diagonal but no impact of the Alps, suggesting that significant discontinuities have biotic rather than physical causes. Detailed analysis of sites in the Carpathian Basin reveal a high diversity and low spatial structure, and identify Central Europe as the source of colonists for Quaternary colonization of Germany, France, and Britain. We found no evidence for host‐associated differentiation of S. umbraculus lineages associated with the most common cynipid host galls, suggesting frequent shifts within the host gall assemblage by inquiline lineages. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102 , 750–764.     

The occurrence and effectiveness of hypersensitive reaction against galling herbivores across host taxa

1. Hypersensitive reaction is an important type of induced defence by which the plant elicits a defence response to pathogens and insects. Hypersensitive reaction has been argued to be the most common plant resistance mechanism against insect herbivores that have intimate associations with their host plants. 2. The work reported here attempted to establish how important and widespread hypersensitive reaction might be against gall‐forming species across host taxa. 3. Hypersensitive reaction was the most important mortality factor against gall formation across host plant taxa in seven out of eight cases. 4. The number of insect galls correlated with the size of the leaves but module (leaf) size was a weak factor influencing the incidence of plant hypersensitive reaction to galling. 5. Insect galls and hypersensitive reactions occurred in genetically distant as well as geographically widespread host plant taxa.     

Plant stress and larval performance of a dipterous gall former

According to the plant vigour hypothesis, galling insects should respond positively and perform better on vigorous plants or plant parts, the opposite of the predictions of the plant stress hypothesis. I carried out field experiments to analyse the effects of sustained abiotic stress on the interactions between the common reed (Phragmites australis) and a gall-forming fly (Lipara lucens). The reed shoot diameter (a measure of plant vigour) is strongly affected by environmental conditions, where dry and/or nutrient-poor habitats produce thinner (stressed) shoots. L. lucens gall density is negatively correlated with shoot diameter. In a survival experiment with a wide range of shoot diameters, larval mortality was also highly correlated with shoot quality. Gall formation was higher on thinner, stressed shoots. An analysis of the gall tissues revealed that galls induced by L. lucens contain a high amount of a nutrient-rich feeding tissue. The impact of L. lucens is higher on thinner shoots. The results of this study showed that L. lucens performs better on stressed hosts, which contradicts the plant vigour hypothesis for galling insects. The low nutrient availability in the stressed shoots can be compensated by the production of galls with a nutrient-rich feeding tissue.     

Effects of host plant architecture on colonization by galling insects

Abstract: To study the abundance and occurrence of herbivore insects on plants it is important to consider plant characteristics that may control the insects. In this study the following hypotheses were tested: (i) an increase of plant architecture increases species richness and abundance of gall‐inducing insects and (ii) plant architecture increases gall survival and decreases parasitism. Two hundred and forty plants of Baccharis pseudomyriocephala Teodoro (Asteraceae) were sampled, estimating the number of shoots, branches and their biomass. Species richness and abundance of galling insects were estimated per module, and mortality of the galls was assessed. Plant architecture influenced positively species richness, abundance and survival of galls. However, mortality of galling insects by parasitoids was low (13.26%) and was not affected by plant architecture, thus suggesting that other plant characteristics (a bottom‐up pressure) might influence gall‐inducing insect communities more than parasitism (a top‐down pressure). The opposite effect of herbivore insects on plant characteristics must also be considered, and such effects may only be assessed through manipulative experiments.     

Gall‐forming insect species richness along a non‐scleromorphic vegetation rainfall gradient in South Africa: The importance of plant community composition

Abstract Currently there is no single accepted hypothesis to explain gall‐forming insect species richness at a particular locality. Hygrothermal stress, soil nutrient availability, plant species richness, plant structural complexity, plant family or genus size, and host plant geographical range size have all been implicated in the determination of gall‐forming insect species richness. Previous studies of such richness at xeric sites have included predominantly scleromorphic vegetation, usually on nutrient‐poor soils. This study is the first to investigate gall‐forming insect species richness of xeric, non‐scleromorphic vegetation. Two habitat types were sampled at each of five localities across a rainfall gradient in the savanna biome of South Africa. The habitat types differed with respect to plant species composition and topography. Gall‐forming insect species richness did not increase with increasing hygrothermal stress or decreasing soil fertility. Rather, gall‐forming insect species richness was largely dependent on the presence of Terminalia sericea as well as other members of the Combretaceae and Mimosaceae. Plots where all these taxa were present had the highest gall‐forming insect species richness, up to 15 species, whereas plots with none of these taxa had a maximum of four galling‐insect species. Despite herb, shrub and tree strata not differing in gall‐forming insect species richness, insect galls were more common on woody than non‐woody plants. Also, stem galls were more frequent than apical or leaf galls. An alternative hypothesis to explain local gall‐forming insect species richness is suggested: galling insects may preferentially select those plant species with characteristics such as chemical toxicity, mechanical strength, degree of lignification or longevity that can be manipulated to benefit the galler. Thus plant community composition should be considered when attempting to explain gall‐forming insect species richness patterns.     

Host plant intraspecific variation determines gall traits

• Galls display a multiplicity of traits, including colours, which are driven by pigment accumulation. Their conspicuousness has attracted researchers' attention and several hypotheses have been raised. However, plants themselves vary intra-specifically, including in their pigment concentrations. As galls are a result of host tissue development, colours may be a by-product of the host's own traits, being more conspicuous simply because the sites where galls develop already have the predisposition to accumulate more pigment. Here, we call this the host variation hypothesis.
• We test this hypothesis using the system of galls induced by Palaeomystella oligophaga on Macairea radula host plant. Using spectrophotometry, we calculated the Anthocyanin Reflectance Index (ARI) of gall projections, which are responsible for their characteristic colours. We tested the influence of occupant identity (galling insect or any natural enemy), gall volume, parenchyma thickness, height from the ground, ARI of leaf, ARI of gall surface and ARI of the respective stem.
• We corroborated the host variation hypothesis since the anthocyanin content in stems and in galls' projections were positively related. Moreover, anthocyanin in galls' projections was positively related to anthocyanin in the gall surface and negatively related to gall volume and parenchyma thickness. This shows that, besides the host specificities, galls' own traits may also be responsible for pigment accumulation, influencing their colours.
• In this study, using colour as an example, we show that although galls tend to be considered complex expressions of galling insects' stimuli, their traits may be simply influenced by previous and specific attributes of the host organs.

     

Factors affecting refuge from parasitoid attack in a cynipid wasp, Aphelonyx glanduliferae

We examined seasonal patterns of gall morphology, growth, and survivorship of the agamic generation of a cynipid wasp, Aphelonyx glanduliferae, and discussed its mortality factors, especially from the point of view of refuge from parasitoid attack. Although the initiation period varied greatly among individual galls, the larvae of A. glanduliferae grew rapidly and reached their maximum size within 3 weeks before pupating in late September to early October. This growth period corresponded to the period when the gall walls became thinner. Parasitoid attack, which was the principal factor in the mortality of A. glanduliferae in the tree crown, was concentrated around the pupation period of the cynipid. Gall walls were significantly thinner in galls attacked by parasitoids than in those still containing a living cynipid. Therefore, the period available to parasitoids seems to be limited by both gall wall thickness and cynipid size. Thus, the growth pattern of A. glanduliferae larvae can have significance in that it narrows the window of vulnerability to parasitoids to a particular period. Although delaying gall initiation will also shorten the exposure period to parasitoid attacks, it was likely to increase the risk of death from gall abortion caused by seasonal degradation in the quality of host plant tissues. Although many cynipids were killed by disease in the galls that fell to the ground, the falling of mature galls to the ground may be another way to a parasitoid-free space. It is thus suggested that a trade-off among life history traits against multiple factors operates in the refuge of A. glanduliferae from parasitoid attack. Received: May 15, 2001 / Accepted: February 1, 2002     

Growth of coyote willow and the attack and survival of a mid-rib galling sawfly,Euura sp.

We studied the relationship between variation in age and shoot characteristics of the host plant Salix exigua Nuttall (coyote or sandbar willow) and the attack and survival of Euura sp. (an unnamed leaf-midrib galling sawfly). Variation in shoot characteristics resulted from reduced growth as willow ramets aged. Mean shoot length per ramet and mean longest leaf length per shoot decreased by 95% and 50% respectively between 1- and 9-year-old willow ramets. All measured shoot characteristics-shoot length, longest leaf length, number of leaves per shoot, and mean internode length-were significantly negatively correlated with ramet age (r ² ranged from –0.23 to –0.41). Correlations between shoot characteristics were highly positive, indicating that plants also grew in a strongly integrated fashion (r ² ranged from 0.54 to 0.85). Four hypotheses were examined to explain sawfly attack patterns. The host-plant hypothesis was supported in explaining enhanced larval sawfly survival through reduced plant resistance. As willow ramets aged, the probability of Euura sp. attack decreased over 10-fold, from 0.315 on 1-year-old ramets to 0.024 on 2- to 9-year-old ramets. As shoot length increased, the probability of sawfly attack increased over 100-fold, from 0.007 on shoots <100 mm, to 0.800 on shoots in the 1001–1100 mm shoot length class. These attack patterns occurred even though 1-year-old ramets and shoots >500 mm each represented less than 2% of the total shoots available for oviposition. Host plant induced mortality of the egg/early instar stage decreased by 50% on longer leaves and was the most important factor determining survival differences between vigorous and non-vigorous hosts. Sawfly attack was not determined by the resource distribution hypothesis. Although shoots <200 mm contained 82% of the total leaves available, they contained only 43% of the galls initiated. The attack pattern also was not explained by the gall volume hypothesis. Although gall volume increased on longer shoots, there was no significant variation in mid or late instar mortality over shoot length, as would be expected if food resources within smaller galls were limited. The natural enemy attack hypothesis could not explain the pattern of oviposition since predation was greater on longer shoots and leaves. In addition, larval survival was related to oviposition behavior. Due to a 69% reduction in late instar death and an 83% reduction in parasitism, survival of progeny in galls initiated close to the petiole base was 2.8 times greater than in galls initiated near the leaf tip. A 75% reduction in gall volume over this range of gall positions may account for the observed increases in late instar mortality and parasitism.     

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.     

Manipulation of food resources by a gall-forming aphid: the physiology of sink-source interactions

Summary We examined the capacity of the galling aphid, Pemphigus betae, to manipulate the sink-source translocation patterns of its host, narrowleaf cottonwood (Populus angustifolia). A series of ¹⁴C-labeling experiments and a biomass allocation experiment showed that P. betae galls functioned as physiologic sinks, drawing in resources from surrounding plant sources. Early gall development was dependent on aphid sinks increasing allocation from storage reserves of the stem, and later development of the progeny within the gall was dependent on resources from the galled leaf blade and from neighboring leaves. Regardless of gall position within a leaf, aphids intercepted ¹⁴C exported from the galled leaf (a non-mobilized source). However, only aphid galls at the most basal site of the leaf were strong sinks for ¹⁴C fixed in neighboring leaves (a mobilized source). Drawing resources from neighboring leaves represents active herbivore manipulation of normal host transport patterns. Neighboring leaves supplied 29% of the ¹⁴C accumulating in aphids in basal galls, while only supplying 7% to aphids in distal galls. This additional resource available to aphids in basal galls can account for the 65% increase in progeny produced in basal galls compared to galls located more distally on the leaf and limited to the galled leaf as a food resource. Developing furits also act as skins and compete with aphid-induced sinks for food supply. Aphid success in producing galls was increased 31% when surrounding female catkins were removed.     

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.     

Host range expansion by Rhopalomyia yomogicola (Diptera: Cecidomyiidae) from a native to an alien species of Artemisia (Asteraceae) in Japan

In 2001, subconical galls were found on the leaves of an alien Artemisia species (Asteraceae) in Ibusuki City, Kagoshima Prefecture, Japan. These galls were quite similar to those induced by Rhopalomyia yomogicola (Diptera: Cecidomyiidae) on Artemisia princeps, Artemisia montana, and Artemisia japonica in Japan. The morphological features of the pupal head and molecular sequencing data indicated that the gall midge from the alien Artemisia was identical to R. yomogicola. Usually, galling insects do not expand readily their host range to alien plants, but R. yomogicola is considered to have expanded its host range to the alien Artemisia by its multivoltine life history trait and oligophagous habit across two different botanical sections of the genus Artemisia. Adult abdominal tergites and sternites and immature stages of R. yomogicola are described for the first time and detailed biological information is presented.     

Modification of tree architecture by a gall-forming aphid

Herbivory may substantially alter the architectural structure of plants. Among insects, gall-formers that substantially manipulate host traits may have a profound effect on the plants even at low densities. The aphid, Baizongia pistaciae induces banana-like large galls on the terminal buds of Pistacia palaestina. We hypothesized that these large galls are associated with the shape of the plant which may grow as a tree or a bush. In the natural Mediterranean forest, we monitored the effects of the galls on infested branches. In the year of gall formation, usually (~95%) there is neither elongation nor branching beyond the position of the gall. However, in the following years, galled branches produced more lateral branches (branching) than ungalled branches. This effect persists for at least 2 years. Consequently, galled branches carried more leaves and tended to gain more biomass than ungalled branches. Galling did not affect fruit yield. We suggest that repeated galling by B. pistaciae may promote bush-like architecture in P. palaestina.     

Very long diapause and extreme resistance to population disturbance in a galling insect

1. Some insects have a prolonged diapause – a dormancy that extends over more than 1 year. In most species prolonged diapause involves one or a few extra years, but in extreme cases diapause may surpass 10 years. Few cases of very long diapause have been described, and very little is known about the population consequences of the temporal refuge formed by the diapausing individuals. 2. The gall midge Contarinia vincetoxici Kieffer galls the flowers of a long‐lived herb Vincetoxicum hirundinaria Med. After completing development, larvae leave the galls for the ground where they enter diapause. Extending an earlier published inoculation experiment, we show that the diapause may last up to at least 13 years, with a median duration of at least 6 years. 3. The gall midge is attacked by two parasitoid species. Dissections of gall midge larvae for presence of parasitoids revealed that Omphale salicis Haliday had a maximum 2 year diapause and Synopeas acuminatus Kieffer a maximum 4 years. The very long diapause of the gall midge may thus provide a temporal refuge from these enemies. 4. In a 15‐year field experiment all galls were removed every year from six isolated habitat patches. Density changes in experimental populations were not statistically different from control populations for over a decade. After 14–15 years a modest decline could be observed. This slow response illustrates that prolonged diapause in C. vincetoxici provides a very strong population buffer against mortality during the galling stage.