Nest composition and worker relatedness in three slave-making ants of the genus Rossomyrmex Arnoldi and their Proformica Ruzsky hosts (Hymenoptera,Formicidae)

Abstract In this paper, we analyze and compare nest composition and architecture as well as worker relatedness in three related species of slave-making ants: Rossomyrmex anatolicus, R. minuchae, and R. quandratinodum. Colony structure within nests is an important trait in ants, especially in the case of mixed societies, when host and parasite coexist in the same nest. Data for their respective free-living hosts, Proformica korbi, P. longiseta and P. sp., are also provided. For our study, we integrated a meticulous excavation procedure with a genetic method. We conclude that the average number of parasites, as well as of slaves, is species-specific, whereas nest depth depends on the nest architecture of the host. The genus Rossomyrmex seems to be monogynous and monandrous, whereas Proformica shows differences in the number of queens and mating frequency. R. quandratinodum shows different traits in nest composition (host/parasite ratio: P/R) and architecture. The difference in traits may account for some differences in parasitism: raid process or avoidance of parasitism.     

Dufour's gland secretion as a repellent used during usurpation by the slave-maker ant Rossomyrmex minuchae

In slave-making ants, the invasion of the host colony by newly mated queens is a critical stage. We studied the strategy used by Rossomyrmex minuchae queens to invade their host Proformica longiseta. Field observations revealed that queens enter the host nest unchallenged by the host workers in the vicinity of the nest entrance. Pre-usurpation queens were found to possess a highly inflated Dufour's gland, which considerably reduces in size after successful usurpation. Chemical analysis of these queen glands revealed tetradecanal to be the major product in pre-usurpation Rossomyrmex queens, but to be almost absent in queens that have been adopted by P. longiseta. We consequently hypothesized that tetradecanal is a repellent that is used by queens to prevent host worker aggression. We tested its repellent effect by attempting to deter starved, highly motivated workers from a droplet of honey. Tetradecanal indeed proved to be highly repellent both to host worker P. longiseta and non-host worker Formica selysi. It was even more powerful than limonene, a reported general ant repellent. These results are consistent with the hypothesis that R. minuchae queens use Dufour's gland secretion as a weapon during nest usurpation. The general use of tetradecanal as a defensive compound, and its seemingly non-specific repellent effect on ants, indicate that it may act as a general ant repellent. Its adoption by R. minuchae queens thus provides them with an efficient defensive and offensive chemical weapon during their long and risky search for new host nests.     

A geographical mosaic of coevolution in a slave-making host-parasite system

Three different isolated populations of the slave‐making ant Rossomyrmex minuchae, sympatric with its obligate host Proformica longiseta, are known from the high mountains of southern Spain. To test the prediction that the slave‐maker and its host represent a coevolutionary geographical mosaic, we studied the variation in the cuticular hydrocarbons (CHCs) as the trait most likely to show the selection mosaic, plus trait remixing by the gene flow in the populations of each species by means of microsatellites. We found within populations, host and parasite had more similar CHC profiles than between the populations or between parasites and allopatric hosts. The differences between the CHC profiles of the host and parasite, which may be responsible for the level of tolerance towards the parasite, varied between the populations suggesting the existence of a selection mosaic of coevolution. Furthermore, P. longiseta showed higher gene flow than R. minuchae, which would allow local variation in the coevolution of the host and parasite while allowing some trait remixing.     

Larval niche selection and evening exposure enhance adoption of a predacious social parasite, Maculinea arion (large blue butterfly), by Myrmica ants

Larvae of the butterfly genus Maculinea feed briefly on a foodplant before being adopted as social parasites into Myrmica ant nests. Each Maculinea species typically survives only with a single Myrmica species, yet the eggs are laid across the overlapping territories of 3-5 Myrmica species and several other ants. The ability of Maculinea arion - a 'predatory' species of Maculinea - to influence its adoption into host Myrmica colonies was studied for the first time in the field. Some earlier reports, involving captive non-host ants, suggested that larvae of the predatory Maculinea follow ant trails into host nests or wander some distance from their foodplant before being discovered and (after a long interaction) carried away by Myrmica foragers. No dispersal from foodplants occurred in wild Maculinea arion larvae. Instead, they increased by >100-fold their probability of being discovered and adopted by Myrmica spp., rather than by ants of other genera, by exposing themselves in the micro-niche occupied by Myrmica foragers at their time of day of peak foraging. Despite a complex, hour-long interaction with Myrmica workers before being carried to the nest, Maculinea arion did not enhance its adoption by host species of Myrmica. Eggs were laid without bias in Myrmica sabuleti (host) and Myrmica scabrinodis (non-host) territories; larval survival on Thymus was the same in both ants' territories; larvae waited to be found beneath their foodplant rather than seek their host; Myrmica sabuleti and Myrmica scabrinodis foraged in the same vertical and temporal niches, and had the same probability of discovering larvae; both ants behaved identically after finding larvae and took the same time to adopt them; and the ratio of wild larvae taken into Myrmica sabuleti or Myrmica scabrinodis nests was the same as the distribution between these ants of Thymus, eggs and pre-adoption larvae.     

Morpho-functional comparison of the Dufour gland in the female castes of the Amazon ant <Emphasis Type="Italic">Polyergus rufescens</Emphasis> (Hymenoptera,Formicidae)

The Dufour gland is crucially involved in main aspects of the parasite habit of the slave-making ant Polyergus rufescens, i.e. slave-raids and host colony usurpation. Workers use chemicals from this gland as recruitment signals during raid organization, while newly-mated queens use its secretion to appease residents during host nest invasion. Here, we report a comparison of the general morphology and fine structure of the Dufour gland in the female castes of P. rufescens: queens, ergatogynes (intermediate forms), and workers. The analysis clearly shows the link between gland structure and its behavioural role in queens and workers. In particular, queens present a hypertrophied gland with an extended lumen and a thin epithelium no more active in secretory function. This is consistent with the fact that usurper queens use the Dufour gland contents only during the short phase of host nest penetration. Contrary to adult queens, the cytoplasmic organization of the Dufour gland epithelium of raiders is typical for a tissue with secretory activity (abundance of mitochondria, free ribosomes, strands of smooth endoplasmic reticulum and a Golgi apparatus). This is consistent with the continuous raiding activity performed by workers throughout their adult life. The biology of ergatogynes is still an enigmatic matter. Their Dufour gland is intermediate in shape and size between that of queens and workers. It presents a fairly thick epithelium with features that are typical of a quite active secretory tissue.     

Raiding Activity of an Obligate (Polyergus breviceps) and Two Facultative (Formica puberula and F. gynocrates) Slave-Making Ants

Slave-making ants are social parasites that exploit the labor of workers from their host species by keeping them captive in the slave-maker nest. Slave-makers vary in their degree of specialization, ranging from obligate slave-makers that cannot survive without captives, to facultative slave-makers, which are often found living independently. Our study system included one obligate slave-maker, Polyergus breviceps, two facultative slave-makers, Formica puberula and F. gynocrates, and two hosts, F. occulta and F. sp. cf. argentea. We observed all raids conducted during two raiding seasons by seven P. breviceps colonies, two F. puberula colonies, and two F. gynocrates colonies. We report on raiding frequency, average raid distances, and then compare the probability of being raided multiple times in a single raiding season for the two host species. We also report on the spatial distribution of slave raids, which suggests that slave-makers avoid raiding in areas used by other slave-maker colonies. This is the first report of raiding activity for P. breviceps in this location, and the first report of raiding activity of any kind for F. puberula and F. gynocrates.     

Prevalence of the parasite Strepsiptera in <Emphasis Type="Italic">Polistes</Emphasis> as detected by dissection of immatures

Summary. hough the paper wasp genus, Polistes, is well studied, we know little of the incidence of parasitism in this group. Here we present details of 45 nest dissections for 4 species: P. dominulus (Christ), P. gallicus (L.), P. stabilinus Richards and P. carnifex (F.) to detail levels of parasitism of colony members by the obligate parasitic group of insects, the Strepsiptera. All 4 species showed evidence of parasitism among immature members. For 3 species, more than 50% of inspected nests were parasitized and the levels of parasitism among brood (larvae and pupae) was very high and did not differ significantly between parasitized nests. One species, P. stabilinus, suffered very low levels of parasitism, which may be related to its habitat choice. The number of parasites per host was positively related to the proportion of infected brood (parasite prevalence) and in some cases reached phenomenally high levels, which casts doubt on previ ously assumed mechanisms of infection for nest-making Hymenoptera, i.e. phoresy. We also document cases of egg parasitism and encapsulation in Polistes nests. Our data show that parasitism levels greatly varied among areas. Finally, the recent debate on the competitive advantage of P. dominulus in its introduced range, USA, has credited an absence of strepsipteran parasites of this species in facilitating its spread. For the first time, we document levels of parasitism for this species in its nature P range and this would appear to corroborate previous claims. We place our work in the context of other studies of parasitism of social insects and posit that the genus Polistes may have much to offer to this field.     

Raiding and emigration dynamics in the ponerine army ant Leptogenys distinguenda (Hymenoptera, Formicidae)

Summary: Field and laboratory observations demonstrate that Leptogenys distinguenda is characterized by typical army ant behavior. Like in the "classical" army ants from the subfamilies Ecitoninae, Dorylinae and Aenictinae, raiding and emigration behavior are closely linked. The direction of raids can be altered in field experiments to a wide extent by offering ample food, suggesting it is highly influenced by the patchiness of prey. The sum of recruitments coming from one direction and the recruitment overrun are primarily responsible for the spatial development and the extension of raids. Emigration frequency can be suppressed by overfeeding a colony in the field. This result is interpreted as a secondary effect of reduced swarming activity, which gets suppressed as well in the same experiment. The discovery of a suitable nest site is considered the proximate stimulus for emigration, and the best explored areas are those that have been most thoroughly raided. As a result, emigrations are likely to lead into areas with high prey densities.     

Convergent evolution of the vertical transmission mode of the cyanobacterial obligate symbiont Prochloron distributed in the tunic of colonial ascidians

In chordates, obligate photosynthetic symbiosis has been reported exclusively in some colonial ascidians of the family Didemnidae. The vertical transmission of the symbionts is crucial in establishing the obligate symbiosis between the cyanobacteria and the host ascidians. The results of comparative surveys on the morphological processes of cyanobacterial transmission suggest the occurrence of convergent evolution of the vertical transmission in the host species harboring symbionts in the cloacal cavity. In Trididemnum species harboring cyanobacterial cells in the tunic, the symbiont cells are transported by the tunic cells to the tunic of embryos brooded in the tunic of the parent colony. The present study examined whether the mode of symbiont transmission is the same in host species harboring the symbionts in the tunic, regardless of host genera, or whether non-Trididemnum hosts have a different vertical transmission mode. Our results showed that the vertical transmission process in Lissoclinum midui was almost the same as in the Trididemnum species, supporting the occurrence of convergent evolution in the two distinct didemnid genera, that is, Trididemnum and Lissoclinum. High plasticity of the embryogenic process in didemnid ascidians may be important in developing the mechanism of vertical transmission; this assumption may also explain why the obligate cyanobacterial symbiosis has been exclusively established in didemnid ascidians among chordates.     

Escape from parasitism: spatial and temporal strategies of a sphecid wasp against a specialised cuckoo wasp

Parasites and parasitoids exert an important selection pressure on organisms and, thus, play an important role for both population dynamics and evolutionary responses of host species. We investigated host-parasite interactions in a brood-caring wasp, the European beewolf, Philanthus triangulum (Hymenoptera, Sphecidae), and asked whether females of this species might employ temporal or spatial strategies to reduce the rate of attack by a specialised brood parasitoid, the cuckoo wasp Hedychrum rutilans (Hymenoptera, Chrysididae). Females of the host species might shift their activity to periods of low parasitoid activity both in the course of the season and in the course of the day. On a spatial scale, aggregated or dispersed nesting might be favoured depending on the form of the density dependence of parasitism. The beginning and end of the flight season of host and parasitoid were nearly identical. Activity of chrysidids relative to beewolves did not change significantly during the flight season. However, relative parasitoid activity declined in the course of the day, suggesting the existence of temporal enemy-free space in the evening hours. Shifting the main activity to the evening hours might be a flexible response of beewolves to the presence of chrysidids. Activity of cuckoo wasps per nest was independent of nest density but the actual rate of parasitism as revealed by nest excavations indicated direct density dependence. Total mortality, however, was inversely density dependent. Thus, in the study population aggregated nesting did not reduce parasitism but minimised total mortality.     

CO2 exchange and thallus nitrogen across 75 contrasting lichen associations from different climate zones

Aiming to investigate whether a carbon-to-nitrogen equilibrium model describes resource allocation in lichens, net photosynthesis (NP), respiration (R), concentrations of nitrogen (N), chlorophyll (Chl), chitin and ergosterol were investigated in 75 different lichen associations collected in Antarctica, Arctic Canada, boreal Sweden, and temperate/subtropical forests of Tenerife, South Africa and Japan. The lichens had various morphologies and represented seven photobiont and 41 mycobiont genera. Chl a, chitin and ergosterol were used as indirect markers of photobiont activity, fungal biomass and fungal respiration, respectively. The lichens were divided into three groups according to photobiont: (1) species with green algae, (2) species with cyanobacteria, and (3) tripartite species with green algal photobionts and cyanobacteria in cephalodia. Across species, thallus N concentration ranged from 1 to 50 mg g^-1 dry wt., NP varied 50-fold, and R 10-fold. In average, green algal lichens had the lowest, cyanobacterial Nostoc lichens the highest and tripartite lichens intermediate N concentrations. All three markers increased with thallus N concentration, and lichens with the highest Chl a and N concentrations had the highest rates of both P and R. Chl a alone accounted for ca. 30% of variation in NP and R across species. On average, the photosynthetic efficiency quotient [K_F=(NP_max+R)/R)] ranged from 2.4 to 8.6, being higher in fruticose green algal lichens than in foliose Nostoc lichens. The former group invested more N in Chl a and this trait increased NP_max while decreasing R. In general terms, the investigated lichens invested N resources such that their maximal C input capacity matched their respiratory C demand around a similar (positive) equilibrium across species. However, it is not clear how this apparent optimisation of resource use is regulated in these symbiotic organisms.     

Compound nesting of <Emphasis Type="Italic">Strumigenys</Emphasis> sp. (Myrmicinae) and <Emphasis Type="Italic">Diacamma</Emphasis> sp. (Ponerinae), and other nesting symbioses of myrmicine and ponerine ants in Southeast Asia

Summary. A new type of compound nest, inhabited by the small Strumigenys sp.1 (Myrmicinae) and the relatively big Diacamma sp.1 (Ponerinae), was found in Java, Indonesia. Field records as well as results of experimental studies were used to describe this association. The compound nests were relatively frequent in the research area: 75% of the examined Diacamma sp.1 nests were also inhabited by Strumigenys sp.1. Strumigenys sp.1 is specialized on nesting in small, excavated nest chambers, in close vicinity to Diacamma sp.1, while Diacamma sp.1 does not depend on Strumigenys sp.1. The rather small workers of this myrmicine species forage for food inside the Diacamma nests as well as outside, favouring mites and collembolans as prey, but principally not rejecting any other nitrogen source. The refuse pile of Diacamma sp.1 inside the nest houses small living invertebrates and insect parts, preyed upon by Strumigenys sp.1. Given the choice between larvae of Diacamma sp.1 and mites, Strumigenys sp.1 clearly preferred the mites. Thus, the association seems to be beneficial to Strumigenys sp.1, and does not harm Diacamma sp.1. We found two more similar compound nests: In Java, a different Strumigenys species was frequently found nesting within the nest of a Pachycondyla (Ponerinae) species. In Sabah, East Malaysia, we recorded for the first time a Pheidole (Myrmicinae) species nesting in chambers coming out of the walls of Diacamma nest chambers. Existing classifications for compound nest associations (i.e. xenobiosis, cleistobiosis etc.) are too restricted, because they were based on a few cases. Hence, we present a list of non-normative traits describing the various types of nest symbioses by ants.     

Burning bridges: priority effects and the persistence of a competitively subordinate acacia-ant in Laikipia, Kenya

Theoretical models suggest that subordinate competitors may rely on strong colonization ability and/or high persistence (e.g., the ability to resist invasion) as a strategy to coexist with competitively dominant species. While strong colonization ability among subordinate competitors has been widely documented, we know less about the role of persistence in facilitating species coexistence. In upland East Africa, four species of acacia-ants (Crematogaster sjostedti, C. mimosae, C. nigriceps, Tetraponera penzigi) compete for possession of Acacia drepanolobium host trees. Despite a strong dominance hierarchy, the four acacia-ant species coexist at fine spatial scales. Here we present evidence that T. penzigi, the least aggressive competitor, modifies host trees in two ways that reduce the probability of aggressive takeover by neighboring colonies. First, T. penzigi workers destroy virtually all leaf nectaries on their host trees. Second, T. penzigi workers create and maintain entryways into their swollen thorn domiciles that are too small to allow entry by their Crematogaster competitors. In a 2Ƕ factorial experiment, we manipulated nectar availability and swollen-thorn entryway size to determine the influence of these factors on the probability of aggressive displacement by a dominant competitor (C. mimosae) in staged conflicts. Addition of artificial nectaries and enlargement of swollen-thorn entryways on T. penzigi-occupied trees increased the probability of aggressive displacement of T. penzigi by C. mimosae from swollen thorns 14-fold and 8-fold, respectively. Further, empty saplings with nectaries destroyed by T. penzigi workers were colonized by half as many C. mimosae workers as saplings where nectaries were left intact. Our results demonstrate that T. penzigi's unusual strategy of nectary destruction and the maintenance of small entryways in swollen thorns produce priority effects, effectively reducing the probability that T. penzigi colonies will be displaced from host trees by more dominant competitors.     

Three new host species of the social wasp parasite, Polistes atrimandibularis (Hymenoptera, Vespidae)

Summary. We report that the social parasite Polistes atrimandibularis (Zimmermann) can exploit at least three more host species than previously described. One of these, P. associus, has never been reported as host of a social parasite. Our data show no constraints in host choice, indicating P. atrimandibularis is a generalist social parasite.     

Pollen grain numbers, ovule numbers and pollen-ovule ratios in Caryophylloideae: correlation with breeding system, pollination, life form, style number, and sexual system

Pollen-ovule ratios (P/O) were measured for 79 species of Caryophylloideae (Agrostemma, Dianthus, Saponaria, Silene, and Vaccaria). We analyzed if these features are best correlated with (1) the breeding system (outcrossing or selfing), (2) diurnal or nocturnal pollination, (3) life form (annual versus perennial), (4) style number, (5) the sexual system (hermaphroditism, gynodioecism, dioecism), or (6) the taxonomy of species. According to the classification of Cruden [(1977) Evolution 31:32-46] most species in the subfamily Caryophylloideae are facultative autogamous or facultative xenogamous. Autogamous or cleistogamous species showed significantly lower P/Os than outcrossing species. We found no differences between night- and day-flowering species; thus from our data diurnal and nocturnal flower visitors may be considered as equally efficient in transferring pollen. However, other factors are also important for the interpretation of P/Os. Pollen grain numbers and ovule numbers were found to correlate with style number, life form, and breeding system. The low P/Os of some dioecious, and therefore obligate outcrossing, species are discussed in relation to morphological traits that improve pollen deposition by pollinators on the stigma, and in relation to different flower numbers of male and female plants.     

Parasitism and biology of Myrmosicarius grandicornis (Diptera, Phoridae) in relationship to its host, the leaf-cutting ant Atta sexdens (Hymenoptera, Formicidae)

Summary. The parasitic phorid Myrmosicarius grandicornis Borgmeier is commonly found around nest entrances of the leaf-cutting ant Atta sexdens (L.) in Brazil, but there is no information about the importance of this fly for A. sexdens. We evaluated the parasitic capability of female M. grandicornis collected in the field and released in laboratory nests of A. sexdens and compared ants' foraging rhythm before and after M. grandicornis were released. We also determined biological characteristics of the parasitoid. Presence of M. grandicornis elicited foragers to abandon their loads and return to the nest, an effect previously described for the phorid Neodohrniphora sp., which is a more abundant A. sexdens parasitoid. Both phorid species occur at the same foraging trails during part of the year and attack ants of different size classes. Therefore, they may have a combined effect on the reduction of A. sexdens foraging. Myrmosicarius grandicornis pupariated inside hosts' head capsules, which are detached from their bodies and deposited in the nest's refuse pile. Adults emerged through the hosts' mouth cavity about a month after oviposition. The characteristics of M. grandicornis biology suggest that this parasitoid completes its development inside A. sexdens nests.     

Extreme population differentiation in a vulnerable slavemaking ant with a fragmented distribution

Understanding levels of population differentiation and inbreeding are important issues in conservation biology, especially for social Hymenoptera with fragmented and small population sizes. Isolated populations are more vulnerable to genetic loss and extinction than those with extended continuous distributions. However, small populations are not always a consequence of a recent reduction of their habitat. Thus, determining the history of population isolation and current patterns of genetic variation of a species is crucial for its conservation. Rossomyrmex minuchae is a slave-making ant with patchy distribution in South Eastern Spain and is classified as vulnerable by the IUCN. In contrast, the other three known species of the genus are presumed to show more uniform distributions. Here we investigate the genetic diversity and population structure of R. minuchae and compare it with that found in two other species of the genus: R. anatolicus and R. quandratinodum. We conclude that although genetic diversity of R. minuchae is low, there is no evidence of a recent bottleneck, suggesting a gradual and natural fragmentation process. We also show extreme population differentiation at nuclear and mitochondrial markers, and isolation by distance at a local scale. Despite some evidence for inbreeding and low genetic variation within populations, we found almost no diploid males, a finding which contrasts with that expected in inbred Hymenoptera with single locus complementary sex determination. This could mean that sex is determined by another mechanism. We argue that continued low population size means that detrimental effects of inbreeding and low genetic variation are likely in the future. We suggest that a policy of artificial gene flow aimed at increasing within population variation is considered as a management option.     

Size and composition of swarming colonies in Provespa anomala (Hymenoptera, Vespidae), a nocturnal social wasp

Summary: Ninety-eight nests of various growing stages of Provespa anomala were found in the lowlands of Sumatra, Indonesia, from August to January. Its colony cycle is considered to be annual, with nests built throughout the year. There were two types of early nests before the emergence of workers, one with a worker number of less than 63 and the other of more than 231. The former were new nests, each containing a new queen and were built by reproductive swarming, whereas each of the latter was possibly re-built by an old queen and an absconding swarm. Ten swarming colonies were attracted by an oil-lamp light; these consisted of a copulated queen with immature oocytes in the ovary and 55 workers on average. No males, or workers stylopized by Xenos provesparum were observed either in colonies before worker emergence or in swarms coming flying into the light. Differences between swarming in Provespa, polygyny and nest relocation in Vespa, and those in swarm-founding Polistinae are discussed.     

Mutualistic nematode-bacteria complexes associated with insects

In the review, the life cycles and mutualistic relations within the nematode-bacteria associations are analyzed: nematodes Bursaphelenchus xylophilus (PWN) with bacteria Pseudomonas fluorescens, Bacillus spp., Burkholderia arboris; entomopathogenic nematodes (EPN) of the genera Steinernema and Heterorhabditis with bacteria of the genera Xenorhabdus and Photorhabdus. The life cycles of PWN and EPN show traits of the primary detrital trophism. Both cycles include invasion of the living host and are completed with death of the host, which is an obligate condition for dispersal of the nematodes and their associated bacteria. Nematodes and bacteria stimulate each other to reproduce fast; the diverse forms of their interactions are considered, including direct and indirect ones (via the plant or insect host). Bacteria of both mutualistic associations produce siderophores and antibiotics that prevent reproduction of other pathogenic and putrefactive microorganisms. Ectosymbiotic bacteria of PWN may be recruited into the association from among the inhabitants of the mucous cover of the nematode body, as well as from the pathogenic bacterial biota of local conifers; thus the PWN and bacteria are facultative synergists in the phytopathogenic process. Endosymbiotic bacteria of EPN are not capable of independent life; they have developed obligate associations with highly specific nematode hosts.     

Plant diversity,herbivory and resistance of a plant community to invasion in Mediterranean annual communities

Several components of the diversity of plant communities, such as species richness, species composition, number of functional groups and functional composition, have been shown to directly affect the performance of exotic species. Exotics can also be affected by herbivores of the native plant community. However, these two possible mechanisms limiting invasion have never been investigated together. The aim of this study was to investigate the relationships between plant diversity, herbivory and performance of two annual exotics, Conyza bonariensis and C. canadensis, in Mediterranean annual communities. We wanted to test whether herbivory of these exotics was influenced either by species richness, functional-group richness or functional-group composition. We also studied the relationship between herbivory on the exotic species and their performance. Herbivory increased with increasing species and functional-group richness for both Conyza species. These patterns are interpreted as reflecting a greater number of available herbivore niches in a richer, more complex, plant community. The identities of functional groups also affected Conyza herbivory, which decreased in the presence of Asteraceae or Fabaceae and increased in the presence of Poaceae. Increasing herbivory had consequences for vegetative and demographic parameters of both invasive species: survival, final biomass and net fecundity decreased with increasing herbivory, leading to a loss of reproductive capacity. We conclude that communities characterised by a high number of grass species instead of Asteraceae or Fabaceae may be more resistant to invasion by the two Conyza species, in part due to predation by native herbivores.