Visitation rate of pollinators and nectar robbers to the flowers and inflorescences of Tabebuia aurea (Bignoniaceae): effects of floral display size and habitat fragmentation

Large floral displays favour pollinator attraction and the import and export of pollen. However, large floral displays also have negative effects, such as increased geitonogamy, pollen discounting and nectar/pollen robber attraction. The size of the floral display can be measured at different scales (e.g. the flower, inflorescence or entire plant) and variations in one of these scales may affect the behaviour of flower visitors in different ways. Moreover, the fragmentation of natural forests may affect flower visitation rates and flower visitor behaviour. In the present study, video recordings of the inflorescences of a tree species (Tabebuia aurea) from the tropical savannah of central Brazil were used to examine the effect of floral display size at the inflorescence and tree scales on the visitation rate of pollinators and nectar robbers to the inflorescence, the number of flowers approached per visit, the number of visits per flower of potential pollinators and nectar robbers, and the interaction of these variables with the degree of landscape disturbance. Nectar production was quantified with respect to flower age. Although large bees are responsible for most of the pollination, a great diversity of flower insects visit the inflorescences of T. aurea. Other bee and hummingbird species are highly active nectar robbers. Increases in inflorescence size increase the visitation rate of pollinators to inflorescences, whereas increases in the number of inflorescences on the tree decrease visitation rates to inflorescences and flowers. This effect has been strongly correlated with urban environments in which trees with the largest floral displays are observed. Pollinating bees (and nectar robbers) visit few flowers per inflorescence and concentrate visits to a fraction of available flowers, generating an overdispersed distribution of the number of visits per inflorescence and per flower. This behaviour reflects preferential visits to young flowers (including flower buds) with a greater nectar supply.     

Argentine ants displace floral arthropods in a biodiversity hotspot

Argentine ant (Linepithema humile (Mayr)) invasions are often associated with the displacement of ground‐dwelling arthropods. Argentine ant invasions can also exert other effects on the community through interactions with plants and their associated arthropods. For example, carbohydrate resources (e.g. floral or extrafloral nectar) may influence foraging behaviour and interactions among ants and other arthropods. In South Africa's Cape Floristic Region, Argentine ants and some native ant species are attracted to the floral nectar of Leucospermum conocarpodendron Rourke (Proteaceae), a native tree that also has extrafloral nectaries (EFNs). Despite having relatively low abundance in pitfall traps, Argentine ants visited inflorescences more frequently and in higher abundance than the most frequently observed native ants, Camponotus spp., though neither native nor Argentine ant floral foraging was influenced by the EFNs. Non‐metric multidimensional scaling revealed significant dissimilarity in arthropod communities on inflorescences with Argentine ants compared to inflorescences with native or no ants, with Coleoptera, Diptera, Hymenoptera, Arachnida, Orthoptera, and Blattaria all being underrepresented in inflorescences with Argentine ants compared to ant‐excluded inflorescences. Native honeybees (Apis mellifera capensis Eschscholtz) spent 75% less time foraging on inflorescences with Argentine ants than on inflorescences without ants. Neither Argentine ant nor native ant visits to inflorescences had a detectable effect on seed set of Le. conocarpodendron. However, a pollen supplementation experiment revealed that like many other proteas, Le. conocarpodendron is not pollen‐limited. Flower predation was negatively associated with increased ant visit frequency to the inflorescences, but did not differ among inflorescences visited by native and Argentine ants. Displacement of arthropods appears to be a consistent consequence of Argentine ant invasions. The displacement of floral arthropods by Argentine ants may have far‐reaching consequences for this biodiversity hotspot and other regions that are rich in insect‐pollinated plants.     

Intra‐floral resource partitioning between endemic and invasive flower visitors: consequences for pollinator effectiveness

1. Sympatric flower visitor species often partition nectar and pollen and thus affect each other's foraging pattern. Consequently, their pollination service may also be influenced by the presence of other flower visiting species. Ants are solely interested in nectar and frequent flower visitors of some plant species but usually provide no pollination service. Obligate flower visitors such as bees depend on both nectar and pollen and are often more effective pollinators. 2. In Hawaii, we studied the complex interactions between flowers of the endemic tree Metrosideros polymorpha (Myrtaceae) and both, endemic and introduced flower‐visiting insects. The former main‐pollinators of M. polymorpha were birds, which, however, became rare. We evaluated the pollinator effectiveness of endemic and invasive bees and whether it is affected by the type of resource collected and the presence of ants on flowers. 3. Ants were dominant nectar‐consumers that mostly depleted the nectar of visited inflorescences. Accordingly, the visitation frequency, duration, and consequently the pollinator effectiveness of nectar‐foraging honeybees (Apis mellifera) strongly decreased on ant‐visited flowers, whereas pollen‐collecting bees remained largely unaffected by ants. Overall, endemic bees (Hylaeus spp.) were ineffective pollinators. 4. The average net effect of ants on pollination of M. polymorpha was neutral, corresponding to a similar fruit set of ant‐visited and ant‐free inflorescences. 5. Our results suggest that invasive social hymenopterans that often have negative impacts on the Hawaiian flora and fauna may occasionally provide neutral (ants) or even beneficial net effects (honeybees), especially in the absence of native birds.     

THE GENETIC CONSEQUENCES OF WORKER ANT POLLINATION IN A SELF-COMPATIBLE,CLONAL ORCHID

The self-compatible orchid Microtis parviflora is pollinated by the flightless worker caste of the ant Iridomyrmex gracilis. The orchid is clonal and forms small patches, usually less than 1 m², of disconnected individual ramets. Ant pollinators visited and revisited a limited proportion of available inflorescences, and 40% of all flower visits occurred within plants promoting self-pollination. Pollen labels indicated that self-pollination accounted for 51% of the pollen transfers, although pollen carryover extended beyond 16 flowers on 2 or 3 inflorescences. The distribution of ant movements between plants was leptokurtic with a mean of 12.4 ± 14.9 cm and a maximum of 89 cm, but a high proportion of movements were within clones accentuating the level of self-pollination. However, some pollen transfers between inflorescences of unlike genotypes contributed to a low incidence (max = 8%) of outcrossing. In 12 patches examined by electrophoresis, the density varied from 11 to 61 inflorescences per m² and a maximum of only 4 genotypes were detected. Electrophoretic analysis revealed populations were highly inbred: only 23% (N = 17) of the loci were polymorphic and the mean gene diversity h, was 2.7%. Heterozygotes were observed in only one population given a mean fixation index F, of 0.982. These results reflect the combined effects of restricted ant foraging and clonality. Nevertheless, while ant foraging was restricted, some outcrossing occurred and in the absence of clonality it is likely that ant foraging would have yielded a mixed mating system similar to those reported for a wide array of insect pollinators. Given the ability of ants to generate pollen flow, the reasons for the rarity of ant pollination appear to lie elsewhere.     

Contrasting movement patterns of nectar-collecting and pollen-collecting bumble bees (Bombus terricola) on fireweed (Chamaenerion angustifolium) inflorescences

Abstract. 1. Movements of nectar and pollen-foraging bumble bees on inflorescences of Chamaenerion angustifolium (L.) J. Holub (fireweed or rosebay willow herb) were compared with predictions based on reward distributions and optimality principles. Observations suggest that nectar and pollen-gathering bumble bees behave according to the same set of reward maximization criteria when foraging from flowers of this species.
2. Both kinds of foragers matched their arrival points with the vertical positions on inflorescences in which the densities of their respective food resources were greatest. For nectar-foragers, this point was located at the lowest tier of flowers, whereas for pollen-foragers it was found in the middle of the inflorescences. Nectar and pollen-foraging bees both moved upward on inflorescences following gradients from high to low reward availability.
3. Nectar-foragers responded to decreases in inflorescence size over the season by reducing the number of flower visits made on each raceme. Number of flowers visited by pollen-foragers was low throughout and reflected the scarcity of male-phase flowers on racemes. Flower revisitation rates were low for both kinds of workers, but were slightly higher for those collecting pollen.     

Production of food bodies on the reproductive organs of myrmecophytic Macaranga species (Euphorbiaceae): effects on interactions with herbivores and pollinators

In protective ant–plant mutualisms, plants offer ants food (such as extrafloral nectar and/or food bodies) and ants protect plants from herbivores. However, ants often negatively affect plant reproduction by deterring pollinators. The aggressive protection that mutualistic ants provide to some myrmecophytes may enhance this negative effect in comparison to plant species that are facultatively protected by ants. Because little is known about the processes by which myrmecophytes are pollinated in the presence of ant guards, we examined ant interactions with herbivores and pollinators on plant reproductive organs. We examined eight myrmecophytic and three nonmyrmecophytic Macaranga species in Borneo. Most of the species studied are pollinated by thrips breeding in the inflorescences. Seven of eight myrmecophytic species produced food bodies on young inflorescences and/or immature fruits. Food body production was associated with increased ant abundance on inflorescences of the three species observed. The exclusion of ants from inflorescences of one species without food rewards resulted in increased herbivory damage. In contrast, ant exclusion had no effect on the number of pollinator thrips. The absence of thrips pollinator deterrence by ants may be due to the presence of protective bracteoles that limit ants, but not pollinators, from accessing flowers. This unique mechanism may account for simultaneous thrips pollination and ant defense of inflorescences.     

An exception to Darwin's syndrome: floral position,protogyny, and insect visitation in Besseya bullii (Scrophulariaceae)

Darwin pointed out that plants with vertical inflorescences are likely to be outcrossed if the inflorescence is acropetalous (flowers from the bottom up), the flowers are protandrous (pollen is dispersed before stigmas are receptive), and pollinators move upward on the inflorescence. This syndrome is common in species pollinated by bees and flies, and very few exceptions are known. We investigated flowering phenology and pollinator behavior in Besseya bullii (Scrophulariaceae) and found that it did not fit Darwin's syndrome. The vertical inflorescence was acropetalous but the flowers were distinctly protogynous, so flowers with newly receptive stigmas appeared on the inflorescence above those with dehiscing anthers. A number of small insects visited B. bullii; bees in the family Halictidae (Augochlorella striata and Dialictus spp.) were most common. When insects moved between gender phases within inflorescences, they moved up more often than down (61% versus 39% of observations, respectively) but this difference was only marginally significant. Most visits were to male-phase flowers only, and this preference was more pronounced for pollen-foraging insects than for nectar-foraging insects. B. bullii was self-compatible, so its flowering characteristics potentially could result in considerable self-pollination. However, an average of 38% of the lowermost flowers opened before any pollen was available on the same inflorescence; these solo females had a high probability of outcrossing (though fruit set was relatively low in the bottom portion of the inflorescence). Upper flowers may also be outcrossed because downward insect movement was not uncommon. Therefore protogyny in B. bullii may not necessarily lead to more selfing than would protandry.     

Floral visitation patterns of two invasive ant species and their effects on other hymenopteran visitors

Abstract.  1. Floral nectar of the native Hawaiian 'ōhi'a tree, Metrosideros polymorpha , is an important food source for several native honeycreepers and yellow-faced bees, Hylaeus spp., but is also attractive to invasive ants.
2. I undertook this study to compare floral visitation patterns of two widespread invasive ants, the Argentine ant, Linepithema humile , and the big-headed ant, Pheidole megacephala , and to determine their effects on nectar volume and floral hymenopteran visitors.
3. In the first year of the study, Argentine ants visited inflorescences more frequently than big-headed ants at mid-day and in the afternoon, but did not occur in higher densities than big-headed ants at any time of day. In the following year, Argentine ants visited inflorescences both more frequently and in higher densities than big-headed ants. Argentine ant density had a stronger association with nectar concentration than big-headed ant density.
4. Nectar volume did not differ between ant-excluded and ant-visited inflorescences for either ant species. However, ant density was negatively associated with nectar volume for both species.
5.  Hylaeus spp. never visited inflorescences with big-headed ants, while non-native honeybees visited inflorescences with and without ants of either species in equal frequency.
6. Most studies of the effects of invasive ants on native arthropods have focused on interactions on the ground. Flowers should not be overlooked as microhabitats from which native arthropods may be displaced by invasive ants.     

Floral biology of Nuphar pumila (Timm) DC. (Nymphaeaceae) in China

Anthesis in individual flowers of Nuphar pumila (Timm) DC. occurs for four consecutive days. First-day flowers are protogynous and functionally female. Flowers can open completely on the first day of anthesis. This contrasts with all previous reports, which state that first-day flowers of Nuphar are characterized by partial expansion of the calyx, leaving a distal small triangular opening just above the stigmatic disc. Flowers close completely on the first night of anthesis and remain partially open on the subsequent three nights. During the entire anthesis period the stigmas emit a sweet, fruity odor and the petal nectaries produce visible nectar drops. The stigma of N. pumila is secretory and unicellular-papillate. Pollen grains are monosulcate with long spines. Our observations on the mating system of N. pumila indicate that neither asexual seed production nor spontaneous self-pollination occurs. Cross-pollination of second-, third- and fourth-day flowers produced few seeds. Flowers of N. pumila were mainly pollinated by sweat bees, with flies playing a minor pollination role. No beetle visits were observed. Our insect-pollination observations substantiate the view that the relative contribution of flies, bees, and beetles to pollination in a single Nuphar population depends on two factors: the relative abundance of the insects, and presence of alternative food sources.     

Nonvolatile chemicals provide a nest defence mechanism for stingless bees Tetragonula carbonaria (Apidae,Meliponini)

Social insects construct nests that protect their brood and food resources from both the physical environment and natural enemies. Stingless bees use plant‐derived resins, mixed with wax to form propolis, in the construction of their nests, and these products can be effective sources of defense against natural enemies, including ants. However, it is not known whether this defense, in the form of deterring or repelling workers, derives from the physical properties or chemical compounds of these products. The nest entrance of Tetragonula carbonaria is constructed with propolis and Corymbia resins, and we ask whether nonvolatile chemicals present in these products act as a defense against ants. Our field experiments revealed that workers of Iridomyrmex mayri Forel were deterred from crossing a chemical barrier comprising nonvolatile, nonpolar (hexane) extracts of propolis and Corymbia tree resin. However, polar (ethanol) extracts did not have this effect. These data are the first to demonstrate that the chemical components alone of entrance propolis and resins can provide a nest‐defense function against ants.     

Conflict resolution in an ant–plant interaction: Acacia constricta traits reduce ant costs to reproduction

Many plant species attract ants onto their foliage with food rewards or nesting space. However, ants can interfere with plant reproduction when they visit flowers. This study tests whether Acacia constricta separates visiting ant species temporally or spatially from newly opened inflorescences and pollinators. The diurnal activity patterns of ants and A. constricta pollinators peaked at different times of day, and the activity of pollinators followed the daily dehiscence of A. constricta inflorescences. In addition to being largely temporally separated, ants rarely visited open inflorescences. A floral ant repellent contributes to the spatial separation of ants and inflorescences. In a field experiment, ants of four species were given equal access to inflorescences in different developmental stages. On average, the frequency with which ants made initial, antennal contact with the floral stages did not differ, but ants significantly avoided secondary contact with newly opened inflorescences relative to buds and old inflorescences, and old inflorescences relative to buds. Ants also avoided contact with pollen alone, indicating that pollen is at least one source of the repellent. The results suggest A. constricta has effectively resolved the potential conflict between visiting ants and plant reproduction.     

Multi-cycle synchronous protandry in raceme-like inflorescences of a bumblebee-pollinated herb Aconitum grossedentatum

Multi-cycle synchronous dichogamy is expected to be a mechanism for reducing self-pollination and sexual interference. It is often found in plants with umbellate inflorescences where pollinator movement is unpredictable, but not in plants with raceme inflorescences that are pollinated by bumblebees. Plants with raceme inflorescences often acropetally open flowers, resulting in an arrangement of females at lower level and males at upper level. This is good enough to preclude geitonogamy because bees tend to move upwardly within the inflorescences. Furthermore, although the degree of segregation of sexes varies among species, their intraspecific variations within a population have rarely been examined. Here, we present a synchronous protandry in bee-pollinated Aconitum grossedentatum, which has a raceme-like inflorescence and opens flowers basipetally. To evaluate the functional significance of synchronous dichogamy in mating, we firstly observed the distribution of sex phases of open flowers. Then, we assessed the effect of each phase flower on foraging behavior by pollinators and seed-set success. The inflorescences tended to exhibit either male- or female-phase flowers at any moment early in the flowering season, but the degree of segregation of sexes declined over time within a population. The degree of the segregation did not affect bumblebee visits to flowers, but it decreased seed-set success of female-phase flowers at that time. Our results demonstrated that synchronous protandry was beneficial for pollination success in A. grossedentatum by avoiding geitonogamy. Nevertheless, we also found asynchronous protandry late in the season, suggesting that the benefits by synchronous protandry decreased over the season.

     

Male-biased sex ratio and promiscuous pollination in the dioecious island treeLaurus azorica (Lauraceae)

Pollination ofLaurus azorica (Lauraceae), a dioecious Macaronesian tree, was studied. Male and female trees had the same size distribution. The population had 2.5 times as many male trees as females. In addition, males produced more flowers, and their inflorescences lasted longer. Individual flower lifetime and length of flowering season were the same in both sexes. Between the years of observation, one tree changed sex. Pollinators wereHalictinae bees and the flyTachina canariensis. The bees collected pollen and nectar and the fly collected nectar from both sexes. Both species visited other plants as well. The evolution of breeding systems inLauraceae is discussed.     

Plant design and non-random foraging by ants on Croton bonplandianum Baill. (Euphorbiaceae)

Croton bonplandianum bears female flowers in inflorescences which are arranged in a regular pattern. Foraging individuals of the ant Camponotus sericius feed on the nectar in the nectary glands of female flowers. The pattern of movement of ants while foraging between these regularly placed inflorescences was highly systematic and distinctly exploratory. The ants tended to visit new inflorescences at each move and avoided revisiting inflorescences. They followed this foraging pattern by adopting circular movements either to the left or to the right and avoiding other complex but equally effective moves. This was probably due to memory constraints. The ants predicted the resource quality of the subset of a patch by sampling a part of it. The inflorescences within a cluster were similar in quality. Using this relation ants could make decisions about continuing to forage in a cluster after sampling any one inflorescence. If the first inflorescence visited was of poor quality they abandoned the cluster. This ensured efficient foraging with minimal expenditure of time and energy.     

ANT-POLLINATION OF THE GRANITE OUTCROP ENDEMIC DIAMORPHA SMALLII (CRASSULACEAE)

Formica schaufussi, a medium-sized ant common throughout the Piedmont and Coastal Plain of the southeastern United States, has been observed in association with Diamorpha smallii, a self-incompatible annual endemic to granite outcrops in the Southeast, over a 6-yr period. Observations of ants collected on the flowers show large numbers of the sticky pollen grains adhering to hairs and indentations primarily on the thoraces of the ants. Though small native bees and flies are frequent and sometimes effective pollinators, it is highly unlikely that the monotypic genus Diamorpha coevolved with the introduced honeybee, as has been suggested. Characteristics indicative of an “ant-pollination syndrome” include occurrence in hot, dry habitats, a high density of very small plants bearing overlapping inflorescences at a uniform height, and low seed number, pollen volume, and nectar quantity.     

Choice of flowers by foraging honey bees (Apis mellifera): possible morphological cues

Abstract.

• 1 Honey bees foraging for nectar on lavender (Lavandula stoechas) chose inflorescences with more of their flowers open. The number of open flowers predicted whether an inflorescence was visited by bees, inspected but rejected, or ignored. Inflorescences chosen arbitrarily by observers had numbers of open flowers intermediate between those of visited and ignored inflorescences.
• 2 Differences in morphological characters between types of inflorescence correlated with nectar volume and sugar weight per flower so that visited inflorescences had a disproportionately greater volume of nectar and weight of sugar per flower and greater variance in nectar volume.
• 3 Although there were significant associations between nectar content and the morphological characters of inflorescences, discriminant function analysis revealed discrimination on the basis of morphology rather than nectar content.
• 4 Visited inflorescences tended to have smaller than average flowers but bees tended to probe the largest flowers on visited inflorescences.
• 5 Choice of flowers within inflorescences is explicable in terms of the relationship between flower size and nectar content.

     

RELATIVE POLLINATOR EFFECTIVENESS AND EVOLUTION OF FLORAL TRAITS IN SPATHIPHYLLUM FRIEDRICHSTHALII (ARACEAE)

We studied the relative effectiveness of different pollinators of Spathiphyllum friedrichsthalii Schott for 15 months on Barro Colorado Island, Panama. Pollen-foraging stingless bees (Apidae: Trigona) made 87% of floral visits. Experiments showed that these bees pollinate flowers, and correlations of fruit- and seed-set with visitation frequencies and floral contact times suggested that they were responsible for the majority of seeds produced. Fifteen species of fragrance-foraging, male euglossine bees (Apidae: Euglossini) collectively accounted for a small portion of seed-set in fewer than 27% of the inflorescences. Neocorynura (Halictidae) were pollen thieves and were unimportant as pollinators. We propose that euglossine and stingless bees differentially influence outcrossing rates and the evolution of floral traits of S. friedrichsthalii. Foraging behavior of male euglossines should allow for more long-distance pollen flow whereas stingless bees are likely to promote near-neighbor and geitonogamous pollinations. We discuss why the prolonged male phase of anthesis in this protogynous species may be maintained through pollination by stingless bees rather than male euglossines. Furthermore, although the floral fragrance is attractive to many species of male euglossines, it attracts few individuals. This condition may represent an intermediate step in the evolution of predominant pollination by male euglossines.     

Solitary and social bees as pollinators of Wahlenbergia (Campanulaceae): single-visit effectiveness, overnight sheltering and responses to flower colour

Solitary bees often form specialised mutualisms with particular plant species, while honeybees are considered to be relatively opportunistic foragers. Thus, it may be expected that solitary bees are more effective pollinators than honeybees when foraging on the same floral resource. To test this, we studied two Wahlenbergia species (Campanulaceae) in South Africa that are visited by both social honeybees and solitary bees, and which are shown here to be genetically self-incompatible and thus reliant on pollinator visits for seed production. Contrary to expectation, the solitary bee Lipotriches sp. (Halictidae) and social bee Apis mellifera (Apidae), which were the two most frequent visitors to flowers of the study species, were equally effective pollinators in terms of the consequences of single visits for fruit and seed set. Both bee species preferentially visited female phase flowers, which contain more nectar than male phase flowers. Male solitary bees of several genera frequently shelter overnight in flowers of both Wahlenbergia species, but temporal exclusion experiments showed that this behaviour makes little contribution to either seed production or pollen dispersal (estimated using a dye particle analogue). Manipulation of flower colour using a sunscreen that removed UV reflectance strongly reduced visits by both bee groups, while neither group responded to Wahlenbergia floral odour cues in choice tests. This study indicates that while flowers of Wahlenbergia cuspidata and W. krebsii are pollinated exclusively by bees, they are not under strong selection to specialise for pollination by any particular group of bees.     

Anthecology ofSchrankia nuttallii (Mimosaceae) on the tallgrass prairie

Schrankia nuttalii flowers through late spring on the tallgrass prairie. Although each stem produces an average of 26 capitate inflorescences only 12% of those inflorescences will open each day to disperse and receive polyads. Each inflorescence may live up to 48 hours but anthers abscise by late afternoon on the first day and the filaments change color and lose their scent. The 78–93 florets comprising each inflorescence open synchronously before dawn or during early morning hours. First day inflorescences ofS. nuttallii are herkogamous and fragrant. They are nectarless. Bombyliid flies and male bees are infrequent floral foragers so the major pollinators include female bees representing five families;Anthophoridae, Apidae, Colletidae, Halictidae, andMegachilidae. All foraging insects ignore second day inflorescences although stigmas are still receptive. Although 97% of all bees collected onS. nuttallii carrySchrankia polyads in their scopae or corbiculae 59% also carry the pollen/pollinaria of one or more coblooming angiosperms. At least 98% of all bees carrying mixed pollen loads incorporate the pollen/pollinaria of one or more nectariferous taxa (e.g.Asclepias spp.,Asteraceae, Convolvulaceae, Delphinium spec., etc.). Species of halictid bees are more likely to carry pure loads ofS. nuttallii polyads (70%) than bees of the four remaining families. Due to the nectarless florets and high degree of polylectic foraging bee-pollination inS. nuttallii converges more closely with the pollination systems of some AustralianAcacia spp. than with most other xeric/tropical genera of mimosoids studied in the western hemisphere.     

A comparison of floral resource exploitation by native and invasive Argentine ants

Ants are often considered antagonists when they visit flowers because they typically steal nectar without providing pollination services. Previous research on ant–flower interactions on two species of South African Proteaceae in the Cape Floral Kingdom revealed that the invasive Argentine ant (Linepithema humile), but not native ants, displace other floral arthropod visitors. To determine how common Argentine ant use of inflorescences is, how Argentine and native ant visits differ in the numbers they recruit to inflorescences, and what factors may affect Argentine and native ant foraging in inflorescences, I surveyed 723 inflorescences in 10 species in the genera Protea and Leucospermum across 16 sites and compared ant presence and abundance in inflorescences with abundance at nearby cat food and jam baits. Argentine ants were the most commonly encountered ant of the 22 observed. Argentine ants, as well as six species of native ants were present in all inflorescences for which they were present at nearby baits. Mean Argentine ant abundance per inflorescence was 4.4 ± 0.84 (SE) ants and similar to that of Anoplolepis custodiens and Crematogaster peringueyi, but higher than observed for the other most commonly encountered native ants, Camponotus niveosetosus and Lepisiota capensis. Both Argentine ants and A. custodiens were more likely to be found foraging in spring and under humid conditions, and in inflorescences closer to the ground, with lower sucrose concentrations, and with a greater proportion of open flowers. Argentine ants were more likely to be found in Protea inflorescences, whereas A. custodiens and L. capensis more often visited Leucospermum inflorescences. Considering its displacement of floral arthropods and widespread use of Proteaceae inflorescences, the Argentine ant could be posing a serious threat to plant and pollinator conservation in this biodiversity hotspot.