Comparison of insecticidal paint and deltamethrin against Triatoma infestans (Hemiptera: Reduviidae) feeding and mortality in simulated natural conditions

The vector of Chagas disease, Triatoma infestans, is largely controlled by the household application of pyrethroid insecticides. Because effective, large‐scale insecticide application is costly and necessitates numerous trained personnel, alternative control techniques are badly needed. We compared the residual effect of organophosphate‐based insecticidal paint (Inesfly 5A IGR? (I5A)) to standard deltamethrin, and a negative control, against T. infestans in a simulated natural environment. We evaluated mortality, knockdown, and ability to take a blood meal among 5^th instar nymphs. I5A paint caused significantly greater mortality at time points up to nine months compared to deltamethrin (Fisher's Exact Test, p < 0.01 in all instances). A year following application, mortality among nymphs in the I5A was similar to those in the deltamethrin (χ2 = 0.76, df=1, p < 0.76). At months 0 and 1 after application, fewer nymphs exposed to deltamethrin took a blood meal compared to insects exposed to paint (Fisher's Exact Tests, p < 0.01 and p < 0.01, respectively). Insecticidal paint may provide an easily‐applied means of protection against vectors of Chagas disease.     

Influence of native ants on arthropod communities in a vineyard

• 1 Ants can have a range of effects on arthropods in crops, including suppressing herbivores such as caterpillars. However, ants can also increase hemipteran densities while reducing natural enemy numbers. In vineyard ecosystem, the effects of native ants and their interactions with other arthropods are poorly understood.
• 2 An ant‐exclusion experiment was designed to test the impact of native ants on both canopy and ground arthropods concurrently. The potential influence of ants on predation and parasitism of light brown apple moth (LBAM) eggs, a grape pest, was also examined. Adult grapevine scale insects and earwigs under bark were counted after a season of ant‐exclusion.
• 3 Among 23 ground ant species collected, six were found to forage in the canopy, with two Iridomyrmex species being the most commonly encountered.
• 4 There was no difference in the abundance of most arthropod orders and feeding groups between ant‐excluded and control vines, although ground spiders were more abundant under ant‐excluded vines, despite increased ground ant foraging pressure. LBAM egg parasitism and predation were low and probably affected by weather and other arthropods. Ant exclusion did not reduce survival of scale insects, although the distribution and abundance of scale insects were negatively associated with earwigs.
• 5 In conclusion, native ants did not consistently suppress arthropod assemblages, including natural enemies, and they did not promote the survival of scale insects. Interactions among native ant species within a vineyard might minimize their effects on other arthropods, although this needs further study.

     

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.     

Spatio‐temporal patterns and interactions with honeydew‐producing Hemiptera of ants in a Mediterranean citrus orchard

• 1 The role of ants in the citrus agro‐ecosystem is controversial and understanding their ecology may help to clarify their function. The present study determined the daily and seasonal foraging patterns, the spatial distribution, the feeding sources and the associations with honeydew‐producing Hemiptera of three ant species that forage in citrus canopies.
• 2 The dominant ants Pheidole pallidula (Nylander) (Myrmicinae) and Lasius grandis Forel (Formicinae) foraged in mutually exclusive territories within the field, although they both shared their territory with the subordinate Plagiolepis schmitzii Forel (Formicinae), a distribution pattern known as ‘ant mosaic’.
• 3 The observed mean overlap for the spatial distribution was significantly lower than the generated by null models, providing strong evidence of spatial interspecific competition, especially between the two dominants.
• 4 Ants ascended to the canopies from April until November. Colony nutritional requirements and temperature probably shape their seasonal foraging patterns. The daily activity pattern of P. schmitzii was strictly diurnal, whereas L. grandis and P. pallidula were active during the entire day.
• 5 The ants' diet in the canopies consisted principally of hemipteran honeydew, whereas citrus nectar and predation/scavenging did not represent important food sources. More than 60% of the total honeydew sources and 100% of the citrus mealybug Planococcus citri colonies were tended by ants during spring and summer.

     

The effects of the invasive Argentine ant (Linepithema humile) and the native ant Prenolepis imparis on the structure of insect herbivore communities on willow trees (Salix lasiolepis)

Abstract 1. We examined the relative effects of the invasive Argentine ant, Linepithema humile, and a common native ant, Prenolepis imparis, on the community of herbivorous insects occurring on willow trees, Salix lasiolepis in Northern California, U.S.A. 2. Using paired control and treatment branches from which we excluded ants and other non‐volant predators, we found that effects of Argentine ants on the herbivore community were generally similar to those of P. imparis. Argentine ants and P. imparis suppressed the damage by skeletonising insects by 50%, but had little effect on most other external‐feeding or internal‐feeding guilds. 3. The abundance of aphids was 100% greater in the presence of Argentine ants, but there was no effect on aphid numbers in the presence of P. imparis. Late season aphid numbers were substantially higher in the presence of Argentine ants, but not P. imparis. 4. The effects of Argentine ants on skeletonising insects and aphids combined with the overwhelming abundance of Argentine ant workers, suggests that they may have substantial, but often overlooked, effects on the herbivore communities on other plant species in or near riparian habitats in which they invade.     

Attractiveness of bait matrices and matrix/toxicant combinations to the citrus pests Iridomyrmex purpureus (F.Smith) and Iridomyrmex rufoniger gp sp. (Hym., Formicidae)

Abstract: Six bait matrices were tested for palatability to the ants Iridomyrmex purpureus and I. rufoniger gp sp., which are important pests of citrus in south‐eastern Australia. Granulated citrus pulp and rice bran impregnated with brown sugar were not accepted by either species, but ground dry dog food and ground insects (with or without added sugar) were highly attractive to both ant species. The ground dog food was impregnated with various toxicants at concentrations of up to 1% (w/w) and tested for palatability to both ant species. Technical grade pyriproxyfen, fipronil, and fenoxycarb were incorporated using organic solvents, whereas formulated fenoxycarb (Insegar^®) was incorporated as an aqueous suspension prior to drying and granulation. Relative to the blank samples (carrier solvents only), bait acceptance by I. purpureus was not significantly reduced (P > 0.05) by any of the treatments except 1% technical fenoxycarb. Bait acceptance by I. rufoniger gp sp. was significantly suppressed by 0.2% fipronil, but not by higher concentrations. When water was used as the carrier solvent the blank sample was significantly (P < 0.05) less attractive to I. purpureus than the untreated control, suggesting that wetting of dog food‐based baits in field situations may irreversibly reduce their attractiveness. Laboratory colonies were used in choice and no‐choice tests to assess the efficacy of dog food baits containing fipronil (0.05–0.2% w/w). The corrected mortality for I. purpureus ranged from 88 to 100% and from 90 to 97% in the no‐choice and choice tests, respectively. In no‐choice tests I. rufoniger gp sp. corrected mortality varied from 52 to 60%, but in choice tests the corrected mortality did not exceed 26%. Ground dog food containing fipronil (0.05–0.2% w/w) has the potential to provide effective control of I. purpureus in citrus orchards, but alternative toxicants or lower fipronil concentrations may be required for control of I. rufoniger gp sp.     

Ecological effects of multi‐species,ant–hemipteran mutualisms in citrus

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Efficacy of aqueous and oil formulations of a specific Metarhizium anisopliae isolate against Aphis craccivora Koch, 1854 (Hemiptera: Aphididae) under field conditions

Cowpea (Vigna unguiculata) production is constrained by biotic and abiotic factors, among which Cowpea aphid (Aphis craccivora) is ranked a key insect pest that severely limits its potential for provision of food and nutritional security to millions of people in sub‐Saharan Africa. The use of entomopathogenic fungi for A. craccivora management has been recently demonstrated at laboratory and field levels as alternative to synthetic insecticides, but with low adoption in Africa. This study assessed the efficacy of aqueous and oil formulations of Metarhizium anisopliae ICIPE 62 against A. craccivora under field conditions. Metarhizium anisopliae formulations and a commonly used insecticide Duduthrin^® were applied using knapsack sprayers with target output of 350 L/ha. Data on aphid infestation levels were collected weekly. ICIPE 62 efficacy in inducing mortality was also assessed 24 hr post‐treatment coupled with mycosis test. Further, leaf and grain yields were determined. After six weeks post‐treatment in the wet season, there was no significant reduction in aphid density in fungus‐treated plots compared to control and Duduthrin^®‐treated plots. However, in the dry season six weeks after applying the treatments, oil formulation spray resulted low aphid density compared to control and Duduthrin^®‐treated plots. ICIPE 62 formulations did not negatively affect the natural enemies’ population. Leaf yield from the various treatments did not differ significantly in the wet season, but the two fungal formulations recorded higher yields in dry season compared to other treatments. Grain yields in wet and dry seasons were lower in control and Duduthrin^®‐treated plots compared to both ICIPE 62 formulations. This study showed that both M. anisopliae ICIPE 62 formulations are effective in suppressing A. craccivora population under field conditions without adverse effects on its beneficial insects. The study also revealed that efficacy of fungal‐based biopesticides is highly dependent on environmental conditions.     

Effects of prey aphid species on the abundance of a parasitoid and two predator species in aphid colonies attended by ants on citrus

This study focused on three species of enemies, the parasitoid wasp Lysiphlebus japonicus Ashmead (Hymenoptera: Aphidiidae), the ladybird Scymnus posticalis Sicard (Coleoptera: Coccinellidae) and the predatory gall midge Aphidoletes aphidimyza (Rondani) (Diptera: Cecidomyiidae), all of which are able to exploit aphids attended by ants. I experimentally evaluated the effects of prey aphid species on the abundance of each of the three enemy species in ant‐attended aphid colonies on citrus. The aphids compared were Aphis gossypii Glover versus Aphis spiraecola Patch in late spring, and Toxoptera citricidus (Kirkaldy) versus A. spiraecola in late summer (all, Hemiptera: Aphididae). Colonies of the three aphid species were attended by the ant Pristomyrmex punctatus Smith (Hymenoptera: Formicidae). The initial number of attending ants per individual aphid did not differ significantly between the colonies of the two aphid species compared in each season. Between A. gossypii and A. spiraecola, there was no significant difference in the number of mummies formed by the parasitoid or foraging larvae of each of the two predators per aphid colony. A significant difference was detected between T. citricidus and A. spiraecola for each of the three enemy species, with a far greater number of L. japonicus mummies in T. citricidus colonies and distinctly more larvae of each of the two predators in A. spiraecola colonies. Thus, the abundance of each of the three enemy species in ant‐attended aphid colonies was significantly influenced by the species of the prey aphids, with the three enemies showing different responses to the three aphid species.     

Stable isotopes analysis to assess the trophic role of ants in a Mediterranean agroecosystem

1 Stable isotopes signatures (δ¹³C and δ¹⁵N) of the most important tree‐dwelling ants in an olive orchard were examined, together with the signatures of the most common herbivores, predators and sap‐sucking insects. The olive orchard consists of separate subunits (trees) surrounded by a matrix of grasses or bare ground, and the role of ants in such a system is not fully understood. 2 None of the selected ant species was exclusive to the olive trees because they were also observed foraging on vegetation (mainly thistle) under the tree crowns. Hence, the relative contributions of these two sources of energy (olive trees versus herbs/grasses) were assessed by comparing the δ¹³C of ants with the signatures of plants and those of other arthropods collected on the trees and on nearby thistles. Next, the trophic level occupied by the ants and their ecological role within the olive food web were determined by examining the δ¹⁵N values and their relationship with indices of ecological performance measuring the potential pressure exerted by each species on the ecosystem. 3 The analysis of ¹³C signatures revealed a different contribution of the two energy sources, olive trees versus herbs and grasses, with the former being more important for ants. The analysis of ¹⁵N signatures suggested separate roles for different ant species: some (Crematogaster scutellaris, Lasius lasioides) occupied a higher trophic level, mostly involved in predation, whereas others (Camponotus piceus, Camponotus lateralis) occupied a lower level, probably involved more in homopteran tending. A fifth species (Camponotus aethiops) was in an intermediate position. Finally, the δ¹⁵N levels of the species were significantly correlated with indices of ecological performance.     

Phylogenetic patterns of ant–fungus associations indicate that farming strategies,not only a superior fungal cultivar,explain the ecological success of leafcutter ants

To elucidate fungicultural specializations contributing to ecological dominance of leafcutter ants, we estimate the phylogeny of fungi cultivated by fungus‐growing (attine) ants, including fungal cultivars from (i) the entire leafcutter range from southern South America to southern North America, (ii) all higher‐attine ant lineages (leafcutting genera Atta, Acromyrmex; nonleafcutting genera Trachymyrmex, Sericomyrmex) and (iii) all lower‐attine lineages. Higher‐attine fungi form two clades, Clade‐A fungi (Leucocoprinus gongylophorus, formerly Attamyces) previously thought to be cultivated only by leafcutter ants, and a sister clade, Clade‐B fungi, previously thought to be cultivated only by Trachymyrmex and Sericomyrmex ants. Contradicting this traditional view, we find that (i) leafcutter ants are not specialized to cultivate only Clade‐A fungi because some leafcutter species ranging across South America cultivate Clade‐B fungi; (ii) Trachymyrmex ants are not specialized to cultivate only Clade‐B fungi because some Trachymyrmex species cultivate Clade‐A fungi and other Trachymyrmex species cultivate fungi known so far only from lower‐attine ants; (iii) in some locations, single higher‐attine ant species or closely related cryptic species cultivate both Clade‐A and Clade‐B fungi; and (iv) ant–fungus co‐evolution among higher‐attine mutualisms is therefore less specialized than previously thought. Sympatric leafcutter ants can be ecologically dominant when cultivating either Clade‐A or Clade‐B fungi, sustaining with either cultivar‐type huge nests that command large foraging territories; conversely, sympatric Trachymyrmex ants cultivating either Clade‐A or Clade‐B fungi can be locally abundant without achieving the ecological dominance of leafcutter ants. Ecological dominance of leafcutter ants therefore does not depend primarily on specialized fungiculture of L. gongylophorus (Clade‐A), but must derive from ant–fungus synergisms and unique ant adaptations.     

Association between the African lycaenid,Anthene usamba,and an obligate acacia ant,Crematogaster mimosae

The African lycaenid butterfly, Anthene usamba, is an obligate myrmecophile of the acacia ant, Crematogaster mimosae. Female butterflies use the presence of C. mimosae as an oviposition cue. The eggs are laid on the foliage and young branches of the host plant, Acacia drepanolobium. Larvae shelter in the swollen thorns (domatia) of the host tree, where they live in close association with the acacia ants, and each larva occupies a domatium singly. Anthene usamba are tended by ants that feed from the dorsal nectary organ at regular intervals. Larvae also possess tentacle organs flanking the dorsal nectary organ and appear to signal to ants by everting these structures. Larvae were observed to spend most of their time within the domatia. Stable isotope analysis of matched host plant–ant–butterfly samples revealed that Anthene usamba are δ¹⁵N enriched relative to the ants with which they associate. These data, based on the increase in δ¹⁵N through trophic levels, indicate that the caterpillars of these butterflies are aphytophagous and either exploit the ant brood of C. mimosae within the domatia, or are fed mouth to mouth by adult workers via trophallaxis. This is the first documented case of aphytophagy in African Anthene. Pupation occurs inside the domatium and the imago emerges and departs via the hole chewed by the larva. The adult females remain closely associated with their natal patch of trees, whereas males disperse more widely across the acacia savannah. Females prefer to oviposit on trees with the specific host ant, C. mimosae, an aggressive obligate mutualist, and avoid neighbouring trees with other ant species. Adult butterflies are active during most months of the year, and there are at least two to three generations each year. Observations made over a 5‐year period indicate that a number of different lycaenid species utilize ant‐acacias in East Africa, and these observations are summarized, together with comparisons from the literature. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013 , 109 , 302–312.     

Two ways to be a myrmecophilous butterfly: natural history and comparative immature‐stage morphology of two species of Theope (Lepidoptera: Riodinidae)

Symbiotic interactions between butterfly larvae and ants, termed myrmecophily, require a range of behavioural and morphological adaptations (ant‐organs). Here, using light and scanning electron microscopy, we describe the complete life cycle of two species of Theope (Lepidoptera: Riodinidae) that have contrasting ways of life. Theope thestias larvae are facultatively tended by several ant species, whereas Theope pieridoides have obligate symbiotic interactions with Azteca ants that inhabit a myrmecophytic tree. Morphological differences associated with their different degrees of intimacy with tending ants are visible from hatching. In T. thestias, the untended first‐instar larva has elongated bifurcated setae and a few tiny perforated cupola organs (PCOs), whereas in T. pieridoides, the ant‐tended first instar has short dendritic setae, larger and more numerous PCOs, and functional tentacle nectary organs (TNOs). Throughout ontogeny, T. pieridoides always shows more conspicuous ant‐organs than T. thestias, with the exception of balloon setae, which are larger and more numerous in T. thestias. In addition, mature T. pieridoides larvae have an anterior set of ant‐organs, including a new type, here described and termed anterior glandular openings (AGOs). Based on the behavioural responses of ants in contact with these structures, a new interpretation for the mechanism whereby Theope larvae can manipulate the behaviour of their tending ants is proposed. Until now, three ecological syndromes can be defined among Theope species: (1) oligophagous larvae with facultative myrmecophily; (2) monophagous larvae with obligate myrmecophily; and (3) polyphagous larvae with obligate myrmecophily. These results suggest that differences in the degree of specificity in the ant–plant interactions may have an important role in the evolution of host‐plant use in Theope. © 2013 The Linnean Society of London     

The effect of ant attendance on the success of rosy apple aphid populations, natural enemy abundance and apple damage in orchards

1 The rosy apple aphid, Dysaphis plantaginea, is the most serious pest of apple in Europe and, although conventionally controlled by insecticides, alternative management measures are being sought. Colonies of D. plantaginea are commonly attended by ants, yet the effects of this relationship have received little attention. 2 An ant exclusion study was conducted in two distant orchards within the U.K. At both sites, ants were excluded from a subset of D. plantaginea infested trees at the beginning of the season and populations were monitored. The number of natural enemies observed on trees was also recorded and, before harvest, the percentage of apples damaged by D. plantaginea calculated. 3 Overall, the exclusion of ants reduced the growth and eventual size of D. plantaginea populations. On trees accessed by ants, greater numbers of natural enemies were recorded, presumably because aphid populations were often greater on such trees. However, this increased natural enemy presence was diluted by the larger aphid populations such that individual aphids on ant‐attended trees were subjected to a lower natural enemy pressure compared with those on ant‐excluded trees. 4 At harvest, apple trees that had been accessed by ants bore a greater proportion of apples damaged by D. plantaginea. There were also differences in cultivar susceptibility to D. plantaginea damage. 5 The present study highlights the importance of the ant–D. plantaginea relationship and it ia suggested that ant manipulation, whether physically or by semiochemicals that disrupt the relationship, should be considered as a more prominent component in the development of future integrated pest management strategies.     

Experimental suppression of ants foraging on rainforest vegetation in New Guinea: testing methods for a whole‐forest manipulation of insect communities

1. Ants are extremely abundant in lowland tropical forests where they are important predators, plant mutualists, and herbivores. Their complex role in tropical plant–insect food webs can be best assessed by experimental manipulation of their abundance. Historically, ant exclusion experiments have had a small‐scale focus, such as single trees. Here, we test a new ‘whole‐forest' method of ant exclusion, using treated canopy bait stations, in a diverse tropical rainforest in New Guinea. 2. We conducted a 10‐month manipulative experiment in primary and secondary rainforests. In each forest type, a 625 m² treatment plot was isolated from the surrounding forest and 135 bait stations treated with fipronil, S‐methoprene, and hydramethylnon were placed in trees to suppress ants. Ant activity was monitored in the forest canopy and understorey with an additional 65 stations in treatment and control plots. 3. We achieved a dramatic decline in ant abundance in treatment plots compared with controls in both forest types, with an average decrease in ant numbers per station of 82.4% in primary and 91.2% in secondary forest. In particular, native dominant species Oecophylla smaragdina, Anonychomyrma cf. scrutator in primary forest, and invasive Anoplolepis gracilipes in secondary forest were greatly affected. In contrast, Tapinoma melanocephalum flourished in treatment plots, perhaps benefiting from reduced competition from other ant species. 4. Our study demonstrates that it is possible to selectively eradicate most of the foraging ants in a structurally complex tropical forest. We propose whole‐forest manipulation as a novel tool for studying the role of ants in shaping plant–insect food webs.     

Out of the Frying Pan and into the Fire: a Novel Trade-Off for Batesian Mimics

A mimicry system was investigated in which the models were ants (Formicidae) and both the mimics and the predators were jumping spiders (Salticidae). By using motionless lures in simultaneous‐presentation prey‐choice tests, how the predators respond specifically to the static appearance of ants and ant mimics was determined. These findings suggest a rarely considered adaptive trade‐off for Batesian mimics of ants. Mimicry may be advantageous when it deceives ant‐averse potential predators, but disadvantageous in encounters with ant‐eating specialists. Nine myrmecophagic (ant‐eating) species (from Africa, Asia, Australia and North America) and one araneophagic (spider‐eating) species (Portia fimbriata from Queensland) were tested with ants (five species), with myrmecomorphic (ant‐like) salticids (six species of Myrmarachne) and with non‐ant‐like prey (dipterans and ordinary salticids). The araneophagic salticid chose an ordinary salticid and chose flies significantly more often than ants. Portia fimbriata also chose the ordinary salticid and chose flies significantly more often than myrmecomorphic salticids. However, there was no significant difference in how P. fimbriata responded to ants and to myrmecomorphic salticids. The myrmecophagic salticids chose ants and chose myrmecomorphic salticids significantly more often than ordinary salticids and significantly more often than flies, but myrmecophagic salticids did not respond significantly differently to myrmecomorphic salticids and ants.     

Impacts of the invasive Argentine ant on native ants and other invertebrates in coastal scrub in south‐eastern Australia

Invasive ants threaten native biodiversity and ecosystem function worldwide. Although their principal direct impact is usually the displacement of native ants, they may also affect other invertebrates. The Argentine ant, Linepithema humile (Dolichoderinae), one of the most widespread invasive ant species, has invaded native habitat where it abuts peri‐urban development in coastal Victoria in south‐eastern Australia. Here we infer impacts of the Argentine ant on native ants and other litter and ground‐dwelling invertebrates by comparing their abundance and taxonomic composition in coastal scrub forest either invaded or uninvaded by the Argentine ant. Species composition of native ants at bait stations and extracted from litter differed significantly between Argentine ant‐invaded and uninvaded sites and this was consistent across years. Argentine ants had a strong effect on epigeic ants, which were either displaced or reduced in abundance. The native ant Rhytidoponera victoriae (Ponerinae), numerically dominant at uninvaded sites, was completely absent from sites invaded by the Argentine ant. However, small hypogeic ants, including Solenopsis sp. (Myrmicinae) and Heteroponera imbellis (Heteroponerinae), were little affected. Linepithema humile had no detectable effect upon the abundance and richness of other litter invertebrates. However, invertebrate group composition differed significantly between invaded and uninvaded sites, owing to the varied response of several influential groups (e.g. Collembola and Acarina). Floristics, habitat structure and measured environmental factors did not differ significantly between sites either invaded or uninvaded by Argentine ants, supporting the contention that differences in native ant abundance and species composition are related to invasion. Changes in the native ant community wrought by Argentine ant invasion have important implications for invertebrate communities in southern Australia and may affect key processes, including seed dispersal.     

Elevated dominance of extrafloral nectary-bearing plants is associated with increased abundances of an invasive ant and reduced native ant richness

Aim Invasive ants can have substantial and detrimental effects on co‐occurring community members, especially other ants. However, the ecological factors that promote both their population growth and their negative influences remain elusive. Opportunistic associations between invasive ants and extrafloral nectary (EFN)‐bearing plants are common and may fuel population expansion and subsequent impacts of invasive ants on native communities. We examined three predictions of this hypothesis, compared ant assemblages between invaded and uninvaded sites and assessed the extent of this species in Samoa. Location The Samoan Archipelago (six islands and 35 sites). Methods We surveyed abundances of the invasive ant Anoplolepis gracilipes, other ant species and EFN‐bearing plants. Results Anoplolepis gracilipes was significantly more widely distributed in 2006 than in 1962, suggesting that the invasion of A. gracilipes in Samoa has progressed. Furthermore, (non‐A. gracilipes) ant assemblages differed significantly between invaded and uninvaded sites. Anoplolepis gracilipes workers were found more frequently at nectaries than other plant parts, suggesting that nectar resources were important to this species. There was a strong, positive relationship between the dominance of EFN‐bearing plants in the community and A. gracilipes abundance on plants, a relationship that co‐occurring ants did not display. High abundances of A. gracilipes at sites dominated by EFN‐bearing plants were associated with low species richness of native plant‐visiting ant species. Anoplolepis gracilipes did not display any significant relationships with the diversity of other non‐native ants. Main conclusions Together, these data suggest that EFN‐bearing plants may promote negative impacts of A. gracilipes on co‐occurring ants across broad spatial scales. This study underscores the potential importance of positive interactions in the dynamics of species invasions. Furthermore, they suggest that conservation managers may benefit from explicit considerations of potential positive interactions in predicting the identities of problematic invaders or the outcomes of species invasions.     

The seasonal dynamic of ant‐flower networks in a semi‐arid tropical environment

1. Several studies have recently focused on the structure of ecological networks involving ants and plants with extrafloral nectaries; however, little is known about the effects of temporal variation in resource abundance on the structure of ant–plant networks mediated by floral nectar. 2. In this study, it was evaluated how strong seasonality in resource availability in a semi‐arid tropical environment affects the structure of ant–flower networks. We recorded ants collecting floral nectar during two seasons (from December 2009 to January 2013): dry and green seasons. Then, we built interaction networks for flower‐visiting ants in the Brazilian Caatinga separately for each combination of transect and season. 3. In general, strong seasonality directly influenced patterns of ant–flower interactions and the overall complexity of these ecological networks. During the dry season, networks were more connected, less modular, and exhibited greater niche overlap of flower‐visiting ants than during the green season. Moreover, resource utilisation by ants during the dry season tended to be more aggregated. These findings indicate that during the dry season, ant species tended to share many resource bases, probably owing to lower overall resource availability during this season. Species composition of the ant network component was highly season specific; however, a central core of highly generalised ants was present during both seasons. 4. The stability of this central core between seasons could strongly affect the ecological and evolutionary dynamics of these interaction networks. This study contributes to the understanding of the structure and dynamics of ant‐flower interactions in extremely seasonal environments.