Herbivory and assemblage structure of myrmecophytous understory plants and their associated ants in the central Amazon

Summary The species combinations of myrmecophytic plants were compared in three different, neighboring local central Amazon forest sites. The proportional contribution of myrmecophytes in each setting varied significantly, withMaieta guainensis being the most abundant in each locality. This pattern resulted in low site similarity values. Other recorded species wereHirtella physophora, Tachigalia myrmecophila, Duroia sp.,Tococa sp., andCordia nodosa. Little variability was found with respect to associated ants that inhabited the myrmecophytes, and mutual entropies indicated a high degree of mutualistic interactions. However, for the majority of myrmecophytes, no differences in herbivore damage levels could be attributed to the presence of ants, with onlyM. guianensis andT. myrmecophila demonstrating significantly lower damages when inhabited by ants. Their respective ant associates,Pheidole minitula andPseudomyrmex concolor, were thus the only plant-ants with a demonstrable ability to reduce the levels of herbivory in their host plant.     

The indestructible insect: Velvet ants from across the United States avoid predation by representatives from all major tetrapod clades

Velvet ants are a group of parasitic wasps that are well known for a suite of defensive adaptations including bright coloration and a formidable sting. While these adaptations are presumed to function in antipredator defense, observations between potential predators and this group are lacking. We conducted a series of experiments to determine the risk of velvet ants to a host of potential predators including amphibians, reptiles, birds, and small mammals. Velvet ants from across the United States were tested with predator's representative of the velvet ants native range. All interactions between lizards, free‐ranging birds, and a mole resulted in the velvet ants survival, and ultimate avoidance by the predator. Two shrews did injure a velvet ant, but this occurred only after multiple failed attacks. The only predator to successfully consume a velvet ant was a single American toad (Anaxyrus americanus). These results indicate that the suite of defenses possessed by velvet ants, including aposematic coloration, stridulations, a chemical alarm signal, a hard exoskeleton, and powerful sting are effective defenses against potential predators. Female velvet ants appear to be nearly impervious to predation by many species whose diet is heavily derived of invertebrate prey.     

Variation in Butterfly Larval Acoustics as a Strategy to Infiltrate and Exploit Host Ant Colony Resources

About 10,000 arthropods live as ants'' social parasites and have evolved a number of mechanisms allowing them to penetrate and survive inside the ant nests. Many of them can intercept and manipulate their host communication systems. This is particularly important for butterflies of the genus Maculinea, which spend the majority of their lifecycle inside Myrmica ant nests. Once in the colony, caterpillars of Maculinea “predatory species” directly feed on the ant larvae, while those of “cuckoo species” are fed primarily by attendance workers, by trophallaxis. It has been shown that Maculinea cuckoo larvae are able to reach a higher social status within the colony''s hierarchy by mimicking the acoustic signals of their host queen ants. In this research we tested if, when and how myrmecophilous butterflies may change sound emissions depending on their integration level and on stages of their life cycle. We studied how a Maculinea predatory species (M. teleius) can acoustically interact with their host ants and highlighted differences with respect to a cuckoo species (M. alcon). We recorded sounds emitted by Maculinea larvae as well as by their Myrmica hosts, and performed playback experiments to assess the parasites'' capacity to interfere with the host acoustic communication system. We found that, although varying between and within butterfly species, the larval acoustic emissions are more similar to queens'' than to workers'' stridulations. Nevertheless playback experiments showed that ant workers responded most strongly to the sounds emitted by the integrated (i.e. post-adoption) larvae of the cuckoo species, as well as by those of predatory species recorded before any contact with the host ants (i.e. in pre-adoption), thereby revealing the role of acoustic signals both in parasite integration and in adoption rituals. We discuss our findings in the broader context of parasite adaptations, comparing effects of acoustical and chemical mimicry.     

Seed removal decrease by invasive Argentine ants in a high Nature Value farmland

Seed dispersal by ants is an important ecological process that maintains the structure anddiversity of natural communities, however, it is vulnerable to biological invasions. Argentine ants are one of the worst invasive ant species and cause severe changes in ecosystem processes and native ant biodiversity declines in invaded sites. Here, we studied seed removal by ants combining observations and a cafeteria experiment with seeds of four myrmecochorous plant species (Centaurea sphaerocephala, Rosmarinus officinalis, Silybum marianum, and Ulex australis) in two sites (invaded and uninvaded) located in the Mediterranean Montado ecosystem and classified as High Nature Value farmland (HNV). Significant differences in daily seed removal rates were found between the two study sites. In uninvaded sites, several native ant species were attracted to the seeds, resulting in all seeds being removed rapidly. The majority of seed removal events were carried out by two key seed disperses Pheidole pallidula (71%) and Aphaenogaster iberica (26%) with a clear preference for diaspored with larger and heavier elaiosome (i.e., C. sphaerocephala, S. marianum). By contrast, while the Argentine ant showed some interest (68% of seeds were interacted with), no seed removal events were observed. The extirpation of the local ant fauna by the Argentine ant and its inability to ensure seed dispersal services may lead to the interference and eventually to the collapse of seed dispersal of the four studied myrmecochorous plants in the invaded site in the future. We argue that these discrete but severe consequences of an invasive species on a key ecological process may strongly affect the functioning of the Montado ecosystem.     

Run,robber, run: parasitic acacia ants use speed and evasion to steal food from ant‐defended trees

Ants that are obligate plant associates protect their host against herbivores and aggressively defend the resources offered by the plant. Workers of Pseudomyrmex nigropilosus Emery (Hymenoptera: Formicidae), an acacia ant that parasitizes the mutualism by not defending the tree, are seen stealing food from other ant‐defended acacia trees. In the present study, hypotheses of evasion, chemical crypsis, chemical repellence and temporal activity patterns are tested in the field aiming to determine how P. nigropilosus enters other acacia trees, successfully circumventing the defence of the resident ants. When parasitic ants are stealing, resident ants are evaded by stopping walking, changing their walking direction or walking faster. Resident and parasitic workers have similar temporal activity patterns. Parasitic workers can walk 2.6‐fold faster compared with any of the three species of acacia‐ants from which they usually steal food. Behavioural assays suggest that P. nigropilosus do not have chemical repellence but that chemical crypsis may be involved in the evasion strategy. This last hypothesis needs to be explored further by chemical and olfactory analyses. The combination of speed and evasive reactions allows parasitic ants to access well‐defended acacia trees.     

Disruption of parasitism of the California red scale (Homoptera: Diaspididae) by three ant species (Hymenoptera: Formicidae)

The relative influence of the southern fire ant, Solenopsis xyloni McCook, Argentine ant, Linepithema humile (Mayr), and native gray ant, Formica aerata (Francoeur), on parasitism of California red scale, Aonidiella aurantii Maskell, was studied in the laboratory for two parasitoids, Comperiella bifasciata Howard and Aphytis melinus DeBach. All three ant species reduced percentage parasitism by C. bifasciata and both percentage parasitism and host mutilation by A. melinus. Southern fire ant was the least disruptive and native gray ant the most disruptive. Southern fire ant removed 12% of scale from the lemons, presumably to feed on them, while the other ant species did not exhibit significant removal of scale compared to the controls. Percentage parasitism of California red scale exhibited by C. bifasciata was more than 2-fold the level exhibited by A. melinus. Percentage mutilation of California red scale, including probing and host feeding, was nearly 5-fold higher for A. melinus than C. bifasciata. Because A. melinus required a longer total host examination + oviposition period in the absence of ants than C. bifasciata and because oviposition occurs as the last act in a sequence of behaviors, disruption by the ants had a more significant negative effect on oviposition by A. melinus.     

Positive and negative impact to decomposition of pig cadavers by ants (hymenoptera: Formicidae) at the Islet Yeongdo in Busan,South Korea

We observed how ants affected the decomposition process of pig cadavers. Experiments were carried out with six pig cadavers during three seasons without winter. Fifteen ant species belonging to 14 genera 3 subfamilies were recorded from pig cadavers. The species richness and species composition of ants were different significantly at bloated and decay stages from the remaining stages, regardless of season. Ant species Nylanderia flavipes, Aphaenogaster japonica, Pheidole fervida, and Ectomomyrmex javanus kept hunting a considerable amount of eggs and maggots of flies in the two stages. In particular, Lasius japonicus continually interrupted landing and ovipositing of flies and removed eggs and maggots from pig cadavers. Our observation suggests that ants may affect decomposition process of dead animals by participating in positive and negative ways by massive removal of eggs and maggots of flies.     

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.

     

Fine structure of the antennal glands of the ant nest beetle Paussus favieri (Coleoptera,Carabidae, Paussini)

The antennae of the ant nest beetle Paussus favieri are studied by using both SEM and TEM. In the myrmecophilous genus Paussus, these structures are composed of three joints: scape, pedicel and a wide third joint, the “antennal club”, resulting from the fusion of antennomeres A3–A11 (flagellum). The antennal club shows an exceptional glandular activity, with the presence of pores mostly crowded in special hairless cuticular areas, surrounding the base of single setae, grouped at the base of tufts of setae, or positioned inside deep pockets that store the secretions, with filiform material arising from them. The surface of A1 and A3 are covered by mechanoreceptors, modified to spread the glandular exudates, while the chemoreceptors are restricted to the apex of the club. The fine structural analysis shows a great number of antennal glands, that can be referred to three main typologies: type A (GhA) bi-cellular, composed of a large secretory cell and a small duct cell, positioned close to the antennal surface; type B (GhB), tri-cellular, composed of two secretory cells and one duct cell, less frequent and positioned deep inside the antennal club; type C (GhC), rare, located deeply within the antennal lumen, in the vicinity of the trophocytes. This complexity indicates that more than one substance could be released from the antennae. Possible functional aspects of the secretions dealing with symbiotic interaction with the host ants are discussed.     

Contents of the poison apparatus of some species of Pheidole ants

Four Old World species of Pheidole ants contain different mixtures of farnesene-type hydrocarbons in their poison apparatus, and the mixture is different between the minor and major workers within a species. A bishomofarnesene (C₁₇H₂₈) provides approximately half of the secretion of the Dufour glands of minor workers of Pheidole pallidula. (Z,E)-α-Farnesene constituted 96% of the Dufour secretion of major workers of P. pallidula, but only 20% of that of minors. The Dufour glands of minor workers of Pheidole sinaitica contain a mixture of farnesene homologues with (Z,E)-α-farnesene and the bishomofarnesene also found in P. pallidula predominant. The mixture in major workers was similar but had, in addition, a small amount of (E)-β-farnesene. The Dufour glands of Pheidole teneriffana minors contain chiefly the same bishomofarnesene found in P. pallidula and P. sinaitica while major workers contain (Z,E)-α-farnesene. Pheidole megacephala minor workers contained small amounts of eight farnesenes, while major workers contained essentially no farnesenes. The poison glands of minor workers of P. pallidula contain 3-ethyl-2,5-dimethylpyrazine. No pyrazine compounds were found in the major workers of P. pallidula or the minor workers of P. sinaitica. The poison glands of the major workers of P. sinaitica contained larger amounts of tetra-substituted pyrazines. No pyrazines were found in the poison reservoirs of major or minor workers of P. teneriffana or P. megacephala.     

Stridulations reveal cryptic speciation in neotropical sympatric ants

The taxonomic challenge posed by cryptic species underlines the importance of using multiple criteria in species delimitation. In the current paper we tested the use of acoustic analysis as a tool to assess the real diversity in a cryptic species complex of Neotropical ants. In order to understand the potential of acoustics and to improve consistency in the conclusions by comparing different approaches, phylogenetic relationships of all the morphs considered were assessed by the analysis of a fragment of the mitochondrial DNA cytochrome b. We observed that each of the cryptic morph studied presents a morphologically distinct stridulatory organ and that all sympatric morphs produce distinctive stridulations. This is the first evidence of such a degree of specialization in the acoustic organ and signals in ants, which suggests that stridulations may be among the cues used by these ants during inter-specific interactions. Mitochondrial DNA variation corroborated the acoustic differences observed, confirming acoustics as a helpful tool to determine cryptic species in this group of ants, and possibly in stridulating ants in general. Congruent morphological, acoustic and genetic results constitute sufficient evidence to propose each morph studied here as a valid new species, suggesting that P. apicalis is a complex of at least 6 to 9 species, even if they present different levels of divergence. Finally, our results highlight that ant stridulations may be much more informative than hitherto thought, as much for ant communication as for integrative taxonomists.     

Evolution of social parasitism in ants

Slave raids of Amazon ants, the beheading of the host colony's queen by a parasitic Bothriomyrmex female, or the protracted throttling of the host queen by an Epimyrma female which has penetrated a Leptothorax nest, are among the most intriguing behaviors to be observed in social parasitic ants. The evolutionary origin of these behaviors, however, is quite obscure, and further work is needed to elucidate how parasitic life cycles could have arisen from the ordinary social organization of ants.     

Host record of the myrmecophilous carabid genus Cryptocephalomorpha (Coleoptera: Carabidae: Pseudomorphinae) with description of a new species from Thailand

Cryptocephalomorpha siamensis sp. nov. is described from Thailand. The type series was collected from a nest of myrmicine ant, Pheidole singaporensis, which is the first exact host record of the genus Cryptocephalomorpha. Collecting circumstances and observed behavior are reported.     

Behavioral differences between two ant cricket species in Nansei Islands: host-specialist versus host-generalist

Ant crickets (Orthoptera, Myrmecophilidae) are typical ant guests that obtain nourishment from the ants in their nests. Some ant crickets are host-specific, whereas other species are host-generalists. We investigated the behavioral polarization between the specialist cricket Myrmecophilus albicinctus and generalist Myrmecophilus formosanus. In the field, M. albicinctus was found exclusively in nests of Anoplolepis gracilipes (185/185), whereas 62 M. formosanus were found in nests of 9 ant species from 3 subfamilies. Behavioral observations revealed that M. albicinctus could not survive in the absence of A. gracilipes and was killed when it was introduced into colonies of non-host ant species. In addition, M. albicinctus showed intimate behavior, such as trophallaxis, with its host. In contrast, M. formosanus swiftly avoided frequent attacks by host ants, independently took food, and survived well in the absence of ants. Overall, the specialist adapted its behavior and physiology to those of a specific ant host, whereas the generalist adopted versatile parasitic behaviors, such as quick movements. Our findings revealed interspecific polarization in the degree of host dependence and inquiline–host interaction, and they indicate that trade-offs occur between specialization to specific hosts and retention of generalization in order to exploit alternative hosts.     

Soldier determination in Pheidole bicarinata: Effect of methoprene on caste and size within castes

Topical application of methoprene to final-instar larvae of the ant Pheidole bicarinata can induce soldier development. Soldier induction takes place if methoprene levels are above a soldier-determining threshold during a critical period of juvenile hormone-sensitivity that occurs during about days 4–6 of the final instar. Furthermore, the amount of exogenous methoprene applied affects the timing of metamorphosis and the adult size in both the minor worker and soldier castes. When larvae that receive methoprene treatment become minor workers these are always larger than acetone-treated controls. In larvae that become soldiers, growth and timing of metamorphosis vary with the dose of methoprene, but in a more complex way. A high dose of methoprene produces a metamorphic delay and large soldiers. However, the lowest effective dose for soldier induction produces early metamorphosis and small adults. On the basis of these results, we have expanded our model of a mechanism by which juvenile hormone could control determination of worker castes in Pheidole bicarinata.     

Strategies of the beetle Oochrotus unicolor (Tenebrionidae) thriving in the waste dumps of seed-harvesting Messor ants (Formicidae)

1. A diverse group of arthropods have adapted to the niches found inside the nests of social insects. Studies mostly focused on very specialised parasites residing in the brood chambers. However, the biology and strategies of symbionts occupying other niches, such as waste dumps, are underexplored. 2. Using a series of complementary experiments, this study demonstrated that the Mediterranean beetle Oochrotus unicolor has adapted to the waste dump niche found in the nests of Messor harvester ants. 3. Laboratory experiments confirmed field observations that the beetle preferentially resided in the refuse pits. Next, it was shown that the beetles readily consumed seeds and flour, whereas other food sources were poorly accepted and ant brood was never even eaten. The beetles did not elicit a strong aggression response in Messor ants, and they could tolerate very high densities of workers without clear costs. The beetles modestly mimicked the nest recognition cues of their Messor host. This imperfect mimicry could promote the adoption of the beetle in the ant colony, in concert with mechanical defence generated by its tank-like body. Isolation of the beetle from its host did not significantly affect the beetle's chemical cuticular profile nor did it provoke elevated ant aggression, indicating that the beetle does not acquire the chemicals passively from its host. 4. This paper discusses the fact that waste dumps in social insect nests are hotspots for arthropod symbionts. It shows that symbionts in this niche may employ behavioural, trophic and chemical strategies that are different from those found in other niches of social insect nests.     

Cryptic diversity,high host specificity and reproductive synchronization in army ant‐associated Vatesus beetles

Army ants and their arthropod symbionts represent one of the most species‐rich animal associations on Earth, and constitute a fascinating example of diverse host–symbiont interaction networks. However, despite decades of research, our knowledge of army ant symbionts remains fragmentary due to taxonomic ambiguity and the inability to study army ants in the laboratory. Here, we present an integrative approach that allows us to reliably determine species boundaries, assess biodiversity, match different developmental stages and sexes, and to study the life cycles of army ant symbionts. This approach is based on a combination of community sampling, DNA barcoding, morphology and physiology. As a test case, we applied this approach to the staphylinid beetle genus Vatesus and its different Eciton army ant host species at La Selva Biological Station, Costa Rica. DNA barcoding led to the discovery of cryptic biodiversity and, in combination with extensive community sampling, revealed strict host partitioning with no overlap in host range. Using DNA barcoding, we were also able to match the larval stages of all focal Vatesus species. In combination with studies of female reproductive physiology, this allowed us to reconstruct almost the complete life cycles of the different beetle species. We show that Vatesus beetles are highly adapted to the symbiosis with army ants, in that their reproduction and larval development are synchronized with the stereotypical reproductive and behavioural cycles of their host colonies. Our approach can now be used to study army ant‐symbiont communities more broadly, and to obtain novel insights into co‐evolutionary and ecological dynamics in species‐rich host–symbiont systems.     

The rove beetle Drusilla sparsa (Coleoptera: Staphylinidae) is a myrmecophilous species associated with a myrmicine ant,Crematogaster osakensis (Hymenoptera: Formicidae)

The rove beetle genus Drusilla includes some myrmecophilous species. The Japanese species Drusilla sparsa (Sharp, 1874) has been regarded as a non‐myrmecophilous beetle. In Kagawa Prefecture, Shikoku Island, western Japan, however, we often observed that D. sparsa adults were walking in the vicinity of foraging workers of the myrmicine ant Crematogaster osakensis Forel, 1990. The body color of the beetle is similar to C. osakensis as in other myrmecophilous beetles found near the trails of the host ants. To examine whether D. sparsa is myrmecophilous, we investigated the distribution of D. sparsa and C. osakensis in the field, as well as their behavior including prey preference of the beetle in the laboratory. Drusilla sparsa beetles were collected only in sites where C. osakensis ants occurred. When the beetles encountered the ant workers, they bent the abdominal tip toward the ants. The ants licked the abdominal tip, and then the beetles usually walked away. Such behavioral reaction of the ants was not observed when the beetles encountered workers of the formicine ant Nylanderia flavipes (Smith, 1874) that continuously attacked the beetles. Drusilla sparsa preferred to feed on dead workers of C. osakensis even when other ants were available as food, indicating that D. sparsa is a myrmecophilous species associated with C. osakensis. Crematogaster osakensis was frequently found in the stomach in the ant predator, the Japanese treefrog Hyla japonica Günther, 1859. Thus, the significance of body color similarity between the host ants and beetles is not a case of Batesian mimicry.     

Aggressiveness of ants attracted to the extrafloral nectary‐bearing plant,Mallotus japonicus,and temporal fluctuations in their abundance

Many plants that bear extrafloral nectaries (EFNs) attract various ant species that can exclude herbivores. The aggressiveness of the attracted ants and their temporal activity patterns are important factors that can affect the efficiency of herbivore exclusion from the plant. However, the characteristics of this mutualistic relationship between EFN‐bearing plants and ants have not been sufficiently elucidated. We investigated the aggressiveness of six ant species against the common armyworm, Spodoptera litura Fabr., and temporal fluctuations in the abundance of four aggressive ant species on an EFN‐bearing plant, Mallotus japonicus (L.f.) Müll. Arg. Workers of Crematogaster teranishii Santschi, Pheidole noda Smith, Pristomyrmex punctatus Smith and Formica japonica Motschoulsky were observed to be highly aggressive. In contrast, workers of Camponotus vitiosus Smith showed low aggressiveness. Paratrechina flavipes Smith workers did not attack the herbivore. The activity patterns of the four aggressive ant species greatly differed. Crematogaster teranishii and Ph. noda workers were constantly active throughout the day and night. In contrast, F. japonica was diurnal. Pristomyrmex punctatus was principally nocturnal. Formica japonica workers foraged solitarily, whereas workers of the other three species foraged in a group or recruited nestmates. Our results suggest that the efficacy of the indirect defense in M. japonicus depends principally on the attracted ant species.     

Visual prey discrimination of queen and worker ants by a generalist lizard

Laboratory experiments were conducted to test the hypothesis that widelyforaging generalist lizard,Eumeces okadae, visually discriminates palatable queen ants from unpalatable worker ants. The workers ofCamponotus japonicus andLasius niger were rejected on sight, while the queens of both species were eaten with little prior chemical examination by tongue flicks or licks. Comparison of the lizards' responses towards the workers and wingless queens of similar size indicated that neither body size nor presence or absence of wings accounted for difference in responses toward the 2 ant castes. The lizards probably discriminated different ant castes by body proportions.