Behavioral strategies of phorid parasitoids and responses of their hosts, the leaf-cutting ants

Host-searching and oviposition behaviors of parasitoids, and defensive responses of the hosts, are fundamental in shaping the ecology of host-parasitoid interactions. In order to uncover key behavioral features for the little known interactions between phorid parasitoids (Diptera: Phoridae) and their leaf-cutting ant hosts (Formicidae: Attini), host-related behavioral strategies (i.e., host searching and oviposition) for 13 phorid species, and host defensive responses (i.e., hitchhikers and particular body postures) for 11 ant species, were studied. Data was collected at 14 localities, one of them characterized by its high species richness for this host-parasitoid system. Phorid species showed both great variation and specificity in attacking behaviors. Some chose their hosts using either an ambush or an actively searching strategy, while some species attacked ants on different body parts, and specialized on ants performing different tasks, such as when ants were foraging, removing wastes to refuse piles, or repairing the nest. Combining all the behaviors recorded, most phorid species differed in performance in at least one, making it possible to recognize species in the field through their behavior. Phorid species that attacked hosts with greater activity levels showed overall higher attack rates, although there was no significant correlation between attack rates by most phorid species and ant activity outside the nest while parasitoids were attacking. The presence of phorids was a significant determinant for the presence of defensive behaviors by the ants. Although ant species varied in the incidence levels of these defensive behaviors, most ant species reacted against different phorids by utilizing similar behaviors, in contrast to what parasitoids do. General features of the observed phorid-ant interactions were parasitoid specialization and corresponding high interspecific variation in their behaviors, while their hosts showed generalized responses to attacks with high intraspecific variation. Behavioral patterns as well as specific features of these ant-parasitoid interactions are described, and their ecological importance discussed.Fil: Elizalde, Luciana. Universidad Nacional de Quilmes; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Folgarait, Patricia Julia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Quilmes; Argentin

Host diversity and environmental variables as determinants of the species richness of the parasitoids of leaf-cutting ants

Aim Because of the obligatory relationship between endoparasitoids and their hosts, we presume that hosts exert strong selection pressure on parasitoids. One prediction is a positive relationship between host diversity and parasitoid richness. This relationship could be the product of resource availability which could lead to more opportunities for speciation, or could represent shared responses to the environment by both groups.Location Argentina and Paraguay.Methods We sampled a 1800-km transect to test for a correlation between the richness of leaf-cutting ant hosts and their phorid parasitoids. Regression models were used to assess if host and environmental variables could explain phorid species richness at nest, hectare and locality spatial scales. We used canonical correspondence analysis (CCA) to explore if there were similar responses of phorid species to particular host and environmental variables at different spatial scales, and partial CCA to separate the relative importance of both groups of variables.Results Phorid richness was positively correlated with host richness. Host richness/abundance accounted for 20-53% of the variation in parasitoid richness at the hectare and locality scales of analysis, with most of the variation accounted for by ant abundance. We were not able to assess the prediction at the nest scale as only one phorid species was found at most nests. Climatic variables did not explain phorid species richness once host variables were in the models. Partial CCA showed that host-related variables accounted for most of the variance associated with phorid species ordination at the nest and hectare scales, but not at the largest grain, the locality, where climatic variables were more important. However, most phorid species did not show particular positions along the climatic gradient.Main conclusions The association between parasitoid richness and host richness and abundance, and the overall weak associations with environmental variables, suggest that these host variables are key factors influencing parasitoid speciation.Fil: Elizalde, Luciana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Folgarait, Patricia Julia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Quilmes; Argentin

Behavioral discrimination between monogyne and polygyne red fire ants (Hymenoptera: Formicidae) in their native range

Nestmate recognition among social insects is presumed to restrict non-nestmates from exploiting nest resources. Here, we developed aggression bioassays to assess the discrimination behaviors of both polygynous and monogynous forms of the red fire ant, Solenopsis invicta Buren, during symmetrical interactions in neutral arenas. Workers from polygyne colonies exhibited risk avoidance behaviors; that is, defensive postures or the avoidance of direct contact during interactions. Workers from monogyne colonies always exhibited aggressive behaviors in the form of physical or chemical attacks. In interactions between both, monogyne workers usually started the aggression by surrounding and biting the polygyne ants. Polygyne S. invicta workers also distinguished nestmates from foreigners, but their response was not as aggressive as that of monogynes. The proposed ethogram that we constructed identified monogyne and polygyne forms of S. invicta colonies in concordance with current measures, including number of queens, and expression of the Gp-9 gene.Fil: Chirino, Monica Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Quilmes. Centro de Estudios e Investigación; ArgentinaFil: Gilbert, Lawrence E.. University of Texas at Austin; Estados UnidosFil: Folgarait, Patricia Julia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Quilmes. Centro de Estudios e Investigación; Argentin

Pseudacteon tricuspis: Its behavior and development according to the social form of its host and the role of interference competition among females

We studied how the behavior and performance of Pseudacteon tricuspis Borgmeier varies with the social form of its host Solenopsis invicta Buren, in its native range in Argentina where monogyne colonies are more abundant than polygynes (≈75 vs. 25%). Female, P. tricuspis took 44% less time (50 vs. 89 s) to attack monogyne than polygyne ants, but oviposition attempts were similar (23 vs. 18 attacks). The presence of the parasitoid affected the average size of foragers on the trail, with the proportion of minor workers increasing on both social forms. In the laboratory, P. tricuspis selected similar host sizes, although pupal survival was 25% higher on monogynes than on polygynes. Developmental times of both genders were similar (3335 d), although larger females emerged from bigger hosts. The sex ratio of P. tricuspis was more male biased when exploiting polygyne ants. Intraspecific competition significantly affected parasitoid reproductive success, being significantly higher for a solitary female than when three females were present, although the size of workers selected did not vary. The male:female ratio also changed, being 1:1 without competition but 2:1 with competition. We demonstrated for the first time the consequences of interference competition among P. tricuspis females, a common behavior observed in others parasitoids. We discuss why P. tricuspis sex ratios are always biased toward males in both social forms and suggest that similar studies of interference competition within and between already naturalized Pseudacteon species in the United States could help predict establishment patterns.Fil: Chirino, Monica Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Quilmes. Centro de Estudios e Investigación; ArgentinaFil: Folgarait, Patricia Julia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Quilmes. Centro de Estudios e Investigación; ArgentinaFil: Gilbert, Lawrence E.. University of Texas at Austin; Estados Unido

Growth and conidiation response of escovopsis weberi (Ascomycota: Hypocreales) against the fungal cultivar of acromyrmex lundii (Hymenoptera: Formicidae)

Leaf-cutter ants (Acromyrmex and Atta spp.) exhibit ancient and complex interactionswith the symbiotic fungus Leucoagaricus (Basidiomycetes: Agaricales) from which they feed, and withthe virulent and speciÞc fungus Escovopsis weberi J.J. Muchovej & Della Lucia (Ascomycetes:Hypocreales) that attacks the antsÕ fungal gardens. This system offers a unique opportunity to studypossible avenues for replacing polluting pesticides with a biological control agent against the ants. Weisolated both Leucoagaricus sp. and E. weberi from the gardens of Acromyrmex lundii Gue´ rin-Me´ nevillecolonies and confronted them with each other by growing Leucoagaricus on petri dishes and placinginoculated pieces of agar inoculated with E. weberi at the edges. Here we present growth curves ofLeucoagaricus sp. and E. weberi in the absence of each other, as a baseline to which we compare theeffect of the fungi on each other. As expected, we found a negative effect of E. weberi on the ant cultivarfrom different colonies of A. lundii. E. weberi increased its growth rate, as well as the levels ofconidiation, in the presence of the ant cultivar. We determined that a soluble and diffusible compound,released by the cultivar, triggered, was responsible for, or did both for the increased levels ofconidiation in E. weberi, and that this response was reversible. We discuss why our results areencouraging from a biological control perspective.Fil: Folgarait, Patricia Julia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnología. Laboratorio de Hormigas; ArgentinaFil: Marfetan, Jorge Ariel. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnología. Laboratorio de Hormigas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Cafaro, M. J.. Universidad de Puerto Rico; Puerto Ric

Preliminary in vitro insights into the use of natural fungal pathogens of leaf-cutting ants as biocontrol agents

Leaf-cutting ants are one of the main herbivores of the Neotropics, where they represent an important agricultural pest. These ants are particularly difficult to control because of the complex network of microbial symbionts. Leaf-cutting ants have traditionally been controlled through pesticide application, but there is a need for alternative, more environmentally friendly, control methods such as biological control. Potential promising biocontrol candidates include the microfungi Escovopsis spp. (anamorphic Hypocreales), which are specialized pathogens of the fungi the ants cultivate for food. These pathogens are suppressed through ant behaviors and ant-associated antibiotic-producing Actinobacteria. In order to be an effective biocontrol agent, Escovopsis has to overcome these defenses. Here, we evaluate, using microbial in vitro assays, whether defenses in the ant-cultivated fungus strain (Leucoagaricus sp.) and Actinobacteria from the ant pest Acromyrmex lundii have the potential to limit the use of Escovopsis in biocontrol. We also explore, for the first time, possible synergistic biocontrol between Escovopsis and the entomopathogenic fungus Lecanicillium lecanii. All strains of Escovopsis proved to overgrow A. lundii cultivar in less than 7 days, with the Escovopsis strain isolated from a different leaf-cutting ant species being the most efficient. Escovopsis challenged with a Streptomyces strain isolated from A. lundii did not exhibit significant growth inhibition. Both results are encouraging for the use of Escovopsis as a biocontrol agent. Although we found that L. lecanii can suppress the growth of the cultivar, it also had a negative impact on Escovopsis, making the success of simultaneous use of these two fungi for biocontrol of A. lundii questionable.Fil: Folgarait, Patricia Julia. Universidad Nacional de Quilmes; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Gorosito, Norma Beatriz. Universidad Nacional de Quilmes; ArgentinaFil: Poulsen, Michael. University of Wisconsin; Estados UnidosFil: Currie, Cameron R.. University of Wisconsin; Estados Unido

A small parasitoid of fire ants, pseudacteon obtusitus (Diptera: Phoridae): native range ecology and laboratory rearing

The high diversity within a guild of Pseudacteon Coquillet (Diptera: Phoridae) parasitoid flies hosted by the red imported fire ant, Solenopsis invicta Buren (Hymenoptera: Formicidae), may be based on several niche axes, including host size specialization, host location cues, climatic responses, and tolerances. The recently described species, Pseudacteon obtusitus Plowes, Folgarait, and Gilbert (Diptera: Phoridae), is one of the smallest species in this group (with a thorax width of only 0.3 mm), and appears to locate ant hosts on foraging trails as well as at nest disturbances. Here we examine the ecology, phenology, and development of this parasitoid at sites in Corrientes, Argentina. Pseudacteon obtusitus has 2 seasons of peak abundance, and exhibits low tolerance for cold temperatures or extended cold periods. It preys on the smallest ant workers (typically 0.6 mm head width) independent of the ant size offered, and has a male biased sex ratio (mean 2.78:1). Developmental times ranged from 35 d at 27 °C to 44 d at 22 °C. This species holds interest for inclusion among the multi-species assemblage of parasitoid flies considered for biological control of S. invicta in its invasive range in North America.La gran diversidad dentro del gremio de moscas parasitoides del género Pseudacteon Coquillet (Diptera: Phoridae), específicas de las hormigas de fuego, Solenopsis invicta Buren (Hymenoptera: Formicidae), puede estar basada en varios ejes de nicho incluyendo una especialización por el tamaño del huésped, claves de localización del huésped y respuestas climáticas o tolerancias. La especie recientemente descripta, Pseudacteon obtusitus Plowes, Folgarait, Gilbert (Diptera: Phoridae), es una de las más pequeñas de este grupo con un ancho de tórax de 0.3 mm y parece localizar a las hormigas huésped en los caminos de forrajeo así como en nidos disturbados. En este trabajo se examina la ecología, fenología y desarrollo de esta especie en sitios de Corrientes, Argentina. Pseudacteon obtusitus tiene 2 picos de abundancia y posee poca tolerancia a las temperaturas bajas o períodos largos de frío. Esta especie ataca a las obreras más pequeñas (típicamente de 0.6 mm de ancho de cabeza) independientemente del tamaño de huésped ofrecido, y tiene una relación de sexos sesgada hacia los machos (promedio 2.78:1). Los tiempos de desarrollo varían de 35 días a 27 °C hasta 44 días a 28 °C. Esta especie es interesante para incluirla en el ensamble multi-específico de moscas parasitoides consideradas para el control biológico de Solenopsis invicta en su rango de invasión en América del Norte.Fil: Folgarait, Patricia Julia. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnología. Laboratorio de Hormigas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Plowes, Robert M.. University of Texas; Estados UnidosFil: Gomila Molina, Carolina Florencia. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnología. Laboratorio de Hormigas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Investigaciones Bioquímicas de Bahía Blanca. Universidad Nacional del Sur. Instituto de Investigaciones Bioquímicas de Bahía Blanca; ArgentinaFil: Gilbert, Lawrence E.. University of Texas; Estados Unido

Insights into the biodiversity and causes of distribution of potential entomopathogens associated with leaf-cutting ants

To our knowledge, this work is the first large-scaled, systematic survey of potential entomopathogens associated with worker ants of several Acromyrmex species. The study was performed at nine sites located in five Phytogeographical Provinces across Argentina. We recorded 28 species of fungi with entomopathogenic behaviour, which infected 24.3% of the 4737 collected ants from 94 colonies. Fusarium oxysporum and F. solani were the most widely distributed, followed by Purpureocillium lilacinum and Beauveria bassiana. The occurrence of species across nests within the same site varied from null to 98%. We did not detect any systematic association between fungi and site, Phytogeographical Province or ant species. Instead the microhabitats that surround each nest appear to play an important role in defining entomopathogen communities. We found that climatic variables like maximum temperature, dew point, and relative humidity helped to account for the distribution of these fungi at the site scale. Besides, colonies from undisturbed sites showed higher abundance of infections with entomopathogens than those from disturbed ones. These results greatly improve the knowledge of the ecology of the filamentous fungi associated with leaf-cutting ants. In addition, we proposed that the combination of the entomopathogen virulence and the resistance of ant colonies may be an important but overlooked effect influencing the diversity of entomopathogens.Fil: Goffré, Daniela. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Folgarait, Patricia Julia. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Conidiobolus lunulus, a newly discovered entomophthoralean species, pathogenic and specific to leaf-cutter ants

Conidiobolus lunulus is a recently described entomophthoralean species isolated from leaf-cutter ants. This fungus discharges not only primary but also secondary conidia and microconidia of different shapes. Because nothing was known about the biology of the fungus, and its interactions with hosts, we first evaluated if its pathogenicity against leaf-cutter ants changes with the fungal age (time grown in vitro), and if it is related to the conidial structures produced. Afterwards, we tested its virulence at three combinations of temperature and relative humidity. In addition, we noted all visible causes of death by recovering different microorganisms from the dead, non-sterilized, ants to evaluate C. lunulus virulence when pathogens carried naturally by the ants were present. Finally, we used the conditions that lead to the highest mortality to evaluate fungal virulence to other host species, including non-leaf-cutter ants. Results indicated that C. lunulus was pathogenic from a culture age of 1 to 5 days, with a peak at 2-days-old, from which we registered median lethal times of 1–2 days and 85% of the cadavers with fungal conidiation. Our results suggest that primary conidia and moon-shaped microconidia were infective. Evaluations of mortality using 2-days-old cultures on several leaf-cutter ant colonies showed 1) significantly faster mortality of C. lunulus inoculated ants in comparison to controls, 2) significantly greater and faster mortality at 23.7 ◦ C than at 21.2 ◦ C, 3) significantly higher and faster mortality at 88% than at 57% RH, and 4) a significant reduction of other pathogens in C. lunulus inoculated ants in comparison to controls. C. lunulus was highly specific to leaf-cutter ants, as hardly any increase in mortality was observed on inoculated ants, and no conidia were recorded on cadavers of the other three non-leaf-cutter ant species tested. Our results highlight that C. lunulus is a very promising biological control agent against leaf-cutter ants.Fil: Folgarait, Patricia Julia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnología. Laboratorio de Hormigas; ArgentinaFil: Goffré, Daniela. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnología. Laboratorio de Hormigas; Argentin

Phorid species from Acromyrmex's hosts and effect on their survival of two fungi proposed for the control of leafcutter ants

Phorid flies (Diptera: Phoridae, Metopinini) are natural enemies of leafcutter ants (Hymenoptera: Formicidae, Attini), which are among the most important pests in the Neotropical region. These parasitoids lay their eggs inside worker ants, causing the death of the parasitized ants, and the oviposition attacks on foraging workers interfere with the collection of vegetal material used in fungal gardens, thereby affecting the whole colony. However, because of the large number of ants per colony, more than one type of biological control agent is needed to have a significant impact. We collected parasitized leafcutter ants Acromyrmex lundii (Guérin-Méneville), Acromyrmex heyeri (Forel), and Acromyrmex ambiguus (Emery) from various places in Argentina and reared their parasitoids. We recorded developmental times, host and phorid sizes, and other aspects of the biology of the phorids Apocephalus neivai Borgmeier, Apocephalus noetingerorum Brown & Disney, Myrmosicarius gracilipes Borgmeier, Myrmosicarius catharinensis Borgmeier, Myrmosicarius crudelis Borgmeier, and Myrmosicarius cristobalensis Disney et al. This is the first record of A. ambiguus, an important pest of pine plantations, being a host of phorids. We found the first cases of gregarious parasitoidism of a parasitoid with no-free pupae: M. catharinensis on A. lundii ants. We also evaluated the effect on pupal survival of two cosmopolitan fungi, Beauveria bassiana (Balsamo) Vuill. and Trichoderma lentiforme (Rehm) Chaverri et al., which are also considered as potential biological control agents of leafcutter ants. Suspensions of conidia were tested on Myrmosicarius and Apocephalus parasitoid pupae of different ages. No negative effect on pupal survival was found under either fungal treatment. Therefore, the use of both natural enemies separately but simultaneously, or the introduction of fungi-inoculated pupae in the pest habitats, seems to be a promising strategy for the multiple biological control of leafcutter ants.Fil: Goffré, Daniela. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnología. Laboratorio de Hormigas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Folgarait, Patricia Julia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnología. Laboratorio de Hormigas; Argentin