Patricia J. Folgarait

Ant biodiversity and its relationship to ecosystem functioning: a review

Ants are important components of ecosystems not only because they constitute a great part of the animal biomass but also because they act as ecosystem engineers. Ant biodiversity is incredibly high and these organisms are highly responsive to human impact, which obviously reduces its richness. However, it is not clear how such disturbance damages the maintenance of ant services to the ecosystem. Ants are important in below ground processes through the alteration of the physical and chemical environment and through their effects on plants, microorganisms, and other soil organisms. This review summarizes the information available on ant biodiversity patterns, how it can be quantified, and how biodiversity is affected by human impacts such as land use change, pollution, invasions, and climate change. The role of ants in ecosystems is discussed, mainly from the perspective of the effects of ground-dwelling ants on soil processes and function, emphasizing their role as ecosystem engineers. Some lines of research are suggested after demonstrating the gaps in our current information on ant-soil interactions.

Phorid parasitoids affect foraging activity of Solenopsis richteri under different availability of food in Argentina

1. In Argentina, six species of Pseudacteon parasitoids (Phoridae) attack Solenopsis richteri, one of the two species of South American fire ant that are exotic pests in North America.

Developmental Rates and Host Specificity for Pseudacteon parasitoids (Diptera: Phoridae) of Fire Ants (Hymenoptera: Formicidae) in Argentina

Abstract This study extends our comparative knowledge of Pseudacteon interactions with Solenopsis fire ant workers. Reported in this work are development times for seven Argentinean parasitoid species reared on two hosts, Solenopsis richteri Forel and Solenopsis invicta Buren, under laboratory temperature regimes comparable with those of the climatic zones occupied by these host species. Developmental times spanned 31–66 d across phorid species, and in general did not differ between genders or host species, but were longer at lower temperatures. The size distribution of flies reared was bimodal, with a group of large (Pseudacteon borgmeieri, Pseudacteon nocens, Pseudacteon obtusus, and Pseudacteon tricuspis) and small (Pseudacteon cultellatus, Pseudacteon curvatus, and Pseudacteon nudicornis) species. P. borgmeieri was exceptional with respect to length of developmental time. Also reported are results of initial oviposition and developmental studies of some of these phorid species on other Argentinean Solenopsis ant species; P. curvatus was the only species able to complete its development on nonhost fire ants. These results support the concept of incorporating several complementary species of Pseudacteon in the biological control of pest fire ants.

Seasonal patterns of activity among species of black fire ant parasitoid flies (Pseudacteon: Phoridae) in Argentina explained by analysis of climatic variables

Abstract We monitored weekly relative abundances of adult female Pseudacteon (Diptera: Phoridae) species between February 1998 and May 2000 in Argentina. Fire ant-phorids were active around mounds of Solenopsis richteri Forel throughout the year. Phorid species richness ranged from six species during the summer-fall, to a single, large species during the winter. Species were classified as winter, summer, or fall-spring species, depending on times of peak mean abundance. We used descriptive multivariate techniques to analyze phorid phenological data (correspondence analysis), climatic data (principal component analysis), and their relationships (canonical correspondence analysis=CCA) at three temporal scales. The long-term mean temperatures, the mean and minimum sampling-time temperature, and the cumulative number of days without rain from the two months preceding each sampling day explained >90% of the variance when the data for sampling dates were averaged across the same months over the two years. Pseudacteon borgmeieri Schmitz, the winter dominant, was associated with lower temperatures and rainfall, whereas Pseudacteon curvatus Borgmeier, the summer dominant, showed the opposite pattern. Among the fall-spring species, Pseudacteon comatus Borgmeier was associated with months of higher maximum temperatures, longer photoperiods, and lower relative humidity. Pseudacteon nudicornis Borgmeier, in contrast, showed the opposite pattern. Pseudacteon tricuspis Borgmeier, was associated with months, typically in fall, having greater rainfall and fewer days with frosts. Implications of these patterns for the process of selecting particular species of S. richteri-attacking Pseudacteon for use in biological control introductions against imported fire ants are discussed in relation to climates of source and release areas.

Leaf‐cutting ant preferences for five native tropical plantation tree species growing under different light conditions

To examine the susceptibility of five Costa Rican tree species to leaf‐cutter ants (Atta cephalotes L.: Formicidae, Attini), young and mature leaves from trees that were grown in a plantation under full sun and partial shade were offered to six leaf‐cutter colonies located in full sun and six in partial shade. In addition to offering leaf disks to the ants, we offered large pieces of leaves to assess the effect of cutting leaves on food choices. Leaf‐cutters responded differently to each plant species, preferring Virola koschyni Warburg (Myristicaceae) and Hyeronima alchorneoides Allemao (Euphorbiaceae) over Stryphnodendrum microstachyum Poeppig & Endlicher (Mimosoideae), Pentaclethra macroloba Willdenow (Fabaceae) and Vochysia ferruginea Martius (Vochysiaceae). In agreement with previous studies, interspecific differences among the tree species in water and saponin content appeared to account for the observed ant preferences among the five tree species: leaf‐cutter ants preferred leaves and disks with more water and less saponins and the five tree species varied significantly in these traits. An observed positive correlation between preference and phenolic/nitrogen ratio appears to be spurious, and is instead due to a negative correlation between water content and nitrogen content. For the first time, Atta nest location has been shown to affect consumption: nests located in partial shade removed more leaf material than those from the sun plots. However, nest location had no effect on preference ranking of the tree species tested. Pieces of leaves from all the tree species grown in partial shade were significantly more removed than those trees grown in full sun. Leaf age, toughness, leaf specific weights, ant activity, and colony were not correlated with food choices. Because of the observed preferences, the five tree species should not be considered as equal candidates for plantation purposes. However, complete characterization of the candidate status of tree species for plantations in the neotropics must include information on the ability of such species to tolerate pest attacks in addition to their natural defenses to attack.

Development of Pseudacteon cultellatus (Diptera: Phoridae) on Solenopsis invicta and Solenopsis richteri Fire Ants (Hymenoptera: Formicidae)

Abstract Nothing was known about the life cycle of Pseudacteon cultellatus Borgmeier. Because this species seems to be a promising candidate for biological control of fire ants, we studied several aspects of its development. We measured selected life history traits of the fire ant parasitoid Pseudacteon cultellatus as a function of (1) host species (Solenopsis invicta Buren versus Solenopsis richteri Forel), (2) temperature (22 versus 25°C), and (3) size distributions of available host ants (homogeneous small versus mixed sizes of workers). We found that larval, pupal, and total developmental periods of this phorid fly were between 12 and 18% longer on S. richteri than on S. invicta, and 11–19% longer at 22 than at 25°C. Although larval developmental times did not differ as a function of sizes of host offered, average time of development in the pupal stage was extended by 12% in the case of host size mixtures which included workers larger than the phorid’s preferred host size in comparison to homogeneously small ants. P. cultellatus exhibited a strong preference for small ants, especially when using S. invicta workers as hosts. We did not find a relationship between size of host and sex of emerging flies as previously documented for some other Pseudacteon species. P. culltelatus seems to be a promising species for controlling S. invicta as it develops faster in this smaller host, and because it prefers to attack small ants and does not need larger hosts to produce female flies. Thus, this P. cultellatus can attack the majority of ants in a colony without the risk of producing a male-biased sex ratio.

Distributional Patterns of Pseudacteon Associated with the Solenopsis saevissima Complex in South America

Abstract Classical biological control efforts against imported fire ants have largely involved the use of Pseudacteon parasitoids. To facilitate further exploration for species and population biotypes a database of collection records for Pseudacteon species was organized, including those from the literature and other sources. These data were then used to map the geographical ranges of species associated with the imported fire ants in their native range in South America. In addition, we found geographical range metrics for all species in the genus and related these metrics to latitude and host use. Approximately equal numbers of Pseudacteon species were found in temperate and tropical regions, though the majority of taxa found only in temperate areas were found in the Northern Hemisphere. No significant differences in sizes of geographical ranges were found between Pseudacteon associated with the different host complexes of fire ants despite the much larger and systemic collection effort associated with the S. saevissima host group. The geographical range of the flies was loosely associated with both the number of hosts and the geographical range of their hosts. Pseudacteon with the most extensive ranges had either multiple hosts or hosts with broad distributions. Mean species richnesses of Pseudacteon in locality species assemblages associated with S. saevissima complex ants was 2.8 species, but intensively sampled locations were usually much higher. Possible factors are discussed related to variation in the size of geographical range, and areas in southern South America are outlined that are likely to have been under-explored for Pseudacteon associated with imported fire ants.

Behavioral Strategies of Phorid Parasitoids and Responses of Their Hosts, the Leaf-Cutting Ants

Abstract 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.

Associations of Fire Ant Phorids and Microhabitats

Abstract We examined flight activity patterns for a guild of fire ant parasitoids in western Argentina in relationship to their host’s location (mound/foraging trail) and light condition (full sun/partial sun/full shade) at different scales, from the individually sampled mound to the full day’s summation for each species. We asked first whether taxa showed preferences among these conditions, and second, whether certain species and sexes might be found together more frequently than expected to by chance. All species, except the P. obtusus species complex, were significantly more likely to be found attacking ants at disturbed mounds than at paired foraging trails. The P. nocens complex and P. litoralis were more likely to be in the shade when temperatures were above the overall mean of the study (28.3°C), whereas others, such as the P. obtusus complex and P. tricuspis, were more likely to be in full sun under these same conditions. Our analyses indicated that a limited set of species, particularly P. nocens with P. litoralis, and males with female P. obtusus and P. tricuspis, were more likely to be found together than expected. We also found decreasing proportions of males with increasing time of analysis. We discuss the implications of host location, metereological conditions, and sex ratios in relationship to ongoing classical biological control efforts using species of these phorids.

Development of Pseudacteon nocens (Diptera: Phoridae) on Solenopsis invicta and Solenopsis richteri Fire Ants (Hymenoptera: Formicidae)

We studied the developmental performance of the large morph of Pseudacteon nocens Borgmeier (Diptera: Phoridae), a prospective biological control agent of imported fire ants (Hymenoptera: Formicidae). We measured selected life history traits of this parasitoid as a function of 1) host species (Solenopsis invicta Buren versus Solenopsis richteri Forel), 2) temperature (22 versus 28 degrees C), 3) source population of the fly (Corrientes and Santiago del Estero, Argentina), and 4) varied size distributions of offered host ants. Developmental periods were influenced by host species, although the populations responded in opposing manners. Developmental times, however, were most strongly influenced by temperature with total developmental periods lengthened by 17-32% at 22 degrees C. Pupal mortality was also significantly lower at this temperature. Although numbers of progeny per female were significantly higher for the Corrientes population, we found no significant differences in progeny per female according to host species. Interestingly, we found that females were larger than males, and flies from Corrientes were larger than those from Santiago del Estero, even after statistical adjustments for host size. The modal frequency of host size elected in all treatment combinations tested was identical (0.6 mm), a size that represented the apparent threshold for producing female progeny. These laboratory and additional field observations demonstrate considerable interpopulational variation in P. nocens and lend further support to the applied approach focusing at the population, as opposed to the species level, with respect to both source and target areas for classical biological control introductions of Pseudacteon flies.