Phorid Species Research Articles

Parasitism and biology of Myrmosicarius grandicornis (Diptera, Phoridae) in relationship to its host, the leaf-cutting ant Atta sexdens (Hymenoptera, Formicidae)

The parasitic phorid Myrmosicarius grandicornis Borgmeier is commonly found around nest entrances of the leaf-cutting ant Atta sexdens (L.) in Brazil, but there is no information about the importance of this fly for A. sexdens. We evaluated the parasitic capability of female M. grandicornis collected in the field and released in laboratory nests of A. sexdens and compared ants' foraging rhythm before and after M. grandicornis were released. We also determined biological characteristics of the parasitoid. Presence of M. grandicornis elicited foragers to abandon their loads and return to the nest, an effect previously described for the phorid Neodohrniphora sp., which is a more abundant A. sexdens parasitoid. Both phorid species occur at the same foraging trails during part of the year and attack ants of different size classes. Therefore, they may have a combined effect on the reduction of A. sexdens foraging. Myrmosicarius grandicornis pupariated inside hosts' head capsules, which are detached from their bodies and deposited in the nest's refuse pile. Adults emerged through the hosts' mouth cavity about a month after oviposition. The characteristics of M. grandicornis biology suggest that this parasitoid completes its development inside A. sexdens nests.

Community Structure and Environmental Stress: Desiccation Promotes Nestedness in Mycophagous Fly Communities

In a previous field experiment, communities of mycophagous flies that emerged from Agaricus bisporus mushrooms exhibited a nested-subset pattern related to mushroom size. A phorid species and Leucophenga varia (Drosophilidae) emerged from small, medium, and large mushrooms, but other drosophilid species were usually limited to large mushrooms. Here, we conducted two experiments and one field survey to determine whether this nestedness pattern is caused by nested desiccation tolerances among species, coupled with the mediating effects of mushroom size. In the first experiment, 20 first instar larvae of either Drosophila tripunctata or D. putrida were added to A. bisporus mushrooms that weighed 5 g, 10 g, or 20 g. Mushrooms were placed in environmental chambers at different temperatures for 5 d (maxima of 25°C, 30°C, or 35°C). Both mushroom size and temperature had significant direct effects on the proportion of larvae completing development; larvae in small mushrooms are more susceptible to desiccation stress than larvae in large mushrooms. In a second experiment, we examined the effect of desiccation stress on community structure. Woodland mushrooms collected in the field were cut in half; the halves were placed at different incubation temperatures (maxima of either 25°C or 35°C) for 5 d, and emerging flies were counted and sorted by species. The halves incubated at 35°C produced significantly nested communities, the halves incubated at 25°C did not. Correlations between fly abundance and mushroom mass were also more significant at higher temperatures. These results were consistent with the hypothesis that desiccation stress, differentially mediated by mushroom size, drives nested subset structure in these communities. In a four-week field survey, however, nestedness was not related to mean temperature or rainfall. We contend that small habitats are less resistant to changes in environmental conditions than larger habitats, so the intensity of environmental stress will correlate with habitat size. So, some initially variable and non-nested communities might decay to a nested-subset pattern of species composition as a result of differential habitat buffering under stressful environmental conditions.

Foraging ecology and patterns of diversification in dipteran parasitoids of fire ants in south Brazil

1. At least sixteen species of parasitoid flies in the genus Pseudacteon (family Phoridae) attack fire ants in the Solenopsis saevissima subcomplex in South America. Little is known of behavioural or ecological differences among Pseudacteon parasitoids of fire ants, although their coexistence in multispecies communities would suggest that important differences exist. Seven Pseudacteon species in two separate communities were studied in south‐east Brazil. The way in which hosts detect and respond to the presence of parasitoids, attack rates of the parasitoids, and host location behaviour of the parasitoids were examined.2. Reductions in fire ant recruitment were more closely related to the number of ants attacked along a foraging trail than to the amount of time that a phorid was present.3. Pseudacteon solenopsidis differed from other phorid species by flying backwards while pursuing ants, by attacking at lower rates than other phorids, and by spending longer around fire ant foraging trails than other phorids before departing. Fire ant recruitment to food often rebounded in the continued presence of P. solenopsidis.4. In each of the two communities, certain Pseudacteon species appeared frequently at Solenopsis foraging trails, whereas others appeared predominantly at mound disturbances. Two distinct size classes of phorids were present in each community, and the community with the larger ant host species also had a third and larger phorid species. No phorid species from the same community had similar body sizes and similar host location behaviours, although numerous species from different communities shared both of these traits.5. Heterogeneity in host size and in the ecological circumstances under which hosts are vulnerable to attack appears to have influenced the evolution and perhaps maintenance of diverse Pseudacteon communities.

Oviposition Behavior and Development of Pseudacteon Flies (Diptera: Phoridae), Parasitoids of Solenopsis Fire Ants (Hymenoptera: Formicidae)

We studied the oviposition behavior and larval development of Pseudacteon phorid flies, which are parasitoids of Solenopsis fire ants. Four South American Pseudacteon spp., P. litoralis Borgmeier, P. tricuspis Borgmeier, P. wasmanni (Schmitz) and P. curvatus Borgmeier (which attack S. invicta Buren), and 2 North American Pseudacteon spp., P. browni Disney and P. crawfordi Coquillett (which attack S. geminata [F.]), were evaluated. In laboratory tests, larger Pseudacteon spp. attacked larger Solenopsis workers. The mean worker size preferred was significantly larger than the colony mean worker size for all but the smallest phorid species, P. curvatus , which preferred workers significantly smaller than the colony mean. Within Pseudacteon spp., larger females preferred larger workers, but this relationship was significant only for the 2 North American species. Natural parasitism rates of Solenopsis workers by the 2 North American Pseudacteon spp. in the field were low (0–2.42% per colony), but >90% of the overall size range of worker ants showed evidence of parasitism. Between 11.8 and 31.0% of apparent oviposition attempts resulted in successful parasitism. Mean larval development times ranged from 13.0 to 18.4 d at 30°C and were shorter for North American species. Larval stages required 24.8–36.5% longer to develop at 25°C than at 30°C. Mean pupal development times ranged from 15.6 to 18.7 d at 30°C. In general, larger Pseudacteon spp. had longer larval and pupal development times. Overall, North and South American Pseudacteon spp. were similar in terms of oviposition behavior and development.

Morphological prediction of worker size discrimination and relative abundance of sympartic species of Pseudacteon (Dipt., Phoridae) parasitoids of the fire ant, Solenopsis saevissima (Hym., Formicidae) in Brazil

AbstractPatterns of attack for collected species of phorids are predicted using multivariate morphometries of female Pseudacteon species and worker size distributions of parasitized fire ants, Solenopsis saevissima. The model assumes that there is a direct correlation between phorid size and the size range of the worker ant attacked, and presumes that worker sizes are a resource that is divided by sympatric phorid species to minimize joint parasitism. These results suggest that the community of sympatric Pseudacteon species on only one host species coexists by restricting the size of workers attacked, and secondarily by differing diel patterns of ovipositional activity. When we compared relative abundance of species of Pseudacteon with the size distribution of foragers of S. saevissima, our observed distribution did not differ significantly from our predicted relative abundance of females of Pseudacteon. The activity of Pseudacteon may be a factor determining forager size distributions.

Life history parameters and description of the larva ofApocephalus paraponerae(Diptera: Phoridae), a parasitoid of the giant tropical antParaponera clavata(Hymenoptera: Formicidae)

Data from laboratory rearing of the parasitoid Apocephalus paraponerae in its ant host, Paraponera clavata, show that the egg stage lasts only 6 ½-7 hours, and the larval feeding period is only 48 hours. These times are extremely short, compared to most other phorids. The pupal stage, however, was 17–26 days, much longer than in other phorids, possibly to compensate in some way for the brief larval stage. Although this fly is a parasitoid its life history is also similar to that of a scavenger, and contains elements of both of these ways of life. The larva of A. paraponerae is described, the first such description for a species of Apocephalus. The larval structure resembles that of other, related phorids in most aspects, but an anterior crosspiece joining the cornua of the cephalopharyngeal skeleton is unusual. The significance of this and other structures cannot be specified until more data are available from larvae of other phorid species.

Three new fossil phorid flies (Diptera: Phoridae) from Canadian Late Cretaceous amber

Three new species of Canadian Late Cretaceous amber phorids are described: Prioriphora intermedia, Prioriphora longicostalis, and Prioriphora setifemoralis. A key to the species of the fossil genus Prioriphora is provided, and the paleoecology of the amber sites is discussed. One piece of amber contained an unusually large number (~30) of specimens.

Defense against parasites by hitchhikers in leaf-cutting ants: a quantitative assessment

A curious behavior in leaf-cutting ants in the genus Atta is the “hitchhiking” of small minim workers on leaf fragments carried by larger workers. Two functions of these hitchhikers have been proposed: (1) defense of leaf carriers against parasitic flies in the family Phoridae (ant protection hypothesis; Eibl-Eibesfeldt and Eibl-Eibesfeldt 1967) and (2) reduction of transport costs of small minims that collect plant fluids (energy conservation hypothesis; Stradling 1978). We studied hitchhiking behavior in colonies of Atta colombica on Barro Colorado Island, Panama, and found strong evidence in favor of the ant protection hypothesis. Females of Apocephalus attophilus (Diptera: Phoridae) attack leaf carriers of A. colombica and deposit eggs in the head capsules of these ants. Our observations indicate that parasites require leaf fragments to stand on during oviposition, and, as a result, only leaf carriers are susceptible to parasitic attack. The presence of hitchhikers reduces significantly both the time parasites spend on leaf fragments and the probability that they will land in the first place. Results of experimental introductions of parasites and a year of biweekly censuses at ten colonies indicate that leaf-cutting ants adjust the level of hitchhiking to accommodate both daily and seasonal changes in the abundance of parasites. We found little evidence in support of the energy conservation hypothesis. If it is assumed that all minim workers hitchhike back to the nest, our calculations indicate that total transport costs along a foraging trail are reduced by 10% or less. However, our observations indicate that only 50% of returning minim workers hitchhike, and therefore energy savings are actually considerably less than 10%. Leaf-cutting ants in the genera Atta and Acromyrmex are attacked by over 20 species of parasitic phorids. In the discussion we review what is known about these associations and suggest that these parasites have influenced the ecology and evolution of polyethism in leaf-cutting ants.

Behavioral Interactions between Ants and Their Parasites

Ectoparasitic and endoparasitic arthropods of ants include species of Acarina (Antennophoridae, Uropodidae, Macrochelidae), Strepsiptera (Myrecolacidae), Hymenoptera (Formicidae, Diapriidae, Eucharitidae), and Diptera (Phoridae). Variation in the style of ectoparasitism is illustrated by the different lifestages involved and differing effects on the hosts by parasitic ants and eucharitids. Considerable variation in behavior occurs between related genera and species of phorids emphasizing the danger of over-generalization on the relationships of ants and their parasites.