Developmental rates and host specificity for Pseudacteon parasitoids (Diptera: Phoridae) of fire ants (Hymenoptera: Formicidae) in Argentina

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.     

Sex ratio variation as a function of host size in Pseudacteon flies (Diptera: Phoridae), parasitoids of Solenopsis fire ants (Hymenoptera: Formicidae)

Some Pseudacteon (Diptera: Phoridae) flies are parasitoids of Solenopsis (Hymenoptera: Formicidae) ant workers in North and South America. Laboratory studies of sex allocation revealed a pattern of sex ratio variation as a function of host size, with more females arising from larger hosts. Environmental sex determination is a possible mechanism for the observed pattern, and examination of Pseudacteon life history reveals several traits assumed to be important in models predicting conditions under which environmental sex determination is favoured. Sex allocation patterns of Pseudacteon are compared with theoretical predictions and empirical data from better-studied hymenoptcran parasitoids that have haplodiploid sex determination. The pattern of sex ratio variation observed has important implications for biocontrol efforts of imported Solenopsis fire ants by the introduction of Pseudacteon parasitoids.     

Temperature-dependent development and parasitism rates of four species of Pteromalidae (Hymenoptera) parasitoids of house fly (Musca domestica) pupae

Parasitoid development, parasitoid-induced host mortality and parasitoid progeny emergence were determined at five constant temperatures for Muscidifurax raptor Girault and Sanders, Muscidifurax zaraptor Kogan and Legner, Spalangia cameroni Perkins and Spalangia endius Walker using pupae of the house fly, Musca domestica L., as hosts. At temperatures of 20, 25, 30 and 35 degrees C the median development times (days from oviposition to adult emergence), respectively, were M. raptor (28.4, 20.7, 14.3, 14.5), M. zaraptor (30.6, 22.8, 14.1, 14.2), S. cameroni (55.6, 35.2, 21.8, 25.0) and S. endius (52.4, 31.5, 16.3, 14.6). All species failed to emerge at 15 degrees C. Using densities of five parasitoids and 100 hosts and a 24 h exposure period, Muscidifurax species oviposited at a greater rate over a wider range of temperatures than Spalangia species. At 15, 20, 25, 30 and 35 degrees C the mean number of pupae killed per parasitoid were, respectively, M. raptor (1.4, 7.4, 10.5, 13.7, 14.1), M. zaraptor (0.0, 3.3, 8.9, 14.4, 15.0), S.cameroni (0.0, 7.8, 11.0, 11.9, 7.4), S.endius (0.6, 4.0, 7.5, 12.0, 11.7), and means of the number of parasitoid progeny per parasitoid were, respectively, M.raptor (0.2, 5.2, 7.9, 11.8, 11.6), M.zaraptor (1.3, 4.4, 8.2, 13.0, 13.7), S.cameroni (0.0, 2.4, 4.7, 5.1, 1.0), S.endius (0.0, 0.9, 3.4, 7.5, 4.9). Development and ovipositional activity in S.cameroni was strongly inhibited at 35 degrees C. The model by Sharpe & DeMichele (1977) was used to describe temperature-dependent development and the number of parasitoid progeny produced per parasitoid at temperatures of 15-30 degrees C in all species.     

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

Summary. 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.     

Competition between grass‐cutting Atta vollenweideri ants (Hymenoptera: Formicidae) and domestic cattle (Artiodactyla: Bovidae) in Argentine rangelands

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Occurrence and biological characteristics of parasitoid phorids (Diptera: Phoridae) of the leaf-cutting ant Atta laevigata (Smith) (Hymenoptera: Formicidae) in Porto Nacional, TO, Brazil

The purpose of this study was to verify the occurrence of parasitism in Atta laevigata (Smith) by phorids in Porto Nacional, Tocantins, Brazil and to evaluate some biological characteristics of those flies. From October/2002 to September/2003, at 15-day intervals, 22 samplings were carried out (149.5 +/- 82.9 workers each) comprising 3,704 ants. In the laboratory, the ants were distributed in groups of five individuals per petri dish and maintained at temperature of 25 +/- 1 masculineC and 80 +/- 5% of RH. They were fed daily with a 50% honey solution until death. The total of 106 workers (2.8%), collected with or without load (plant fragment), were parasitized by phorids: 72 workers (68%) were parasitized by Apocephalus vicosae Disney, 28 individuals (26.4%) by Neodohrniphora erthali Brown, and six (5.6%) by Apocephalus attophilus Borgmeier. The higher parasitism rates by A. vicosae (3.9-5.4%) were observed during the dry season (June-August), while the parasitism by N. erthali was lower than 2.3% throughout the year. The bigger workers were parasitized by bigger parasitoid N. erthali or by parasitoid with larger number of larvae A. attophilus. The occurrence of three phorid species in Tocantins broadens the distribution of these flies in Brazil. The development of A. vicosae larva within the thorax of the host as well as the rupture between the ant pronotum and propleuron so that the emergence of the fly can take place are characteristics not yet described on parasitism of leaf-cutting ants by phorids.     

蚁属（膜翅目：蚁科）4种的形态测量学分析

运用形态测量学分析方法,对蚁属Formica中的光亮黑蚁F.candida、亮腹黑褐蚁F.gagatoides、北京凹头蚁F.beijingensis和满洲蚁F.manchu 4种共296头蚂蚁标本进行研究。选取头长(HL)、头宽(HW)、复眼最大直径(ED)、触角柄节长(SL)、并腹胸长(AL)、前胸背板宽(PW)、并胸腹节宽(DPW)和体长(TL)8个度量数据为变量进行相关性、配对T检验、均值±SD与主成分散点分布图分析,探讨形态测量学方法在蚁科昆虫分类中的应用。结果表明:形态测量学方法能够将4种蚂蚁进行有效识别区分,可作为形态分类学研究的一种有效、快速的辅助方法。     

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.     

Spatial distribution of ants (Hymenoptera: Formicidae), vine mealybugs and mealybug parasitoids in vineyards

The mutualistic association between some ant species and honeydew‐producing Hemiptera has been shown to influence the distribution patterns and abundance of these hemipterans and their natural enemies. We studied the spatial distribution patterns of three ant species, mealybugs and mealybug parasitoids for two consecutive growing seasons on three wine grape farms in the Western Cape, South Africa. During the study period, no ant or mealybug controls were applied. Ant and mealybug monitoring was conducted on a total of 21 ha using a presence/absence sampling system, while parasitoids were collected from infested mealybug females. Spatial analysis by distance indices was used to analyse spatial distribution of insects and ArcView? was used to map the gap, patch and local association indices where significant association and disassociation occurred. Significant associations were found between some ants and parasitoids, while significant disassociations between the ants Crematogaster peringueyi and Linepithema humile; and also between Crematogaster peringueyi and Anoplolepis steingroeveri were found. Interspecific competition between ant species could play a role in the distribution of parasitoids and mealybugs. Our results stress the importance of monitoring for ants and mealybugs and further highlight the importance of restricted chemical applications against ants during the growing season.     

External and internal structure of Atta bisphaerica Forel (Hymenoptera: Formicidae) nests

Abstract:  This work was carried out to determine the internal and external structures of Atta bisphaerica (Forel) nests. Six nests were excavated and during excavation, all data referring to chambers and tunnels were recorded. Three nests had been internally cement-moulded, which enabled a better view of the chamber and tunnel structures. Atta bisphaerica nests presented a similar structural pattern, varying only in the number of chambers as a function of external mound area. Chambers were spherical with two communication tunnels. Internal tunnels had an elliptical section, sometimes circular, indirectly linked to chambers through ramifications and directly through short tunnels. Entrance holes were linked to the area of highest chamber concentration by tunnels from the elliptical section, which led to the nest in a radial manner. Knowledge of the colony's three-dimensional architecture permits successful application of chemical control processes, reduces the quantity of product applied, and consequently diminishes costs and environmental damage.     

Oviposition behavior of an ant-parasitizing fly,Neodohrniphora curvinervis (Diptera: Phoridae), and defense behavior by its leaf-cutting ant hostAtta cephalotes (Hymenoptera: Formicidae)

This study examines the oviposition behavior of the phorid parasitoid Neodohrniphora curvinervisand the antiparasitoid defense behavior of its leafcutting ant host Atta cephalotes. N. curvinervisfemales are diurnal sit- and- wait parasitoids that attack only outbound foragers of head width 1.6 mm or greater. Females deposit a single egg through the foramen magnum of each host successfully parasitized. Pursuit of hosts is usually initiated when an outbound forager of acceptable size passes by a parasitoid perch site. Individual foragers defend themselves against pursuing parasitoids by outrunning them along the foraging trail or by standing their ground and fending them off with their legs,antennae, and mandibles. At the colony level, susceptible foragers are protected against parasitism by a shift in the forager size distribution toward smaller unsusceptible sizes during the day when parasitoids are active and toward larger sizes at night when parasitoids are inactive. The frequency of parasitism of susceptible foragers was 15%, which is more than five times the frequency found in another system involving the phorid parasitoid Apocephalus attophilusand the leafcutting ant host Atta colombica.We offer several possible explanations for such differences in the frequency of parasitism and also examine reasons for the high incidence of superparasitism (19%) observed in the system studied.     

Mandibular gland chemistry of four Caribbean species of Camponotus (Hymenoptera: Formicidae)

The volatile components of whole-body extracts of males, females and workers were analyzed in four species of Neotropical ants in the formicine genus, Camponotus. The species, C. kaura, C. sexguttatus, C. ramulorum and C. planatus, represent three different subgenera. Volatile mandibular gland components were found only in male extracts in three of the species. In C. ramulorum, volatile components were found in male and female reproductives and workers. 3,4-Dihydro-3,5-dihydroxy-6-methylpyran-4-one and octanic acid were found in different sets of three of the species. Methyl 6-methyl salicylate was found in two species and the isocoumarin, mellein, was found in a third species. The significance of the mandibular gland secretion for formicid systematics is discussed.     

Bionomics of Orasema simplex (Hymenoptera: Eucharitidae), a parasitoid of Solenopsis fire ants (Hymenoptera: Formicidae) in Argentina

Biological characteristics of the parasitoid Orasema simplex Heraty (Hymenoptera: Eucharitidae), a potential candidate for the biological control of fire ants in the United States were investigated. Female survivorship, fertility and oviposition preferences were studied in the laboratory. Naturally parasitized colonies were examined to determine offspring sex ratio, development success and time, and to artificially parasitize healthy ant colonies. In addition, field studies were carried out to establish natural oviposition substrates and adult activity patterns. Orasema simplex female survivorship was 3.6 ± 1.5 days. Newly emerged females contained 613.5 ± 114.0 mature eggs. The adult development success in natural parasitized colonies was 22.2% with a female-biased sex ratio (4:1). The time required from planidia to adult was 29.5 ± 5.4 days. In the field, adults were mostly found around the ant nests at midday. A broad range of plant species was observed as oviposition substrates. The transfer of planidia to healthy ant colonies was achieved but the development success was very low. Orasema simplex appears to have a limited potential as a fire ant biocontrol agent because of cosmetic damage to a wide variety of plants used for oviposition. However, further studies are necessary to evaluate the real damage exerted by oviposition punctures.     

Interference of beta-eudesmol in nestmate recognition in Atta sexdens rubropilosa (Hymenoptera: Formicidae)

Leaf-cutter ant species (Atta spp.) are key pests of cultivated crops in the Neotropics, and recent studies have demonstrated that workers of Atta spp., particularly of Atta sexdens rubropilosa, exhibit aggressive behavior among nestmates when in contact with the sesquiterpene beta-eudesmol, found in leaves of Eucalyptus maculata. However, the underlying mechanism sparking this behavior pattern has yet to be investigated. This work aimed to elucidate the mechanism by which this substance elicits aggression in workers of A. sexdens rubropilosa. The results, thus obtained, showed that beta-eudesmol is able to modify the chemical composition of the workers cuticle, impairing nestmate recognition, triggering alarm behavior and leading to nestmate aggression.     

Community dynamics of leafminers (Diptera: Agromyzidae) and their parasitoids (Hymenoptera) in a natural habitat from Central Argentina

We examined the temporal community dynamics of leafminers (Agromyzidae: Diptera) and their mainly polyphagous parasitoids in a natural habitat from Central Argentina. Changes in community composition are shown by changes in dominant species and similarity coefficients. Abundance of leafminers was highest in winter, and was not related to their species richness. Abundance and species richness were correlated in the parasitoid community. Temporal variation in parasitoid diversity and abundance were positively correlated with species number and density in the host community. Apparent parasitism was greater when parasitoid species richness was high and parasitoid community dominance was low.     

Phorid flies, Pseudacteon spp. (Diptera: Phoridae), affect forager size ratios of red imported fire ants Solenopsis invicta (Hymenoptera: Formicidae) in Texas

Multiple species of Pseudacteon phorid flies (Diptera: Phoridae) are currently being released throughout the southern United States to aid biological control of red imported fire ants, Solenopsis invicta Buren (Hymenoptera: Formicidae). It is anticipated that these flies will interfere with S. invicta foraging, allowing native ant assemblages to outcompete S. invicta for available resources. Numerous studies have shown a decrease in S. invicta foraging intensity when exposed to phorids. This study documents a behavioral change in phorid-exposed S. invicta colonies at a phorid release site in central Texas. Significant differences in forager size ratios were detected between phorid-exposed and phorid-absent colonies. A similar phenomenon was recently documented in the native range of these insects in South America as well. Experimental manipulation of ratios of S. invicta worker sizes has been shown to have important effects on colony success. This newly documented phorid-mediated S. invicta colony-level effect represents a significant shift in S. invicta foraging dynamics and may provide an additional mechanism by which phorids can influence S. invicta populations in their United States range.     

Dynamic expansion in recently introduced populations of fire ant parasitoids (Diptera: Phoridae)

Combating invasive species requires a detailed, mechanistic understanding of the manner and speed with which organisms expand their ranges. Biological control efforts provide an opportunity to study the process of species invasions and range expansions under known initial conditions. This study examines the rate, pattern and mechanisms of spread for two populations of the biological control agent Pseudacteon tricuspis, phorid-fly parasitoids of imported fire ants. We employ a trap-based survey method that detects phorid flies in low-density populations, and provides data on abundance. This technique allows us to differentiate between continuous population spread and effective long-distance dispersal and to examine density gradients of phorid flies across the expanding population front. We find that occupied sites in front of the leading edge of continuous populations were common; forming small populations we refer to as satellite populations. Satellite populations are tens of kilometers from the nearest possible source. Wind governs the dynamics of spread in these two central Texas populations. Population edges expanding with the wind exhibited a higher frequency of effective long-distance dispersal than did populations expanding into the wind. This enhanced effective long-distance dispersal rate translated into a five times faster rate of spread for population edges traveling with the wind. This planned invasion shares many characteristics in common with unplanned species invasions including: protracted establishment phase during which densities were below detection thresholds, and slow initial spread immediately after establishment followed by rapid, accelerating spread rates as population sizes grew.     

Orientation by magnetic field in leaf-cutter ants, Atta colombica (Hymenoptera: Formicidae)

Leaf‐cutter ants (Atta colombica) use trail following to travel between foraging sites and the home nest. However, this combination of pheromone and visual cues is likely to be complemented by a directional reference system such as a compass, used not only when foraging but also during colony formation, where foraging trails degrade or where ants become displaced. One candidate system is the magnetic polarity compass. We tested the orientation of leaf‐cutter ants under a magnetic field of reversed‐polarity, with the prediction that the ants would show 180° deflection compared with control ants in an unchanged geomagnetic field. When the sun's disc was unobstructed by clouds, orientation was the same as that of control ants, implying that magnetic cues were not used to orient. However, when the sky was overcast, ants in the experimental treatment significantly shifted their mean orientation both in comparison with controls and reversed‐polarity ants under the sun. Although a total reversal in orientation was not induced, the results demonstrate that Atta respond to magnetic reversal in the absence of sunlight cues, and suggest a role for magnetic cues in determining direction during orientation.