Zombie fire ant workers: behavior controlled by decapitating fly parasitoids

Laboratory observations were conducted on four separate red imported fire ant, Solenopsis invicta, colonies that contained workers parasitized by the decapitating fly, Pseudacteon tricuspis. Parasitized S. invicta workers remained inside the nest during parasitoid larval development and left the nest approximately 8 – 10 hours before decapitation by the parasitoid. When parasitized ants left the nest, they were highly mobile, were responsive to tactile stimuli, and showed minimal defensive behavior. Ants ultimately entered into a grass thatch layer, where they were decapitated and the fly maggots pupariated. This study reveals that parasitized ants exhibit behaviors that are consistent with host manipulation to benefit survival of the parasitoid. Received 9 November 2006; revised 26 January 2007; accepted 7 February.     

Parasitism <Emphasis Type="Italic">versus</Emphasis> mutualism in the ant-garden parabiosis between <Emphasis Type="Italic">Camponotus femoratus</Emphasis> and <Emphasis Type="Italic">Crematogaster levior</Emphasis>

Ant-gardens represent a special type of association between ants and epiphytes. Frequently, two ant species can share the same nest in a phenomenon known as ‘parabiosis’, but the exact nature (i.e., mutualistic or parasitic) of this interaction is the subject of debate. We thus attempted to clarify the mutual costs and benefits for each partner (ants and plants) in the Crematogaster levior/Camponotus femoratus ant-garden parabiosis. The ants’ response to experimental foliar damage to the epiphytes and to the host tree as well as their behavior and interactions during prey capture were investigated to see if the purported parasitic status of Cr. levior could be demonstrated in either the ant-ant or in the ant-plant interactions. The results show that both species take part in protecting the epiphytes, refuting the role of Cr. levior as a parasite of the ant-garden mutualism. During capture of large prey Ca. femoratus took advantage from the ability of Cr. levior to discover prey; by following Cr. levior trails Ca. femoratus workers discover the prey in turn and usurp them during agonistic interactions. Nevertheless, the trade-off between the costs and benefits of this association seems then to be favorable to both species because it is known that Cr. levior benefits from Ca. femoratus building the common carton nests and furnishing protection from vertebrates. Consequently, parabiosis can then be defined as the only mutualistic association existing between ant species, at least in ant-gardens. Received 31 August 2006 ; revised 8 December 2006 ; accepted 12 December 2006     

Behavioral mechanisms of collective nest-site choice by the ant Temnothorax curvispinosus

This paper examines the individual behavior underlying collective choice among nest sites by the ant Temnothorax (formerly Leptothorax) curvispinosus. Colonies can actively compare options, rejecting a mediocre site when it is paired with a good one, but accepting the same mediocre design if it is instead paired with a worse site. This ability emerges from the behavior of an active minority of workers who organize emigrations. When one of these finds a promising site, she recruits nest mates to it, but only after a delay that varies inversely with site quality. Ants first recruit fellow active ants via slow tandem runs, but eventually switch to speedier transports of the colony’s passive majority. Later transports grow faster still, as ants improve their speed with experience. An ant’s choice of recruitment type is governed by a quorum rule, such that her likelihood of starting to transport increases with the population of the new site. The size of the quorum depends on experience, with ants demanding a larger population to launch immediately into transport than they do to switch to transport after first leading a few tandem runs. Perception of quorum attainment requires direct contact between ants. The ants’ behavior qualitatively matches that of T. albipennis, where models have shown that decentralized choice of the best site depends on quality-dependent recruitment delays, amplified by a quorum rule for initiating transport. Parameter estimates for an agent-based model show significant quantitative differences between the species, and suggest that T. albipennis may place relatively greater emphasis on emigration speed. Received 11 February 2005; revised 10 May 2005; accepted 20 May 2005.     

Nesting biology of the arboreal fungus-growing ant <Emphasis Type="Italic">Cyphomyrmex cornutus</Emphasis> and behavioral interactions with the social-parasitic ant <Emphasis Type="Italic">Megalomyrmex mondabora</Emphasis>

We describe the extraordinary nesting habits of the fungus-growing ant Cyphomyrmex cornutus (Formicidae, Myrmicinae, Attini) and the natural history of Megalomyrmex mondabora (Formicidae, Myrmicinae, Solenopsidini), a social parasite that inhabits nests of C. cornutus and other small attine ants. The study was carried out at two sites on the Atlantic slope of Costa Rica. The C. cornutus nest is an oblong mass of accreted soil, attached to or suspended from low vegetation in wet forest understory. Less than a fourth of the nest volume has chambers and is inhabited by C. cornutus; the remainder is a semi-solid mass of accreted soil often housing a variety of arthropods, including other unspecialized commensal ant species. Five C. cornutus colonies examined were parasitized by M. mondabora. Colonies of M. mondabora inhabited chambers very near those of the host. In laboratory observations, M. mondabora and C. cornutus workers interacted with little aggression despite the consumption of C. cornutus larvae and fungi by M. mondabora. During most interactions, C. cornutus workers responded submissively, whereas M. mondabora appeared indifferent or nonresponsive. Megalomyrmex mondabora parasitizes several other attine species (Cyphomyrmex costatus, Cyphomyrmex salvini, and Apterostigma goniodes), and it appears therefore a relatively unspecialized social parasite with broad attine hostassociation. The size of M. mondabora workers vary with host species, suggesting M. mondabora sensu lato comprises either cryptic species or the host environment affects worker size. Received 14 September 2006; revised 1 February 2007; accepted 6 February 2007.     

The reproductive phenology of an Amazonian ant species reflects the seasonal availability of its nest sites

In saturated tropical ant assemblages, reproductive success depends on queens locating and competing for scarce nest sites. Little is known about how this process shapes the life histories of tropical ants. Here I investigate the relationship between nest site availability and an important life history trait, reproductive phenology, in the common Amazonian ant species Allomerus octoarticulatus. A. octoarticulatus is a plant-ant that nests in the hollow, swollen stem domatia on Cordia nodosa. I provide evidence that nest sites are limiting for A. octoarticulatus. Most queens produced by A. octoarticulatus colonies died before locating suitable host plants, and most queens that located hosts died before founding colonies, probably from intraspecific competition among queens for control of host plants. I further show that the reproductive phenology of A. octoarticulatus closely matches the seasonal availability of its nest sites, domatia-bearing C. nodosa saplings. Both the production and flight of A. octoarticulatus reproductives, and the number of C. nodosa saplings available for colonization by ants, peaked from March to May. There was correlative evidence that A. octoarticulatus colonies use temperature as a cue to synchronize their reproduction to the availability of C. nodosa saplings: both the production of reproductives by ant colonies and the number of C. nodosa saplings available for colonization were correlated with temperature, and not with rainfall. All of these results suggest that nest site limitation constrains the reproductive phenology of A. octoarticulatus.     

Costs and benefits of joint colony founding in Australian Acacia thrips

Facultative joint colony founding by social insects (pleometrosis) provides an outstanding opportunity to analyze the costs and benefits of sociality. Pleometrosis has been documented for a range of social insects, but most studies on the adaptive benefits of this behavior are restricted to the Hymenoptera. In this study, we provide the first analysis of costs and benefits associated with pleometrosis for Australian Dunatothrips, which form domiciles by glueing together phyllodes (leaves) of their Acacia host plant. In Dunatothrips aneurae, the distribution of foundress numbers per nest indicated that females formed associations non-randomly. Furthermore, average group size was independent of both the number of foundresses on the host plant and the number of mature colonies, suggesting that this behavior was not simply a response to limited availability of nesting sites. Although per capita reproduction declined with increasing group size, we also identified two benefits of pleometrosis: (1) individual foundresses in groups had higher survival than solitary foundresses during the brood development period, and (2) larger colony sizes resulting from pleometrosis provided a benefit later in colony development, because a higher proportion of D. aneurae adults survived invasions by the kleptoparasite Xaniothrips mulga when colony size was larger. These results demonstrate that the reproductive costs of pleometrosis are at least partially counterbalanced by survival benefits. Received 4 April 2006; revised 9 September 2006; accepted 20 September 2006.     

Excavation and architecture of Argentine ant nests

We used x-ray computed tomography to study the elaboration of nest structures in small sand-filled nest boxes by Argentine ant (Linepithema humile) colonies composed of 10, 100, and 1000 workers. The pattern of nest growth was consistent with a process of density-dependent stimulation of excavation, which subsided as nests grew and the density of digging stimuli declined. Thus, nest excavation would be auto-regulating, and final nest size should be adjusted to colony size. We found that excavation rates and final nest sizes increased with colony size, but were not tenfold greater in 1000-worker colonies than in 100-worker colonies. In the largest colonies, the internal surface area scaled allometrically with volume, so that more surface was obtained relative to volume excavated as the nest grew. Although the gross features of Argentine ant nests, such as total size, seem explicable by a simple, self-organized regulatory process, other features of the nest architecture will require further investigation. Received 3 March 2005; revised 26 April 2005; accepted 3 May 2005.     

Larval aquatic and terrestrial mites infesting a temperate assemblage of mosquitoes

We collected 22,769 adult female mosquitoes, representing 27 species, from light traps in Norfolk, Virginia (2006–2007) and examined them to assess infestation by larval mites. Mosquitoes were parasitized by two species of aquatic (Acari: Arrenuridae: Arrenurus) and three species of terrestrial mites (Acari: Erythraeidae). The prevalence of infestation varied from 0.55% (2006) to 0.17% (2007). The mean intensity of parasitism ranged from 3.6 mites per host (2006) to 1.8 mites per host (2007). The most common host species for aquatic mites was Culex erraticus, while the most common host for terrestrial mites was Anopheles quadrimaculatus. Relationships between biotic and abiotic factors were investigated in an attempt to provide insight into temporal, spatial, and interspecific variation in mite–mosquito interactions. Scanning electron microscopy was used to examine the mode of attachment for larval mites. While the prevalence of aquatic mite parasitism was correlated for Culex erraticus, the invasive mosquito, Aedes albopictus, was never parasitized through the duration of the study. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Diel changes of temperature in the nests of two Polybia species, P. paulista and P. occidentalis (Hymenoptera, Vespidae) in the subtropical climate

Temperatures in two mature Polybia nests were measured to study the thermal conditions of nests. Temperatures in a Polybia paulista nest were measured when it had adult wasps (trial 1) and after the adult wasps were removed (trial 2), and temperatures in a P. occidentalis nest were measured when inhabited by adult wasps (trial 3). In each trial, C–C thermocouples were set at four points in the nest and at two points outside to discover the ambient and substratum temperatures. In trial 1, nest temperatures basically followed the ambient temperature, but during the day the nest temperatures were lower than the ambient temperature and this relationship was reversed during the night. The temperature fluctuation of the inner substratum points was smaller than that of the outer points. The trend of trial 2 was closely similar to that of trial 1, showing a virtual lack of thermal effects from the presence of adult wasps. In trial 3, the changing pattern in the P. occidentalis nest showed a trend similar to that in the P. paulista nest, but the inside temperatures rose quickly when the nest received direct sunlight in the morning. From these results, thermal characteristics in the Polybia nests are discussed in relation to the nest architecture and their geographical distribution.     

The development and multiple uses of a standardised bioassay method to select hypocrealean fungi for biological control of aphids

A technically standardised bioassay method was designed, evaluated and used to assess virulence and host range of hypocrealean fungi against aphids. A track mounted sprayer was used to apply conidia because hand held versions of the same sprayer can be used for field applications, thereby allowing the outcome from laboratory experiments to predict activity in the field accurately. Eighteen fungal isolates were assessed in single concentration bioassays against the black bean aphid Aphis fabae Scopoli. Isolates comprised commercially available mycoinsecticides (based on Beauveria bassiana and Lecanicillium longisporum) and isolates of B. bassiana, Lecanicillium spp., Paecilomyces fumosoroseus and Metarhizium anisopliae. Aphid mortality was in excess of 80% for 15 isolates, and HRI 1.72 (L. longipsorum), Z11 (P. fumosoroseus), Mycotech strain GHA (B. bassiana) and ARSEF 2879 (B. bassiana) were studied further. Multiple concentration bioassays identified HRI 1.72 as the most virulent isolate against A. fabae with significantly smaller LC₅₀ and LT₅₀ values compared to other isolates. A precise LC₅₀ value (2.95 × 10² conidia ml⁻¹) was calculated for HRI 1.72 using a second multiple concentration assay with smaller concentrations of conidia. The four isolates were applied at a single concentration (1 × 10⁸ conidia ml⁻¹) against Myzus persicae, A. fabae, Acyrthosiphon pisum, Metopolophium dirhodum, Sitobion avenae and Rhopalosiphum padi. A ranking of aphid susceptibility was obtained, such that S. avenae > M. persicae, A. pisum, A. fabae > R. padi. Results indicate the importance of standardising bioassay methods to reduce bioassay variability without compromising the ability to use the bioassay to investigate fungus–host interactions under varying abiotic and biotic conditions.     

Impacts of Argentine ants on avian nesting success

Biological invasions can have severe and widespread impacts on ecological communities. A few species of ants have become particularly damaging invaders but quantitative data of their impacts on many taxa is still lacking. We provide experimental evidence using artificial nests baited with quail eggs that the invasive Argentine ant (Linepithema humile) can be a significant avian nest predator – Argentine ants recruited to more nests and in higher abundance than the native ant species they displace. However, at a site invaded by Argentine ants, we monitored over 400 nests of a ground-nesting species, the Dark-eyed Junco (Junco hyemalis), and found that less than 2% of nests failed as a result of Argentine ant predation/infestation. A review of the literature also suggests that Argentine ants may not be a serious threat to bird nests relative to other predators or parasites. However, invasive ants with the capability of overwhelming prey though stinging (specifically the red-imported fire ant, Solenopsis invicta), may have a higher impact on avian nesting success. Received 14 January 2005; revised 28 April 2005; accepted 12 May 2005.     

Colony size affects collective decision-making in the ant Temnothorax albipennis

Social insects are well-known for their ability to achieve robust collective behaviours even when individuals have limited information. It is often assumed that such behaviours rely on very large group sizes, but many insect colonies start out with only a few workers. Here we investigate the influence of colony size on collective decision-making in the house-hunting of the ant Temnothorax albipennis. In experiments where colony size was manipulated by splitting colonies, we show that worker number has an influence on the speed with which colonies discover new nest sites, but not on the time needed to make a decision (achieve a quorum threshold) or total emigration time. This occurred because split colonies adopted a lower quorum threshold, in fact they adopted the same threshold in proportion to their size as full-size colonies. This indicates that ants may be measuring relative quorum, i.e. population in the new nest relative to that of the old nest, rather than the absolute number. Experimentally reduced colonies also seemed to gain more from experience through repeated emigrations, as they could then reduce nest discovery times to those of larger colonies. In colonies of different sizes collected from the field, total emigration time was also not correlated with colony size. However, quorum threshold was not correlated with colony size, meaning that individuals in larger colonies adopted relatively lower quorum thresholds. Since this is a different result to that from size-manipulated colonies, it strongly suggests that the differences between natural small and large colonies were not caused by worker number alone. Individual ants may have adjusted their behaviour to their colony’s size, or other factors may correlate with colony size in the field. Our study thus shows the importance of experimentally manipulating colony size if the effect of worker number on the emergence of collective behaviour is to be studied. Received 13 December 2005; revised 9 May 2006; accepted 15 May 2006.     

Evaluating the impact of a biological control parasitoid on invasive Vespula wasps in a natural forest ecosystem

The overall impact of the parasitoid Sphecophaga vesparum vesparum on invasive Vespula wasps in New Zealand native beech forest was evaluated by assessing the levels of parasitism achieved and the parasitoid’s effect at nest level and population level. The maximum proportion of nests parasitised was 17%, but there was no significant increase with time (r² = 0.139; p = 0.115). However, there was an exponential reduction in the number of parasitoids produced per parasitised nest from a peak of 570 (SE = 143) parasitoids per nest in 1990, declining to only 15 (SE = 6) parasitoids per nest in 2004. Even when parasitoid density was high, the parasitoid had no detectable impact on the number of small cells or the total host nest size, but it halved the number of large (reproductive) cells produced. This may have resulted in fewer queens produced per parasitised nest. Wasp nest density was highly variable from year to year, but there was no evidence that the wasp population density at the parasitised site (Pelorus Bridge) had declined relative to the five sites where the parasitoid had not established. We conclude that the parasitoid is unlikely to have had any significant effect on wasp populations hitherto, nor is it likely to impact host populations in the future. We recommend other biological control programs adopt pre-release assessment of per capita impact as a way of identifying agents that are more likely to be successful and hence minimising economic and potential ecological costs of biocontrol.     

Releases of Trichogramma platneri (Hymenoptera: Trichogrammatidae) in Apple Orchards under a Sterile Codling Moth Release Program

Based on the premise that augmented host numbers may help multiply and support parasitoid populations, the egg parasitoid Trichogramma platneri Nargarkatti was released in apple orchards which were participating in a sterile codling moth, Cydia pomonella (L.), release program. Nonviable eggs resulting from matings involving at least one sterile codling moth partner can be successfully parasitized by T. platneri. Grain moth-reared, as well as codling moth-reared, T. platneri were released either in the spring or in the spring and summer oviposition period(s) of wild codling moth. Sentinel codling moth eggs were hung weekly, for 3-day periods, from May until September to determine fluctuations in T. platneri populations both during and between releases. Low numbers of wild or nonviable codling moth eggs or other susceptible host eggs resulted in sufficient eggs to maintain low spring- or summer-introduced T. platneri populations. T. platneri reduced codling moth damage in trees in which the Trichogramma were released.     

Metapopulation genetic structure of two coexisting parasitoids of the Glanville fritillary butterfly

We investigated the metapopulation genetic structure of two specialist parasitoids, Cotesia melitaearum and Hyposoter horticola, attacking the Glanville fritillary butterfly (Melitaea cinxia) in the Åland Islands south-western Finland. The host butterfly persists as a classic metapopulation in a network of 4,000 small habitat patches within an area of 50 by 70 km . The two parasitoids are known to differ greatly in their population dynamics and spatial pattern of occupancy in local host populations. Analysis of genetic population structure using F_ST and clustering of multilocus genotypes revealed a distinct large-scale spatial structure in C. melitaearum but a very weak pattern in H. horticola. This result is consistent with the known difference in the dispersal range (much longer in H. horticola) and population size (much greater in H. horticola) of the two parasitoids.     

Are ecological compensation areas attractive hunting sites for common kestrels (Falco tinnunculus) and long-eared owls (Asio otus)?

Common kestrels (Falco tinnunculus) and long-eared owls (Asio otus) in intensively farmed areas in Switzerland decreased markedly as a result of declining vole (Microtus spp.) populations. In order to counteract the loss of biodiversity in intensively farmed areas, the Swiss agri-environment scheme stipulates several types of ecological compensation areas, which together should take up 7% of the farmland. Among them are wild flower and herbaceous strips, which are not mown every year and which in summer support up to 8 times more small mammals than ordinary fields and grassland. This study investigates whether kestrels and long-eared owls preferentially hunt on ecological compensation areas and whether preferred hunting areas are related to the density of small mammals or to the density and height of the vegetation. Both kestrels and long-eared owls mainly hunted on freshly mown low-intensity meadows and artificial grassland, despite low densities of small mammals. Therefore, vegetation structure was more important for the selection of hunting sites than prey abundance. However, both predators preferred to hunt on freshly mown grassland and meadows bordering a wild flower or herbaceous strip. Voles from these strips probably invaded the adjacent freshly mown grassland and became an easy prey for kestrels and owls. In intensively farmed regions, ecological compensation areas, particularly those not mown each year, are an important refuge for small mammals, although in summer the small mammals are not directly accessible to hunting birds. Hence, a mosaic of different habitat types with grassland mown at different times of the year together with undisturbed strips is best suited to provide a year-round supply of accessible food for vole hunters.     

Intraspecific nest parasitism in the grey starling (Sturnus cineraceus)

We studied intraspecific nest parasitism in the grey starling (Sturnus cineraceus) in 1992 and 1993. We used three criteria to detect nest parasitism: (i) the appearance of more than one egg per day while the host was laying; (ii) the appearance of extra eggs after the host completed its clutch; and (iii) the appearance of eggs which were of a different shape, size and color to other eggs in the clutch. There were 290 nests (157 nests in 1992; 133 nests in 1993) in which the clutch was completed early (clutches initiated before May 10). Twenty-nine (1992) and 32 (1993) nests contained at least one parasitic egg. Parasitic eggs hatched if they were laid during the laying period and early in the incubation period of their host, and a few of them fledged. Fledging success of parasitic eggs was not different from that of eggs in non-parasitized nests if parasitic eggs were laid during the host's laying period. However, fledging success of all parasitic eggs was fewer than that of eggs in non-parasitized nests. By comparison, fledging success of parasitized nests was not a great as that of non-parasitized nests.     

Geographic locality and host identity shape fungal endophyte communities in cupressaceous trees

Understanding how fungal endophyte communities differ in abundance, diversity, taxonomic composition, and host affinity over the geographic ranges of their hosts is key to understanding the ecology and evolutionary context of endophyte–plant associations. We examined endophytes associated with healthy photosynthetic tissues of three closely related tree species in the Cupressaceae (Coniferales): two native species within their natural ranges [Juniperus virginiana in a mesic semideciduous forest, North Carolina (NC); Cupressus arizonica, under xeric conditions, Arizona (AZ)], and a non-native species planted in each site (Platycladus orientalis). Endophytes were recovered from 229 of 960 tissue segments and represented at least 35 species of Ascomycota. Isolation frequency was more than threefold greater for plants in NC than in AZ, and was 2.5 (AZ) to four (NC) times greater for non-native Platycladus than for Cupressus or Juniperus. Analyses of ITS rDNA for 109 representative isolates showed that endophyte diversity was more than twofold greater in NC than in AZ, and that endophytes recovered in AZ were more likely to be host-generalists relative to those in NC. Different endophyte genera dominated the assemblages of each host species/locality combination, but in both localities, Platycladus harboured less diverse and more cosmopolitan endophytes than did either native host. Parsimony and Bayesian analyses for four classes of Ascomycota (Dothideomycetes, Sordariomycetes, Pezizomycetes, Eurotiomycetes) based on LSU rDNA data (ca 1.2 kb) showed that well-supported clades of endophytes frequently contained representatives of a single locality or host species, underscoring the importance of both geography and host identity in shaping a given plant's endophyte community. Together, our data show that not only do the abundance, diversity, and taxonomic composition of endophyte communities differ as a function of host identity and locality, but that host affinities of those communities are variable as well.     

Nesting habits of two spider wasps: Anoplius infuscatus and Episyron sp. (Hymenoptera: Pompilidae), with a review of the literature

Many behavioural aspects of Anoplius infuscatus (Vander Linden) and Episyron sp. Schioedte were examined in detail, both on a qualitative and, when possible, on a quantitative level, during a long-term field study in Northern Italy. Both wasps dig unicellular nests on bare soil, which are filled with a single spider to feed the brood. The main differences regard the way to hunt their prey, that of burrowing, that of transporting and introducing the spider into the nest, the habit of amputating spider legs and the abdominal movements during nest closing. On the whole, starting from prey capture to nest closure, A. infuscatus is significantly slower than Episyron. The observed ethological differences are well fitted to the exploitation of the different preys consisting in wolf spiders (Lycosidae) and orb weaving spiders (Araneidae), respectively. Some flexibility in the observed behaviour is described. A critical re-examination of the literature shows that, even if most results agree with those of previous authors, two controversial points remain open regarding Episyron species: the position of the egg (on the prey or on the cell wall) and the way to grasp the spider during tranport and introdution into the nest.