Macrodinychus mites as parasitoids of invasive ants: an overlooked parasitic association

First Record of the Elusive Ant Parasitoid Horismenus floridensis (Hymenoptera: Eulophidae) in Mexico and New Association with an Ant Host

Most eulophid wasps are primary parasitoids, mainly of endophytic insect larvae (Diptera, Coleoptera, Lepidoptera, Hymenoptera, Hemiptera, and Thysanoptera), but can also attack spider eggs, gall-forming mites, or nematodes. A few species are known to parasitize ants. Here we report on the occurrence of Horismenus floridensis (Schauff and Bouček) attacking Camponotus atriceps (Smith) in southern Mexico (Campeche), expanding the distribution for this eulophid species and the range of its potential hosts. We also provide an updated list of the Horismenus Walker species found in Mexico, which currently includes 21 identified species. This is the second host ant ever recorded for H. floridensis and the first reliable record of C. atriceps as a host for this eulophid wasp. The first host ant reported from Florida 35 years ago was the closely related valid species, C. floridanus (Buckley), erroneously synonymized at that time with C. atriceps (formerly, C. abdominalis (Fabricius)).

Phoresy and Mites: More Than Just a Free Ride

Mites are masters at attaching to larger animals, often insects, in a temporary symbiosis called phoresy that allows these tiny animals to exploit patchy resources. In this article, we examine phoresy in the Acari, including those that feed on their carriers in transit, from a broad perspective. From a phylogenetic perspective, phoresy has evolved several times from free-living ancestors but also has been lost frequently. Rotting logs appear to be the first patchy resource exploited by phoretic mites, but the evolution of rapid life cycles later permitted exploitation of short-lived resources. As phoresy is a temporary symbiosis, most species have off-host interactions with their carrier. These relationships can be highly complex and context dependent but often are exploitative of the carrier's resources or progeny. Transitions from phoresy to parasitism seem widespread, but evidence for transitions from obligate phoretic parasitism to permanent parasitism is weak.

Honey bees increase social distancing when facing the ectoparasite Varroa destructor

Social distancing in response to infectious diseases is a strategy exhibited by human and nonhuman animals to counteract the spread of pathogens and/or parasites. Honey bee (Apis mellifera) colonies are ideal models to study this behavior because of the compartmentalized structure of these societies, evolved under exposure to parasite pressure and the need to ensure efficient functioning. Here, by using a combination of spatial and behavioral approaches, we investigated whether the presence of the ectoparasite mite Varroa destructor induces changes in the social organization of A. mellifera colonies that could reduce the spread of the parasite. Our results demonstrated that honey bees react to the intrusion of V. destructor by modifying space use and social interactions to increase the social distancing between young (nurses) and old (foragers) cohorts of bees. These findings strongly suggest a behavioral strategy not previously reported in honey bees to limit the intracolony parasite transmission.

Feeding design in free-living mesostigmatid chelicerae (Acari: Anactinotrichida)

A model based upon mechanics is used in a re-analysis of historical acarine morphological work augmented by an extra seven zoophagous mesostigmatid species. This review shows that predatory mesostigmatids do have cheliceral designs with clear rational purposes. Almost invariably within an overall body size class, the switch in predatory style from a worm-like prey feeding ('crushing/mashing' kill) functional group to a micro-arthropod feeding ('active prey cutting/slicing/slashing' kill) functional group is matched by: an increased cheliceral reach, a bigger chelal gape, a larger morphologically estimated chelal crunch force, and a drop in the adductive lever arm velocity ratio of the chela. Small size matters. Several uropodines (Eviphis ostrinus, the omnivore Trachytes aegrota, Urodiaspis tecta and, Uropoda orbicularis) have more elongate chelicerae (greater reach) than their chelal gape would suggest, even allowing for allometry across mesostigmatids. They may be: plesiosaur-like high-speed strikers of prey, scavenging carrion feeders (like long-necked vultures), probing/burrowing crevice feeders of cryptic nematodes, or small morsel/fragmentary food feeders. Some uropodoids have chelicerae and chelae which probably work like a construction-site mechanical excavator-digger with its small bucket. Possible hoeing/bulldozing, spore-cracking and tiny sabre-tooth cat-like striking actions are discussed for others. Subtle changes lead small mesostigmatids to be predator-scavengers (mesocarnivores) or to be predator-fungivores (hypocarnivores). Some uropodines (e.g., the worm-like prey feeder Alliphis siculus and, Uropoda orbicularis) show chelae similar in design to astigmatids and cryptostigmatids indicating possible facultative saprophagy. Scale matters-obligate predatory designs (hypercarnivory) start for mesostigmatids with chelal gape > 150 μm and cheliceral reach > 350 μm (i.e., about 500-650 μm in body size). Commonality of trophic design in these larger species with solifugids is indicated. Veigaia species with low chelal velocity ratio and other morphological strengthening specialisms, appear specially adapted in a concerted way for predating active soft and fast moving springtails (Collembola). Veigaia cerva shows a markedly bigger chelal gape than its cheliceral reach would proportionately infer suggesting it is a crocodile-like sit-and-wait or ambush predator par excellence. A small chelal gape, low cheliceral reach, moderate velocity ratio variant of the worm-like feeding habit design is supported for phytoseiid pollenophagy. Evidence for a resource partitioning model in the evolution of gnathosomal development is found. A comparison to crustacean claws and vertebrate mandibles is made. Alliphis siculus and Rhodacarus strenzkei are surprisingly powerful mega-cephalics for their small size. Parasitids show a canid-like trophic design. The chelicera of the nematophagous Alliphis halleri shows felid-like features. Glyphtholaspis confusa has hyaena-like cheliceral dentition. The latter species has a markedly smaller chelal gape than its cheliceral reach would suggest proportionately, which together with a high chelal velocity ratio and a high estimated chelal crunch force matches a power specialism of feeding on immobile tough fly eggs/pupae by crushing (durophagy). A consideration of gnathosomal orientation is made. Predatory specialisms appear to often match genera especially in larger mesostigmatids, which may scale quite differently. Comparison to holothyrids and opilioacarids indicates that the cheliceral chelae of the former are cutting-style and those of the latter are crushing-style. A simple validated easy-to-use '2:1 on' predictive algorithm of feeding habit type is included based on a strength-speed tradeoff in chelal velocity ratio for ecologists to test in the field.

Emigrating Together but Not Establishing Together: A Cockroach Rides Ants and Leaves

AbstractSymbionts of ant colonies can hitchhike on winged ant reproductives (alates) during colony nuptial flights. Attaphila fungicola Wheeler, a miniature cockroach that lives in the nests of Texas leaf-cutter ants (Atta texana Buckley), hitchhikes on female alates (winged queens). Hitchhiking roaches are presumably vertically transmitted from leaf-cutter parent colonies to daughter colonies, remaining with female alates as they transition into foundresses (workerless queens); however, foundresses have limited resources and high mortality rates. Rather than remaining with foundresses likely to die (vertical transmission), roaches might abandon them during dispersal to infect higher-quality later stages of colony development (female alate-vectored transmission). In field experiments, I find evidence for female alate-vectored transmission and discover that roaches use a second hitchhiking step (riding foraged plant material) to infect established colonies. This work reveals a novel relationship between host dispersal and symbiont transmission and shows that colony development can be an important selection pressure on transmission.

Genetic Diversity and Wolbachia Infection Patterns in a Globally Distributed Invasive Ant

Understanding the phylogeographic history of an invasive species may facilitate reconstructing the history and routes of its invasion. The longhorn crazy ant, Paratrechina longicornis, is a ubiquitous agricultural and household pest throughout much of the tropics and subtropics, but little is known about the history of its spread. Here, we examine worldwide genetic variation in P. longicornis and its associated Wolbachia bacterial symbionts. Analyses of mtDNA sequences of 248 P. longicornis workers (one per colony) from 13 geographic regions reveal two highly diverged mtDNA clades that co-occur in most of the geographic regions. These two mtDNA clades are associated with different Wolbachia infection patterns, but are not congruent with patterns of nDNA (microsatellite) variation. Multilocus sequence typing reveals two distinct Wolbachia strains in P. longicornis, namely, wLonA and wLonF. The evolutionary histories of these two strains differ; wLonA appears to be primarily transmitted maternally, and patterns of mtDNA and nDNA variation and wLonA infection status are consistent with a relatively recent Wolbachia-induced selective sweep. In contrast, the observed patterns of mtDNA variation and wLonF infections suggest frequent horizontal transfer and losses of wLonF infections. The lack of nDNA structure among sampled geographic regions coupled with the finding that numerous mtDNA haplotypes are shared among regions implies that inadvertent long-distance movement through human commerce is common in P. longicornis and has shaped the genetic structure of this invasive ant worldwide.

Context dependent life-history shift in Macrodinychus sellnicki mites attacking a native ant host in Colombia

Ant parasitoidism has been reported in seven of the 26 recognized species of the mite genus Macrodinychus (Machrodynichidae). Macrodynichus sellnicki, previously reported as a parasitoid of the invasive ant Nylanderia fulva in Colombia, is now reported, in the same region, as attacking a native host, Ectatomma sp. 2 (E. ruidum complex). The mite develops within the protective silk cocoon of an Ectatomma pupa and waits for the emergence of the young ant before leaving the cocoon, unmolested. Overall nest prevalence was relatively high (34.6% of the 52 nests containing cocoons) but pupae prevalence was low (4.0%, n = 1401 cocoons). Mite life-history (parasite or parasitoid) was context dependent, shifting according to the intensity of the attack on a same host. Contrary to the strictly parasitoidic association of M. sellnicki with N. fulva, single mite attacks against E. ruidum did not result in host killing and solitary M. sellnicki (78.6% of the cases) behaved as parasites. However, in 21.4% of the attacks (0.9% of all available host pupae) more than one mite was involved and behaved as parasitoids, draining the host of its internal fluids and killing it. This is the first association of a macrodinychid mite with a species of the subfamily Ectatomminae, and the first ant associated mite for which such a context dependent life-style shift is described.

Fine-tuned intruder discrimination favors ant parasitoidism

A diversity of arthropods (myrmecophiles) thrives within ant nests, many of them unmolested though some, such as the specialized Eucharitidae parasitoids, may cause direct damage to their hosts. Ants are known to discriminate between nestmates and non-nestmates, but whether they recognize the strength of a threat and their capacity to adjust their behavior accordingly have not been fully explored. We aimed to determine whether Ectatomma tuberculatum ants exhibited specific behavioral responses to potential or actual intruders posing different threats to the host colony and to contribute to an understanding of complex ant-eucharitid interactions. Behavioral responses differed significantly according to intruder type. Ants evicted intruders that represented a threat to the colony's health (dead ants) or were not suitable as prey items (filter paper, eucharitid parasitoid wasps, non myrmecophilous adult weevils), but killed potential prey (weevil larvae, termites). The timing of detection was in accordance with the nature and size of the intruder: corpses (a potential source of contamination) were detected faster than any other intruder and transported to the refuse piles within 15 min. The structure and complexity of behavioral sequences differed among those intruders that were discarded. Workers not only recognized and discriminated between several distinct intruders but also adjusted their behavior to the type of intruder encountered. Our results confirm the previously documented recognition capabilities of E. tuberculatum workers and reveal a very fine-tuned intruder discrimination response. Colony-level prophylactic and hygienic behavioral responses through effective removal of inedible intruders appears to be the most general and flexible form of defense in ants against a diverse array of intruders. However, this generalized response to both potentially lethal and harmless intruders might have driven the evolution of ant-eucharitid interactions, opening a window for parasitoid attack and allowing adult parasitoid wasps to quickly leave the natal nest unharmed.

Infection of army ant pupae by two new parasitoid mites (Mesostigmata: Uropodina)

A great variety of parasites and parasitoids exploit ant societies. Among them are the Mesostigmata mites, a particularly common and diverse group of ant-associated arthropods. While parasitism is ubiquitous in Mesostigmata, parasitoidism has only been described in the genus Macrodinychus. Yet information about the basic biology of most Macrodinychus species is lacking. Out of 24 formally described species, information about basic life-history traits is only available for three species. Here we formally describe two new Macrodinychus species, i.e. Macrodinychus hilpertae and Macrodinychus derbyensis. In both species, immature stages developed as ecto-parasitoids on ant pupae of the South-East Asian army ant Leptogenys distinguenda. By piercing the developing ant with their chelicera, the mites apparently suck ant hemolymph, ultimately killing host individuals. We compare infection rates among all studied Macrodinychus species and discuss possible host countermeasures against parasitoidism. The cryptic lifestyle of living inside ant nests has certainly hampered the scientific discovery of Macrodinychus mites and we expect that many more macrodinychid species await scientific discovery and description.

Rediscovery and reclassification of the dipteran taxon Nothomicrodon Wheeler, an exclusive endoparasitoid of gyne ant larvae

The myrmecophile larva of the dipteran taxon Nothomicrodon Wheeler is rediscovered, almost a century after its original description and unique report. The systematic position of this dipteran has remained enigmatic due to the absence of reared imagos to confirm indentity. We also failed to rear imagos, but we scrutinized entire nests of the Brazilian arboreal dolichoderine ant Azteca chartifex which, combined with morphological and molecular studies, enabled us to establish beyond doubt that Nothomicrodon belongs to the Phoridae (Insecta: Diptera), not the Syrphidae where it was first placed, and that the species we studied is an endoparasitoid of the larvae of A. chartifex, exclusively attacking sexual female (gyne) larvae. Northomicrodon parasitism can exert high fitness costs to a host colony. Our discovery adds one more case to the growing number of phorid taxa known to parasitize ant larvae and suggests that many others remain to be discovered. Our findings and literature review confirm that the Phoridae is the only taxon known that parasitizes both adults and the immature stages of different castes of ants, thus threatening ants on all fronts.