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.     

Costs of secondary parasitism in the facultative hyperparasitoid Pachycrepoideus dubius: does host size matter?

Although hyperparasitism frequently occur in parasitic insects, many aspects of this strategy remain unknown. We investigated possible fitness costs of hyperparasitism as influenced by host size. Our study was conducted with the facultative hyperparasitoid Pachycrepoideus dubius Ashmead (Hymenoptera: Pteromalidae), which parasitizes host species differing greatly in size. We compared some fitness traits (level of successful parasitism, development time, sex ratio and offspring size) of P. dubius developing on large secondary/primary (Delia radicum L. (Diptera: Anthomyiidae)/Trybliographa rapae Westwood (Hymenoptera: Figitidae)) or small secondary/primary host species (Drosophila melanogaster L./Asobara tabida Nees (Hymenoptera: Braconidae)). In no-choice and choice experiments, P. dubius was able to develop on different stages of T. rapae (L2 (endophagous), L4 (ectophagous), and pupae) but that it preferred to parasitize unparasitized D. radicum pupae over pupae parasitized by T. rapae. Furthermore, in P. dubius, hyperparasitism was associated with fitness costs (lower level of successful parasitism, smaller adult size) and these costs were greater on the smallest host complex. We hypothesize that the size of D. melanogaster pupae parasitized by A. tabida may be close to the suboptimal host size for P. dubius beneath which the costs of hyperparasitism make this strategy nonadaptive. Hyperparasitism in terms of trade-offs between host quality and abundance of competitors is discussed.     

Interference and exploitation competition of three nectar-thieving invasive ant species

Summary. Plant and insect exudates are known to play a key role in structuring tropical ant communities, but less is known about the utilization of these resources in communities dominated by invasive ants. Invasive ants are thought to require large amounts of carbohydrates such as honeydew or nectar to maintain their high abundances. Invasive ants that consume floral nectar may compete with legitimate floral visitors through interference or exploitation competition. I compared the nectar-thieving behavior of three widespread invasive ant species: long-legged ants (Anoplolepis gracilipes), Argentine ants (Linepithema humile), and big-headed ants (Pheidole megacephala) in inflorescences of the native Hawaiian ‘ōhi’a tree, an important food source for native fauna. A. gracilipes was least likely to leave inflorescences unvisited and visited inflorescences in higher numbers than both L. humile and P. megacephala. A. gracilipes and L. humile visited more flowers in an inflorescence and were less likely to retreat from a flower with a competitor than P. megacephala. A. gracilipes was able to take 5.5 and 11.3 times the amount of nectar than L. humile and P. megacephala, respectively. Thus, A. gracilipes may be effective at both interference and exploitation competition against other nectarivores, L. humile may be effective at interference competition, and P. megacephala may be relatively weak at both types of competition against other nectarivores. Ascertaining the competitive abilities of invasive ants against legitimate floral visitors will be especially important in agricultural and other systems that are nectar or pollinator limited.Received 6 December 2004; revised 13 January 2005; accepted 14 January 2005.     

Herbivory-induced extrafloral nectar increases native and invasive ant worker survival

Ascertaining the costs and benefits of mutualistic interactions is important for predicting their stability and effect on community dynamics. Despite widespread designation of the interaction between ants and extrafloral nectaries (EFNs) as a mutualism and over 100 years of studies on ant benefits to plants, the benefits to ants have never been experimentally quantified. The success of invasive ants is thought to be linked to the availability of carbohydrate-rich resources, though reports of invasive ant visits to EFNs are mixed. In two laboratory experiments, we compared worker survival of one native (Iridomyrmex chasei) and two invasive ant species (Linepithema humile and Pheidole megacephala) exposed to herbivorized or non-herbivorized EFN-bearing plants (Acacia saligna) or positive and negative controls. We found that non-herbivorized plants did not produce any measurable extrafloral nectar, and ants with access to non-herbivorized plants had the same survival as ants with access to an artificial plant and water (unfed ants). Ants given herbivorized plants had 7–11 times greater worker survival relative to unfed ants, but there were no differences in survival between native and invasive ants exposed to herbivorized plants. Our results reveal that ants cannot induce A. saligna extrafloral nectar production, but workers of both native and invasive ant species can benefit from extrafloral nectar as much as they benefit from sucrose.     

High prevalence but relatively low impact of two eucharitid parasitoids attacking the Neotropical ant Ectatomma tuberculatum (Olivier)

Composition and dynamics of ant communities may be influenced by highly specialized, specific parasitoids such as eucharitids. Yet, little is known about their prevalence in ant societies. Through systematic monthly excavation of ant nests, we evaluated the impact on the Neotropical ant Ectatomma tuberculatum of two eucharitid parasitoid species, Dilocantha lachaudii and Isomerala coronata, which simultaneously attack the same host populations in southern Mexico. Nearly 90% of all the nests collected through the year were parasitized, with an average of 13% ant pupae and 6.7% ant larvae parasitized by eucharitids, and an annual loss of 17% of the ant brood. Eucharitid prevalence among host nests was, however, very variable, and only some E. tuberculatum nests were severely weakened (100% of ant brood parasitized). Parasitism was highest during the dry season (January–March), just when the production of ant pupae was minimum: up to 50.6% of the ant pupae were destroyed in March. However, production of E. tuberculatum males and females occurred later (June–July), and the reproductive potential of the host colonies did not ultimately seem to be heavily affected by eucharitid parasitism. Differences in the seasonal timing of eucharitid attack and ant reproduction thus have the potential to modulate the impact of eucharitids on ants. Our results are discussed in the context of the impact of eucharitids upon E. tuberculatum colonies and their possible effect on the community structure of this potential biocontrol agent ant.     

Detrimental effects of two widespread invasive ant species on weight and survival of colonial nesting seabirds in the Hawaiian Islands

Invasive ants are a significant conservation concern and can have far-reaching effects in ecosystems they invade. We used the experimental control of ant numbers on two pairs of small (<5 ha) offshore islets dominated by either the big-headed ant, Pheidole megacephala or the tropical fire ant, Solenopsis geminata to investigate the influence of these species on seabird hatching success, fledging success and weight. Limited unpublished observations of both ant species attacking nesting seabirds exist, but the frequency of attacks or how they affect seabird growth and survival are unknown. Island-wide treatments with hydramethylnon resulted in the eradication of P. megacephala and the temporary reduction of S. geminata densities. No difference in hatching success, growth, or fledging success of Wedge-tailed Shearwaters (Puffinus pacificus), a common colonial nesting seabird in the Hawaiian Islands was observed on the pair of islets dominated by P. megacephala. On islets dominated by S. geminata, ant control resulted in a temporary increase in fledging success. Injury frequency increased dramatically on the untreated islet (8.3–100%) while remaining the same on the treated islet (27–38%). Severely injured chicks (i.e., chicks that lost >20% of tissue on their feet) weighed significantly less than uninjured chicks and did not fledge. It is unclear if the chicks were being preyed upon or stung in defense of nearby ant colonies. Radical changes in invasive ant populations have been noted, and booming ant populations could cause short-term, but widespread damage to seabird colonies. The negative effects of invasive ants on seabirds may be difficult to detect, and therefore unknown or underestimated throughout the world where the two groups overlap.     

Search Efficiency of Spalangia cameroni and Muscidifurax raptor on Musca domestica Pupae in Dairy Cattle Farms in Denmark

Indoor releases of Spalangia cameroni Perkins and Muscidifurax raptor Girauelt & Sanders (Hymenoptera: Pteromalidae) were conducted in five organic dairy cattle farms to evaluate the overall effect on parasitism and efficiency at different pupal depths of Musca domestica L. (Diptera: Muscidae). Overall, parasitism increased significantly from 5.3 to 28.8–28.7% of the exposed house fly pupae due to the release of pupal parasitoids. Spalangia cameroni was by far the most dominant species, contributing approximately 71.5–72.3% of the parasitism in the release and post-release period, whereas 20.9–24.4% could be attributed to Muscidifurax raptor. A naturally occurring ichneumonid, Phygadeuon fumator Gravenhorst (Hymenoptera: Ichneumonidae) parasitized 4.1–6.8% of the exposed fly pupae. The placement of house fly pupae at two depths of the bedding, 5–10 and 15–20 cm had no significant effect on overall parasitism whereas M. raptor attacked the house fly pupae significantly more when placed in the 5–10 cm stratum (10.0%) compared to the 15–20 cm stratum (3.2%). The two pupal depths had no significant effect on parasitism by S. cameroni and P. fumator. Albeit S. cameroni contributed significantly to overall parasitism, M. raptor had a significantly higher attack rate when first a female had located bags with sentinel pupae. Based on the above results, however, S. cameroni seems the most appropriate species for managing house flies in straw bedded dairy cattle farms in Denmark. A biological control strategy of simultaneous releases of S. cameroni and M. raptor is discussed.     

Studies on an overwintering population of the mushroom phorid Megaselia halterata (Diptera: Phoridae) parasitized by Howardula husseyi (Nematoda: Allantonematidae)

An overwintering population of the mushroom phorid fly Megaselia halterata parasitized by Howardula husseyi was studied in an attempt to explain the winter decline in incidence of parasitism that has been observed in flies from mushroom farms. Fly larvae from eggs hatching in November developed into pupae in December and flies emerged in May. No selective mortality of parasitized specimens of larvae, pupae, or flies was observed. Dead parasites were found in only 10% of parasitized flies. The incidence of parasitism in the emerging flies (50%) was five times that of their parental generation and although parasitism significantly delayed fly emergence the delay was only 2–3 days. There was no evidence of winter decline in parasitism; instead there was strong evidence that parasitism enhanced phorid survival through the winter.     

Response of an open‐forest ant community to invasion by the introduced ant,Pheidole megacephala

The introduced tramp ant, Pheidole megacephala, is a well‐known pest of urban areas and coastal dune ecosystems in eastern Australia. Until recently, establishment and spread of P. megacephala colonies has been regarded as likely only in disturbed areas. Here we describe the extent of an established colony of P. megacephala in a long undisturbed open forest near Maryborough in southeast Queensland and compare ant community structure with those of nearby uninfested sites. Tuna baiting revealed three distinct zones: (i) a zone totally dominated by P. megacephala (at least 10 ha) where few other ant ant species were detected; (ii) a zone where P. megacephala was absent and many other ant species were found; and (iii) a zone where opportunists (species of Ochetellus and Paratrechina) competed with P. megacephala at baits. Pitfall trapping over a 9‐month period resulted in 12 species being recorded at the infested site, compared with a mean of 25 species recorded at adjoining uninfested forest. Over 94% of ants recorded in pitfalls at the infested site were P. megacephala. Most notably, P. megacephala had completely displaced dominant Dolichoderines (species of Iridomyrmex), subordinate Camponotini (species of Camponotus, Opisthopsis and Polyrhachis) and other species of Pheidole which are common at forest sites.     

Interspecific competition between Xanthopimpla stemmator Thunberg and Dentichasmias busseolae Heinrich (Hymenoptera: Ichneumonidae), pupal parasitoids attacking Chilo partellus (Lepidoptera: Crambidae) in East Africa

Interspecific competition between Xanthopimpla stemmator and Dentichasmias busseolae was studied using pupae of the invasive crambid stemborer Chilo partellus as the host. While X. stemmator is an old association, D. busseolae formed a relatively new association with C. partellus in East Africa. Two different time intervals between parasitism (0 and 48 h) and two parasitoid sequences [i.e., X. stemmator before D. busseolae (Xs–Db) and D. busseolae before X. stemmator (Db–Xs)] were chosen. In addition, the parasitoids’ performance on pupae in maize stems and ears was assessed. For both X. stemmator and D. busseolae, there was no difference in foraging time between unparasitized pupae and pupae previously parasitized by the other species, indicating that the two species were not capable of interspecific host discrimination. In the Xs–Db sequence, the time interval between parasitism did not have an influence on the percentage of pupae producing either parasitoid species. By contrast, in the Db–Xs sequence, the percentage of pupae producing X. stemmator was almost 8 times higher in the 0-h than the 48-h interval, while for D. busseolae it was the reverse. In the 0-h interval, X. stemmator outcompeted D. busseolae irrespective of whether it parasitized first or second, while in the 48-h interval, the parasitoid parasitizing first won. While D. busseolae successfully searched for and parasitized pupae in both stems and ears, parasitism of pupae in ears by X. stemmator was negligible. It was concluded that the two species could co-exist because they partly exploit different ecological niches.     

Ecological barriers to early colony establishment in three coexisting acacia-ant species in Kenya

In black cotton uplands in East Africa, four symbiotic acacia-ant species compete for possession of a single swollen thorn tree species, Acacia drepanolobium, and yet coexist at fine spatial scales. Three of the four ant species produce independent foundress queens that establish colonies claustrally within swollen thorns, most often on small saplings. We conducted surveys of such saplings at two sites in 2001 and 2004, and examined foundresses and incipient colonies within their swollen thorns to determine what factors influence their success. Competition among foundresses for nest initiation sites was intense, with an average of over one founding attempt per swollen thorn in all samples, and with living and dead queens significantly hyper-dispersed among available thorns. Combat with other foundresses was the most common cause of death among claustral queens, especially for Tetraponera penzigi. In interspecific battles for nest initiation sites, T. penzigi was dominant over Crematogaster nigriceps and C. mimosae, and C. nigriceps won over 80% of its contests with C. mimosae foundresses. For singleton foundresses, brood parasitism by the braconid wasp Trigastrotheca laikipiensis typically results in the death of the entire ant brood. Host queens defend parasite larvae, pupae and eclosed adults, apparently unable to distinguish the wasps from legitimate offspring. Rates of brood parasitism were as high as 15–20% for incipient colonies of both Crematogaster species, but were extremely low for T. nigriceps in all samples. Although T. penzigi and C. nigriceps foundresses are always solitary, approximately 18% of claustral C. mimosae colonies contain cooperating pleometrotic queens. For unparasitized, claustral C. mimosae colonies, brood production per queen did not differ between solitary and cooperating foundresses. However, the per-capita risks associated with parastitism were reduced for pleometrotic queens. Received 8 March 2005; revised 23 May 2005; accepted 3 June 2005.     

Clonal damselflies (Ischnura hastata) are not significantly affected by mite parasitism

We studied parasitism rate by the terrestrial mite Leptus killingtoni Turk (Acari: Erythraeidae) on asexual parthenogenetic damselflies, Ischnura hastata (Say), and sexual Ischnura pumilio (Charpentier) (Odonata: Coenagrionidae) on Pico island (Azores, Portugal). We sampled 52 water bodies on the island and recorded whether Ischnura specimens were parasitized. Half of the water bodies had either dried up or were almost dry or did not have Ischnura populations. In the remaining 23 ponds, mite parasitism was extremely low, with only 3.6% of I. hastata females bearing one or more mites. Ischnura pumilio was rare on the island (61 specimens examined) and had also very few parasites (9.8% parasitism). We examined the biology of the mite and its effects on the host, by studying mite attachment behavior and seasonal abundance, in an intensive study of one pond (Lagoa do Landroal). At this pond, mite prevalence peaked at the start of the sampling period, with 32% of females of I. hastata parasitized and decreased continuously until the end of the study, when only 2% were parasitized. The analysis of mark–recapture histories of 1 748 females of I. hastata indicates that mites did not affect female survival or recapture rate. Our results suggest that L. killingtoni is unlikely to represent a significant selective factor for odonates on the island of Pico, if its density is as low as during the period of our study, although it could be relevant when it is locally abundant or during periods of outbreak.     

Wood-nesting ants and their parasites in forests and coffee agroecosystems

Agricultural intensification is linked to reduced species richness and may limit the effectiveness of predators in agricultural systems. We studied the abundance, diversity, and species composition of wood-nesting ants and frequency of parasitism of poneromorph ants in coffee agroeco systems and a forest fragment in Chiapas, Mexico. In three farms differing in shade management and in a nearby forest fragment, we surveyed ants nesting in rotten wood. We collected pupae of all poneromorph ants encountered, and incubated pupae for 15 d to recover emerging ant parasites. If no parasites emerged, we dissected pupae to examine for parasitism. Overall, we found 63 ant morphospecies, 29 genera, and 7 subfamilies from 520 colonies. There were no significant differences in ant richness or abundance between the different sites. However, there were significant differences in the species composition of ants sampled in the four different sites. The parasitism rates of ants differed according to site; in the forest 77.7% of species were parasitized, and this number declined with increasing intensification in traditional polyculture (40%),commercial polyculture (25%), and shade monoculture (16.6%). For three of four poneromorph species found in >1 habitat, parasitism rates were higher in the more vegetatively complex sites. The result that both ant species composition and ant parasitism differed among by site indicates that coffee management intensification affects wood-nesting ant communities. Further, coffee intensification may significantly alter interactions between ants and their parasites, with possible implications for biological control in coffee agroecosystems.     

Survey of brown soft scale Coccus hesperidum L. parasitoids in southern California citrus

The parasitoid complex of brown soft scale, Coccus hesperidum L., a multivoltine soft scale, was determined in southern California citrus over the period February 2004–March 2006. The survey was conducted by placing brown soft scale-infested yucca leaves in the canopy of citrus trees and subsequently rearing individually isolated parasitized scales in the laboratory. A total of 14 species parasitized brown soft scale in the field, the most abundant ones belonging to the genus Metaphycus Mercet (75%). The most abundant parasitoid species was Metaphycus angustifrons Compere (38% parasitism), and this is a new record of establishment for this species in California. Coccophagus species accounted for only 11% parasitism. There were important spatio-temporal differences across the parasitoid complex survey locations. We also found that the five most abundant encyrtid parasitoid species showed preferences for scales of different sizes. Our results have implications for biological control of citricola scale, Coccus pseudomagnoliarum (Kuwana), an important pest of citrus in the San Joaquin Valley of central California. Notably, this species is nearly absent in southern California. Brown soft scale is considered to be an alternate host for parasitoids of citricola scale, a univoltine soft scale, at times when the latter species is unavailable for parasitism.     

Pisonia grandis monocultures limit the spread of an invasive ant—a case of carbohydrate quality?

The mechanisms by which invasive species are able to spread into and dominate natural communities are poorly understood and remain a focus of invasion research. In this quest, studying invasions that are limited by a controlling factor will be more informative than will studies documenting unabated spread and impacts. Some ant species are very successful invaders, and research demonstrating abiotic and biotic factors limiting their success has aided the understanding of invasion ecology. We report here a study showing the highly invasive African big headed ant Pheidole megacephala having a novel distribution on coral cays within Australia’s Great Barrier Reef. These patterns displayed a clear limitation of its distribution with monocultures of the tree Pisonia grandis. This distribution was contrary to the known environmental limitations of the ant, and the limitation could not be associated with an underlying abiotic determinant of the vegetation type. We present these distributional patterns, and following consideration of all known biotic and abiotic limitations of ant invasions we discuss the potential that the peculiar ecophysiology of P. grandis is the causal factor. Specifically, we suggest that the quality of carbohydrate supply to ants is a limitation to invasive spread in much the same way that carbohydrate quantity is known to affect ant population densities in other ecosystems.     

Body size variation and caste ratios in geographically distinct populations of the invasive big‐headed ant,Pheidole megacephala (Hymenoptera: Formicidae)

Body size is an important life history trait that can evolve rapidly as a result of how species interact with each other and their environment. Invasive species often encounter vastly different ecological conditions throughout their introduced range that can influence relative investment in growth, reproduction and defence among populations. In this study, we quantified variation in worker size, morphology and proportion of majors among five populations of a worldwide invasive species, the big‐headed ant, Pheidole megacephala (Fabricius). The sampled populations differed in ant community composition, allowing us to examine if P. megacephala invests differently in the size and number of majors based on the local ant fauna. We also used genetic data to determine if these populations of P. megacephala represented cryptic species or if morphological differences could be attributed to change following introduction. We found significant variation in worker mass among the populations. Both major and minor workers were largest in Australia, where the ant fauna was most diverse, and minor workers were smallest in Hawaii and Mauritius, where P. megacephala interacted with few to no other ants. We also found differences in major and minor worker morphology among populations. Majors from Mauritius had significantly larger heads (width and length) relative to whole body size than those from Hawaii and Florida. Minors had longer heads and hind tibias in South Africa compared with populations from Australia, Hawaii and Florida. The proportion of majors did not differ among populations, suggesting that these populations may not be subject to trade‐offs in investment in major size versus number. Our molecular data place all samples within the same clade, supporting that these morphologically different populations represent the same species. These results suggest that the variation in shape and morphology of major and minor workers may therefore be the result of rapid adaptation or plastic responses to local conditions. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113 , 423–438.     

Ecological restoration following the local eradication of an invasive ant in northern Australia

There have been many management programs for invasive ants, yet few have achieved eradication. Of those that were successful, none have documented the subsequent recovery of the affected ecological system. Here I document the ecological impact and eradication of a 5 ha infestation of the African big headed ant Pheidole megacephala from an intact habitat in northern Australia, as well as the subsequent recovery of the native ant fauna. Pre-treatment, the impact of P. megacephala on the native ant fauna was clear. Native ant abundance and species richness were almost always significantly lower in infested compared to uninfested samples. Multivariate analysis statistically separated sample grids from infested and uninfested areas. Following treatment, no P. megacephala individuals were detected for 2 years and it was therefore declared eradicated. Ecological recovery post treatment was also clear. Twenty-one months post-treatment, native ant abundance and species richness within the treated (infested) area were always almost always significantly greater than in the pre-treatment sample, corresponding with no change in the control area (uninfested area). Total species richness from plots in the treated area was identical to that from plots in the control area. Multivariate analysis showed no statistical separation of the treated or control plots. Species richness within lure plots displayed no trend within the treated area relative to the treatment boundary or locations away from the treated area. This project demonstrates the feasibility of eradicating this ant, and that ecological systems are capable of recovering following removal of an exotic invader.     

Performance of Two Fruit Fly (Diptera: Tephritidae) Pupal Parasitoids (Coptera haywardi [Hymenoptera: Diapriidae] and Pachycrepoideus vindemiae [Hymenoptera: Pteromalidae]) under Different Environmental Soil Conditions

We evaluated the performance of Coptera haywardi (Ogloblin) (Diapriidae) and Pachycrepoideus vindemiae (Rondani) (Pteromalidae), both hymenopteran pupal parasitoids of Anastrepha spp. (Diptera: Tephritidae). Performance was studied by manipulating the following environmental conditions in the laboratory: (1) soil type, (2) soil moisture content, (3) soil compaction, and (4) depth at which pupae were buried in the soil. There were two experiments: in the first, exposure time of pupae was held constant and in the second, it varied. In the first experiment, C. haywardi was significantly more effective than P. vindemiae in parasitizing fly pupae. With exposure time held constant (36 h), only soil type and pupal burial depth were significantly related to parasitism rates. While P. vindemiae only parasitized pupae located on the soil surface, C. haywardi attacked pupae that were buried up to 5 cm deep, performing better in clayey than in loamy soil. In the second experiment, exposure time (24, 36, 48, and 72 h) had no significant effect on parasitism rates, but soil type did. P. vindemiae again only attacked pupae on the soil surface while C. haywardi was also able to parasitize pupae that were buried up to 5 cm deep. We conclude that C. haywardi represents a viable candidate to replace the environmentally unfriendly P. vindemiae in augmentative biological control programs against fruit flies.