Predicting socio‐economic and biodiversity impacts of invasive species: Red Imported Fire Ant in the developing western Pacific

Effective biosecurity and pest management are fundamental to sustainable development. Invasive ants pose significant risks to the environment and economy, which are well‐managed by biosecurity agencies in developed countries. However, a comprehensive view of the potential impacts of invasive ants in developing Pacific Island Countries and Territories (PICTs) is lacking. We quantified the potential costs of the Red Imported Fire Ant (Solenopsis invicta Buren) across multiple sectors using an extrapolation analysis. Overall, we estimated that the impacts of Red Imported Fire Ant on developing PICTs could amount to over USD 329 million annually, corresponding to approximately 0.7% of combined GDP. Over half of the costs were predicted to result from impacts on the agriculture sector, a major source of employment and subsistence. We found that over 350 highly threatened species could be at risk from Red Imported Fire Ant. We would expect countries with Least Developed Country status and relatively low GDP to be least able to respond to an incursion of these ants, and as a result the costs could be higher than we have extrapolated. Red Imported Fire Ant could therefore potentially have considerable impact on the on‐going development of the region.     

Red Imported Fire Ant in Australia: What if we lose the war?

In Australia, a national eradication programme for the Red Imported Fire Ant (Solenopsis invicta Buren), one of the world's most invasive species, has been in operation since 2001 when the pest was first detected in Brisbane, Queensland. Since that time, four separate incursions of this ant have been successfully eradicated from this country, but the main Brisbane population remains. Cost‐benefit analyses already conducted put the likely impact of Red Imported Fire Ant in Australia, if not eradicated, at between A$8.5 and A$45 billion. Despite this, ongoing funding for the eradication programme is not assured. A recent external review has concluded that it remains technically feasible, cost beneficial and in the national interest to eradicate. In support of previous analyses, our study highlights some of the potential impacts of Red Imported Fire Ant in Australia in more detail and provides case examples. Results show that adverse impacts are likely in most sectors of the economy, and will be felt not only by agricultural industries, but also the building and construction, tourism, electrical and communications industries. In addition to industry effects, there will also be negative impacts on public health and lifestyle, the environment and infrastructure such as main roads, airports and schools. Our estimates of potential cost impacts in the case examples where extrapolation was possible exceed A$1.65 billion/year and support previous predictions. We conclude that increased spending is justified to avert ‘invasion debt’ – the future cost of battling pests that escape today. This is a war that Australia cannot afford to lose.     

红火蚁的危害及其防治

一种非常危险的入侵性害虫——红火蚁近年在我国台湾和香港登陆,对中国大陆和亚洲其他地区构成严重威胁。本文介绍了红火蚁的危害以及对红火蚁的防治方法。     

Ontogeny of the Defensive Stinging Behavior of the Fire Ant, Solenopsis invicta

The fire ant, Solenopsis invicta, appears to deviate from the usual age-related pattern of defensive behavior seen in other social insects; instead of older workers being more defensive than younger ones, they are less so. Here I test this pattern by quantifying changes in the defensive stinging behavior of S. invicta workers of known age. I found defensiveness, measured as both the number of stings delivered and the amount of venom delivered per sting (venom dose), to increase with age initially but then decline after a mid-age peak. This hump-shaped ontogeny may be the result of S. invicta's foraging strategy, which effectively shifts the responsibility of nest defense to workers younger than foraging age. It is S. invicta's mid-aged workers that are the most defensive, probably because they are both physiologically and spatially the most suitable nest defenders.     

Eradication of the House Mouse (Mus musculus) from Montague Island,New South Wales,Australia

Summary Of all the introduced mammalian pests, rodents are the most common invaders of islands and have triggered numerous extinctions around the globe. They have a short gestation period and large litter size, giving them the ability to colonise new areas rapidly. The same biological traits make them difficult to eradicate. Although the biodiversity benefits of removing exotic rodents from islands are increasingly being recognised, there are few published analyses of eradication attempts that critically evaluate eradication tools. This study examined the response of House Mouse (Mus musculus) populations to an eradication operation on Montague Island, Australia. While the specific impacts of mice have not been studied on this particular island, elsewhere they have been shown to have negative impacts on a range of species including plants, invertebrates, lizards and seabirds. On Montague Island, mouse abundance across different habitats was examined using mark–recapture data collected before and after the deployment of brodifacoum baits. Data obtained before baiting showed significantly lower numbers of mice in sites dominated by exotic grass compared with those dominated by native vegetation. Mouse numbers overall were declining during winter and the population was not breeding, making this an optimal time to undertake the eradication. Trapping immediately after the initial bait drop failed to capture any survivors, and no individuals have been detected during the 3 years since the deployment of baits. This study demonstrated that both small and large baits (0.6 and 2 g pellets) were effective in eradicating the House Mouse from Montague Island. While present, mice were probably slowing the re‐establishment of native vegetation by grazing seedlings and consuming seeds. With this pest now gone, the process of natural regeneration is expected to accelerate. The eradication of the House Mouse from Montague is likely to have other positive effects on the island’s biodiversity. The operation itself contributed to enhancing local capacity to eradicate exotic rodents from larger or more complex islands.     

Stable isotope enrichment in laboratory ant colonies: effects of colony age,metamorphosis, diet,and fat storage

Ecologists use stable isotopes to infer diets and trophic levels of animals in food webs, yet some assumptions underlying these inferences have not been thoroughly tested. We used laboratory‐reared colonies of Solenopsis invicta Buren (Hymenoptera: Formicidae: Solenopsidini) to test the effects of metamorphosis, diet, and lipid storage on carbon and nitrogen stable isotope ratios. Effects of metamorphosis were examined in ant colonies maintained on a control diet of domestic crickets and sucrose solution. Effects of a diet shift were evaluated by adding a tuna supplement to select colonies. Effects of lipid content on stable isotopes were tested by treating worker ants with polar and non‐polar solvents. δ¹³C and δ¹⁵N values of larvae, pupae, and workers were measured by mass spectrometry on whole‐animal preparations. We found a significant effect of colony age on δ¹³C, but not δ¹⁵N; larvae, pupae, and workers collected at 75 days were slightly depleted in ¹³C relative to collections at 15 days (Δδ¹³C = ?0.27‰). Metamorphosis had a significant effect on δ¹⁵N, but not δ¹³C; tissues of each successive developmental stage were increasingly enriched in ¹⁵N (pupae, +0.5‰; workers, +1.4‰). Availability of tuna resulted in further shifts of about +0.6‰ in isotope ratios for all developmental stages. Removing fat with organic solvents had no effect on δ¹³C, but treatment with a non‐polar solvent resulted in enriched δ¹⁵N values of +0.37‰. Identifying regular patterns of isotopic enrichment as described here should improve the utility of stable isotopes in diet studies of insects. Our study suggests that researchers using ¹⁵N enrichment to assess trophic levels of an organism at different sites need to take care not to standardize with immature insect herbivores or predators at one site and mature ones at another. Similar problems may also exist when standardizing with holometabolous insects at one site and spiders or hemimetabolous insects at another site.     

The apparent establishment and subsequent eradication of the Australian giant bulldog ant Myrmecia brevinoda Forel (Hymenoptera: Formicidae) in New Zealand

Abstract

The Australian giant bulldog ant Myrmecia brevinoda Forel was first observed in New Zealand in 1940 (Keall 1981). Further observations of this species were made at a location in Devonport in 1948 and 1965, and a nest destroyed at this site in 1981. Since this time no further observations have been made, yet the status of this species is commonly listed as “uncertain establishment” on New Zealand faunal lists. We describe the control procedure used in 1981. In addition, to determine its current status we resurveyed ants in the area of earlier infestation using visual searches, pitfall trapping, and a reward for discovery posted to local residents. No evidence of M. brevinoda was found, though several other invasive species were found, including the Argentine ant Linepithema humile (Mayr), Pheidole rugosula Forel, and a recently established Australian cryptic Solenopsis species. Given the results of our survey and the absence of other reports of M. brevinoda over the last 24 years, we consider this species to be extinct or eradicated from New Zealand.     

Colony‐level behavioural variation correlates with differences in expression of the foraging gene in red imported fire ants

Among social insects, colony‐level variation is likely to be widespread and has significant ecological consequences. Very few studies, however, have documented how genetic factors relate to behaviour at the colony level. Differences in expression of the foraging gene have been associated with differences in foraging and activity of a wide variety of organisms. We quantified expression of the red imported fire ant foraging gene (sifor) in workers from 21 colonies collected across the natural range of Texas fire ant populations, but maintained under standardized, environmentally controlled conditions. Colonies varied significantly in their behaviour. The most active colonies had up to 10 times more active foragers than the least active colony and more than 16 times as many workers outside the nest. Expression differences among colonies correlated with this colony‐level behavioural variation. Colonies with higher sifor expression in foragers had, on average, significantly higher foraging activity, exploratory activity and recruitment to nectar than colonies with lower expression. Expression of sifor was also strongly correlated with worker task (foraging vs. working in the interior of the nest). These results provide insight into the genetic and physiological processes underlying collective differences in social behaviour. Quantifying variation in expression of the foraging gene may provide an important tool for understanding and predicting the ecological consequences of colony‐level behavioural variation.     

Impact of the Little Fire Ant,Wasmannia auropunctata,on Native Forest Ants in Gabon1

The Neotropical little fire ant, Wasmannia auropunctata, is notorious for its negative impacts on the native biota of tropical islands, such as the Galapagos and New Caledonia, where it has been introduced. Here, I evaluate the impact of exotic W. auropunctata populations on continental Africa. I surveyed ants at nine sites in Lopé National Park in Gabon, Central Africa, and found a highly significant correlation between ant diversity and length of infestation by W. auropunctata. I found many more native ant species present in areas not infested with W. auropunctata (39.0 ± 4.6) compared with areas infested by W. auropunctata for approximately 5–10 yr (7.0 ± 6.2 and 1.7 ± 1.2, respectively). In infested areas, W. auropunctata made up the bulk of specimens collected in every plot. This study demonstrates that the threat posed by W. auropunctata to biodiversity is as serious in continental ecosystems as it is in the more fragile island ecosystems of previous studies. Introductions near waterways are particularly devastating: in Lopé, the infested territory is most extensive along waterways and occurs in a pattern that strongly suggests moving water facilitates colonization.     

中国红火蚁入侵扩散、防控及对策

红火蚁Solenopsis invicta Buren是全球百种最具危险性的外来入侵物种之一,被列为我国农业、林业和进境植物检疫性有害生物。红火蚁入侵我国初期,发生区域数量少、面积小,制定了相应的应急防控和根除策略。随着该蚁在我国呈现扩散加快、多区域多生境发生、多途径扩散等新态势新特点,其防控策略转向“老疫区常态治理、新疫区力争根除”。为了更好地防控红火蚁,未来工作应从部门协作、队伍建设、综合治理、检疫监管和宣传培训等多个方面加强。     

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.     

Frequency of cyanogenesis in tropical rainforests of far north Queensland, Australia

BACKGROUND AND AIMS: Plant cyanogenesis is the release of toxic cyanide from endogenous cyanide-containing compounds, typically cyanogenic glycosides. Despite a large body of phytochemical, taxonomic and ecological work on cyanogenic species, little is known of their frequency in natural plant communities. This study aimed to investigate the frequency of cyanogenesis in Australian tropical rainforests. Secondary aims were to quantify the cyanogenic glycoside content of tissues, to investigate intra-plant and intra-population variation in cyanogenic glycoside concentration and to appraise the potential chemotaxonomic significance of any findings in relation to the distribution of cyanogenesis in related taxa. METHODS: All species in six 200 m(2) plots at each of five sites across lowland, upland and highland tropical rainforest were screened for cyanogenesis using Feigl-Anger indicator papers. The concentrations of cyanogenic glycosides were accurately determined for all cyanogenic individuals. KEY RESULTS: Over 400 species from 87 plant families were screened. Overall, 18 species (4.5 %) were cyanogenic, accounting for 7.3 % of total stem basal area. Cyanogenesis has not previously been reported for 17 of the 18 species, 13 of which are endemic to Australia. Several species belong to plant families or orders in which cyanogenesis has been little reported, if at all (e.g. Elaeocarpaceae, Myrsinaceae, Araliaceae and Lamiaceae). A number of species contained concentrations of cyanogenic glycosides among the highest ever reported for mature leaves-up to 5.2 mg CN g(-1) d. wt, for example, in leaves of Elaeocarpus sericopetalus. There was significant variation in cyanogenic glycoside concentration within individuals; young leaves and reproductive tissues typically had higher cyanogen content. In addition, there was substantial variation in cyanogenic glycoside content within populations of single species. CONCLUSIONS: This study expands the limited knowledge of the frequency of cyanogenesis in natural plant communities, includes novel reports of cyanogenesis among a range of taxa and characterizes patterns in intra-plant and intra-population variation of cyanogensis.     

Aboriginal fire regimes in Queensland, Australia: analysis of the explorers' record

ABSTRACT. The record of eighteenth and nineteenth century explorers' references to Aboriginal fire in Queensland was stratified according to fourteen vegetation typcs and season of fire. It was demonstrated that references to 'current' fire (i.e. flames or smoke) may not represent traditional Aboriginal activity and that many fires were lit to frighten or harm, to protect themselves from, or to signal to kinfolk the presence of the European intruders. Because of this interpretational difficulty the records to 'current' fire were treated separately from 'past' fire (i.e. burnt ground). The data were analysed as the number of observations per 100 km spent in each vegetation type for any one season to compensate for bias created by differing amounts of travel. The record suggests highest frequency of burning in grassland around the Gulf of Carpentaria, relatively high fire frequency of most coastal and subcoastal vegetation types and relatively infrequent burning of inland Queensland. The analysis indicates a propensity for winter and autumn fue relative to spring and summer fire in all vegetation types combined and in most individual vegetation types.     

Population genetic structure of the red imported fire ant, <Emphasis Type="Italic">Solenopsis invicta</Emphasis>, in Taiwan

We generated and analyzed microsatellite genotypic data and mtDNA sequence data from the fire ant Solenopsis invicta collected from two separate infested areas (Taoyuan and Chiayi) in Taiwan to infer the population and colony structure of these recently established populations. These genetic analyses revealed the following patterns: 1) Relatedness among worker nestmates was significantly greater than zero for both social forms from both populations; 2) No significant isolation by distance was found among nests within each social form from either population; 3) Significant mtDNA but no nuclear differentiation occurs between sympatric social forms in Taoyuan; 4) Molecular signatures of genetic bottlenecks associated with recent introductions are evident in both populations; and 5) The two sampled populations, Taoyuan and Chiayi, are highly genetically differentiated at both the nuclear or mtDNA genomes and most likely derive from two separate introductions into Taiwan. While results from these analyses generally were consistent with predictions based on the known biology of these ants and similar studies of S. invicta in the U.S.A. and South America, some patterns likely reflect the recent introduction and human-mediated inadvertent transport of ants in Taiwan. This is the first study to investigate the population and colony structure of fire ants in Taiwan and results from our study represent an important contribution to the ongoing efforts aimed at eradicating this invasive pest in Taiwan. Received 18 June 2007; revised 11 October 2007; accepted 17 October 2007.     

中国和美国红火蚁毒腺生物碱组分的比较分析

【目的】比较两个入侵地红火蚁Solenopsis invicta毒腺生物碱成分及相对含量的地区间差异。【方法】以在中国广东省惠州、 广州、 深圳、 东莞、 珠海和美国阿拉巴马州采集的红火蚁工蚁为材料, 用正己烷溶剂浸提48 h获得浸提液, 将浸提液进行硅胶柱层析分离, 用气相色谱-质谱联用仪（GC-MS）分析其所含的生物碱成分及其相对含量。【结果】红火蚁毒腺生物碱含顺式生物碱组分和反式生物碱组分。通过总离子图对比, 得到了7种顺式生物碱、 8种四氢吡啶和7种反式生物碱, 并计算得到这些组分的相对百分含量。【结论】中国广东省5个地区红火蚁生物碱组成无差别, 相对含量略有差异, 惠州种群和深圳种群差别最大, 其他地区间没有差别。中美两国入侵地的红火蚁种群生物碱成分种类无差别, 其各个组分之间相对含量略有差异, 美国阿拉巴马州种群与中国深圳种群各组分相对含量差别最大, 与中国广州种群差别最小。另外, 在检测的中国广东样品中, 只确认了红火蚁的存在, 提示杂合蚁与黑火蚁还未传入中国。     

Population structure and dispersal of the saltmarsh mosquito Aedes vigilax in Queensland, Australia

Population genetics of the mosquito Aedes vigilax (Skuse) (Diptera: Culicidae), a major vector of arboviruses (e.g. Barmah Forest, Ross River), were investigated to obtain an indirect estimate of mosquito dispersal characteristics in typical habitats of Aedes vigilax in south-east Queensland: on the off-shore islands of Moreton Bay and on the mainland where disjunct breeding populations of Ae. vigilax are distributed along intertidal marsh. Six allozyme loci were assessed for genetic differentiation between samples from 11 localities. Significant larval variation between some breeding sites was attributed to site-specific selection. Nonsignificant genetic differentiation was found among collections of adult mosquitoes caught in light traps throughout the study area (exceeding 60x27 km), indicating widespread dispersal. As distances of < or = 9 km over water did not appear to act as effective barriers to Ae. vigilax dispersal, localized control activities applied to Ae. vigilax breeding sites are unlikely to be effective against the vagile adult population. Therefore, the contiguous shires programme of broad acre control is endorsed to prevent the spread of arboviruses carried by Ae. vigilax     

Development of RAPD markers in two introduced fire ants, Solenopsis invicta and S. richteri, and their application to the study of a hybrid zone

We developed RAPD DNA markers useful in distinguishing the fire ants Solenopsis invicta and S. richteri. An initial survey of 200 primers revealed seven informative markers; family studies allowed us to determine expression patterns and to confirm Mendelian inheritance of these markers. The seven RAPD markers, one of which is inherited as a codominant marker, were employed along with three allozyme markers to describe the structure of a hybrid zone that has formed between the two species in the USA, where they have been introduced. The data suggest minor introgression of alleles from one parental species ( S. richteri ) into the other ( S. invicta ), which most likely reflects the documented recent movement of this hybrid zone. This pattern is interpreted as interspecific introgression rather than shared intraspecific polymorphism on the basis of comparisons with samples from native, non-hybridizing populations in South America that lack such polymorphism. The data further reveal that the structure of the hybrid zone in the USA varies geographically. One parental species ( S. invicta ) and the hybrids exhibit a mosaic distribution in the east; a gradual transition between the parental species occurs in the centre, with a large intervening area of hybrid genotypes only; and there is apparent contact between parental populations with a small or no intervening zone of hybridization in the west. These differing patterns in the structure of the hybrid zone presumably reflect the unique histories of colonization in different parts of the range of introduced fire ants.     

Effects of Phenology at Burn Time on Post‐Fire Recovery in an Invasive C4 Grass

The spread of non‐indigenous, C₄ grasses threatens global conservation of savannas and subtropical grasslands. Identifying control methods to selectively target these invasives has proven difficult. Here, we tested the hypothesis that the effectiveness of prescribed burns for control is determined, in part, by the phenology of the target species at burn time. We conducted two experiments in a subhumid, C₄ grassland in central Texas. The focal invasive was the C₄, perennial bunchgrass Bothriochloa ischaemum (L.) Keng (KR bluestem). Burns were conducted in early and late fall when plants were in different phenological states. In addition, we attempted to manipulate phenological state through temporary rainout shelters to expedite maturation. The two experiments differed in the timing of the rainout shelter application (experiment 1: May to July, experiment 2: August and September), but otherwise had the same complete factorial design (burn time × shelter). Across experiments, when at least 50% of all tillers were pre‐reproductive at burn time, either due to shelter treatment or time of year, spring tiller densities were significantly lower than when plants were burned in a more advanced reproductive state. Trends in fall biomass generally followed trends in spring tiller densities, with one exception where plants in no‐shelter plots burned in October had lower biomass than expected based on tiller densities. Treatment responses for the native C₄ grass B. laguroides were consistent with those of B. ischaemum. These findings suggest that strategic burns can be used to reduce the subsequent recovery of invasive C₄ grasses while not disadvantaging native grasses.     

An invasive tree facilitates the persistence of native rodents on an over‐grazed floodplain in tropical Australia

In an ecosystem under simultaneous threat from multiple alien species, one invader may buffer the impact of another. Our surveys on a remote floodplain in the Kimberley region of north western Australia show that invasive chinee apple trees (Ziziphus mauritiana) provide critical refuge habitat for native rodents (pale field rats, Rattus tunneyi). Feral horses (Equus caballus) have trampled most of the remaining floodplain, but are excluded from the area around each chinee apple tree by thorny foliage. Although chinee apple trees constituted <10% of trees along our transects, they represented >50% of trees that harboured rat burrows. The mean number of burrows under each chinee apple tree was twice as high as under most other tree species, and we trapped more than seven times as many rats under chinee apple trees as under other types of trees. The extensive burrow systems under chinee apple trees contained female as well as male rats, whereas we only captured males around the smaller burrow systems under other tree species. Our data suggest that this invasive tree plays a critical role in the persistence of pale field rat populations in this degraded ecosystem, and that managers should maintain these trees (despite their alien origins) at least until feral horses have been removed.     

GP-9s Are Ubiquitous Proteins Unlikely Involved in Olfactory Mediation of Social Organization in the Red Imported Fire Ant,Solenopsis invicta

The red imported fire ant (RIFA), Solenopsis invicta, is an invasive species, accidentally introduced in the United States that can cause painful (sometimes life-threatening) stings to human, pets, and livestock. Their colonies have two social forms: monogyne and polygyne that have a single and multiple functional queens, respectively. A major gene (Gp-9), identified as a putative pheromone-binding protein on the basis of a modest amino acid sequence identity, has been suggested to influence the expression of colony social organization. Monogyne queens are reported to possess only the GP-9B alleles, whereas polygyne queens possess both GP-9B and GP-9b. Thus, both social forms are reported to express GP-9B, with GP-9b being a marker expressed in polygynes but it is absent in monogynes. Here, we report two types of polygyne colonies, one that does not express GP-9b (monogyne-like) and the other expressing both proteins, GP-9B and GP-9b. Given their expression pattern, GP-9s are hemolymph proteins, which are more likely to be involved in the transport of lipids and small ligands within the homocoel. GP-9B existed in two forms, one of them is phosphorylated. The helical-rich content of the protein resembles the secondary structures of a beetle hemolymph protein and moth pheromone-binding proteins. An olfactory role is unlikely given the lack of specific expression in the sensillar lymph. In marked contrast to GP-9s, a chemosensory protein, SinvCSP, is demonstrated to be specifically expressed in the antennae. Within the antennae, expression of SinvCSP is restricted to the last two segments, which are known to house olfactory sensilla.