Brachyponera chinensis
(Asian needle ant)

Brachyponera chinensis is a temperate ant species native to East Asia, including China, Taiwan, North Korea, South Korea and Japan.

The first records of B. chinensis in the USA were from the states of Georgia, North Carolina and Virginia in 1932, but distribution patterns within these states suggest it may have been present from the early 1900s. It is likely to have been introduced from Japan, probably via shipping ports. This species is now one of the most widespread invasive ant species in the USA, recorded along a continuous range on the East Coast from Florida to Connecticut, west to Arkansas and isolated records from Wisconsin and Washington State. While not aggressive, individuals will sting when disturbed. The sting is painful with pain lasting for a few hours and more rarely leading to urticaria and anaphylaxis in the most serious cases.  

It has naturalized in urban areas and in natural forest, and there is evidence that it is displacing native ant species, such as species of the Aphaenogaster rudis complex, in Georgia and North Carolina. In some areas studied in North Carolina, it may be more abundant than all native species combined, disrupting native ecological communities.

B. chinensis does not disperse plant seeds as efficiently as species of the A. rudis complex, and there is some evidence that this is affecting plant distribution patterns in areas where B. chinensis has displaced native species.     

There is evidence that B. chinensis is also expanding its range into the eastern coast of the Black Sea (Georgia and Southern Russia).

Native to East Asia including Japan and China where it is widespread, and introduced to the southwestern states of the USA in addition to records from Washington and Wisconsin (Guénard et al., 2018; Antmaps, 2019). Expanding into the eastern coast of the Black Sea (Georgia and Southern Russia).

It is possible that B. chinensis has been accidentally introduced into the southeastern USA several times (Paysen, 2007). Multiple primary introductions may have occurred due to the lack of quarantine measures against B. chinensis, introducing genetic diversity and allowing viable populations to emerge (Paysen, 2007).

As international trade grows, there is a continued chance of introductions.

Found in dark, damp, urban environments and disturbed rural environments (Smith, 1934; Mackay and Mackay, 2010). Colonies occur in rotten wood or in soil under stones, logs and debris (Mackay and Mackay, 2010).

B. chinensis build nests in both disturbed and natural areas. They are a temperate species, and are found in deciduous forests, hardwood forests, agricultural land, and in urban and suburban areas such as office parks and backyards (Miner, 2014). Nests are built on the forest floor, often in decaying logs and piles of leaves (Miner, 2014). 

In the USA, B. chinensis is particularly abundant in mature, temperate, hardwood forests including the Great Smoky Mountains National Park on the North Carolina/Tennessee border and several state parks in North Carolina, South Carolina and Alabama.

Colonies tend to establish nests near mature forests in termite galleries within logs or, in more urban areas, under the pavement, lawn ornaments or other man-made structures, for example, railroad ties, bricks and pavers (Paysen 2007, Guénard and Dunn 2010, Pećarević et al. 2010; MacGown et al., 2013; Miner, 2014).

In China, B. chinensis is ubiquitous on rice-paddy dykes (Brown 1958; Paysen, 2007).

On Yakushima Island, Japan, B. chinensis has been found in forests, forest edges, parks and residential areas (Harada et al., 2009).

Genetics

The chromosome number of B. chinensis is 2n=22 (Imai and Kubota, 1972). The karyotype consists of five pairs of metacentric, five pairs of submetacentric and one pair of acrocentric or telocentric chromosomes (Imai and Kubota, 1972).

It appears that B. chinensis do not suffer from the deleterious genetic effects of a population bottleneck when introduced to new areas because sibling mating is a pre-existing behaviour in the native population (Eyer et al., 2018). Rather than being a consequence of the founder effect following introduction, inbreeding between sister queens and their brothers occurs in native populations and may have reduced inbreeding depression through purifying selection of deleterious alleles (Eyer et al., 2018).

Activity Patterns

A study of B. chinensis nests collected from North Carolina, USA, revealed that alate females and males were found within the nests continuously from early April to early September (Fig. 4, Guénard et al., 2018). Brood production was found continuously from early April to early October (n.b. no collections were made between mid-February to mid-March. Fig. 4, Guénard et al., 2018). 

In South Carolina, USA, a similar pattern of activity has been found; workers were found to be active from January to October, with low activity levels from January to March, increasing significantly from April and peaking in July/August (Zungoli and Benson, 2008). From mid-September, activity declined sharply and ceased by the end of October (Zungoli and Benson, 2008). When worker activity declined, ground colonies disappeared, although some colonies were located in stumps and logs in December (Zungoli and Benson, 2008). Activity was documented when mean weekly temperature was 15˚C or above (Zungoli and Benson, 2008). A later study by Allen (2017) showed that worker numbers were highest in May, August and October, with the majority of reproductive male and females produced in July and August.

In China, B. chinensis has been reported t­o forage in the open on tree trunks and on the ground in daylight (Brown, 1958). Foragers are more active on cloudy days compared to sunny days (Mackay and MacKay, 2010). 

Physiology and Phenology

B. chinensis is a temperate ant species which can live at a wide range of altitudes from sea-level up to 1100 m with a few records from higher elevations, including up to 2400 m in Nepal (Fig. 3,Guénard et al., 2018). It is found in disturbed habitats, such as parks, under paving slabs and near housing, but also in undisturbed forest locations, even in its introduced range (e.g. USA) (Guénard et al., 2018). The global range for B. chinensis sensu stricto according to Guénard et al. (2018) is from Washington State, USA, in the north (48°N) to Hong Kong (22°N). Records from further south require verification (e.g. southern China and Vietnam where B. chinensis can be easily confused with the slightly smaller B. obscurans (Guénard et al., 2018)).

Climate modelling has suggested that by 2080 the suitable range for B. chinensis could increase by 210.1% in Europe, 75.1% in Oceania, 74.9% in North America and 62.7% in Asia. Conversely, suitable climatic range is predicted to decrease in Africa by 22.9% (Bertelsmeier et al., 2013).

B. chinensis is not aggressive and generally attempts to flee from human contact, although will sting when pressured. Stings tend to occur when humans accidentally come into contact with the ants or their nests (Rice and Waldvogel, 2017).

Unlike most invasive ants, there is no evidence that B. chinensis use chemical signposts to mark the route to a food source, instead employing a relatively slower process known as tandem carrying (Guénard and Silverman, 2011). This process involves workers being carried individually under the belly of the carrier ant (using the mandibles) to a food resource and then released (Guénard and Silverman, 2011). This may be repeated until there are enough ants to retrieve the food source (Han, 2013). Guénard and Silverman (2011) found that this foraging behaviour was context dependent; tandem carrying occurred three to ten times more often with large non-moveable prey than with small moveable prey. B. chinensis appears to be able to detect its main prey, Reticulitermes termites, using olfactory cues (Bednar and Silverman, 2011).

Population Size and Structure

Colony sizes range from a single nest with 39 individuals up to multiple contiguous nest sites with over 5000 individuals (Zungoli and Benson, 2008).  

Nutrition

B. chinensis is a predator of termites in its native and introduced ranges, specifically preying on those in the genus Reticulitermes (Suehiro et al., 2017). It does not tend honeydew excreted by hemipterans, as relied upon by many other species of ants. While termites make up the majority of the diet of B. chinensis (estimated to be around 80%), their reliance on termites seems to be more marked in their native range rather than where they have been introduced (Suehiro et al., 2017). Radiocarbon analysis revealed a younger diet age in introduced populations, suggesting that while B. chinensis is still reliant on termites, it also feeds on other invertebrates with younger diet ages such as herbivorous insects; “We found that B. chinensis has markedly changed its prey composition and now relies less on termites in introduced range and more on other non-decomposer invertebrates.” (Suehiro et al., 2017).

B. chinensis has been observed scavenging crane flies, crickets, cockroaches, beetles, grasshoppers, collembolans, spiders, centipedes, earthworms and other dead organisms (Rice and Waldvogel, 2017). B. chinensis also directs other colony members to sugar sources such as apple jelly and scavenges food from bins (Rice and Waldvogel, 2017).

B. chinensis do not occur in habitats lacking Rhinotermitidae and its likely that the year round, high-quality food source provided by termites has contributed to the invasive success of this species in the USA, where subterranean termites are widespread and abundant (Bednar and Silverman, 2011).

Distinguishing B. chinensis from other ant species in Japan:

B. nakasujii is common in Honshu, Shikoku, and Kyushu, Japan, where it is sympatric with B. chinensis (Yashiro et al., 2010). B. nakasujii is easy to distinguish from B. chinensis; the B. nakasujii worker has a proportionally wider petiole and the male has much darker coloration and more well-developed mandibles. The B. nakasujii worker is easily distinguished from another closely related species, B. luteipes, by B. nakasujii having a proportionally wider petiole and a sculptured propodeum (largely smooth in B. luteipes) (Yashiro et al., 2010). Although B. nakasujii and B. chinensis are sympatrically distributed in temperate zones, B. nakasujii is rare in dry and disturbed area, where B. chinensis remains common. Both species have been observed to nest near termite nests frequently and to carry termites back to their nests as food (Yashiro et al., 2010).

Distinguishing B. chinensis from other ant species in the USA, amended from MacGown (2016):

This species is similar in size to average-sized fire ants, but differs by having only only node and by its nesting in wooded habitats. In the Southeast USA, it could be possibly be confused with other ponerine ants (e.g. Hypoponera, Leptogenys, Pachcondyla, and Ponera), but differs by the the promesonotum being distinctly set off from the propodeum, by the very shiny mesopleura, and by large super colonial nesting behaviour. 

A further distinguishing feature from other species in the USA is its inability to cling to smooth surfaces such as glass (Rice and Waldvogel, 2017).

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Biological Control

Soldiers of Reticulitermes speratus produce the terpenoid hydrocarbon β-selinene as a defence against predators such as B. chinensis (Iida and Akino, 2016) and investigations have shown that B. chinensis avoids this chemical (Iida and Akino, 2016).

Chemical Control

B. chinensis will scavenge on protein-based insecticide baits, with suitable insecticides including hydramethylnon, s-methoprene [methoprene], indoxacarb and thiamethoxam (Rice and Waldvogel, 2017). It is suggested that starting treatments in April (if B. chinensis activity is observed) may help reduce the impact of the baits on non-target ant species (Rice and Waldvogel, 2017).

Granular bait containing hydramethylnon dispersed in the territory of B. chinensis reduced populations one day after application, and the effects were still apparent 28 days after application (Rice et al., 2012).  

Prey-baiting was used to control B. chinensis in laboratory and field investigations (Buczkowski, 2016; Buczkowski, 2017). Live fipronil-treated termites (Reticulitermes flavipes) were used as bait and were highly effective against B. chinensis, while detrimental effects against non-target species were minimal (Buczkowski, 2017).  

The terpenoid hydrocarbon β-selinene is produced by Reticulitermes speratus as a chemical defence against predators such as B. chinensis (Iida and Akino, 2016); it is therefore a potential chemical control agent.

At the National Zoological Park in Washington DC, USA, granular carbohydrate and protein baits were used to try and control B. chinensis but proved to be largely ineffective (Hiza et al., 2012). B. chinensis control was more effective when chemical sprays were used on foragers, nests and travel routes and when it was repeated the following year (Hiza et al., 2012).

More research is needed on the impact of B. chinensis on seed dispersal mutualisms and ecosystem function (Rodriguez-Cabal et al., 2012).

More information on the seasonality of colony structure in the USA is required if an integrated pest management programme is to be developed (Zungoli and Benson, 2008).

13/12/18 Original text by:

Vicki Cottrell, Consultant, UK