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Invasive : Risks and Pathways Project WORLD’S WORST INVADERS: SOCIAL

UPDATED: JUNE 2019

he Invasive Insects: Risks and Pathways project has found that the world’s environmentally harmful Tinvasive insect species are dominated by just one insect – that of , and (Hymenoptera)1. This order accounts for 16 of the 17 insect invaders known to be causing environmental harm in Australia. Why are ants, bees and wasps so successful and so harmful? One answer is that they are habitual and versatile world travellers. Of the dozen main pathways by which invasive insects reach new countries, Hymenoptera use them all and frequently so1. Another clue is that most invasive Hymenoptera are social, and the most Western , invasive in , are aggressive hunters. harmful of them – typically ants – tend Photo: TJ Gehling | Flickr CC BY-NC-ND 2.0 to live in extremely large societies, which most other from their invasive can be more populous than the biggest range2,3. benefit enormously by human megapolises. ‘farming’ an invasive from which they gain . They have DOMINANT INSECT killed tens of millions of red land crabs by INVADERS spraying their eyes and mouthparts with formic acid. Because the crabs eat leaf Of the world’s 24 insect orders, the litter, seeds and seedlings, their absence Hymenoptera accounts for half the has drastically altered the structure and species in the assessment pool of the In their invasive range, European fire ants composition of invaded forests, and the Invasive Insects: Risks and Pathways reach extremely high densities, displacing forest canopy is suffering dieback due project (made up of species for which nearly all other ants. to the outbreaks of invasive scale insects there is evidence of environmental harm Photo: Ryszard | Flickr | CC BY-NC 2 protected by the crazy ants and from 1 somewhere in the world) . The leading sooty mould caused by honeydew4. The invaders are ants (all social), accounting loss of crabs also enables the spread of for more than one in eight species national eradication of red imported fire another , the giant African assessed – three times as many as any land snail5. other insect family. Bees, most of which ants, electric ants and browsing ants, and are social, and wasps, which partial eradication of yellow crazy ants are not, are also common invaders. (Wet Tropics) and Argentine ants (Norfolk WHAT WE MUST KEEP Island). Of Australia’s 17 insect invaders known to OUT OF AUSTRALIA be causing environmental harm, 16 are The impacts of social hymenopteran Of the 27 social hymenopteran species Hymenoptera (9 ants, 3 wasps, 3 bees) species are complex, brought about assessed so far in the Invasive Insects: and 1 is a (Table 1)1. Three have mainly by predation, competition, and Risks and Pathways project, 24 have been 1 been recorded in Australia for the first interaction with other exotic species . rated as ‘of concern’ or ‘of substantial time just this century. As one indicator of Yellow crazy ants on Christmas Island concern’ (15 ants, 5 wasps, 4 bees)1. Of the harm caused by social hymenopteran demonstrate all these mechanisms. these, more than half (7 ants, 3 bees species, Australia is currently spending Capable of achieving extremely high and 3 wasps) are already established in over $60 million a on eradication population densities (more than 2000 a Australia. It is important to stop more programs for five species – seeking square metre), they aggressively displace introductions of these species – to

INVASION WATCH: Social Hymenoptera Table 1: Invasive insect species for which there is evidence of environmental harm in Australia Order Family Species Common name Date of first detection First state or territory or mention record

Hymenoptera Apis mellifera European 1820 Queensland

Hymenoptera Formicidae Solenopsis geminata Tropical 1863 ?

Paratrechina Hymenoptera Formicidae longicornis Black crazy ant 1886 Queensland

Hymenoptera Formicidae floricola Floral ant 1910 Queensland Monomorium Hymenoptera Formicidae destructor Singapore ant 1910 Queensland

Hymenoptera Formicidae megacephala African big-headed ant 1911 Queensland

Coleoptera Scarabaeidae Heteronychus arator African black beetle 1920 South Australia

Hymenoptera Formicidae humile 1939 Victoria

Hymenoptera vulgaris Common 1959 Victoria

Hymenoptera Vespidae European wasp 1959 Tasmania

Hymenoptera Formicidae gracilipes 1975 Northern Territory

Hymenoptera Vespidae chinensis Asian 1979 New South Wales

Hymenoptera rotundata Leafcutting bee 1987 New South Wales

Hymenoptera Apidae Large earth 1992 Tasmania

Hymenoptera Formicidae Solenopsis invicta 2001 Queensland Hymenoptera Formicidae auropunctata 2006 Queensland

Hymenoptera Apidae Asian 2007 Queensland prevent re-invasion of those being eradicated and new areas being invaded, Table 2: The invasive social Hymenoptera not established in and to stop new genetic material from Australia that are of concern or substantial concern due to boosting their invasiveness. This leaves environmental impacts elsewhere in the world at least 11 additional species that are likely to be a high priority to keep out of Family Species Common name Australia (subject to Australia-specific risk Apis mellifera assessment), including 8 ants, Apidae East African lowland honey bee 2 wasps and 1 bee (see Table 2). There scutellata are likely to be other priority species Formicidae rubra European fire ant once 28 additional Hymenoptera in the assessment pool have been assessed. Formicidae chinensis Asian needle ant WHY ANTS ARE SUCH Formicidae fulva tawny crazy ant SUCCESSFUL INVADERS Formicidae Solenopsis richteri The Hymenoptera is one of, if not the albipes largest of, insect orders, abundant Formicidae white-footed ant everywhere except in polar regions Formicidae neglectus invasive garden ant and ecologically highly influential. A major reason for their success is the Formicidae melanocephalum ghost ant nutritious food they provide to their 6 offspring . in this order Formicidae Solenopsis papuana Papuan thief ant has been taken to a new level with the evolution of , which has Vespidae western occurred several times, being the case Vespidae Vespa velutina Asian for some bee and vespid wasp species and for all ants. Social structures enable The most successful invasive attended by her sterile daughters, who dozens to millions of individuals to work Hymenoptera are the ants – which aggressively defend their territory, cooperatively to exploit resources, build achieve an extreme form of sociality. particularly against members of their nests, care for young, and maintain A typical has one queen own species7. But many invasive ants strong defences.

INVASION WATCH: Social Hymenoptera Coleoptera Dermaptera Diptera Hymenoptera Isoptera Thysanptera

Biological control

Contaminant nursery material

Food contaminant

Contaminant on plants

Timber trade

Transportation of habitat material

Container/bulk

Hitchhikers on ship/boat

People and their luggage

Vehicles

Organic packing material

Natural dispersal across borders

Figure 1: The use of introduction pathways by invasive insect orders. Only the most prevalent pathways and insect orders are shown. Circles and their sizes represent the relative contribution (%) of each insect order to the number of species using a particular pathway. Circle sizes (from smallest to largest) represent 1-10%, 11-20%, 21-30%, 31-40%, 41-50%, 51-60%. form supercolonies, with many queens a few , probably due to competition with other species7, 8. Extremely high and many interconnected nests. The with other supercolonies and other ant densities can be achieved, allowing individuals from different nests behave ant species9. But their supercolonies in domination over other species. Over 1 amicably rather than aggressively towards invaded areas can cover hundreds of million Argentine ant queens and 4.4 each other and can move freely between kilometres, and some are more than cubic metres of workers and brood were nests. ‘Thus, the cooperation that a century old. One colony along the captured from one 8-hectare orchard in promotes the success of social insects Mediterranean coast extends more the United States (cited in 10). generally appears to be exaggerated in than 6000 km, and one in Australia Ants also have flexible diets (as many invasive ants’8. spans 2800 km9. These and several omnivores), easy-to-fulfil nesting other supercolonies have their origins The largest known supercolonies are requirements, and an association with in just one ancestral supercolony from those of the Argentine ant (Linepithema humans that allows them to travel around Argentina, and represent ‘the most humile). In its native range, it usually the world in traded products and as populous known society’10. forms colonies with small territories that stowaways on ships. The Invasive Insects are aggressively defended against other Normally, low genetic diversity is thought Risks and Pathways project found they Argentine ants, and lives among many to be harmful but, for ants, by reducing travel frequently on all 10 of the most other native ant species8. Sometimes it their aggression towards their own kind, prevalent unintentional pathways for forms supercolonies spanning hundreds it frees up a lot of extra energy for colony insect introductions (see Figure 1). of metres, although these endure for only growth, foraging, defence and competing

INVASION WATCH: Social Hymenoptera Asian needle ant. Photo: © Matt Bertone

IMPLICATIONS FOR Recommendation 3 density and biomass. Insectes Soc. 52: 266–273. 4. O’Dowd DJ, Green PT, Lake PS (2003): BIOSECURITY As a high biosecurity priority, reduce Invasional ‘meltdown’on an oceanic island. The prevalence and harmfulness of the risks of unintentional introduction Ecology Letters. 6: 812–817. Given the invasive hymenopteran species, pathways for the Hymenoptera. 5. Green PT, O’Dowd DJ, Abbott KL, Jeffery particularly ants, means they should be their flexible travel habits – with ants M, Retallick K, Mac Nally R (2011): Invasional a top biosecurity priority in Australia. As in particular common on all 10 of the meltdown: invader–invader mutualism facilitates tiny, tough and versatile travellers, they most prevalent unintentional pathways a secondary invasion. Ecology. 92: 1758–1768. are also very challenging for biosecurity. worldwide for invasive insects – the only 6. Quicke DLJ (2009): Chapter 127 - We must strive to prevent new feasible way to prevent new invasive Hymenoptera: Ants, Bees, Wasps. In: Resh ncyclopedia of Insects introductions, including of the species hymenopteran species is to reduce the VH, Cardé RT, editors. E (Second Edition) already here, eradicate those we can, and frequency by which they travel with . San Diego: Academic Press, pp 473–484. protect Australian from their traded products and as stowaways on impacts. ships and planes. This requires assessing 7. Holway, Suárez ML, Case T (1998): Loss of the risks of each of these pathways, intraspecific aggression in the success of a widespread invasive social insect. Science. 282: Recommendation 1 imposing import conditions to reduce the risks and improving inspection and 949–952. Fully implement Australia’s invasive diagnostic protocols. 8. Tsutsui ND, Suarez AV (2003): The colony ant biosecurity plan11. This plan was structure and population biology of invasive adopted in mid 2019 by all national, state Recommendation 4 ants. Conservation Biology. 17: 48–58. and territory governments but has no 9. Vogel V, Pedersen JS, D’Ettorre P, Lehmann L, targeted funding for implementation. As a high biosecurity priority, improve Keller L (2009): Dynamics and genetic structure One particularly important action, Australia’s preparedness to respond to of Argentine ant supercolonies in their native essential for coordination and motivation, incursions of social Hymenoptera. This range. Evolution. 63: 1627–1639. is to establish a ‘permanent national requires developing effective surveillance 10. Van Wilgenburg E, Torres CW, Tsutsui ND body to coordinate national actions on programs and being ready to efficiently (2010): The global expansion of a single ant invasive ants.’ This is consistent with the eradicate new incursions. Hymenopteran supercolony. Evolutionary Applications. 3: seriousness of both existing and potential surveillance in Australia can be boosted 136–143. threats to the Australian environment, as by supporting citizen science programs. 11. Department of the Environment and Energy Draft National Invasive Ant Biosecurity well as human amenity and the economy. (2018): Plan 2018-2028 SOURCES . Australian Government. Recommendation 2 1. Invasive Insects Risks and Pathways project Develop a biosecurity plan (or plans) unpublished data (2019): Monash University and ABOUT THIS PROJECT for other social Hymenoptera. With the Invasive Species Council. The Invasive Insects: Risks and potential for invasive bees and wasps to 2. Abbott KL, Green PT (2005): Collapse of an Pathways Project is a partnership between Monash University and the Invasive disrupt communities, and the ant–scale mutualism in a rainforest on Christmas Island. . 116(7): 1238-1246 Species Council. To find out more visit predatory efficiency of invasive wasps, Oikos . invasives.org.au/risks-and-pathways. they can have profound ecological 3. Abbott KL (2005): Supercolonies of the impacts. invasive yellow crazy ant, Anoplolepis gracilipes, on an oceanic island: Forager activity patterns,

INVASION WATCH: Social Hymenoptera