A global review of socioeconomic and environmental impacts of ants reveals new insights for risk assessment.

Risk assessments are fundamental to invasive species management and are underpinned by comprehensive characterization of invasive species impacts. Our understanding of the impacts of invasive species is growing constantly, and several recently developed frameworks offer the opportunity to systematically categorize environmental and socioeconomic impacts of invasive species. Invasive ants are among the most widespread and damaging invaders. Although a handful of species receives most of the policy attention, nearly 200 species have established outside their native range. Here, we provide a global, comprehensive assessment of the impacts of ants and propose a priority list of risk species. We used the Socioeconomic Impact Classification for Alien Taxa (SEICAT), Environmental Impact Classification for Alien Taxa (EICAT) and Generic Impact Scoring System (GISS) to analyze 642 unique sources for 100 named species. Different methodologies provided generally consistent results. The most frequently identified socioeconomic impacts were to human health. Environmental impacts were primarily on animal and plant populations, with the most common mechanisms being predation and competition. Species recognized as harmful nearly 20 years ago featured prominently, including Wasmannia auropunctata (little fire ant, electric ant), Solenopsis invicta (red imported fire ant), Anoplolepis gracilipes (yellow crazy ant), and Pheidole megacephala (African big-headed ant). All these species except W. auropunctata have been implicated in local extinctions of native species. Although our assessments affirmed that the most serious impacts have been driven by a small number of species, our results also highlighted a substantial number of less well publicized species that have had major environmental impacts and may currently be overlooked when prioritizing prevention efforts. Several of these species were ranked as high or higher than some of the previously recognized "usual suspects," most notably Nylanderia fulva (tawny crazy ant). We compared and combined our assessments with trait-based profiles and other lists to propose a consensus set of 31 priority species. Ever-increasing global trade contributes to growing rates of species introductions. The integrated approaches we used can contribute to robust, holistic risk assessments for many taxa entrained in these pathways.

Honey Bee (Apis mellifera) Pollen Foraging Reflects Benefits Dependent on Individual Infection Status.

Parasites often modify host foraging behavior, for example, by spurring changes to nutrient intake ratios or triggering self-medication. The gut parasite, Nosema ceranae, increases energy needs of the European or Western honey bee (Apis mellifera), but little is known about how infection affects foraging behavior. We used a combination of experiments and observations of caged and free-flying individual bees and hives to determine how N. ceranae affects honey bee foraging behavior. In an experiment with caged bees, we found that infected bees with access to a high-quality pollen were more likely to survive than infected bees with access to a lower quality pollen or no pollen. Non-infected bees showed no difference in survival with pollen quality. We then tested free-flying bees in an arena of artificial flowers and found that pollen foraging bees chose pollen commensurate with their infection status; twice as many infected bees selected the higher quality pollen than the lower quality pollen, while healthy bees showed no preference between pollen types. However, healthy and infected bees visited sucrose and pollen flowers in the same proportions. Among hive-level observations, we found no significant correlations between N. ceranae infection intensity in the hive and the proportion of bees returning with pollen. Our results indicate that N. ceranae-infected bees benefit from increased pollen quality and will selectively forage for higher quality while foraging for pollen, but infection status does not lead to increased pollen foraging at either the individual or hive levels.

A mutualism with a native membracid facilitates pollinator displacement by Argentine ants.

The loss of biodiversity and associated ecosystem services are major threats posed by the spread of alien invasive species. Invasive ants are frequently associated with declines in the diversity of ground-dwelling arthropods but also may affect plants through their attraction to floral nectar and tending of hemipterans. Protea nitida is a tree native to the South African fynbos that hosts a native membracid, Beaufortiana sp., which is tended by ants. Here I compare Argentine ants (Linepithema humile) to native ants in their attraction to P. nitida inflorescences in the presence and absence of the membracid, and their effects on other floral arthropod visitors, seed set, and ovule predation. Argentine ant discovery of inflorescences increased at least 13-fold when membracids were present on the branch, whereas native ant discovery of inflorescences was only doubled by membracid presence at one site in one study year and was unaffected in the other three site-years. Excluding Argentine ants from inflorescences resulted in an increase in several arthropod taxa and potential pollinators; native ant exclusion had no positive effects. Thus the mutualism between Argentine ants and the membracid is facilitating pollinator deterrence by the ants. Though Argentine ants were not associated with a decline in P. nitida seed set or ovule predation, declines in generalist insect pollinators may have ramifications for the 83% of fynbos plants that are insect pollinated. Pitfall traps showed that Argentine ants were not more abundant than native ants in non-invaded sites. Focusing only on abundance on the ground and displacement of ground-dwelling arthropod fauna may lead to an underestimate of the effects of invasive ants on their adopted communities.