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[This corrects the article DOI: 10.1371/journal.pone.0194941.].

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Terrestrial arthropods play an important role in saltmarsh ecosystems, mainly affecting the saltmarsh's primary production as the main consumers of terrestrial primary production and decomposition. Some of these arthropods, including selected insects and spiders, can be used as ecological indicators of overall marsh environmental health, as they are differentially sensitive to ecological stressors, such as land loss, erosion, oil spills, and tropical storms. In the present study, we used terrestrial arthropods collected from seven (three lightly-oiled, four heavily-oiled) sites in Barataria Bay and from three unoiled reference sites in Delacroix, Louisiana, to determine the impacts of the distribution and re-distribution of Deepwater Horizon (DWH) oil on these saltmarsh ecosystems. A total of 9,476 and 12,256 insects were collected in 2013 and 2014, respectively. The results show that the terrestrial arthropods were negatively affected by the re-distribution of DWH oil by Hurricane Isaac in 2012, although the level of impacts varied among the arthropod groups. Moreover, the mean diversity index was higher (>1.5) in 2014 than in 2013 (<1.5) for all sites, suggesting a recovery trajectory of the saltmarsh arthropod population. The higher taxonomic richness observed in the reference sites compared to the oiled sites for both years also indicated long-term impacts of DWH oil to the saltmarsh arthropod community. Whereas a slow recovery of certain terrestrial arthropods was observed, long-term monitoring of arthropod communities would help better understand the recovery and succession of the marsh ecosystems.

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Many previous studies have focused on the foraging behaviors and strategies of the red imported fire ants, Solenopsis invicta Buren on solid food or granular bait; little attention has been paid to how liquid sugar is fed upon. In the present study, behavioral responses of S. invicta to 25% sucrose water droplets were observed. Five foraging patterns were identified in S. invicta colonies under laboratory conditions: (i) no feeding, no sucrose water feeding was observed; (ii) surround feeding, ants surrounded and fed along the edge of the sucrose droplet; (iii) stacked feeding, ants stacked and fed along the edge of the sucrose droplet; (iv) droplet-break feeding, ants broke the liquid droplet and sucked sucrose water that spread on surface of the substance or soil particles previously transported by ants; and (v) cover feeding, whole surface of the sucrose droplet was covered by layers of feeding ants. This is the first time cover feeding in S. invicta has been reported, which obviously requires more ants compared to the other patterns. In addition, individual ants were tracked in videos under laboratory conditions, and behavioral repertoires that led to stacking, covering and droplet-breaking were identified and described. The field investigation showed that surround feeding was most frequently performed by S. invicta foragers; however, cover feeding was not observed under field conditions during this study. Both laboratory and field studies showed colony-level variations in sugar-water feeding.

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In the present study, the repellent effects of essential balm, a traditional medicine product in China, was tested against foraging and defending red imported fire ants, Solenopsis invicta Buren, under laboratory and field conditions. The laboratory study showed that both band- (width = 1 cm) and patch-smearing of essential balm at each concentration (0.5, 1, or 2 µl/cm(2)) significantly decreased the number of S. invicta foragers within the 6-h observation period. Moreover, band-smearing of 2 µl/cm(2) essential balm and patch-smearing of 0.5, 1, and 2 µl/cm(2) essential balm inhibited most S. invicta foraging activity at 3, 6, 6, and 24 h into the experiment, respectively. The field study showed that after a disturbance was created on the S. invicta mound, there were significantly less defending ants on the substance treated (patch-smeared) with 0.5, 1, and 2 µl/cm(2) essential balm than the controls, but the number of ants on the substance of these three concentrations was similar. Our study suggested that essential balm is a strong repellent against foraging and defending S. invicta and could be applied when temporary protection from S. invicta is needed.

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The raft behavior of the invasive red imported fire ant, Solenopsis invicta Buren (Hymenoptera: Formicidae), has been documented for over a century. However, no rigorous tests have been performed elucidating the structure, limits, and important characteristics of this behavior. Rafting makes S. invicta competitive in both native and foreign environments. Further understanding of this behavior will provide critical advancement to the comprehension of this ant's global invasion ecology. Though speculations exist, no one has looked at the movements of individuals within the raft formation, the longevity of rafts, raft success rate, or the importance of different life stages and varying types of adults to raft formation. Furthermore, bubble use has been extensively studied in arthropods, but it has never been documented in social insects. The use of bubbles as a means of floatation has never before been noted in raft formation. This study shows that ants trapped under water escape by lifting themselves to the air-water interface through the use of bubbles collected from submerged substrate. The presence of larvae was noted to increase colony survival and maximize raft longevity due in part their ability to hold bubbles under hydrophobic setae.

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