Effect of Irradiation on Queen Survivorship and Reproduction in the Invasive Fire Ant Solenopsis invicta (Hymenoptera: Formicidae) and a Proposed Phytosanitary Irradiation Treatment for Ants.

We studied radiation tolerance in queens of the red imported fire ant Solenopsis invicta Buren (Hymenoptera: Formicidae) to identify a dose that prevents reproduction. Virgin or fertile queens were collected from Santa Fe and Formosa provinces in Argentina and reared in the laboratory in microcolonies. Virgin queens were irradiated at 0 (control), 70, 90, 120, or 150 Gy, and fertile queens were irradiated at 0, 60, 125, and 190 Gy, and then followed for 11 wk in the microcolonies to evaluate survival and reproduction. Virgin queens lay trophic eggs that do not hatch, whereas fertile queens lay eggs that hatch and develop into brood. In general, queen oviposition and survival decreased with increasing irradiation dose. For virgin queens, no eggs were laid by irradiated queens after the third week, whereas the control queens continued laying eggs throughout the 11-wk experiment. For fertile queens, only one larva and no pupae was observed in the 60 Gy treatment and no larvae or pupae were observed in the 125 and 190 Gy treatments, whereas a total of 431 larvae and 83 pupae were produced by untreated control queens during 11 wks. Survivorship of virgin and fertile queens was similarly reduced by irradiation treatment. These results with S. invicta are consistent with previous findings for three other invasive ants, Wasmannia auropunctata (Roger), Pheidole megacephala (F.), and Linephithema humile (Mayr), that are hitchhiker pests on fresh horticultural commodities. A radiation dose of 150 Gy is proposed as a phytosanitary treatment to prevent reproduction in ants.

Light and dark adaptation mechanisms in the compound eyes of Myrmecia ants that occupy discrete temporal niches.

Ants of the Australian genus Myrmecia partition their foraging niche temporally, allowing them to be sympatric with overlapping foraging requirements. We used histological techniques to study the light and dark adaptation mechanisms in the compound eyes of diurnal (Myrmecia croslandi), crepuscular (M. tarsata, M. nigriceps) and nocturnal ants (M. pyriformis). We found that, except in the day-active species, all ants have a variable primary pigment cell pupil that constricts the crystalline cone in bright light to control for light flux. We show for the nocturnal M. pyriformis that the constriction of the crystalline cone by the primary pigment cells is light dependent whereas the opening of the aperture is regulated by an endogenous rhythm. In addition, in the light-adapted eyes of all species, the retinular cell pigment granules radially migrate towards the rhabdom, a process that in both the day-active M. croslandi and the night-active M. pyriformis is driven by ambient light intensity. Visual system properties thus do not restrict crepuscular and night-active ants to their temporal foraging niche, while day-active ants require high light intensities to operate. We discuss the ecological significance of these adaptation mechanisms and their role in temporal niche partitioning.

Experience-related reorganization of giant synapses in the lateral complex: Potential role in plasticity of the sky-compass pathway in the desert ant Cataglyphis fortis.

Cataglyphis desert ants undergo an age-related polyethism from interior workers to relatively short-lived foragers with remarkable visual navigation capabilities, predominantly achieved by path integration using a polarized skylight-based sun compass and a stride-integrating odometer. Behavioral and physiological experiments revealed that the polarization (POL) pattern is processed via specialized UV-photoreceptors in the dorsal rim area of the compound eye and POL sensitive optic lobe neurons. Further information about the neuronal substrate for processing of POL information in the ant brain has remained elusive. This work focuses on the lateral complex (LX), known as an important relay station in the insect sky-compass pathway. Neuroanatomical results in Cataglyphis fortis show that LX giant synapses (GS) connect large presynaptic terminals from anterior optic tubercle neurons with postsynaptic GABAergic profiles of tangential neurons innervating the ellipsoid body of the central complex. At the ultrastructural level, the cup-shaped presynaptic structures comprise many active zones contacting numerous small postsynaptic profiles. Three-dimensional quantification demonstrated a significantly higher number of GS (∼ 13%) in foragers compared with interior workers. Light exposure, as opposed to age, was necessary and sufficient to trigger a similar increase in GS numbers. Furthermore, the increase in GS numbers was sensitive to the exclusion of UV light. As previous experiments have demonstrated the importance of the UV spectrum for sky-compass navigation in Cataglyphis, we conclude that plasticity in LX GS may reflect processes involved in the initial calibration of sky-compass neuronal circuits during orientation walks preceding active foraging.

Ants can be used as bio-indicators to reveal biological effects of electromagnetic waves from some wireless apparatus.

Society is confronted with an increasing number of applications making use of wireless communication. We also notice an increasing awareness about potentially harmful effects of the related electromagnetic fields on living organisms. At present, it is not realistic to expect that wireless communication will decrease or disappear within the near future. That is why we currently are investigating the mechanisms behind these effects and the effectiveness of possible solutions. In order to be efficient and effective, we designed and validated a fast and easy test on ants - these insects being used as a biological model - for revealing the effect of wireless equipments like mobile phones, smartphones, digital enhanced cordless telephone (DECT) phones, WiFi routers and so on. This test includes quantification of ants' locomotion under natural conditions, then in the vicinity of such wireless equipments. Observations, numerical results and statistical results allow detecting any effect of a radiating source on these living organisms.

Acute exposure to low-dose radiation disrupts reproduction and shortens survival of Wasmannia auropunctata (Hymenoptera: Formicidae) queens.

Irradiation is a postharvest quarantine treatment option to control ants and other hitchhiker pests on fresh horticultural products exported from Hawaii. The radiotolerance of the invasive little fire ant, Wasmannia auropunctata (Roger) (Hymenoptera: Formicidae: Myrmicinae), was studied to determine a dose sufficient for its control. Queens from each of five laboratory microcolonies started from five geographic locations in Argentina were irradiated at 20, 50, 70, or 100 Gy or left untreated as controls and then followed for 13 wk to observe colony growth. In general, queen survivorship, and the number of eggs, larvae, and pupae observed in the microcolonies decreased with increasing irradiation dose. In the 50-, 70-, and 100-Gy treatments, the number of eggs observed was reduced by 68, 66, and 76%, respectively, compared with untreated control microcolonies. The number of larvae in the 50-, 70-, and, 100-Gy treatments was reduced by 99.6%, and only one pupa was observed in the 50-Gy treatment and none in the 70- and 100-Gy treatments during the 13-wk experiment. Queens in the 100-Gy treatment had significantly reduced longevity compared with queens in the other treatments. Radiation doses > or = 70 Gy stopped reproduction in W. auropunctata queens and should be sufficient as a phytosanitary treatment. Information from additional invasive ants in Myrmicinae and other subfamilies is needed before recommending a generic irradiation treatment for ants.

GSM 900 MHz radiation inhibits ants' association between food sites and encountered cues.

The kinetics of the acquisition and loss of the use of olfactory and visual cues were previously obtained in six experimental colonies of the ant Myrmica sabuleti meinert 1861, under normal conditions. In the present work, the same experiments were conducted on six other naive identical colonies of M. sabuleti, under electromagnetic radiation similar to those surrounding GSM and communication masts. In this situation, no association between food and either olfactory or visual cues occurred. After a recovery period, the ants were able to make such an association but never reached the expected score. Such ants having acquired a weaker olfactory or visual score and still undergoing olfactory or visual training were again submitted to electromagnetic waves. Not only did they lose all that they had memorized, but also they lost it in a few hours instead of in a few days (as under normal conditions when no longer trained). They kept no visual memory at all (instead of keeping 10% of it as they normally do). The impact of GSM 900 MHz radiation was greater on the visual memory than on the olfactory one. These communication waves may have such a disastrous impact on a wide range of insects using olfactory and/or visual memory, i.e., on bees.

Frequency distributions of 90Sr and 137Cs concentrations in an ecosystem of the "Red Forest" area in the Chernobyl exclusion zone.

In the most highly contaminated region of the Chernobyl Exclusion Zone, the "Red Forest" site, the accumulation of the major dose-affecting radionuclides (90Sr and 137Cs) within the components of an ecological system encompassing 3,000 m(2) was characterized. The sampled components included soils (top 0-10 cm depth), Molina caerulea (blue moor grass), Camponotus vagus (carpenter ants), and Pelobates fuscus (spade-footed toad). In a comparison among the components of this ecosystem, the 90Sr and 137Cs concentrations measured in 40 separate grids exhibited significant differences, while the frequency distribution of the values was close to a logarithmically-normal leptokurtic distribution with a significant right-side skew. While it is important to identify localized areas of high contamination or "hot spots," including these values in the arithmetic mean may overestimate the exposure risk. In component sample sets that exhibited logarithmically normal distribution, the geometric mean more accurately characterizes a site. Ideally, risk assessment is most confidently achieved when the arithmetic and geometric means are most similar, meaning the distribution approaches normal. Through bioaccumulation, the highest concentrations of 90Sr and 137Cs were measured in the blue moor grass and spade-footed toad. These components also possessed distribution parameters that shifted toward a normal distribution.

Ant antennae: are they sites for magnetoreception?

Migration of the Pachycondyla marginata ant is significantly oriented at 13 degrees with respect to the geomagnetic north-south axis. On the basis of previous magnetic measurements of individual parts of the body (antennae, head, thorax and abdomen), the antennae were suggested to host a magnetoreceptor. In order to identify Fe(3+)/Fe(2+) sites in antennae tissue, we used light microscopy on Prussian/Turnbull's blue-stained tissue. Further analysis using transmission electron microscopy imaging and diffraction, combined with elemental analysis, revealed the presence of ultra-fine-grained crystals (20-100 nm) of magnetite/maghaemite (Fe(3)O(4)/gamma-Fe(2)O(3)), haematite (alpha-Fe(2)O(3)), goethite (alpha-FeOOH) besides (alumo)silicates and Fe/Ti/O compounds in different parts of the antennae, that is, in the joints between the third segment/pedicel, pedicel/scape and scape/head, respectively. The presence of (alumo)silicates and Fe/Ti/O compounds suggests that most, if not all, of the minerals in the tissue are incorporated soil particles rather than biomineralized by the ants. However, as the particles were observed within the tissue, they do not represent contamination. The amount of magnetic material associated with Johnston's organ and other joints appears to be sufficient to produce a magnetic-field-modulated mechanosensory output, which may therefore underlie the magnetic sense of the migratory ant.

Exposure to light enhances pre-adult fitness in two dark-dwelling sympatric species of ants.

BACKGROUND: In insects, circadian clocks play a key role in enhancing fitness by regulating life history traits such as developmental time and adult lifespan. These clocks use environmental light/dark (LD) cycles to fine-tune a wide range of behavioral and physiological processes. To study the effect of environmental LD conditions on pre-adult fitness components, we used two dark-dwelling sympatric species of ants (the night active Camponotus compressus and the day active Camponotus paria), which normally develop underground and have fairly long pre-adult developmental time. RESULTS: Our results suggest that ants develop fastest as pre-adults when maintained under constant light (LL), followed closely by 12:12 hr light/dark (LD), and then constant darkness (DD). While light exposure alters developmental rates of almost all stages of development, the overall pre-adult development in LL is speeded-up (relative to DD) by approximately 37% (34 days) in C. compressus and by approximately 35% (31 days) in C. paria. In LD too, development is faster (relative to DD) by approximately 29% (26 days) in C. compressus and by approximately 28% (25 days) in C. paria. Pre-adult viability of both species is also higher under LL and LD compared to DD. While pre-adult development time and viability is enhanced in LL and LD, clutch-size undergoes reduction, at least in C. compressus. CONCLUSION: Exposure to light enhances pre-adult fitness in two dark-dwelling species of Camponotus by speeding-up development and by enhancing viability. This suggests that social ants use environmental light/dark cycles to modulate key life history traits such as pre-adult development time and viability.

An experimental analysis on the magnetic field sensitivity of the black-meadow ant Formica pratensis Retzius (Hymenoptera: Formicidae).

Ant responses were tested under both the natural geomagnetic and artificially induced Earth-strength electromagnetic field. Foragers were trained for a month to visit a food source at the north arm accessed through an orientation platform assembly. Under the natural geomagnetic field, when all other orientational cues were eliminated, results indicated significant heterogeneity of ant distribution with the majority seeking geomagnetic north in darkness. However, in light, foragers failed to discriminate geomagnetic north. Under shifted artificial electromagnetic field, orientation was predominantly on the artificial magnetic N/S axis with a significant preference for the artificial north in both light and dark conditions.

The influence of red light on the aggregation of two castes of the ant, Lasius niger.

Insects are generally described as essentially blind to red wavelengths but sensitive to ultraviolet. Therefore, ants are generally reared in nests where "obscurity" is obtained by the use of a red filter. Yet, no study has been done in order to confirm this idea and to verify whether ants behave differently with or without red light. We performed aggregation experiments with the ant Lasius niger under red light and in total darkness to control the sensitivity of workers. Aggregation is a basic behavior associated with the origin of sociality and with the spatial organization of the colony. We demonstrate that L. niger is sensitive to red wavelengths. Moreover, we show that workers behave differently depending on their ethological caste: foragers aggregate well in total darkness but show low assembly under red light, whereas brood-tenders aggregate well in both conditions. For the first time, a link between vision, social organization and spatial patterns is revealed. The results are discussed relative to their adaptive value and relative to the physiology of the workers. Hypotheses are formulated concerning the acquisition of this change of behavior between castes.

[Modifications of oxygen consumption in the ant Dolichoderus quadripunctatus exposed to very powerful gamma irradiation]. / Modifications de la consommation d'oxygène de la fourmi Dolichoderus quadripunctatus, exposée à des irradiations gamma de forte puissance.

The oxygen consumption of irradiated workers ants of Dolichoderus quadripunctatus, shows a significant increase when ants received a hight dose (50 000 or 100 000 Rad) of gamma rays.