Impact of vegetation removal on the temperature and moisture content of red wood ant nests

We studied the influence of vegetation growing on red wood ant, Formica polyctena, hills and its removal, by cutting, on the temperature and moisture content of the nests. Vegetation was removed from half of nests (n = 10) in June and August. Generally, ant hills were small (0.1–1.1 m³) and their daily temperature fluctuations and moisture (16–38%) were low. The centre temperature of ant hills was positively correlated with ambient air temperature. Daily temperatures peaked at 13:00 and slowly decreased until 09:00 then increased again until 13:00. Nest moisture content was not related to nest volume. All the ant hills were covered with Reed Grass (Calamagrostis arundinacea) that grows through nests and reaches about 185–1085 g/dcm² of dry matter. Dry vegetation matter (g/dcm² of anthill surface) was the same on cut and uncut nests as well because all ant hills were under long-term management (vegetation removal) for at least 10 years. Although vegetation removal did not result in an immediate increase in the temperature of denuded ant hills removal did results in higher daily and night temperatures during the July-September period. The moisture content of nests with undisturbed and intact vegetation was the same. The dry matter content of vegetation strongly affected their moisture content. However, temperature at the inside centre of nests decreased as vegetation dry matter increased, i.e. there was a statistically negative correlation between temperature and moisture. The results support removing grass as a suitable management tool to facilitate the survival of wood ants. Received 30 December 2007; revised 22 April 2008; accepted 10 June 2008.     

The effect of queen ants on the survival of Maculinea arion larvae in Myrmica ant nests

Summary The mortality of Maculinea arion caterpillars was measured in both laboratory and wild Myrmica nests, and found to be nearly 3 times higher in nests that had queen ants present. This is attributed to queen effect, which causes worker ants in nests with queens to attack large ant larvae (gynes) that would otherwise develop into new queens. Maculinea arion caterpillars mimic Myrmica larvae, and are usually attacked during the first 10 days after adoption, when they pass through the size range of ant gyne larvae. Caterpillars are also likely to be attacked during this period because their nethod of feeding brings them into close contact with the skins of large ant larvae, which contain gyne larval pheromones; older caterpillars are large enough to eat larvae without their exposed surfaces contacting the larval skin. In the wild, many caterpillars of Maculinea arion die in ant nests, and this has been shown in previous work to be the key factor that determines changes in their abundance from year to year. It is suggested that queen effect can be an important cause of these deaths, and one that particularly affects populations of butterflies that breed on sites with long-established plagioclimaxes of short turf rather than short-lived grass-land successions.     

A climate room for precise regulation of temperature and humidity in connection with a temperature-regulated nest site for wood ants

Summary A climate room is described for precise regulation of temperature and humidity. Humidity is regulated by regulation of the dew-point temperature of the air. The ranges for both dew-point and air temperature are from 2°C to 45°C. The precision of regulation for the temperature is ±0.05°C, for the dew-point temperature ±0.1°C. In the climate room very homogeneous temperatures can be obtained (±0.1°C). The relative humidity is homogeneous within ±1%.It is also possible to make air temperature different from floor temperature. The dimensions of the experimental room are 200×50×17 cm.A temperature-regulated nest site for Red Wood Ants is also described.     

Limited impacts of the fungus Syncephalastrum on nests of leaf-cutting ants

Leaf-cutting ants interact naturally with a range of antagonistic microorganisms, among them the soil-borne fungus Syncephalastrum. The antagonism of this fungus to the leaf-cutting ants’ fungal cultivar has been shown in studies without the ant queens. So far, the impacts of this fungus on whole colonies (queenright) of leaf-cutting ants are unknown. We assessed the impacts of Syncephalastrum on queenless and queenright colonies of Acromyrmex subterraneus subterraneus. In general, Syncephalastrum negatively impacted leaf cutting but not midden production or colony weight. This impact was greater in queenless colonies. Nevertheless, it did not compromise the survival of any colony. This indicates that the virulence of this fungus to leaf-cutting ant colonies may be limited in a more realistic set-up than previously reported. We propose that future laboratory studies also use queenright colonies where possible, and that the diverse species of leaf-cutting ants also be considered.     

The allocation of foragers in red wood ants

Abstract. 1. We studied how colonies of the red wood ant, Formica polyctena , adjust the numbers of foragers allocated to different foraging trails. In a series of field experiments, foragers were marked and transferred from one nest to another, related nest, where they joined the foraging force. Transferred workers acted as a reserve of uncommitted, available foragers.
2. Previous work shows that each individual forager habitually uses one trail. We found that for an uncommitted forager, the influence of recruitment initially is stronger than that of directional fidelity. Transferred workers were likely to use trails leading to new food sources. When transferred to a new nest, foragers were not likely to use a trail in the same direction as their original trail in the donor nest.
3. After a week, transferred foragers tended to develop route fidelity. Even after bait was no longer present, they continued to use the trail that had formerly led to a bait source.
4. We examined how colonies adjust numbers on a trail by experimentally depleting some trails. Colonies usually did not compensate for depletion: foragers were not recruited to depleted trails.
5. In general, the dynamics of foraging in this species facilitate a consistent foraging effort rather than rapid adjustments of forager allocation.     

Discussion of development processes in insect‐fungus association derived from the shaggy parasol fruiting on the nests of hairy wood ants

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The effects of nest size and insulation on thermal properties of tree swallow nests

The nest environment can have important influences on incubation behavior and nestling development in birds. Nest thermal properties, particularly nest composition and size, can have a major influence on heat loss. To examine the role of nest size and insulation on clutch cooling rates, we collected tree swallow Tachycineta bicolor nests and measured the cooling rate of eggs in a controlled thermal environment. We also examined the thermal benefits of nest feathers by comparing the cooling rates of nests with and without feathers. Nests with more feather insulation and heavier, deeper cupped nests cooled at slower rates. In addition, nests with feathers cooled at much slower rates than did the same nests without feathers. Our results show that nest insulation and size play important roles in nest cooling rates, which may ultimately affect incubation costs and thus reproductive performance.     

基于红外相机技术和人工巢试验分析白冠长尾雉巢潜在捕食者

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Keep the nest clean: survival advantages of corpse removal in ants

Sociality increases exposure to pathogens. Therefore, social insects have developed a wide range of behavioural defences, known as ‘social immunity’. However, the benefits of these behaviours in terms of colony survival have been scarcely investigated. We tested the survival advantage of prophylaxis, i.e. corpse removal, in ants. Over 50 days, we compared the survival of ants in colonies that were free to remove corpses with those that were restricted in their corpse removal. From Day 8 onwards, the survival of adult workers was significantly higher in colonies that were allowed to remove corpses normally. Overall, larvae survived better than adults, but were slightly affected by the presence of corpses in the nest. When removal was restricted, ants removed as many corpses as they could and moved the remaining corpses away from brood, typically to the nest corners. These results show the importance of nest maintenance and prophylactic behaviour in social insects.     

Effects of nest features and surrounding landscape on predation rates of artificial nests

Artificial nest predation experiments were carried out in northern Italy in woods which varied in size, isolation and surrounding landscape structure. Multivariate analyses, including logistic regression, showed that: (1) size and isolation of woods did not significantly affect predation rates; (2) nests on the edge of woods did not suffer higher predation rates than nests inside the wood; (3) nest camouflage greatly influenced predation rates, suggesting that predators were mainly using visual clues to identify nests; (4) the type of habitat that surrounded the woods emerged as a crucial factor in nest survival and the amount of human settlements in the vicinity of the wood was inversely correlated with nest survival, probably due to predators associated with humans; (5) other habitat variables, which were apparently individually unimportant, were found to have an effect on nesting success, if combined in a single ‘suitability index’. It is impossible to generalize about the influence of landscape fragmentation on nest predation because local landscape history and predator guilds, together with the scale of fragmentation, probably interact to determine the suitability of nest sites and their vulnerability to predators.     

The carrying of ants (Cataglyphis bicolor Fab.) by others of the same nest

The carrying of ants from the nest by others of the same species ( Cataglyphis bicolor Fab.) is described. Two types of carrying are distinguished, systematic removal of many adults and larval stages to a new nest, and carrying of individuals, alive or dead, that are dropped at distances up to 35 metres from the nest. The rate of carrying of individual ants from a nest varied from 0–15 per day in a population of foragers estimated as about 200, making 1500–2000 exits per day. Live and dead ants appeared to be treated similarly. Live ants, in the cases examined, went back to the nest. Evidence was obtained by marking ants that carriers were distinct in habits from non-carriers, and also excavated earth from the nest.     

The effect of nest temperature on growth and survival in juvenile Great Tits Parus major

1. For birds, maintaining an optimal nest temperature is critical for early‐life growth and development. Temperatures deviating from this optimum can affect nestling growth and fledging success with potential consequences on survival and lifetime reproductive success. It is therefore particularly important to understand these effects in relation to projected temperature changes associated with climate change.
2. Targets set by the 2015 Paris Agreement aim to limit temperature increases to 2°C, and, with this in mind, we carried out an experiment in 2017 and 2018 where we applied a treatment that increased Great Tit Parus major nest temperature by approximately this magnitude (achieving an increase of 1.6°C, relative to the control) during the period from hatching to fledging to estimate how small temperature differences might affect nestling body size and weight at fledging and fledging success.
3. We recorded hatching and fledging success and measured skeletal size (tarsus length) and body mass at days 5, 7, 10, and 15 posthatch in nestlings from two groups of nest boxes: control and heated (+1.6°C).
4. Our results show that nestlings in heated nest boxes were 1.6% smaller in skeletal size at fledging than those in the cooler control nests, indicating lower growth rates in heated boxes, and that their weight was, in addition, 3.3% lower.
5. These results suggest that even fairly small changes in temperature can influence phenotype and postfledging survival in cavity‐nesting birds. This has the potential to affect the population dynamics of these birds in the face of ongoing climatic change, as individuals of reduced size in colder winters may suffer from decreased fitness.

     

Soil temperature, digging behaviour, and the adaptive value of nest depth in South American species of Acromyrmex leaf-cutting ants

In leaf-cutting ants, workers are expected to excavate the nest at a soil depth that provides suitable temperatures, since the symbiotic fungus cultivated inside nest chambers is highly dependent on temperature for proper growth. We hypothesize that the different nesting habits observed in Acromyrmex leaf-cutting ants in the South American continent, i.e. superficial and subterranean nests, depend on the occurrence, across the soil profile, of the temperature range preferred by workers for digging. To test this hypothesis, we first explored whether the nesting habits in the genus Acromyrmex are correlated with the prevailing soil temperature regimes at the reported nest locations. Second, we experimentally investigated whether Acromyrmex workers engaged in digging use soil temperature as a cue to decide where to excavate the nest. A bibliographic survey of nesting habits of 21 South American Acromyrmex species indicated that nesting habits are correlated with the soil temperature regimes: the warmer the soil at the nesting site, the higher the number of species inhabiting subterranean nests, as compared to superficial nests. For those species showing nesting plasticity, subterranean nests occurred in hot soils, and superficial nests in cold ones. Experimental results indicated that Acromyrmex lundi workers use soil temperature as an orientation cue to decide where to start digging, and respond to rising and falling soil temperatures by moving to alternative digging places, or by stopping digging, respectively. The soil temperature range preferred for digging, between 20°C and maximally 30.6°C, matched the range at which colony growth would be maximized. It is suggested that temperature-sensitive digging guides digging workers towards their preferred range of soil temperature. Workers’ thermopreferences lead to a concentration of digging activity at the soil layers where the preferred range occurs, and therefore, to the construction of superficial nests in cold soils, and subterranean ones in hot soils. The adaptive value of the temperature-related nesting habits, and the temperature-sensitive digging, is further discussed.     

The influence of nest availability on the abundance and diversity of twig-dwelling ants in a Papua New Guinea forest

Tropical ant communities are frequently diverse, but highly patchy in nature. The availability of suitable nest sites may be a regulating force in structuring litter ant communities. Our aim was to examine ant resource utilization in naturally occurring twigs, and to modify the availability of these resources in order to quantify the influence of nest availability on ant communities in a Papua New Guinean forest. First, we compared ant communities that assemble in artificial twigs (drilled, wooden dowels), naturally occurring twigs, and the leaf litter. A total of 55 ant species were captured: 33 from the leaf litter, 29 from naturally occurring twigs, and only 12 from artificial nests. Significantly different communities formed in each of the three nest types. Second, we examined how the density of natural or artificial nest material influenced the ant abundance and species richness. Plots had between 5 and 96 potential nest sites. An average of only 11.2% of these twigs was colonized. Both species richness and the total abundance of adult ants were significantly positively correlated with increasing naturally occurring twig density. Conversely, increasing the availability of artificial nests from 5 to 20 per plot had no significant effect on the proportion of artificial nests colonized, species richness, or the colony size. We observed that ant species richness and abundance increased with natural twig density, at least for naturally occurring communities. But why so many twigs remain vacant and available for ant colonization remains unknown. Other biotic and abiotic factors likely influence the use of nesting habitat in these ant communities.     

The life history continuum hypothesis links traits of male ants with life outside the nest

Biological control of bruchid beetles, Callosobruchus maculatus (Fabricius) (Coleoptera: Bruchidae), infesting cowpea seeds, Vigna unguiculata (L.) Walpers (Fabaceae), can be performed via augmentative releases of Dinarmus basalis Rondani (Hymenoptera: Pteromalidae) parasitoid wasps. Females of the latter species are therefore likely to experience intense intraspecific competition: they should encounter numerous previously parasitized hosts but also conspecific competitors, with which they may fight to secure hosts on which to lay their eggs. Such contests might therefore disrupt biological control programs. Here, we studied aggressive behavior that D. basalis females show toward conspecific competitors and subsequent host exploitation strategies. We further investigated factors that classically affect contest intensity and outcomes in animals, such as the effect of ownership status, by manipulating the residency period before the intruder's arrival. In addition, we tested the effect of the size of female reproductive tissue (measured in terms of egg load) and the quality of the habitat previously experienced by females (either rich or poor in hosts). These two factors are expected to influence the value that females place on the host and therefore the costs they are willing to pay to win it. Finally, we discussed the consequences of agonistic behaviors on females' host exploitation strategies. Our results suggest that contest competition may actually enhance host control by favoring parasitoid dispersion, rather than disrupting it.     

The thermoregulatory benefits of the communal nest of sociable weavers Philetairus socius are spatially structured within nests

Structures built by animals, such as nests, mounds and burrows, are often the product of cooperative investment by more than one individual. Such structures may be viewed as a public good, since all individuals that occupy them share the benefits they provide. However, access to the benefits generated by the structure may vary among individuals and is likely to be an important determinant of social organisation. Here we use the massive, communal nests of sociable weavers Philetairus socius, to investigate whether their thermoregulatory function varies in relation to the size of communal nests, and the position of individual nest chambers within the communal structure. We then examine whether this spatial variation in thermoregulatory function predicts the social organisation of colonies. First, we show that the sociable weavers’ communal nests buffer variation in ambient temperature, and reduce temperature variability within nest chambers. The extent of this buffering effect depends significantly on the position of nest chambers within the communal structure, and on the depth to which chambers are embedded within the nest mass. We detected no effect of nest volume on thermoregulatory benefits, suggesting that there are likely to be additional, non‐thermoregulatory benefits leading to communal nests. Finally, our results indicate that there may be competition for access to the benefits of the public good, since older birds occupied the chambers with the highest thermoregulatory benefits, where breeding activity was also more common. We discuss how the spatial structure of the benefits of the public good might influence social organisation in the unique communal lifestyle of sociable weavers.     

The effect of daily exposure to low hardening temperature on plant vital activity

Phenomenological responses of plants to daily short-term exposure to low hardening temperature was studied under chamber and field conditions. Experiments were carried out on cucumber (Cucumis sativus L.), barley (Hordeum vulgare L.), marigolds (Tagetes L.), and petunia (Petunia × hybrida) plants. The obtained data demonstrated a similar pattern of response in all studied plant species to different variants of exposure to low hardening temperature. The main features of plant response to daily short-term exposure to low hardening temperature include: a higher increment in cold tolerance (cf. two-or threefold increase relative to constant low hardening temperature) that peaked on day 5 (cf. day 2 at constant low hardening temperature) and was maintained for 2 weeks (cf. 3–4 days at constant low hardening temperature); a simultaneous increase in heat tolerance (cf. twofold relative to constant low hardening temperature) maintained over a long period (cf. only in the beginning of the exposure to constant low hardening temperature); a sharp drop in the subsequent cold tolerance after plant incubation in the dark (cf. a very low decrease in cold tolerance following the exposure to constant low hardening temperature); a combination of high cold tolerance and high photochemical activity of the photosynthetic apparatus (cf. a low non-photochemical quenching at constant low hardening temperature); and the capacity to increase cold tolerance in response to repeated short-term exposures to low hardening temperature in plants grown outdoors (cf. a gradual increase after repeated exposure to constant low hardening temperature). Possible mechanisms underlying the plant response to daily short-term exposure to low temperature are proposed.