Rubra Workers Research Articles

Ants detect but do not discriminate diseased workers within their nest.

Social insects have evolved an array of individual and social behaviours that limit pathogen entrance and spread within the colony. The detection of ectoparasites or of fungal spores on a nestmate body triggers their removal by allogrooming and appears as a primary component of social prophylaxis. However, in the case of fungal infection, one may wonder whether ant workers are able to detect, discriminate and keep at bay diseased nestmates that have no spores over their cuticle but which constitute a latent sanitary risk due to post-mortem corpse sporulation. Here, we investigate the ability of Myrmica rubra workers to detect and discriminate a healthy from a diseased nestmate infected by the entomopathogen Metarhizium anisopliae. During dyadic encounters in a neutral location, workers were more aggressive towards isolated sick nestmates on the 3rd post-infection day. However, no such detection or discrimination of fungus-infected nestmates occurred in a social context inside the nest or at thenest entrance. Gatekeepers never actively rejected incoming diseased nestmates that rather spontaneously isolated themselves outside the nest. Our study reveals that ant workers may detect health-dependent cues and that their 'acceptance level' of sick nestmates is tunable depending on the social context. This raises questions about possible trade-offs between a social closure to pathogens and risks of erroneous rejection of healthy nestmates. Social isolation of moribund ants also appears as a widespread prophylactic strategy of social insects allowing them to reduce exposure to pathogens and to spare costs associated with the management of infected individuals.

Tetracosane on the cuticle of the parasitic butterfly Phengaris (Maculinea) nausithous triggers the first contact in the adoption process by Myrmica rubra foragers

AbstractPhengaris (Maculinea) butterflies are social parasites of Myrmica ant colonies. Larvae of the parasite are adopted by the ant workers into the colonies. Apparently, chemical signals are used by Phengaris nausithous Bergsträsser larvae to mimic those of the host brood to be recognized by the ants. In the present study, chemical extracts of ant brood and butterfly larvae using four different solvents are tested in behavioural choice assays in search of compounds involved in the adoption process. Tetracosane is the main shared compound in all brood extracts of Myrmica rubra L. and in all larvae of P. nausithous. The attractiveness of tetracosane for M. rubra workers is confirmed by testing synthetic tetracosane in behavioural choice assays, suggesting that the adoption ritual may be initiated by tetracosane.

Comparative outlook over physiological and ecological characteristics of three closely-related Myrmica species

This paper summarizes our findings on the eye morphology, visual perception, learning abilities, navigation system and recruitment strategy of three Myrmica species, pointing out the agreement between each species’ morphological, physiological and behavioral characters as well as the accordance between these characters and each species’ environmental preferences. We also draw biological generalities and report other similar studies. Myrmica sabuleti workers have small eyes, perceive the dimension, number of basic elements and orientation of a visual cue but do not distinguish shapes from one another. They see the colors, perceive UV light and the perspective, and adapt their vision to the light intensity. They learn odors better than visual cues and essentially use odors to navigate. Myrmica ruginodis workers have large eyes, distinguish shapes, small see-through forms as well as patterns of luminous points located above them. They have no olfactory memory but a very long lasting visual one. They exclusively use visual cues located above them while travelling, relying on odors only when they no longer see. Myrmica rubra workers have eyes of middle size and distinguish filled shapes but not hollow forms. Their olfactory and visual conditioning lead to equivalent learning in the course of time and they use all available olfactory and visual elements for navigating.

Trail following Learning by Young Myrmica rubra Workers (Hymenoptera, Formicidae)

Ants use chemical trails, laid down on the ground, for recruiting congeners and helping them to return to the nest. The present work shows that young ants, less than one year old, though obviously reacting to the trail pheromone, are unable to efficiently follow a trail. These young ants begin to better walk along a trail when being in presence of trail following older congeners. Later on, they can by themselves rather efficiently follow a trail. Queens removed from their nest correctly move along a trail. The knowledge of the trail pheromone is thus native, while the trail following behavior is both partly native and partly learned. The latter learning is rapid and may be induced and/or enhanced by older trail following nestmates.

Choice behaviour of Myrmica rubra workers between ant larvae and larvae of their Phengaris (Maculinea) nausithous nest parasites

Larvae of Phengaris (Maculinea) butterflies are adopted by Myrmica workers and are obligate myrmecophiles. Brood recognition by Myrmica rubra workers was tested for concolonial larvae (M. rubra) versus allocolonial larvae (M. rubra and P. nausithous) to assay the mimetic efficiency of P. nausithous. In addition, we tested M. rubra ant colonies from different populations with and without the presence of Phengaris, to test for potential local adaptation in adoption behaviour. We show that M. rubra can distinguish between nest-mate and foreign larvae as well as between P. nausithous and their own larvae. Workers from the allopatric population inspected and rejected more P. nausithous larvae than workers from the sympatric population. This might reflect a local host adaptation in which the social parasite more efficiently mimes its sympatric host ants than allopatric ones.

Social prophylaxis through distant corpse removal in ants

Living in groups raises important issues concerning waste management and related sanitary risks. Social insects such as ants live at high densities with genetically related individuals within confined and humid nests, all these factors being highly favorable for the spread of pathogens. Therefore, in addition to individual immunity, a social prophylaxis takes place, namely, by the removal of risky items such as corpses and their rejection at a distance from the ant nest. In this study, we investigate how Myrmica rubra workers manage to reduce encounters between potentially hazardous corpses and nestmates. Using both field and laboratory experiments, we describe how the spatial distribution and the removal distance of waste items vary as a function of their associated sanitary risks (inert item vs. corpse). In the field, corpse-carrying ants walked in a rather linear way away from the nest entrance and had an equal probability of choosing any direction. Therefore, they did not aggregate corpses in dedicated areas but scattered them in the environment. In both field and laboratory experiments, ants carrying corpses dropped their load in more remote-and less frequented-areas than workers carrying inert items. However, for equidistant areas, ants did not avoid dropping corpses at a location where they perceived area marking as a cue of high occupancy level by nestmates. Our results suggest that ants use distance to the nest rather than other occupancy cues to limit sanitary risks associated with dead nestmates.

Development of parasitic Maculinea teleius (Lepidoptera, Lycaenidae) larvae in laboratory nests of four Myrmica ant host species

Maculinea butterflies are social parasites of Myrmica ants. Methods to study the strength of host ant specificity in the Maculinea–Myrmica association include research on chemical and acoustic mimicry as well as experiments on ant adoption and rearing behaviour of Maculinea larvae. Here we present results of laboratory experiments on adoption, survival, development and integration of M. teleius larvae within the nests of different Myrmica host species, with the objective of quantifying the degree of specialization of this Maculinea species. In the laboratory, a total of 94 nests of four Myrmica species: M. scabrinodis, M. rubra, M. ruginodis and M. rugulosa were used. Nests of M. rubra and M. rugulosa adopted M. teleius larvae more readily and quickly than M. ruginodis colonies. No significant differences were found in the survival rates of M. teleius larvae reared by different ant species. Early larval growth of M. teleius larvae differed slightly among nests of four Myrmica host species. Larvae reared by colonies of M. rugulosa which were the heaviest at the beginning of larval development had the lowest mean larval body mass after 18 weeks compared to those reared by other Myrmica species. None of the M. teleius larvae was carried by M. scabrinodis or M. rubra workers after ant nests were destroyed, which suggests a lack of integration with host colonies. Results indicate that Myrmica species coming from the same site differ in their ability to adopt and rear M. teleius larvae but there was no obvious adaptation of this butterfly species to one of the host ant species. This may explain why, under natural conditions, all four ants can be used as hosts of this butterfly species. Slight advantages of particular Myrmica species as hosts at certain points in butterfly larval development can be explained by the ant species biology and colony structure rather than by specialization of M. teleius.

Anti-predator defence mechanisms in sawfly larvae of Arge (Hymenoptera, Argidae)

Larvae of the sawfly Arge (Hymenoptera, Argidae) are exposed to predators such as ants. Their defence mechanisms, which have been almost unstudied, were investigated by behavioural observations coupled to a morphological approach and by testing the bioactivity of several body parts. Arge larvae raised their abdomen when contacted by Myrmica rubra workers. The ants rarely bit a larva and generally retreated immediately, sometimes without contacting it. Most of those few ants that bit a larva then showed an uncoordinated walk. Crude hemolymph from a common species, A. pagana, was a feeding deterrent towards ants. Hemolymph extracts remained active up to a concentration of 0.8 μg DW extract per microlitre solution, and were more active than integument and gut extracts. We also observed ants paralysed by extracts, especially from the gut. It is likely that this toxicity is due to a polypeptide, lophyrotomin, which is known to occur in A. pullata. Six or seven non-eversible ventro-abdominal glands occurred in all species studied ( A. fuscipes, A. nigripes, A. ochropus, A. pagana, A. pullata, A. ustulata). These glands contain volatiles. We consider both types of chemicals to be important in defence, and we propose that the paralysing effect is a common feature among Arge species.

Anatomical origin and isolation of an ethological factor found on the last sternite of the workers of Myrmica rubra L. ( Formicidae, Myrmicinae)

On the basis of a logical series of deductions from experiments, it has been shown that the previously described ethological factor found on the last visible sternite of Myrmica rubra workers is a small amount of Dufour gland contents modified on the inner face of the last sternite. The factor may soak the outer surface of the sting or the gonostyles. This factor has, among others, a synergistic effect on the trail pheromone. When laying a trail, food-collecting ants deposit this factor on the ground together with the trail pheromone from their poison glands. The factor can be isolated on silica-gel plates and eluted once with acetone; its R f is 0.36. It resists a temperature of 100°C for at least 5 min and is more volatile than 3-ethyl-2,5-dimethylpyrazine, the trail pheromone of the species.

The control of Myrmica rubra workers by queens of their own and other Myrmica species and the interaction between queenless groups of workers

ABSTRACT. Queens of two species of the ant genus Myrmica bonded to workers of the species M. rubra L. as the latter emerge from the pupal skin can use these workers nearly 6 months later to arrest gyne formation in sex‐competent larvae of the same species. Queens of M. ruginodis Nylander var. microgyria (Brian & Brian, 1949) are as good at this as the natural M. rubra, but those of M. sabuleti Meinert (of a race close to M. scabrinodis) are not. Though the M. sabuleti queens induce normal aggression against sexualizing larvae, they are unable to prevent some or all of the workers feeding larvae as though they were queenless. However, queens from different colonies of M. rubra adopted by queenless populations of workers in spring, control their brood‐rearing behaviour perfectly. M. rubra workers from different colonies bring gynes to maturity from female sexual larvae at different average sizes. When workers from two such sources are mixed in equal proportions, the size of gyne larva produced after a week's culture corresponds with that of one of the worker populations; it is not intermediate in size. Also, large workers can rear larger gyne‐larvae than small workers of the same age. This is only true if the workers have been living with queens all the time from emergence as an imago to the moment the experiment was set. Size mixtures only achieve the same size larvae as a pure culture of small workers would. A possible reason for this is that small workers exclude the larger ones from the nursery areas of the nest.

3-ethyl-2,5-dimethylpyrazine, the trail pheromone from the venom gland of eight species of Myrmica ants

Trail-following behaviour is evoked by a single substance from the venom gland of the ant Myrmica rubra L. The compound has been identified as 3-ethyl-2,5-dimethylpyrazine by microchemical methods and by comparison with the synthetic compounds. Seven other Myrmica species, which follow trails made with each other's venom glands and show no species selectivity, have all been shown to produce the same substance in similar quantities. Individual analyses on 10 samples of single venom glands by a solid sampling technique showed that M. rubra workers contain a mean of 5.8 ± 1.7 ng of the substance (± S.D.). The synthetic substance also evoked a strong trail-following response in workers at the same concentration, and statistical tests revealed no difference between synthetic pyrazine and venom gland contents.

Phéromones stimulant et inhibant l'agressivité chez Myrmica rubra

The aggressiveness of Myrmica rubra workers is stimulated by their poison gland secretion. On the other hand, the major compound of the mandibular gland, 3-octanone, markedly suppresses their aggressiveness. The inhibitory activity of 3-octanone is still effective when dissolved in liquid paraffin at a concentration of 10 −9 vol./vol. At a concentration 100 times greater in liquid paraffin, 3-nonanone may also suppress the aggressiveness of the ants. This substance however represents only a trace of the mandibular secretion. Neither 6-methyl-3-octanone, nor 3-octanol, possesses an inhibitory effect on the aggressiveness of the ants even when present in liquid paraffin at a concentration 10 4 times greater than the lowest effective dilution of 3-octanone. The relative proportions of 3-octanol and 3-octanone vary greatly in the mandibular gland secretion of the workers from the same nest or from different nests of the same species. The proportions of 3-octanol in the mixture of octanol+octanone present in the vapour released by one crushed worker head range from 4·6 to 38·0 per cent. The histogram of these proportions is unimodal, with the mode situated near 15 per cent of 3-octanol. A mixture of 3-octanol and 3-octanone in liquid paraffin, releasing a vapour containing 15 per cent of 3-octanol, has no more activity than a solution containing only 3-octanone. There is no reason to believe so far that a mixture of 3-octanol and 3-octanone of precise composition has any particular meaning for the ants. We suggest that the ants when attacked emit the inhibitory and stimulative pheromones in such a way that the aggressiveness of the alarmed workers is directed toward the enemy without their being themselves the victims of this aggressiveness.

The transport of prey by ants.

I. Myrmica rubra L. and Formica lugubris Zett. treated insect prey in one of two ways; either they licked and bit it without moving it or they siezed it and transported it to the nest. 2. The transport of prey to the nest was by carrying for light prey, and by dragging for heavy prey. 3. Ants dragging prey orientated visually, but the orientation was complicated in certain respects by the possession of prey. 4. When transport was difficult or impossible, for instance because the prey caught on a rough surface, ants swung out of their orientated line of march. This usually freed the prey, either by increasing the force on it through leverage or by sliding it sideways to clear the obstacle. 5. Single workers of M. rubra were able to exert forces of about 100 mg-wt against a spring, single workers of F. lugubris about 300mg-wt and pairs of F. lugubris workers from 400 to 600 mg-wt. The mean power developed by single M. rubra workers was 5.84 ergs/sec., of single F. lugubris workers 24.2 ergs/sec. and of pairs of F. lugubris workers 61.2 ergs/sec. Pairs of F. lugubris workers thus had an advantage over single ants of the same species in this respect. 6. The contribution which each of a pair of F. lugubris workers made to the resultant force they exerted against a spring was found. When the resultant force was small it was possible for the individual efforts of the two ants to be so applied that only a small proportion of them was contributed to the resultant force, and the rest was wasted by opposition between the two ants. When the resultant force was large more efficient application of effort occurred. Large forces and high efficiency were found only when the ants had been pulling together for 8-10 minutes. 7. In both species pairs of ants often failed to move prey because they pulled antagonistically. 8. When groups of F. lugubris moved prey in natural conditions the speed of movement of the prey was at first slow and often stopped as the number of ants attending it rose. After six or more minutes the speed of transport rose to a higher level. This was due to an increased orderliness which showed itself as a straightening-out of the line of transport. The spatial arrangement of ants in these groups was at no time random. Arrangements in which ants held opposite ends of the prey were significantly less common during the phase of straightened-out movement than at other times. 9. It is suggested that the changes in the efficiency with which forces were generated and with which prey was moved (referred to in paragraphs 6 and 8 of this summary) were brought about by the changes in position which ants made in response to difficulty of transport (paragraph 4).