Anne-Catherine Mailleux

How do ants assess food volume

By comparing the behaviour of Lasius niger scouts at sucrose droplets of different volumes, we empirically identified the criterion used by each scout to assess the amount of food available as well as the rules governing its decision to lay a recruitment trail. When scouts discovered food volumes exceeding the capacity of their crop (3 or 6 µl), 90% immediately returned to the nest laying a recruitment trail. In contrast, when smaller food droplets (0.3, 0.7 or 1 µl) were offered, several scouts stayed on the foraging area, presumably exploring it for additional food. If unsuccessful, they returned to the nest without laying a trail. The droplet volume determined the percentage of trail-laying ants but had no influence on the intensity of marking when this was initiated. The key criterion that regulated the recruiting behaviour of scouts was their ability to ingest their own desired volume. This volume acted as a threshold triggering the trail-laying response of foragers. Collective regulation of foraging according to food size resulted from the interplay between the distribution of these desired volume thresholds among colony members and the food volume available. We relate some aspects of the foraging ecology of aphid-tending ants to this decision-making process. Copyright 2000 The Association for the Study of Animal Behaviour.

Regulation of ants' foraging to resource productivity

We investigate the behavioural rule used by ant societies to adjust their foraging response to the honeydew productivity of aphids. When a scout finds a single food source, the decision to lay a recruitment trail is an all–or–none response based on the opportunity for this scout to ingest a desired volume acting as a threshold. Here, we demonstrate, through experimental and theoretical approaches, the generic value of this recruitment rule that remains valid when ants have to forage on multiple small sugar feeders to reach their desired volume. Moreover, our experiments show that when ants decide to recruit nest–mates they lay trail marks of equal intensity, whatever the number of food sources visited. A model based on the ‘desired volume’ rule of recruitment as well as on experimentally validated parameter values was built to investigate how ant societies adjust their foraging response to the honeydew productivity profile of aphids. Simulations predict that, with such recruiting rules, the percentage of recruiting ants is directly related to the total production of honeydew. Moreover, an optimal number of foragers exists that maximizes the strength of recruitment, this number being linearly related to the total production of honeydew by the aphid colony. The ‘desired volume’ recruitment rule that should be generic for all ant species is enough to explain how ants optimize trail recruitment and select aphid colonies or other liquid food resources according to their productivity profile.

How does colony growth influence communication in ants

Summary. As Lasius niger societies grow from incipient nests to mature colonies, their foraging strategies shift from the individual exploitation of food sources to mass recruitment. Colony size instead of age is the key factor that shapes the exploratory and foraging responses of Lasius niger: a drastic reduction (or increase) of the population elicits an activity profile similar to that observed in younger (or older) societies of the same size. As a colony grows, the proportion of patrollers significantly decreases while the proportion of conveyors remains rather constant. As regards the energetic return, it increases with incipient nest size due to the replacement of minims by ordinary workers of larger crop capacity. We also demonstrate that minims of incipient nests modulate their trail-laying behaviour according to the social context, in this case the colony size. During their ontogenesis, L. niger colonies exhibit a progressive integration of individual foragers into a network of communication, the adaptive significance of which is discussed.

Probiotic Escherichia coli Nissle 1917 activates DC and prevents house dust mite allergy through a TLR4-dependent pathway

Experimental animal and human studies have demonstrated that probiotic strains have beneficial effects on allergy. Here we report that the probiotic Escherichia coli Nissle 1917 strain (EcN) is able to activate DC, as shown by important cytokine synthesis together with up‐regulation of membrane expression of CD40, CD80 and CD86. This EcN‐induced DC activation was strictly dependent on the TLR4 signaling pathway and was also associated with stimulation of NF‐κB and MAPK. We next investigated the prophylactic potential of i.n. co‐administration of EcN with a recombinant form of Der p 1 (ProDer p 1) in a murine model of mite allergy. I.n. vaccinations with EcN plus ProDer p 1 prevented the subsequent allergic response following Der p 1 sensitization and airway challenge with aerosolized mite extracts through the induction of an allergen‐specific IgG2a response, the prevention of specific IgE production and a strong reduction of IL‐5 secretion by allergen‐restimulated splenocytes. EcN alone or in combination with ProDer p 1 inhibited the development of airway eosinophilia and neutrophilia. This in vivo protective effect of EcN was, in part, mediated by TLR4 signaling. Our results suggest that EcN represents an efficient adjuvant to prevent allergic responses.

Group effect on fertility, survival and silk production in the web spinner Tetranychus urticae (Acari: Tetranychidae) during colony foundation

In many vertebrates and invertebrates, individuals reared in isolation show biological modifications compared with those reared in groups of two of more. The spider mite Tetranychus urticae is characterised by a communal organization and displays some forms of cooperative behaviour (aggregation and common web spinning). To evaluate the potential fitness cost or gain of group living, we investigated the effect of being in group on life history parameters (silk production, fecundity, death rate, feeding rate). In this respect, virgin single females and grouped females (two to six individuals) were compared every day for 5 days. Grouped mites produced significantly more web/mite per day (since the second day of experiment) and more eggs/mite per day (since the fourth day of experiment) than single mites. Moreover, single mites had a higher death rate than mites living in groups. However, no difference was found concerning feeding rate. We assume that mites could benefit from the web production of other individuals and invested resources in other activities such as egg production. We showed that these group effects already exist in small groups. In natural conditions with a higher group size, the impact of group living might be stronger for the dynamics of T. urticae populations and the colony foundation.

Spatial distribution and inbreeding in Tetranychus urticae.

In group living, species spatial distribution results from responses to environmental heterogeneity and/or mutual interactions between individuals. These mutual interactions can be regulated by genetic and/or epigenetic factors. In this study, we focus on genetic factors and investigate how the spatial distribution of some individuals colonizing a new environment is influenced by inbreeding. Our biological model is Tetranychus urticae, a phytophagous mite considered as a major pest of many cultivated plants. Groups of T. urticae were composed of individuals from successive inbreeding (sister-brother sib-mating). Our results show that the inter-individual distances increase with inbreeding. Indeed, inbreeding level seems to be an important factor affecting the intra-plant spatial distribution of mites. These results confirm that mites have the capability to discriminate their kin and, moreover, that they are able to accurately perceive differences between close relatives from sib-mating lines.

Acaricidal activity of 31 essential oils extracted from plants collected in Tunisia

The two-spotted spider mite Tetranychus urticae Koch is a worldwide pest, feeding on a large variety of plant families. As its resistance to acaricides spreads rapidly, it is crucial to develop new biological control tactics to manage its populations. In this respect, essential oils may be a good alternative, as they are currently considered minimum-risk pesticides. In this paper, we conducted a series of laboratory experiments to determine the susceptibility of adult females to 31 essential oils extracted from plants collected from Tunisia and compare it with the results obtained with two synthetic acaricides (spirodiclofen and fenbutatin oxide). Details of the essential oil yield of these plants were also recorded. A maximum yield of 0.5% was obtained. Laboratory bioassay indicated that the development of the tetranychid mite population was significantly affected by the use of Deverra scoparia, Haplophyllum tuberculatum, Chrysanthemum coronarium and Mentha pulegium plant extracts that killed 97%, 93%, 93% and 91% of T. urticae, respectively. The chemical composition of the most effective extracts were characterized by gas chromatography–mass spectrometry (GC–MS) and fast GC–flame ionization detector (FID). The evaluation of the potential of biologically active plant volatiles against T. urticae might provide a new approach to the development of natural acaricides to be used both in biological and integrated pest management strategies for controlling two-spotted spider mites.

Effective concentrations of garlic distillate (Allium sativum) for the control of Tetranychus urticae (Tetranychidae)

The two‐spotted spider mite, Tetranychus urticae Koch, is a worldwide pest that feeds on a large variety of plant families. Because its resistance to acaricides is spreading rapidly, the development of new biological control tactics for population management is crucial. Plant extracts, such as garlic extract (Allium sativum Linn.), may represent viable alternatives, because they are currently considered to be minimum‐risk pesticides. Although garlic is known for its acaricidal properties, the extract concentration that provides the most efficient control has not yet been precisely determined.

How to Visualize the Spider Mite Silk

Tetranychus urticae (Acari: Tetranychidae) is a phytophagous mite that forms colonies of several thousand individuals. Like spiders, every individual produces abundant silk strands and is able to construct a common web for the entire colony. Despite the importance of this silk for the biology of this worldwide species, only one previous study suggested how to visualize it. To analyze the web structuration, we developed a simple technique to dye T. urticaesilk on both inert and living substrates. Fluorescent brightener 28 (FB) (Sigma F3543) diluted in different solvents at different concentrations regarding the substrate was used to observe single strands of silk. On glass lenses, a 0.5% dimethyl sulfoxide solution was used and on bean leaves, a 0.1% aqueous solution. A difference of silk deposit was observed depending the substrate: rectilinear threads on glass lenses and more sinuous ones on bean leaves. This visualizing technique will help to carry out future studies about the web architecture and silk used by T. urticae. It might also be useful for the study of other silk‐spinning arthropods. Microsc. Res. Tech. 2009.

How non-nestmates affect the cohesion of swarming groups in social spiders

Abstract.In social biology, it is often considered that an organized society cannot exist without exclusion behaviour towards newcomers from another nest. Unlike most vertebrate and invertebrate social species, social spiders such as Anelosimus eximius accept unrelated migrants without agonistic behaviour. Does it imply that spiders cannot recognize non-nestmates from nestmates or is there any evidence of recognition without aggression ? In order to answer this question, we studied behavioural differences between groups coming from single and mixed-nests in the overall context of swarming.Our study shows that the presence of non-nestmate conspecifics reduces the cohesion of the swarm groups during the settlement process and increases the spatial dispersion of spiders, the asymmetry in the spatial distribution being less pronounced. Individuals belonging to different nests are not as mutually attractive. This paper shows that, during the induced migration, two processes counteract each other: the amplification process resulting from the addition of silk drives individuals to form groups with non-nestmates and the recognition process reduces the cohesion of groups composed of non-nestmates. The collective decision-making during migration results from the balance between these two trends.