Claudia Bruschini

High Varroa mite abundance influences chemical profiles of worker bees and mite-host preferences

Honeybee disappearance is one of the major environmental and economic challenges this century has to face. The ecto-parasitic mite Varroa destructor represents one of the main causes of the worldwide beehive losses. Although halting mite transmission among beehives is of primary importance to save honeybee colonies from further decline, the natural route used by mites to abandon a collapsing colony has not been extensively investigated so far. Here, we explored whether, with increasing mite abundance within the colony, mites change their behaviour to maximize the chances of leaving a highly infested colony. We show that, at low mite abundance, mites remain within the colony and promote their reproduction by riding nurses that they distinguish from foragers by different chemical cuticular signatures. When mite abundance increases, the chemical profile of nurses and foragers tends to overlap, promoting mite departure from exploited colonies by riding pollen foragers.

Cuticular Hydrocarbons Rather Than Peptides Are Responsible for Nestmate Recognition in Polistes dominulus

A colony of social insects is like a fortress where access is allowed only to colony members. The epicuticular mixture of hydrocarbons has been widely reported to be involved in nestmate recognition in insects. However, recent studies have shown that polar compounds (mainly peptides) are also present, mixed with hydrocarbons, on the cuticle of various insects, including the paper wasps of the genus Polistes. As these polar compounds are variable among Polistes species and are perceived by the wasps, this cuticular fraction could also be involved in nestmate recognition. Through MALDI-TOF (Matrix-Assisted Laser Desorption Ionization Time of Flight) mass spectrometry analysis, we assessed, for the first time, the intercolonial variability of the cuticular polar fraction of Polistes dominulus in order to evaluate its reliability as source of nestmate recognition cues. We then tested through behavioral assays the importance of the 2 isolated fractions (apolar and polar) in nestmate recognition by presenting them separately to colonies of P. dominulus. Our results showed that the cuticular polar compounds are not colony specific and they are not used by paper wasps to discriminate nestmates from non-colony members. On the contrary, we confirmed that the isolated cuticular hydrocarbons are the chemical mediators prompting nestmate recognition in paper wasps.

Caste differences in venom volatiles and their effect on alarm behaviour in the paper wasp Polistes dominulus (Christ).

SUMMARY Foundresses and workers of Polistes paper wasps show slight morphological and physiological differences. However, after the emergence of the workers, the castes can be readily discriminated by their behaviour: the dominant foundress is the principal egg-layer, whereas workers perform different tasks linked to colony development. Previous studies have demonstrated in this genus that defence of the colony by the workers is more effectively carried out by a collective response elicited by venom volatiles used as alarm pheromones. In the present study, gas chromatography–mass spectrometry analyses of the venom volatiles of foundresses and workers of Polistes dominulus (Christ) show predominantly quantitative differences. Spiroacetals, mainly (E,E)-2,8-dimethyl-1,7-dioxaspiro[5.5]undecane, are significantly higher in the venom volatiles fraction of workers, whereas the amount of N-(3-methylbutyl)acetamide is almost double in foundresses. On the basis of the chemical results, behavioural assays were performed on fifteen field colonies to test the alarm response of the resident wasps to venom extracts from foundresses and workers. Our behavioural results suggest that worker venom has a stronger alarm effect on the colonies than that of the foundresses, which seems unable to elicit the complete alarm response ending with a final attack and sting. The venom volatiles of P. dominulus workers serve mainly to alarm the colony whilst those of foundresses may also be linked to additional functions related to conspecific interactions.

Evidence of alarm pheromones in the venom of Polistes dominulus workers (Hymenoptera: Vespidae)

Abstract The active and coordinating capacity of defending the nest is a key feature of social insects. The present study investigates the presence of alarm pheromones in the venom of workers of the social wasp, Polistes dominulus. Laboratory experiments were performed with caged colonies of P. dominulus using a wind tunnel apparatus to test the behavioural response of workers to venom released by other workers and to venom extracts. Contrary to that previously reported for European paper wasps, the present results show that the venom is the source of alarm pheromones. Field experiments combining a visual (black target) and a chemical stimulus (venom extract) were performed to test the effect of the venom on the reaction of colonies. Wasps leave the nest, land on the visual target and attack the target significantly more once exposed to venom extract plus target than to solvent plus target. This work shows that the venom of P. dominulus workers elicits an alarm response, reduces the threshold for attack and acts as an attractant on targets. These results using P. dominulus indicate that, in both American and European species, colony defence is based on the same features, suggesting that chemical alarm is a widespread trait in the genus Polistes.

Hydrocarbon rank signatures correlate with differential oophagy and dominance behaviour in Polistes dominulus foundresses.

SUMMARY Social life offers animals increased fitness opportunities. However, the advantages are not evenly distributed and some individuals benefit more than others. The ultimate advantage of reaching the highest rank in a dominance hierarchy is the achievement of reproduction monopoly. In social insects, dominant individuals and queens keep their reproductive control through differential oophagy of unwanted eggs (egg policing). Egg recognition is the main proximate mechanism for maintaining reproductive dominance. In the social wasp Polistes dominulus, subordinate queens often lay eggs in the presence of the dominant individual. Combining gas chromatography–mass spectrometry (GC-MS) analysis and laboratory bioassays, we found that chemical differences between eggs of subordinate and dominant foundresses can explain the differential success in oophagy enjoyed by dominant individuals. We propose that dominance behaviour is an investigative behaviour as well as a ritualized agonistic behaviour. In fact, the frequency of dominance acts increases with the chemical similarity of the surfaces of dominant- and subordinate-laid eggs. Therefore, dominant individuals probably perform dominance behaviour to test the cuticular signatures of subordinates and so better assess the chemical profiles of subordinate eggs. Finally, we provide evidence that in particular social contexts, subordinate Polistes foundresses can develop ovaries as large as those of dominant individuals but nevertheless lay very few eggs. The subordinates probably lay a limited number of eggs to avoid unnecessary energy loss, as a result of efficient queen policing, but will start laying eggs as soon as the queen fails.

Metabolic responses of the limpet Patella caerulea (L.) to anoxia and dehydration.

This study examined the metabolic responses of the limpet Patella caerulea (L.) to anoxia and dehydration, attempting to tease apart the effect of these two stressful conditions, which are often not clearly distinguished in experiments. Specimens were exposed to: (a) oxygen-free sea water; (b) oxygen-saturated water (controls); (c) low-humidity air (55% RH); and (d) high-humidity air (100% RH). For each of the treatments, we took samples of five specimens after 6 and 18 h of exposure to the experimental conditions and determined the concentrations in the foot muscle of succinate, acetate, propionate, aspartate and alanine. Exposure to anoxia caused an increase in the levels of succinate (6 and 18 h) and acetate and propionate (18 h) with respect to control specimens. Anoxia also induced a decrease of aspartate and an increase of alanine after both 6 and 18 h. Exposure to both moist and dry air generally had negligible effects on the organic acid levels. Aspartate content increased after 18 h of exposure to moist air. Alanine levels also increased with respect to control values after exposure to air, with dry air having the more pronounced effect. In conclusion, the results of this study suggest that one should be cautious when inferring anaerobic conditions from the simple exposure of intertidal species to air, without strict control of the experimental conditions and actual respiration rates.

Invading a refugium: post glacial replacement of the ancestral lineage of a Nymphalid butterfly in the West Mediterranean

The power of a fixed scenario was compared to that of a dynamic scenario, in order to explain the distribution pattern of two well established subspecies (morphotypes) of the model butterfly species Maniola jurtina in the central Mediterranean. Samples were collected from a transect of 21 sites along the western side of the Italian Peninsula as well as in Sicily, North Africa and some Italian islets in the Tyrrhenian sea. Samples from the Balkans Peninsula have been added for comparison. Geometric morphometrics, suggested as a reliable marker to identify hybrid individuals, were applied to 150 male genitalia. Their shape was analysed by the means of the partial least square (PLS) discriminant analysis and then modelled through geographic information system (GIS) spatial analyses. The timing of invasion was reconstructed by comparing sea-level changes with the recent isobaths both on the mainland and on islands. The occurrence of the eastern morphotype on the Italian Peninsula and of the western morphotype in North Africa and Sicily was confirmed. However, we found intermediate populations at the tip of the Italian Peninsula and on the islands of Ischia and Capri. No intermediate populations were found in Sicily. The fixed scenario is unlikely, since a dispersal of the western morphotype from Sicily to the distant islands of Ischia and Capri might be hypothesized. A more parsimonious hypothesis minimises dispersal across the sea barriers. It assumes the ancestral presence over the entire study area of the western morphotype, which was later replaced on the Italian mainland but maintained on the islands. These rapid movements could drastically modify European biogeographic patterns.

Sensing the intruder: a quantitative threshold for recognition cues perception in honeybees

The ability to discriminate among nestmates and non-nestmate is essential to defend social insect colonies from intruders. Over the years, nestmate recognition has been extensively studied in the honeybee Apis mellifera; nevertheless, the quantitative perceptual aspects at the basis of the recognition system represent an unexplored subject in this species. To test the existence of a cuticular hydrocarbons’ quantitative perception threshold for nestmate recognition cues, we conducted behavioural assays by presenting different amounts of a foreign forager’s chemical profile to honeybees at the entrance of their colonies. We found an increase in the explorative and aggressive responses as the amount of cues increased based on a threshold mechanism, highlighting the importance of the quantitative perceptual features for the recognition processes in A. mellifera.

The chemical basis of host nest detection and chemical integration in a cuckoo paper wasp.

SUMMARY Insect social life is governed by chemicals. A great number of studies have demonstrated that the blend of hydrocarbons present on the cuticle (CHCs) plays a pivotal role in intra- and inter-specific communication. It is not surprising, therefore, that social parasites, specialized in exploiting the costly parental care provided by host workers, exploit the host chemical communication system too. Throughout their life cycle, social parasites intercept and break this CHC-based code. Recently, however, several polar compounds (mainly peptides) have been found in addition to CHCs both on the cuticle and on the comb surface of social insects, and their semiochemical role has been demonstrated in some circumstances. In the present study, we used the paper wasp social parasite–host system Polistes sulcifer (Zimmerman)–Polistes dominulus (Christ) to evaluate the relative importance of the CHCs and polar compounds in two different steps of the host exploitation process: host nest detection by the pre-usurping parasite and parasite chemical integration into the host colony. After separating the polar and apolar fractions of the host nest as well as those of pre- and post-usurpation parasites, we carried out laboratory assays based on the binary choice model. Our results show that nest polar compounds neither are used by the parasite to detect the hosts nest nor play a role in parasite chemical integration into the host colony. In contrast, we demonstrate that CHCs are fundamental in both steps, thus confirming their primary role in social insect life and consequently in social parasite–host interactions.

Breeding range of the last eastern colony of Critically Endangered Northern Bald Ibis Geronticus eremita in the Syrian steppe: a threatened area

Summary Eight years after the discovery of the last survivors of the eastern population of Northern Bald Ibis in Syria, their breeding grounds within the Palmyra steppe remain threatened by habitat degradation, human disturbance and uncontrolled infrastructural development whilst the ibis colony size has continued to decline. This study is aimed at assisting national and international stakeholders in strengthening the Ibis Protected Area, established in 2004 and still lacking a clear boundary and management zonation, by quantitatively establishing the range used by these birds through use of satellite tracking and field observations collected between 2006 and 2009. The core breeding range used by the ibises is 224–253 km 2 while the full home range is c.1,500 km 2 , encompassing a mountainous area north of Palmyra, ranging from 400 to 1,000 m asl. Locations from satellite tracking also revealed an important unknown post-breeding site. The ibis breeding area is also home to a range of other rare and endangered fauna as well as significant landscape, cultural and recreational assets, establishing it as an area of international importance. The Syrian steppe is a crucial socio-economic asset for the country, not only for the indigenous pastoralist people, but also because Syria seeks to develop and promote ecotourism in the Palmyra region. The steppe is increasingly suffering from damaging desertification. The need for investment in protection and management of key biodiversity and landscape assets is a precondition that needs greater recognition by the authorities. Recommendations are provided for decision makers and conservationists aimed at mitigating threats and making the Ibis Protected Area fully functional.