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Eusocial insect colonies represent some of the most extreme examples of specialized division of labor. Ageing in workers is often associated with a temporal polyethism in the tasks performed both inside and outside the colony. Such behavioral transition is sometimes linked to a gradual reduction in individual immunity. Here, we studied the immune ability of Apis mellifera guard bees, which represent an intermediate stage between house bees working inside the nest and foragers collecting resources outside, to assess if their specific task is associated with an immune specialization. Through immune challenge with Gram-negative bacteria Escherichia coli, we compared the guards ability to clear bacterial cells from their haemolymph with respect to house bees and foragers. Our findings demonstrate that guards do not show an immune specialization linked to their task but seem to represent a transition also in terms of immunity, since their anti-bacterial response appears intermediate between house bees and foragers. [ABSTRACT FROM AUTHOR]

In the early stage of the invasion process, alien species may face costs linked to pioneer effect due to genetic bottleneck, drift and the consequential inbreeding depression. Thus, introduced species that show an immediate exponential growth in their invasive population should have some mechanisms to reduce such costs minimising the chance of inbreeding or allowing them to cope with them. The yellow-legged hornet Vespa velutina nigrithorax has been spotted in France in 2004; since then, the species has been invading Europe with a relentless pace. In their native range, males and reproductive females of a Chinese non-invasive sub-species of V. velutina seem to leave their nests to search for unrelated partners. However, previous studies showed a low genetic diversity and a high rate of diploid males in colonies of the invasive population, suggesting that mating could occur inside nests, where males should be able to discriminate between reproductive gynes and sterile workers. Here, we used laboratory behavioural assays to investigate the mating preferences of yellow-legged hornet males from the recent invasive population in Italy. We assessed the importance of nestmateship and female morpho-physiological traits, likely indicators of caste, in determining male attraction towards potential partners. Our results demonstrate that males are more attracted to bigger females with more abundant fat storage, good indicators of female reproductive caste in wasps, regardless of nestmateship. Our findings represent a first step in understanding the reproductive biology of V. velutina nigrithorax in its invasive range, providing a framework for future research in the field to prevent or reduce the species expansion. [ABSTRACT FROM AUTHOR]

Communication through vibrational signals is widespread among social insects and regulates crucial social activities. Females of the social wasp Polistes dominula produce substrate-borne vibrations on the combs by performing a conspicuous abdominal oscillatory behavior, known as abdominal wagging. Several studies have reported correlative evidence in support of its signaling role, but direct evidence is still lacking. Because abdominal wagging is strictly associated with the presence of larvae in the nest and with cell inspection, it has been suggested that it could be involved in adult--larvae communication. According to this hypothesis, abdominal wagging vibrations would have short-term effects related to food and trophallactic exchanges between adults and larvae by modulating salivary secretion (decreasing its amount, to prepare larvae to receive food, or stimulating the release of larval saliva to adults). Here, by using an electro-magnetic shaker, we assessed, for the first time, the short-term effects of abdominal wagging on larval behavior by recording larval responses and by measuring the amount of saliva released immediately after abdominal wagging playback. Our results show that larvae are able to perceive the substrate-borne vibrations produced by abdominal wagging and react by increasing the movement of their body, possibly in order to attract the attention of adult females during feeding nest inspection. Yet, we found that vibrations neither increase nor decrease the release of larval saliva. Our results support the hypothesis of the alleged role of vibrations in adult--larvae communications; however, they do not support the long- lasting hypothesis of salivary release modulation. [ABSTRACT FROM AUTHOR]