Fight and rescue or give up and flee? Behavioural responses of different ant species tending the mutualist walnut aphid Panaphis juglandis to native and exotic lady beetles.

Mutualism between ants and honeydew-producing hemipterans is a highly successful evolutionary innovation that attains the status of ecological keystone across many terrestrial ecosystems, involving a multitude of actors through direct or cascading effects. In these relationships, ants often protect their hemipteran partners against their arthropod natural enemies, sometimes interfering with the biological control of pest species. However, the dynamics of these interactions are highly variable based on the specific identity of all the actors involved, and baseline data remain scarce. We performed a field experiment exposing colonies of the walnut aphid Panaphis juglandis attended by five European ant species (Camponotus piceus, Ca. vagus, Crematogaster scutellaris, Dolichoderus quadripunctatus, Lasius emarginatus) to a native and an exotic lady beetle (Adalia bipunctata and Harmonia axyridis), documenting the behavioural interactions between these insects and the performance of ants in the protection of the aphids. Our results reveal a significant behavioural diversity among the ant species involved, with D. quadripunctatus and L. emarginatus being the most aggressive and having the best performance as aphid defenders, and Ca. piceus being least effective and often fleeing away. Cr. scutellaris displayed a rare rescue behaviour attempting to pull away the aphids that the lady beetles grabbed. On the other hand, behavioural responses to A. bipunctata and H. axyridis were similar. Further investigations are needed to understand the eco-ethological implications of these differences, while a better understanding of ant behavioural diversity may help refine biological control strategies.

Do It by Yourself: Larval Locomotion in the Black Soldier Fly Hermetia illucens, with a Novel "Self-Harvesting" Method to Separate Prepupae.

The neotropical insect Hermetia illucens has become a cosmopolite species, and it is considered a highly promising insect in circular and sustainable economic processes. Being able to feed on a wide variety of organic substrates, it represents a source of lipids and proteins for many uses and produces recyclable waste. We investigated the characteristics and differences in the poorly-known locomotory behaviour of larvae of different instars, paying particular attention to the unique characteristics of the prepupal stage, key to farming and industrial processes. Moreover, we attempted to develop a "self-harvesting" system relying on the behavioural traits of prepupae to obtain their separation from younger larvae under rearing condition with minimum effort. Prepupae differ from younger larvae in their response to physical disturbance in the form of tonic immobility and significantly differ in their locomotory movements. Both prepupae and younger larvae reacted similarly to heat or light-induced stress, but low light and high moisture induced only prepupae to migrate away, which resulted in the development of a highly efficient separation methodology. The new data on the behaviour of H. illucens not only shed new light on some unexplored aspects of its biology, but also led to develop an inexpensive self-harvesting system that can be implemented in small-scale and industrial farming.

First Report on the Acrobat Ant Crematogaster scutellaris Storing Live Aphids in Its Oak-Gall Nests.

This study provides new data about the role of ants in mutualistic interactions with aphids mediated by galls. We focused our investigation on galls induced by the cynipid Andricus kollari by conducting a survey and a subsequent experiment in an Italian oak forest. The ants Crematogaster scutellaris, Colobopsis truncata and Temnothorax italicus frequently used the galls as nests: Crematogaster scutellaris occupied galls which were located higher on the oak trees, while C. truncata and T. italicus were located at lower positions. In addition, galls occupied by C. scutellaris showed varied internal architecture in relation to the colony composition. Importantly, field surveys revealed for the first time that C. scutellaris nest galls also contained live individuals of the non-galligenous aphid Panaphis juglandis. Field experiments suggested that the ants actively seek, collect and stock live aphids. No signs of predation and injuries were detected on the stored aphids, which were probably kept for safe overwintering, though we cannot exclude a possible occasional use as food. This report reveals a possible novel relationship which could have important consequences on the phenology and presence of aphids on the host plant.

Rolling away: a novel context-dependent escape behaviour discovered in ants.

For animals facing dangers, the best option to optimize costs and benefits of defence sometimes may be avoidance. Here we report the discovery of a peculiar strategy adopted by Myrmecina graminicola, a cryptic ant living in forest floor. Experiments showed that when disturbed these ants respond with immobility. However, upon perceiving disturbance but under specific inclinations of the substrate, they shift to an active escaping strategy: rolling away. This is a context-dependent behaviour adopted only in appropriate circumstances. During rolling, the ants assume a ball-like shape using antennae and hind legs to obtain an active movement along a stable trajectory. Finally, we assessed the adaptive value of this strategy measuring its effectiveness in defence against enemies. This is the first example of locomotion by rolling discovered in ants and one of the very few among animals, offering opportunities for multidisciplinary research on the adaptations and biomechanics underlying it.

Gall-Colonizing Ants and Their Role as Plant Defenders: From 'Bad Job' to 'Useful Service'.

Galls are neoformed structures on host plant tissues caused by the attack of insects or other organisms. They support different communities of specialized parasitic insects (the gall inducers), and can also provide refuge to other insects, such as moths, beetles and ants, referred to as secondary occupants. This study focuses on galls induced by the oak gall wasp Andricus quercustozae and secondarily colonized by ants in a mixed oak forest. A field survey and two experiments were carried out to a) study ant (species-specific) preferences for different features of the galls, b) describe differences in gall architecture due to ant activity, c) analyse the effects of the presence of gall-dwelling ants on plant health. The results show that there are differences between ant species in gall colonization and in the alteration of gall opening and inner structure. We verified that gall-dwelling ants protect their host plants efficiently, offering them an indirect defence mechanism against enemies (predators and pathogens). The data suggest a new paradigm in ant-plant relationships mediated by the presence of galls on the plants whose ecological and evolutionary implications are discussed.