Conflict and Harmony Among Floricole Insects

Almost 90 % of flower plants pollinated by insects, floral insects are a pillar of our food security and our savings. At a time when insect populations collapse, with a third of the European species of bees, butterflies and syrphes in decline, mainly because of the destruction of their habitats and the massive use of phytosanitary products, observing insects during pollination turns out to be both banal and extremely precious.

In particular because the cohabitation between several individuals is not as peaceful as one could assume: it is not uncommon to observe aggressive, even violent behaviors, between two individuals of the same species, or of different species.

Until recently, a general description of the aggressive behavior of insects on flowers in real conditions was not documented: if the concepts of aggressive interaction and competition are well anchored, the studies have hitherto focused mainly on competitions within the same species or interactions between species in very limited frames, as conflicts between whole colonies of different species, for example.

Aggressive behavior and the dominance hierarchy

The interindividual interactions of aggression between floral insects can be classified into 5 categories in order of violence: “neutral interaction” when two individuals meet without happening; the “stationary flight” of an individual behind another; “Intimidation” when an individual flies or turns very close to a second individual; “Aggression” when an individual strikes or hits another individual (as in the photo); And the “fight” when an individual catches another by dropping him from his flower.

These different interactions are not used in the same way and with the same frequency by all species or groups of species. Thus, large syrphs (size greater than 15 millimeters), gray bee Anthophora and other wild bees are more likely to show aggressive behavior than domestic bees and number of bumblebees (genus Bombus).

On the other hand, certain species and groups of species are privileged targets. This is the case, for example, of domestic bees, which are mainly targeted by large syrphes or bumblebees striped with yellow. Bourdons are attacked by the largest syrphes and gray bees of the anthophora genre.

A hierarchy of dominance can then be established on the basis of the behaviors suffered and initiated, and their level of violence. Three main groups can be isolated: the dominant group, with large syrphes and gray bees of the genre Anthophorahaving a greater propensity to initiate aggressive behavior; the group of dominated, with domestic bees, bumblebees and butterflies, more inclined to undergo aggressive behavior; and an intermediate group with species or groups of species initiating as many aggressive interactions as they undergo them, whose beetles, small syrphes, flies of the subordinating of the brachycera, carpenter bees, polish wasps, and most wild bees.

However, it was not possible to explain for the moment the propensity to initiate aggressive behaviors by the characteristics of species such as insect size, sociability or specialization on resources. Studies benefiting from a finer identification of each species, often difficult in natural conditions, will be necessary to be able to better understand the hierarchy of dominance between species.

From observation to theorization

The frequency and nature of aggressive behaviors change with environmental factors such as sunshine or wind, which suggests that their appearance is linked to the stress and excitation of the moment.

That said, the vast majority of interactions between individuals of the same species or different species are of “neutral” nature, that is to say without aggression. At the same time, the majority of aggressive interactions do not lead with the attacker taking possession of the flower. Being stressed or excited by the sun and the wind does not fully explain why insects engage in costly and risky behavior, without obvious benefit. What is the reason that motivate floricoles to attack, and by only targeting certain other species?

Existing theories on the interests of interest indicate that the aggression is unstable and must lead to a sharing of space and time between different species. These theories do not give any track to imagine the benefit that this aggression hierarchy could have for floric insects, because theories predict that such hierarchy should not exist. Aggressiveness hierarchies can exist within a population of the same species. But according to the current theory, rather to fight continuously between dominant and subordinate to protect their flowers, a set of different species must evolve from floral preferences, fodder territories, or differentiated hours. The case of aggressive floric insects presents a little evolutionary mystery that will have to be studied … Another reason to motivate their conservation!