Campaign newspaper: Insects thicken the air with chemical signals | Environment


Ttwo insects rotate like compasses on a leaf the joy of the traveler. They look very different from each other, but they are the same species – the common green bug, Palomena prasina. One is more animated and moves quickly on the sheet; its head and antennae protrude from the top of its green, pointed, shield-shaped body that is wide along the pronotum above and pointed at its end below. It is an adult shieldbug, an imago.

The other is more sedentary, a circular pea-green shield with black heraldic markings; this is a shieldbug nymph, in its fifth and final stage of development – or developmental stage – before it sheds its pupa shield to become an imago.

Although at different stages of development, the two green Shieldbugs physically connect, aware of each other’s excretions of a defensive pheromone from which they get the name stink. In that rare moment of autumn sunshine that galvanizes the insect world with an electric shock, the air must be as charged with swirling chemical signals as it is with wings.

The static around a bunch of ivy, in full bloom and in full sun, is as if the insect volume dial has climbed to 11. Hundreds of bees, hoverflies, flies and wasps swarm around the ivy. , stopping to take nectar and pollen from the flowers. A lonely hornet, Vespa crabro, massive and pirate in comparison, melts, grabs a wasp and eats it upside down, throwing only the wings. The hornet devours the wasp within a minute, then flies off to its nest to feed the last batch of larvae in a process called trophallaxis – it regurgitates the protein-rich and chewed remains of the wasp for the larvae, which in turn produce a salivary liquid rich in carbohydrates for the adult hornet.

Another hunter, the common darter, Sympetrum striolatum, a long red needle of a dragonfly, comes to rest on a fence post – the same from which the spotted flycatcher used to launch itself to cut gnats dancing in the air. The stinger, having left the envelope of its nymph in a pond somewhere, turns its head towards the sun knowingly.