Function of the siphunculi in aphids with particular reference to the sycamore aphid, Drepanosiphum platanoides

Sycamore aphids with occluded siphunculi survive, give birth to as many offspring and maintain their weight as well as aphids with normal siphunculi and it is therefore unlikely that siphunculi have an excretory function. Blocking the siphunculi of sycamore aphids does not affect the way they space out. Siphunculi are used in defence against predators most effectively when the aphid and predator are similar in size.The smell of siphuncular exudate causes aphids like Myzus persicae to scatter but in the sycamore aphid the smell has to be accompanied by the sight or vibration of a struggling aphid to induce an alarm response. Prodding the abdomen and pinching the legs of a sycamore aphid induces it to produce siphuncular exudate.