FNZ 25 - Cercopidae (Insecta: Homoptera) - Biology
Hamilton, KGA; Morales, CF 1992. Cercopidae (Insecta: Homoptera). Fauna of New Zealand 25, 40 pages.
( ISSN 0111-5383 (print), ; no. 25. ISBN 0-477-02636-2 (print), ). Published 25 May 1992
The biology of only a few species of Cercopidae is known, and the New Zealand fauna has yet to be studied in any detail. The following information, drawn from Northern Hemisphere species, is offered as a guide only, to be qualified by observation.
Gravid females lay relatively few eggs, usually not exceeding 35. The eggs are usually inserted into plant tissue by means of the female's knifelike ovipositor, which cuts a slit into a stem or petiole. Some spittlebugs may simply insert the eggs into crevices, such as leaf sheaths, under bud scales, or under bark. The few eggs that are laid at one time are embedded in a whitish, gluelike substance which tears to expose the egg shortly before the nymph hatches. The egg shell is broken with the aid of a hardened plate, or egg burster, on the outer embryonic cuticle, which the young insect presses against the shell.
Newly hatched spittlebugs wander over the plant on which the eggs were laid until a suitably succulent feeding site is found on the aerial parts of the plant or on the root crowns. They may wander a considerable distance, or even drop from tree branches to the ground before reaching their host plant. Having.selected a feeding site, the young insect inserts its beak and proceeds to draw sap. A filtering chamber in its oesophagus passes much of the excess water and a considerable amount of sugar directly to the posterior part of the gut, and results in less sap being digested than is ingested. The excess flows from the anus and adheres to the plant and the nymph, until sufficient has accumulated to enclose the tiny insect in a shining droplet. The nymph breathes by means of a tubelike canal below its abdomen, which is formed by the large plates fringing the abdomen and almost meeting below the body. The breathing pores, or spiracles, lie within this canal. The air in the canal is replenished by thrusting the tip of the abdomen outside the droplet.
Spittlebug nymphs grow in a series of five stages, or instars, separated by moults which permit a larger cuticle to form around the body. These moults usually occur within the fluid in which the nymphs live; the cast-off skins remain clinging to the plant, or floating in the fluid.
As the insect grows its droplet increases in size, and bubbles begin to appear. The first of these may be due to the breathing activity of the nymph, but by the second instar the nymph begins to actively produce bubbles, permitting a larger liquid mass to accumulate. This remarkable process of bubble production involves vigorous motions of the abdomen: the air canal is filled with air as the abdomen is thrust outside the fluid mass; the abdomen is then strongly contracted within the fluid, forcing a bubble out of the tip. Dipping or rolling motions of the abdomen accompanied by contractions produce several bubbles before the air supply need be replenished. Enough bubbles can be made to cover the body in 15-30 minutes. The bubbles do not immediately collapse, as the fluid is mixed with a sticky secretion exuded from the side of the abdomen.
Spittlebug nymphs may become restless and vagile, especially when disturbed. They will then begin to wander apparently aimlessly over their host and grope in the air at the edge of leaves. There may be a variety of reasons for such wandering behaviour. Nymphs are apparently sensitive to fluctuations in the availability of sap, and will quickly move from a cut or withered plant. The bugs are not content to remain long in one place until the preferred host is found.
Having selected a new feeding site, a nymph takes its position head down, inserts its beak, and begins to exude more fluid. When the fluid begins to fill the air canal it is forced out by contractions of the abdomen, and bubble formation commences. This action is interrupted by irregular resting periods. As the bubbles accumulate around the abdomen, the nymph uses its two front pairs of legs to kick the bubbles forwards. Bubble formation continues until the insect is again buried in foam. Some nymphs, in wandering, encounter the spittle masses of other nymphs and enter them, anchoring and producing more bubbles. In this way a number of nymphs may come to occupy the same spittle mass.
Nymphs take at least a month to develop fully, and poor weather or unhealthy food-plants may extend the growth period considerably. Under ideal conditions the early instars may moult within 2 days, but later instars take longer to develop. The last nymphal instar differs considerably from the previous instars in appearance. Short wing pads become obvious, and the body changes colour, usually either losing all its dark pigmentation or becoming entirely blackish.
The full-grown nymph may emerge from the fluid and cling to an exposed part of the stem or branch, where the drying spittle fluid on its body cements the shed cuticle to the plant. Others select an open but usually shaded situation on the underside of a leaf or grass blade and construct a new spittle mass. This mass is more gelatinous than the previous ones, and soon dries and hardens around the insect, to form a moulting chamber. The empty chamber with its round exit hole may remain for some time in the field, and numbers of these may occasionally be found.
The adult has quite different behaviour from its immature forms. Usually indolent, it walks slowly and awkwardly, dragging its hind legs, which are used only for powerful leaps. The bugs are agile in jumping but clumsy in landing, seldom recovering their footing quickly.
When feeding, adults may sit for hours in one place, not even changing position. They never form a spittle mass, living instead in exposed situations on leaves or hugging a stem or twig. They apparently rely on their mottled colour pattern and remarkable dodging and jumping abilities for protection against predators.
Feeding by adult spittlebugs can cause severe loss of sap. Ingested sap passes through the filter chamber, as in the nymphs, and is emitted as droplets of a clear, sugary liquid known as honeydew. These droplets are ejected forcibly over the head with a faint cracking sound, often at a considerable rate.