Sycamore Aphid Research Articles

Seasonal changes in fat content, form, state of gonads and length of adult life in the sycamore aphid, Drepanosiphum platanoides (Schr.)

SUMMARY Even when reared under similar conditions of crowding and nutrition, first and second generation adult sycamore aphids differ in their morphology and physiology. Second generation adults have a smaller abdomen, a longer gut, greater fat reserves, less developed gonads, a longer reproductive diapause and live longer than first generation aphids. Second generation nymphs reared in isolation develop into adults which have less well‐developed gonads but a reproductive delay similar to that of first generation adults. Crowding of second generation adults prolongs the reproductive diapause.

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.

Aggregation in the Birch Aphid Euceraphis punctipennis (Zett.) in Relation to Food Quality

The concentration of soluble nitrogen in the leaves of many deciduous trees declines markedly as summer approaches and the leaves mature; there is a slight recovery at senescence (Lindemann 1948; Mittler 1958; Dixon 1963, 1971). The reproductive and growth rates of some tree-dwelling aphids such as the sycamore aphid (Drepanosiphum platanoidis (Schr.)) also decline in mid-summer and reproduction may cease or remain at a low level for up to 2 months, mainly in response to the deterioration in food quality. At this time the population consists almost entirely of adults in reproductive diapause (Dixon 1963). The reproductive rate of the birch aphid Euceraphis punctipennis also declines in mid-summer, but for a relatively short period. The extent to which this aphid, through its aggregation behaviour, overcomes the disadvantages of the variable quality of its food through the year is discussed in this paper.

Metabolic acclimatization to seasonal changes in temperature in the sycamore aphid, Drepanosiphum platanoides (Schr.), and lime aphid, Eucallipterus tiliae L.

Both sycamore and lime aphids live on the leaves of their respective host trees. The sycamore aphid unlike the lime aphid has the ability to adapt metabolically to changes in temperature. The difference in ability of these two tree-dwelling aphids to adapt metabolically to changes in temperature can be related to their mode of life. The sycamore aphid lives on sycamore which is native to the mountainous areas of southern and central Europe where conditions are cool. Sycamore also has a longer growth period than lime as its buds burst earlier and it sheds its leaves later. Sycamore aphids are therefore naturally exposed to a wider range of temperatures than lime aphids.

Leaf Size and Availability of Space to the Sycamore Aphid Drepanosiphum Platanoides

Sycamore aphids feed on the contents of sieve tubes in leaf veins. The smallest aphids prefer to settle on the minor veins of small leaves, but larger aphids select larger veins. On large leaves, however, even the adult aphids prefer to settle on the minor veins. Aphids feeding on large leaves are unable to reach the deeper sieve tubes in the thicker part of the main veins as their stylets are too short. However, the length of the aphids' stylets cannot account for the absence of aphids from the lateral veins of large leaves or the distribution of the various instars on the veins of small leaves. The preference shown by an aphid for leaf veins of a particular size is probably imposed on the aphids by the structure and physiology of leaf veins of different sizes. The outcome of this is that only a part of a leaf is suitable for colonization by aphids.

Population Density and Spacing in the Sycamore Aphid, Drepanosiphum platanoides (Schr.), and its Relevance to the Regulation of Population Growth

Population Density and Spacing in the Sycamore Aphid, Drepanosiphum platanoides (Schr.), and its Relevance to the Regulation of Population Growth

Control and Significance of the Seasonal Development of Colour Forms in the Sycamore Aphid, Drepanosiphum platanoides (Schr.)

In spring and summer alate virginoparae of the sycamore aphid are present but with the onset of autumn apterous oviparae and alate males appear. These mate, and the oviparae lay the overwintering eggs. This polymorphism is controlled by the aphid's response to changes in its environment (Dixon 1971). In addition to this polymorphism there are changes in the background colour of the aphid. Adult aphids of the spring and autumn generations have black bands on their abdomen and are generally darker in colour. In addition to this pigmentation of bands of the cuticle the body fluids and tissues range in colour from green to red. As the abdominal sclerites are transparent, except in the areas that are melanized, the aphid has a green or reddish ground colour. Aphids with a reddish ground colour are the rarer and they first appear in summer. The aim of this paper is to determine what factors in the sycamore aphid's environment regulate the appearance of the reddish and melanic forms and to discuss the adaptive significance of these forms.

Defensive Responses of the Aphid Drepanosiphum Platanoides in Encounters with the Bug Anthocoris Nemorum

The reactions of sycamore aphid Drepanosiphum platanoides (Schr.) nymphs and adults to attacks by different instars of the predatory bug Anthocoris nemorum (L.) were observed. Aphids which avoided capture did so either by moving away from the predator by walking, swivelling, or dropping, or by actively defending themselves by kicking. Large aphids were much better at avoiding capture than small aphids, and were seldom captured even by large anthocorids. Walking and kicking were by far the most frequent responses observed in each aphid instar and bore an inverse relationship to each other, walking becoming increasingly common as a response to successive anthocorid instars. Kicking at predators became more effective as the size of the aphid relative to the anthocorid increased. The mode of capture of prey by anthocorids is poorly suited to prey such as sycamore aphids, which employ their defensive responses with increasing success as they become older. The most certain way for an aphid of any instar to avoid capture is to walk away, but this can affect growth by interrupting feeding.

The ‘interval timer’ and photoperiod in the determination of parthenogenetic and sexual morphs in the aphid, Drepanosiphum platanoides

The ability of the sycamore aphid to produce sexuales (males and females) is regulated by a timing mechanism (‘interval timer’) which restrains the appearance of these morphs in the spring under short day conditions. In this species there are two ‘interval timers’: one, sensitive to day-length and controlling the production of sexual females, and another insensitive to day-length and controlling the production of males. In the production of sexual females day-length acts directly on the aphid and not through the host plant. The restraining effect of the ‘interval timer’ results in a gradual transition from parthenogenetic to gamic reproduction over a period of several generations and is still operational in the autumn. This enables the sycamore aphid to continue very effectively to exploit its host plant at a time when it provides a rich food source, although some individuals ensure continuity of the population by laying eggs before any premature adverse conditions.

Stabilization of Aphid Populations by an Aphid Induced Plant Factor

MANY tree dwelling aphids such as the sycamore aphid, Drepanosiphum platanoides (Schrk.), feed on the phloem sap of leaves and are restricted to one host plant. If therefore the aphids affect the metabolism of the leaves of deciduous trees while they are still developing in the spring, this may subsequently affect later generations of aphids.

Migration in aphids: response to current adversity.

Johnson1–3, Kennedy4 and Southwood5 state that migration occurs in alate aphids whether the alate population is large or small, and this behaviour of the alatae is not due to population pressure or to current lack of food; in other words, the migration of alatae is an evolved adaptation rather than a response to current adversity. This hypothesis does not apply to the sycamore aphid, Drepanosiphum platanoides (Schr.), in which migration is more marked in conditions of over-population (unpublished results of A. F. G. D.). The sycamore aphid, however, which is a tree dwelling aphid and therefore occupies a permanent habitat5, does not show the same degree of polymorphism as polyphagous aphids. It could be regarded as an exception to this hypothesis, which has been developed to explain migratory activity in aphids occupying temporary habitats.