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Phylloxerids - their Biology and MorphologyOn this page: Biology Morphology Genera
The Phylloxeridae is a small family of soft-bodied tiny insects that have paired membranous wings and feed on plant sap. Together with the Aphididae and the Adelgidae they comprise the sole living members of the superfamily Aphidoidea and infraorder Aphidomorpha. Like other Aphidomorpha, the Phylloxeridae exhibit cyclical parthenogenesis, and like the Adelgidae, they are entirely oviparous (parthenogenesis in Aphididae is viviparous). They are also polymorphic, and at least some species host-alternate (some on a yearly cycle, some 2-yearly) with various modifications thereof. Most of our knowledge of this family is due to the grape phylloxera (Daktulosphaira vitifoliae) which alternates between the roots and leaves of its host, producing galls on both, and correspondingly many morphs. This important grape pest is holocyclic on North American Vitis species, from whence it spread.
Summarizing Blackman & Eastop (2021): the Phylloxeridae family are Holarctic in origin, feed on dicotyledons, and have perhaps 83 species in 8 genera. Roughly half of Phylloxeridae species produce galls, mostly on species of Carya (North American hickories) especially pecan. Most of the other Phylloxeridae feed on the leaves or stems or roots of Juglandaceae (the walnut family) or Fagaceae (the oak family).
A non-gall-former: Phylloxera glabra aptera with eggs. Sample courtesy Alan Outen.
Despite being a species-poor family compared to the 5000+ species of Aphididae, the Phylloxeridae has 2 subfamilies, the Phylloxerininae and Phylloxerinae.
Subfamily Phylloxerininae has just 1 genus (Phylloxerina) of perhaps nine species (4 Nearctic, 4 Palaearctic, 1 Cuban) none of which host alternate. Seven species live on Salicaceae (willows), one on Cornaceae (Nyssa), and one (Phylloxerina populi) on Populus (poplar). Their apterae are usually covered in dense white wax. No alatae have ever been recorded for this genus. Only one (Phylloxerina nyssae) causes galls (on Nyssa sylvatica leaves).
Subfamily Phylloxerinae are mostly Nearctic, either forming galls on Juglandaceae (Carya) or on leaves of Fagaceae (at least two host-alternate between the two) and a few species on Ulmaceae, Rosaceae and Vitaceae. The Phylloxerinae has 6 genera of perhaps 74 species in two tribes (Acanthochermesini, Phylloxerini). Tribe Acanthochermesini has one genus, of two Palaearctic species (Acanthochermes quercus, Acanthochermes similiquercus), both of which cause galls on Quercus. Like Phylloxera and Daktulosphaira (=Viteus), they have spiracles on abdominal segments 2-5, but their immatures have unusual star-like tubercles - and the adult fundatrices have small spiculose tubercles on their head, thorax and abdomen. Their life cycle is also unusually truncated in having just two generations per year, fundatrices and sexuales.
Tribe Phylloxerini has 5 genera and perhaps 65 species, 60 of which are in genus Phylloxera. This classification may change since most of the Palaearctic species have spiracles on abdominal tergites 1-5, and most of the Nearctic species (including the gall-making Phylloxera on Carya) lack spiracles on tergites 2-5. Aphanostigma is a Palaearctic genus of 2 species (Aphanostigma iaksuiense, Aphanostigma piri) found in bark crevices on Pyrus (pear). They are of economic importance - and lack spiracles on abdominal segments 2-5. Genus Foaiella is Palaearctic and has one species (Foaiella danesii). This is holocyclic on Quercus robur roots, which become tuberose. Its apterae have fine hairs, the alatae have a round distal rhinarium. Genus Olegia has one Palaearctic species (Olegia ulmifoliae). It is unusual in having one-segmented tarsi, and forms galls on Japanese elm (Zelkova serrata) upon whose leaves it is monoecious and holocyclic. Alatae are unknown, it disperses via wind-blown first instars. Genus Daktulosphaira has one species, of Nearctic origin, (Daktulosphaira vitifoliae). On American vine species it alternates 2-yearly between its leaf galls (where sexual forms occur) and root galls. On European vines the sexual phase is rare. Nymphs that overwinter on roots may mature to alates. Like Phylloxera species, it has spiracles on abdominal segments 2-5, but its alatae lack a greatly enlarged distal antennal sensorium.
Genus Phylloxera has perhaps 60 species, of which 31 were described from galls on Carya in North America. Of the non-gall-formers, there are 20 species on Quercus (11 Palaearctic, 8 Nearctic, 1 Cuban) and 2 on Castanea (Phylloxera castaneae, which is Nearctic, and Phylloxera castaneivora, Palaearctic). Although many Phylloxera are clearly monoecious on either Carya or Fagaceae, two gall-forming Nearctic species host-alternate between Carya (their primary host) and either Castanea (Phylloxera castanea) or Quercus (Phylloxera texana) as secondary hosts. Four other species (3 Nearctic on Carya gall-formers, plus Phylloxera kunugi, a Palaearctic non-gall-former on Quercus) are suspected to host alternate. Phylloxera quercus, a non-gall-forming Palaearctic species, overwinters on evergreen oaks, which function as primary hosts - in May some fly to deciduous oaks, from which sexuales return in autumn. Seven non-galling species on Quercus (1 Nearctic, 5 Palaearctic) and 6 on Carya gall-makers are non-alternating. Whilst a few of the remainder appear to be anholocyclic 'species', in most cases their life cycle is simply unknown.
Phylloxeridae lack the wax glands or plates found in Adelgidae and some Aphididae. The adult aptera body is pear-shaped, nearly semi-globular with a flat underside, and normally narrowing towards the end.
Their antennae are short, with just 3 segments in all morphs and instars. (Adelgidae species have 3, 4 or 5 antennal segments; adult Aphididae have 5 or 6, rarely 4; the immatures have 1-fewer). Winged females of Phylloxera notabilis appear to have 4 antennal segments because the third segment is usually divided into two elongate masses - but these are not articulated. As in Adelgidae, the basal two segments are of similar size, the third antennal segment (=flagellum) is longer and slightly thinner and bears a primary rhinarium at its tip - the size and location of which varies with species. Some winged adult females have one or two additional sensoria on the flagellum. The terminal process of the last segment is little-developed or non-existent. The rostrum is short. Apterae only have triommatidia but alatae have a pair of compound eyes.
Phylloxera glabra forewing (notation amended). Image after Vickery, R.A. (1908).
The wings of the alate are held flat in repose. The fore wing is without a radial sector, the media is unbranched, and the anal (=Cu1b) and cubital (=Cu1a) veins arise on a common stalk. The hind wing is without oblique veins. Most of the Palaearctic species have spiracles on abdominal tergites I-V, but the mainly Nearctic species only have them on abdominal tergite I. Siphunculi are absent, even as pores. Immature sexuales are pupiform, which is unique among Aphidomorpha. They neither feed nor move (other than some undulations when moulting) but undergo a rapid succession of moults to adulthood. Mature sexuales are apterous and dwarfish with vestigial mouthparts, and do not feed. The sexual female lays a single egg, about the same size as herself. There is no ovipositor except in Acanthochermes.
Subfamily Phylloxerinae : Tribe Acanthochermesini
Subfamily Phylloxerinae : Tribe Phylloxerini
Phylloxera are small pear-shaped aphids (using 'aphids' in the loose sense, phylloxerids are not 'true' aphids). Both the sexual and parthenogenetic females are oviparous. The wings are held flat over the abdomen at rest. The ovipositor is vestigial or absent.
Phylloxera feed on plants in the walnut (Juglandaceae) and oak/chestnut (Fagaceae) families.