Author: Linnaeus, 1758
Green oak tortrix moth
Species Overview:
Adult: 17-24 mm wingspan; head, thorax and forewings light green; hindwings light grey. Smaller specimens are known, the smallest having a wingspan of barely 13 mm, but such undersized specimens are rare.
Egg: pale yellow at first, becoming orange-brown later, lenticular, delicately sculptured, usually covered by green scales from the upper surface of the forewings; deposited in small batches, usually on the bark of the branches.
Larva: 15-18 mm long; greenish-grey to light olive-green, with prominent blackish-brown or black pinacula; head blackish-brown to black; prothoracic plate greenish-brown to greyish, marked with blackish-brown, often edged anteriorly with white and with a pale median line; anal plate green or black; anal comb with eight prongs; thoracic legs black [Tortrix viridana larva].
Pupa: 10-12 mm long; brownish-black to black.
Taxonomic Description:
Male:
Tortrix viridana adult
Tortrix viridana male 1
Tortrix viridana male 2
External characters: Antenna weakly dentate, densely ciliate, cilia less than width of flagellum, posterior margin of flagellum thinly clad with whitish scales; head cream or light green; labial palpus whitish, suffused with fuscous exteriorly; thorax light green; abdomen greyish. Forewing slightly expanding posteriorly; costa gently curved throughout. Forewing colour light green (viridine), darker basally, delicately strigulated distally; whole of costal margin of forewing narrowly edged with whitish yellow, base of costa sometimes suffused with fuscous; dorsal scale-tuft tinged with yellow; cilia whitish, a pale green sub-basal line. Hindwing light grey; cilia whitish, with a grey sub-basal line around apex and along termen (Bradley et al., 1973).
male genitalia T. viridana
Genitalia: Tegumen small compared to valva, concave in middle posteriorly; socii large, tapering terminally, with bases large anteriorly and with long hairs; tuba analis weak. Valva large, elongate, with costa thin but heavily sclerotized; sacculus strong, elongate, well sclerotized dorsally, termination of sacculus short, spined; brachiola fairly large, protruding distally, rounded apically. Transtilla broad, not sclerotized. Aedeagus elongate, slightly tapering terminally, 6-8 cornuti in vesica.
Female:
External characters: Antenna filiform, sparsely ciliate, more densely clad with whitish scales; abdomen stouter and wings broader, forewing not expanding posteriorly, costa strongly curved at base, then rather straight. Colour similar to male.
female genitalia T. viridana
Genitalia: Papillae analis very broad, rounded posteriorly, with short but strong hairs in median portions and very short, rounded apically, anterior parts; apophyses posteriores rather long, broad basally; eighth tergite very broad but short and rather delicate; apophyses anteriores short; sterigma very broad, close to eighth tergite, concave ventrally (in ostium area); ostium bursae large, rounded; antrum very short; ductus bursae long, broadest medially; corpus bursae small; signum small, dentate.
Variation:
This species shows little variation except in the depth and intensity of the green colouration of the forewing and in the strength of the strigulation. Specimens are sometimes found in which the green colouration is replaced by dull yellow or primrose yellow; these apparently represent a recurring genetical form and are not due to abrasion or discolouration (Bradley et al., 1973).
Biology:
Tortrix viridana is a univoltine species with a main flight period from late April/early May (Portugal) to late June/early July (former USSR). In the UK, adults are most numerous in June and July, and are especially abundant in oak woodlands. They rest on host trees during the daytime but are readily disturbed. Eggs are laid in pairs on the bark, especially close to the leaf bases and where the shoots and small branches divide. They hatch in the following spring at about bud-burst. The larvae feed from late April to June, at first entering the opening buds but later inhabiting rolled or folded leaves. There are 5 larval instars. Pupation usually occurs in a folded leaf on the host tree, but larvae may also descend on a silken thread and pupate on underlying plants. When larvae are present in large numbers they may defoliate the trees before becoming fully fed; in such circumstances the larvae will attack the foliage of various other trees, shrubs and nearby herbage (Bogenschütz, 1991; Alford, 1995).
Host plants:
Quercus; also on Fagus, Acer, Populus, Salix, Carpinus, Vaccinium, Urtica. Older larvae may sometimes complete their development on raspberry (Rubus idaeus) as well.
Du Merle, 1981, observed at Mont Ventoux (France) that there are two genetically distinct but interfertile populations of the green oak tortrix, Tortrix viridana Linnaeus. One, with earlier egg-hatching, is adapted to Quercus pubescens, the other, with later egg-hatching, to Quercus ilex.
Damage:
rolled oak leaf (viridana)
Tortrix viridana is an important pest of oak, especially English oak (Quercus robur). Although primarily a forest pest, damage is also caused to trees in parks, garden and nurseries. An outbreak of Tortrix viridana causes defoliation, but the oaks form new foliage during the same vegetation period, thanks to the excellent recuperative power of the trees. Even defoliation during several subsequent years does not lead to dying off of the trees. Dying off may occur only when the assimilation of the second growth of foliage is seriously affected by, for example, the oak mildew Microsphaera alphitoides Griffon and Maublane. Partial defoliation (less than 50%) does not only cause a decrease in timber increment in the year of infestation, but also in the subsequent year. It is not so much the early wood, formed in spring out of reserve material, that is affected by the infestation, but the autumn wood. The consequence is a decrease in wood quality. Heavy infestations cause a loss in production of 2-4 cubic meters of timber per hectare per year. More important, however, is the decrease in value of the commercial bole after several years of infestation: the stems become shorter, bent and taper. The formation of water shoots is stimulated and the stems become more knotty. Destruction of blossom may also be of considerable importance. The shortage of acorns hampers the natural and artificial culture of oaks in the following years. The natural rejuvenation is in danger when, after defoliation, caterpillars move out of the trees towards the soil (Bogenschütz, 1991; Bogenschütz, 1978).
Distribution:
Europe to Azerbaijan, Asia Minor and Iran.
Pheromone:
Z 11-14Ac : 4
(Arn et al., 1979)
Attractantia:
E 11-13Ac : 9
Z 11-13Ac : 1
(Voerman, 1979)
or
Z 11-14Ac : 9
Z 11-14OH : 1
(Novotny et al., 1990)
Parasitoids:
Actia pilipennis Fallén (Tachinidae)
Actia crassicornis Meigen (Tachinidae)
Actia exoleta Meigen (Tachinidae)
Arrhinomya tragica Meigen (Tachinidae)
Bessa fugax Rondani (Tachinidae)
Compsilura concinnata Meigen (Tachinidae)
Bessa selecta Meigen (Tachinidae)
Pseudoperichaeta insidiosa Robineau-Desvoidy (Tachinidae)
Nemorilla maculosa (Meigen) (Tachinidae)
Nemorilla floralis Fallén (Tachinidae)
Pales pavida Meigen (Tachinidae)
Discochaeta hyponomeutae Rondani (Tachinidae)
Zenilla libatrix Panzer (Tachinidae)
Blondelia nigripes Fallén (Tachinidae)
Amblymerus mediterraneus Mayr. (Pteromalidae)
Amblymerus tibialis Westwood (Pteromalidae
Pteromalus cupreus Nees (Pteromalidae)
Stenomalus muscorum Linnaeus (Pteromalidae)
Apanteles emarginatus Nees (Braconidae)
Apanteles solitarius Ratzeburg (Braconidae)
Eubadizon extensor Linnaeus (Braconidae)
Macrocentrus abdominalis Fabricius (Braconidae)
Brachymeria minuta Linnaeus (Chalcididae)
Brachymeria intermedia Nees (Chalcididae)
Apechthis rufata (Gmelin) (Ichneumonidae)
Apechthis resinator Thunberg (Ichneumonidae)
Campoplex difformis Gmelin (Ichneumonidae)
Diadromus candidatus Gravenhorst (Ichneumonidae)
Diadromus troglodytes Gravenhorst (Ichneumonidae)
Euclytus fontinalis Hlgr. (Ichneumonidae)
Eulimneria albida Gmelin (Ichneumonidae)
Gelis rusticus Förster (Ichneumonidae)
Glypta bipunctoria Thunberg (Ichneumonidae)
Glypta cicatricosa Ratzeburg (Ichneumonidae)
Habrocryptus defensor Seyrig (Ichneumonidae)
Hemiteles areator Panzer (Ichneumonidae)
Itoplectis maculator (Fabricius) (Ichneumonidae)
Labrorychus nigricornis Wesmael (Ichneumonidae)
Theronia atalantae Poda (Ichneumonidae)
Trichomma enecator Rossi (Ichneumonidae)
Triclistus globulipes Desvign. (Ichneumonidae)
Comedo cristator Gravenhorst (Eulophidae)
Pseudoperichaeta nigrolineata (Walker) (Tachinidae)
Pseudoperichaeta palesoidea (Robineau-Desvoidy) (Tachinidae)
Tortrix viridana (Linnaeus)
Tortrix viridana is easily recognized by its nearly monochromatic light green forewings.
In Acleris literana , a species that can also be found on oak, the forewing ground colour is also green [adults Acleris literana ]. It differs in the black markings and the scattered groups of raised scales on the forewing.