Zeiraphera griseana

Status

EXOTIC

PORT INTERCEPT

Taxonomy

Zeiraphera griseana (Hübner) (Tortricidae: Olethreutinae: Eucosmini)

Common name: larch tortrix

Synonyms: desertana (Steganoptycha diniana var.), diniana (Sphaleroptera), occultana (Poecilochroma), pinicolana (Grapholitha)

Adult Recognition

FWL: 7.5–10.5 mm

Head and thorax dark gray with scattered black and white scales. Labial palpi moderate, porrect, dark brown or black laterally. Ground color of forewing dirty gray with large, black basal fascia angled at approximately 90 degrees medially, closely approaching median fascia; black median fascia running from midpoint of costa to just below termen, and black patch variously developed at apex; scattered rusty orange or dusty gray scales may be present throughout forewing; a dirty gray triangular marking is often apparent along the inner margin; fringe gray. hindwing dark gray; fringe concolorous. Abdomen dark gray dorsally, off-white ventrally.

Male genitalia are characterized by the absence of an uncus; socii thumb-like; valvae curved, cucullus large, well-developed, with row of short, spine-like setae on distal margin. Female genitalia are characterized by a simple ring-like ostium; basal half of ductus bursa sclerotized; moderate, tack-like signum present in corpus bursae.

Larval Morphology

Two distinct ecotypes or “forms” occur: the larch form has a black head capsule and is initially light yellow-green but later turns grey-black, whereas larvae of the pine and spruce form have an orange-yellow head capsule and yellowish-grey body.

Detailed descriptions of larval chaetotaxy are available in Swatschek (1958)Swatschek (1958):
Swatschek, B. 1958. Die larval systematik der wickler (Tortricidae und Carposinidae) aus dem zoologischen Institut der Universitat Erlangen. Akademie-Verlag, Berlin. 269 pp. [Abhandlungen zur larvalsystematik Insekten 3.], but closely match that of Zeiraphera canadensis.

Similar Species

Several species of Zeiraphera and even other genera of Eucosmini are superficially similar. Identification is best done through examination of the genitalia.

Distribution

Zeiraphera griseana is distributed across most of Central and Northern Europe, extending in range as far east as Siberia. It is not known from North America, but several closely related species, such as Z. canadensis, are known from the United States and Canada.

Biology

The following account is summarized from Wermelinger et al. (2018)Wermelinger et al. (2018):
Wermelinger, B., Forster, B., Nievergelt, D. 2018. WSL Fact Sheet: Cycles and importance of the larch budworm. Notice for the Practictioner. 61. 12 pp. https://www.wsl.ch/en/publications/cycles-and-importance-of-the-larch-budmoth.html [accessed 22 October 2020].

The biology of Zeiraphera griseana is well-known, as it is one of the most celebrated (albeit destructive) examples of periodical mass outbreaks. Eggs overwinter under lichen, bark, or cone scales. Eggs hatch in mid May and larvae feed on short shoots inside fresh clusters of needles for the first two instars. The third and fourth instar larvae construct spun-together silken tubes made from clusters of needles, feeding at the tips, until the clusters dry out and they move on to construct more cases. During the fifth instar, the larva moves freely between clusters of needles in a silken web, often feeding on only the tips before the whole cluster dries out and dies.

A single larva needs between 10 and 20 clusters of needles to complete its development but consumes just half their mass, contributing to massive canopy losses and reddish brown stands of trees. Fully mature larvae appear for about a month of feeding, usually in mid June. They then lower themselves to the ground to pupate. Adults begin to eclose about one month later, from the end of July to September to mate and lay eggs.

Two different ecotypes or “forms” occur, one on larch and one on pines and spruce. Outbreaks occur, on average, every 8–9 years but are only predictable at higher elevations with a more continentally influenced climate. For a detailed review of the biology and population cycles of Z. griseana, see Wermelinger et al. (2018)Wermelinger et al. (2018):
Wermelinger, B., Forster, B., Nievergelt, D. 2018. WSL Fact Sheet: Cycles and importance of the larch budworm. Notice for the Practictioner. 61. 12 pp. https://www.wsl.ch/en/publications/cycles-and-importance-of-the-larch-budmoth.html [accessed 22 October 2020].

Z. griseana feeds exclusively on trees in the family Pinaceae, primarily spruce (Picea spp.), larch (Larix spp.), pine (Pinus spp.), fir (Abies spp.), hemlock (Tsuga spp.), and Douglas-fir (Pseudotsuga spp.).

Plant Associations

View full screen host table here