Author: (Guenee, 1845)
Larch tortrix
Grey larch budmoth
Species Overview:
Adult: 16-22 mm wingspan; forewing ground colour white, variably suffused with light grey and sparsely strigulated with usually indistinct pale ochreous strigulae; markings grey to whitish grey with an admixture of ochreous and black. Hindwing fuscous, darker apically.
Egg: flat ovoid, 0.6-0.7 mm long and 0.4-0.5 mm broad, yellowish, with finely sculptured shagreened chorion [Zeiraphera diniana eggs ].
Larva: instars 1 to 4: body yellowish grey; head capsule, neck, and anal shields black.
The 5th larval instar is darker in colour [Zeiraphera diniana larva 1 ]. In the Alps two colour morphs have been distinguished; the 'cembran pine form' is brownish with two yellowish latero-dorsal stripes, a light to dark brown head capsule, neck, and anal shield as well as dark brown thoracic legs, whereas the 'larch form' is dark grey, and the head capsule and sclerites are black, as in the younger instars. The different larval colour morphs are genetically determined. In the Siberian larch biotype the larval skin is light-grey to greenish brown and the head capsule, the sclerites, and the thoracic legs are dark brown. They represent a colour type intermediate between the dark grey type on Alpine larch and the light type on cembran pine. In Britain almost the complete range of larval colour types on larch, whereas the majority of the last instar larvae on pine belonged to the extreme light type. The light type is also found on spruce in the Ore Mountains, the Giant Mountains, the Low Tatra and the High Tatra. It seems that the lighter coloured pine and spruce varieties represent the basic type of the species, whereas the dark form on Alpine larch might be an adaptation to the specific conditions in Alpine larch forests.
Pupa: 7.5-12.5 mm long, dark reddish brown; frons narrow and convex between antennae; abdominal segments 2-7 with two transverse rows of spines oriented backwards (spines of caudal row smaller than those of anterior row); segments 8-9 bear single rows of spines. The anal segment bears four pairs of thick hooked bristles dorsally and 1 pair ventrally [Zeiraphera diniana pupa ; Zeiraphera diniana pupae under forest litter (inverted)].
Taxonomic Description:
Male:
Zeiraphera diniana adult 1 (larch biotype)
Zeiraphera diniana adult 2
Zeiraphera diniana adults
External characters: 16-22 mm wingspan. Head, thorax, patagium and tegula grey, farinose. Forewing narrow, without costal fold; termen slightly convex. Ground colour white, variably suffused with light grey (appearing farinose in costal and distal areas), sparsely strigulated with usually indistinct pale ochreous mixed with fuscous strigulae; markings grey to whitish grey, farinose (apices of individual scales variably tipped with whitish), with an admixture of ochreous and black; basal and subbasal fasciae forming a rather indistinct basal patch, its outer edge acutely angulated medially; median fascia oblique, narrow, confluent with pre-tornal marking, edges somewhat diffuse and irregular; a large subquadrate to subtriangular blotch of light ground colour on dorsum between basal patch and median fascia, usually reaching costa and then forming a fasciate band; subterminal fascia usually indeterminate, but sometimes evident as a narrow band extending obliquely inwards from lower part of termen to below costa; cilia white, suffused with grey, with a fuscous sub-basal line. Hindwing fuscous, darker apically; cilia light grey, with a dark sub-basal line (Bradley et al., 1979).
male genitalia Z. diniana
Genitalia: Uncus rudimentary; gnathos absent; socii large and curved outward. Valva without clasper; ventral margin of valva with shallow notch before cucullus. Basal projection of valva biramose. Cucullus narrowing towards apex, evenly covered with setae.
Female:
External characters: Similar to male.
female genitalia Z. diniana
Genitalia: Ovipositor telescopic; apophyses long; eighth tergite partially membranous; sterigma strongly reduced, represented by aciculate patches of membrane; antrum sclerotized; cingulum situated posterior to middle of ductus bursae; corpus bursae with strong signum.
Variation:
Zeiraphera diniana adult 3 (cembran pine ecotype)
The markings of the forewing vary in depth and clarity and become stronger and better defined as the suffusion of the ground colour decreases. As a rule the forewing markings of the adult pine-and-spruce biotype are more distinct and browner. However, since transitional forms are numerous, these criteria do not allow a separation of races in the adult stage.
Taxonomic notes:
Following Benz, 1991a, the species name diniana Guenée is used here for the larch budmoth, although the older griseana Hübner 1799 is the older name. Two reasons speak in favour of diniana :
1. griseana Hübner is a nomen dubium, based on a doubtful picture (Herrich-Schäffer, 1843-1856, p. 152) that cannot be recognized as larch budmoth.
2. diniana is used in 90% of the papers dealing with the larch budmoth.
Although the different biotypes of Zeiraphera diniana and their larval colour morphs are quite distinct and occur sympatrically in the Alps - indicating some genetic isolation of the populations - the isolation is not complete. Interbreeding occurs and intermediate morphotypes exist. Therefore, subspecies cannot be established (Benz, 1991a).
Biology:
5th inst. larvae-larch biotype
5th inst. larvae-cembran pine ecotype
5th inst. larvae-spruce ecotype
Two basic biotypes of Zeiraphera diniana may be distinguished: the monophagous larch biotype with mostly dark last instar larvae and the oligophagous non-larch biotype or pine-and spruce biotype with light-coloured last instar larvae. These basic biotypes may comprise a series of sub-biotypes or ecotypes such as the Alpine and the Asian larch ecotypes, the cembran pine ecotype and the spruce ecotype.
Larch biotype:
Z. diniana embryo in diapause stage
Defoliated larch tree covered with thick silk webbing
Fascicles - fifth instar larvae
Z. diniana L4 larva in fascicle
opened fascicle showing larva (head turned towards tips of needles)
The larch biotype in the Alps shows cyclic mass multiplication with gradations of 8-10 years. At altitudes below 1000m above sea level, moth flight occurs in the second half of June and in July, and from mid July to October at higher altitudes. The moths fly at dusk and dawn as well as during the day, a minimum temperature of 8° C and wind velocities below 2.8 m/s being necessary for flight. The main flight activity begins at sunset, the male moths swarming vivaciously around the tree crowns. Swarming may last until midnight as long as the temperature remains above 8°C. Active dispersion flights of males and females over considerable distances are possible. Under outbreak conditions, the moths emerging in defoliated larch stands fly to undamaged green stands for oviposition until, towards the end of the emergence period, the defoliated trees have reflushed.
The sexual activity of the adults also begins in the late afternoon and lasts until midnight. The "calling" female extrudes the ovipositor, thus exposing the opening of the bilobate pheromone gland situated dorsally in the intersegmental folds between the eighth and ninth segments. The pheromone is a far-distant attractant; near-distant orientation of the males is based on vision as long as light conditions permit. Diminishing light and temperature, as well as thermic air flow, in the evening are factors releasing male appetitive behaviour of female searching, followed by copulation upon visual cues even in the absence of the female pheromone. Upon arrival near a female the male positions itself parallel with and slightly behind the female, starts vibrating its wings, bends its abdomen sideward and forward, and tries to seize the female's abdominal tip with his claspers. As a rule, the female then starts running a few steps, stops abruptly, and lifts her wings, whence copulation starts. It lasts for 2-24 hours and may be repeated several times.
Since oogenesis in Zeiraphera diniana is postmetabolic, the realization of the maximum egg potential is influenced by female weight, longevity (20-40 days in the subalpine region), insemination, and a number of environmental stimuli. In the oviposition mood, occurring in the inseminated females in the evening and early night, the females protrude the ovipositor and move along thin branches (3 years old or older), touching the surface of the branch with the ovipositor in search of oviposition sites. The presence of green larch needles is important for the full stimulation of oviposition. In the colline region the females deposit the eggs in crevices of the bark and in cones, whereas in the subalpine region they prefer ovipositing underneath the thalli of lichens covering the branches. In the forest, mean fecundity is as high as 174 eggs (maximum 354 eggs).
After deposition, the eggs develop for a certain time (about a fortnight in subalpine regions) and then pass the rest of the summer, autumn, and winter in an obligate diapause stage.
Emergence of first instar larvae extends over 2-3 weeks. At low altitudes (500 m) it occurs at the end of March to mid April, at 800 m in April, at 1200 m from the end of April to the beginning of May, at 1800 m in May, and at 2100 m (at the timberline) it may last more than 4 weeks, from May to June. The first instar larvae (L1) crawl to young needle tufts, search for the tips of the tufts, and penetrate between the central needles to the vegetation point, where they start feeding. If the needles are still short (< 4 mm), the L1 cannot penetrate; if the needles are too long (> 20 mm), they are too tough for the larva to feed upon. Therefore, the successful installation of the L1 in the needle tufts depends on a good coincidence of L1 emergence with larch flushing, optimum mean needle length being 6-8 mm. The first, the second, and the young third larval instars feed with their head directed towards the tender vegetation point of the needle tufts. They change tufts 3-4 times, usually in the early morning hours. The changes are combined with more or less extended excursions on the twig or branch. In the middle of the third instar the larva, settling on a new tuft, spins the needles together to form a fascicle in which it feeds with the head directed towards the tips of the needles. These fascicles are characteristic for the L3, L4 and L5. Feeding occurs round the clock, but mainly during the night and early in the morning, with maximum activity around midnight. In dry weather, the L4 and L5 rest during daytime and feed only at night. The almost mature L5 leave the fascicles and live in secondary webbings along the branch axis. Damage becomes visible in this stage, if the population density surpasses the critical number of 100 larvae per kg branches, because a drastic change in larval feeding behaviour takes place. The larvae in the secondary webbings start wasting food, gnawing only small pieces from a large number of needles or eating only their tender base. Since these needles become desiccated, the larvae destroy more needles than would be necessary for their satiation. On the other hand, this behaviour is necessary for inducing the reflushing within a month's time and the post-damage reactions of the larch. The complete larval feeding period lasts 40-60 days at 1800 m. During this period a larva consumes about 1.3 g needle mass or more than ten needle tufts. At the climax of a gradation, when the larvae destroy the nutritional base before they are ready for pupation, they move in masses to and fro along the branches and the tree trunk in search of food, covering trunk and branches with a dense web of white silk. Large numbers descend to the ground, where they cause damage by defoliating the undergrowth of young cembran pine and spruce. These may be killed directly or by secondary invaders, such as bark beetles and weevils. Thus, the natural succession may be ruptured locally and permanent pure or almost pure stands of larch result.
For pupation the mature larvae descend to the ground, as a rule by means of a silk thread, but sometimes they simply drop. Only on rare occasions observed they spin their loose cocoon in secondary webbings on the tree. The larvae on the ground penetrate 1-3 cm deep into the forest litter, where they spin their cocoon-like pupation chamber containing soil particles. At 1800 m the pupal stage lasts approximately a month. The moths eclose in the early morning hours, the males eclosing earlier than the females. Before the adult ecloses from the pupal exuvia the pupa moves to the surface of the ground by contracting the abdomen with its backwards oriented spines. When the head and thorax of the pupa are above the ground surface, the exuvia ruptures on the back of the thorax and the moth escapes (Benz, 1991a).
Cembran pine ecotype:
larva on shoot of cembran pine
The population cycles of the cembran pine ecotype and the larch ecotype in the Alps are synchronized, indicating some interdependence. The biology of the two ecotypes is not fundamentally different. The following account is therefore restricted to the differences. As indicated by its name, the cembran pine ecotype is found mainly on cembran pine (Pinus cembra). However, it can be regarded as oligophagous, since it is also found on mountain pine, Engadine pine, and very rarely on spruce. This distribution results both from the females' oviposition preference and the late hatching of the larvae, which is synchronized with the late flushing of the cembran pine. Since the cembran pine ecotype needs about the same (or more) time to complete its development as the larch ecotype, the various stages of a population of the cembran pine ecotype always lag behind those of a sympatric population of the larch biotype. This leads to a transitory temporal isolation of the moth populations.
The larvae enter the flushing buds of their host and feed on the growing needles. If a single larva occupies a bud, it can terminate development without destroying all the needles of the developing shoot. Mass multiplication of the insect leads to multiple infestation of the buds and to their destruction. However, since the old needles are spared, even heavily attacked trees look green and resprout, as a rule, in the following spring. An exception may be found when the mass multiplications of Zeiraphera diniana and the cembran pine needle miner, Ocnerostoma copiosella Zeller, coincide. Pupation occurs often in the attacked buds, but more often in the needle litter on the ground (Benz, 1991a).
Spruce ecotype:
Damage on young shoots of Norway spruce
On spruce, the females deposit the eggs underneath the remains of bud scales of old nodes and between the scales of galls and cones. Additional oviposition in male inflorescences, old webbings of budmoth larvae, and niches created by branch breaking triples the egg density per tree top. As in the related cembran pine ecotype the larvae of the spruce ecotype hatch relatively late in spring. At altitudes of 800-1000 m hatching begins at the end of May and ends at the beginning of July. It coincides with the flushing of the early sprouting spruce varieties. Since the individual flushing periods of spruce vary much more than those of larch, coincidence with the phenology of the spruce is locally very important. The young larvae penetrate into buds, spin the cap of the bud envelope to the growing needles, and feed under this cap on the young needles. The larvae leave the buds after their third moult and spin a silk tunnel along the axis of a fresh side-shoot. The last instar larvae move freely about and feed on the needles of these shoots, which may become fully defoliated at high population density. The terminal bud is usually not attacked, but the larvae may tunnel the shoots and kill them or damage the soft rind and cause malformations. Viewed from a distance the damage resembles the damage caused by the Norway spruce sawfly, Pristiphora abietina. However, it differs from sawfly damage by the presence of webbings.
Larval development usually lasts 4-6 weeks, but may last up to 8 weeks. Each of the first four instars (L1 to L4) needs 5-7 days, and the fifth instar 10-14 days. Pupation occurs mostly on the ground. Only at high population density are some pupae formed in bark crevices at the base of the trunk. The pupal stage lasts 2 -3 weeks, and the flight period of the moths lasts for 40-60 days (Benz, 1991a).
Host plants:
Larix, Pinus and Picea.
Abies is only attacked by fourth and fifth instar larvae descending from defoliated trees to the undergrowth. Such larvae may feed and develop normally on many plants, including the flowers of Berberis vulgaris leaves of Rumex acetosa. However, these plants do not support the development of the younger stages.
Damage:
Normal larch forest at Lake Sils, Switzerland
Same forest one year later, defoliated by Zeiraphera diniana
short stout needles of tree defoliated in preceding year
Fifth instar larva Z. diniana in secondary webbing along brach axis
Young cembran pines below a defoliated larch tree are also defoliated by fifth instar larvae from the larch tree
Z. diniana damage on Pinus cembra
Z. diniana damage on Picea abies
Zeiraphera diniana is a defoliating pest of various conifers, including Larix, Pinus and Picea. Mass multiplications of Zeiraphera diniana occur periodically (with cycles of 8-10 years duration) on the European larch and on the cembran pine or stone pine in the Alps, as well as on the Siberian larch, Sukachev's larch, and Dahurian larch in Siberia. The larch budmoth does not destroy the larch forest, but modifies its structure and growth. Seed production and natural rejuvenation of the damaged stands are reduced. Tree are defoliated but the most important damage consists in the killing of the larch, spruce, and cembran pine seedlings and young trees in the undergrowth, either directly or by the action of secondary pests such as bark beetles and weevils. This suppresses or delays locally rejuvenation and the natural succession in to the climax community, the subalpine larch-cembran pine forest.
Considerable loss of cembran pines may result when a heavy attack by Zeiraphera diniana causing the destruction of the current year's shoots coincides with a strong attack of the old needles by the cembran needle pine miner. The cembran pine survives the separate attacks of both pests very well, but may succumb to their concerted action, either directly or because the trees are weakened and consequently attacked by secondary pests such as bark beetles and weevils.
The economic importance of Zeiraphera diniana on spruce varies, depending on the duration of the mass multiplication. Short gradations (3 years) may reduce timber production without seriously harming tree vitality, whereas gradations of long duration (> 5 years) lead to the thinning of the foliage (as indicated by the growth of a dense cover of herbs and shrubs on the forest floor) and to attacks of the bark beetle Ips typographus (Linnaeus) and/or the fungus Armillaria mellea, leading eventually to the death of the trees (Benz, 1991a).
Distribution:
Northern and Central Europe to Eastern Russia and Japan.
Also recorded from Korea, but Byun et al., 1998, have not found specimens of this species.
References of Zeiraphera diniana in America refer to Zeiraphera improbana.
Pheromone:
E 9-12Ac : 0.5 * (cembran pine)
E 11-14Ac : 0.005
12Ac : 0.05
(Guerin et al., 1984)
or
E 11-14Ac : 0.05 * (larch)
E 9-12Ac : trace
14Ac : 0.1
16Ac : 0.1
(Guerin et al., 1984)
Components marked with * are involved in attraction.
Attractantia:
E 9-12Ac (spruce; cembran pine)
(Vrkoc et al., 1979; Baltensweiler et al., 1978)
Parasitoids:
Ichneumonidae:
Phytodietus griseanae Kerr.
Campoplex occipitor Aub.
Diadegma dinianator Aub.
Diadegma patens Aub.
Triclistus pallipes Holm.
Triclistus podagricus Grav.
Phaeogenes osculator Thun.
Phaeogenes ischiomelinus Grav.
Phaeogenes lascivus Wesm.
Microcryptus micropterus Grav.
Stilocryptus erythrogaster Grav.
Hemiteles fulvipes Grav.
Pimpla examinator F.
Pimpla brevicornis Grav.
Pimpla epinotiae Uch
Pimpla turionellae
Plectocryptus arrogans Grav.
Therion circumflexum L.
Lissonota transversa Bridgm.
Lampronota melancholica Grav.
Angitia cerophaga Grav.
Aphanistes biguttatum Grav.
Aphanistes xanthopus Schrank.
Astomaspis nanus Grav.
Banchus femoralis Thomps.
Erromenus punctulatus Grav.
Eulimneria turionum Ratz.
Leptocryptus claviger Taschb.
Phytodietus obscurus Desvignes
Braconidae:
Eubasidion extensor L.
Apanteles murinanae Cap. and Zwölf.
Apanteles uchidae Watan.
Meteorus albiditarsis Curt.
Rogas circumscriptum Nees
Chalcidoidea:
Dirhicnus alboannulatus Ratz.
Eulophidae:
Elachertus argissa Walk.
Dicladocerus westwoodi Westw.
Sympiesis punctifrons Th.
Tachinidae:
Nemorilla floralis Fall.
Nemorilla maculosa Meig.
Lydella nigripes Fall.
Phryxe vulgaris Fall.
Actia maksymovi Mesn.
Lypha dubia Fall.