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Insect pests - life histories and habits | AG0800 |
Nick Collett, Forest Science Centre, Heidelberg
December, 2001 |  |
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This Agriculture Note summarises the biology and symptoms of pests that are destructive to young eucalypt plantations.
Wingless grasshopper
Figure 1. Adult wingless grasshopper
These insects produce one generation per year with females laying their eggs into the soil during late summer. With the onset of cool winter conditions, the eggs enter diapause which prevents hatching until warmer conditions prevail in the following late spring/ early summer (Figure 1). The nymphs moult four times and grow into wingless adults about 1.6 cm long. Plagues of grasshoppers occur generally during drought years when warm, dry conditions accelerate hatching and enhance survival (Table 1). Once pasture and grasses have been either consumed or have desiccated in the dry conditions, grasshoppers turn to predominantly eucalypt or pine seedlings and sometimes older trees as an alternative food source. When this occurs, they initially consume the lower leaves before stripping the entire plant of foliage as the attack intensifies. Trees may subsequently die as a result of foliage loss and desiccation of the bare stems during hot and dry summer conditions.
Autumn gum moth
Figure 2. Autumn gum moth larvae
One generation emerges each year with adults laying rafts of 50-100 eggs, predominantly on the underside of juvenile leaves from late summer to mid-autumn. In autumn, newly hatched larvae are approximately 3-4 mm long, and grow to about 4 cm in length following four moults by mid-winter. They are characterised by a greenish brown colour with two distinct yellow spots on the mid-dorsal surface (Table 1, Figure 2). Young larvae skeletonise the leaves (Figure 3a), while the older stages consume the entire leaf down to the mid-rib (Figure 3b). The upper crowns are usually attacked first, but as the larvae increase in size and numbers, the whole crown is consumed. Larvae feed mostly at night and shelter during the day in small groups in leaf fragments webbed together with silken threads, or in rolled leaves attached to branch tips. The preferred hosts are eucalypts with glaucous, juvenile foliage, although many other species of eucalypt are also susceptible (Tables 1 and 2). Larvae enter a 5 to 7 month pupal stage within cocoons to a depth of 5 cm in soil. Adult moths emerge between late summer and mid-autumn.
Figure 3. Typical leaf damage by (a) young and, (b) older larvae of the autumn gum moth (Mnesampela privata) ; (c) adult Christmas beetle (Anoplognathus hirsutus) on blue gum and, (d) and (e) adults and larvae respectively of chrysomelid leaf beetles (Paropsis spp. or Chrysophtharta spp.)
Table 1. Summary of principal insect defoliators and features of their life cycle, host preferences and type of foliage attacked in young Victorian eucalypt plantations prior to canopy closure.
Insect species | No. generations per year | Damaging part
of life cycle | Primary eucalypt
host species | Foliage attacked | Comments |
Wingless grasshopper
(Phaulacriduium vittatum)
| One | Nymphs and adults (mid-summer to early autumn) | Most spp. of eucalypt at the seedling stage | Juvenile |
Attack generally confined to first year after planting during drought years
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Autumn gum moth
(Mnesampela privata)
| One | Larvae (March to August) | E. globulus
E. nitens
E. dunnii
E. bridgesiana | Juvenile |
Attack ceases once trees have adult foliage
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Leaf blister sawfly
(Phylacteophaga froggatti)
| Four to five | Larvae (mainly over winter in north-central Victoria) | E. botryoides
E. grandis
E. saligna | Juvenile |
Attack ceases once trees have adult foliage
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Steelblue sawfly
(Perga affinis affinis)
| One | Larvae (April to September) | E. camaldulensis
E. globulus
E. occidentalis
E. melliodora
E. viminalis | Juvenile and adult |
Attack declines once trees achieve canopy closure
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Christmas beetles
(Anoplognathus spp.)
| One or two | Adults (November to January) | E. grandis
E. globulus
E. blakelyi
E. botryoides
E. viminalis | Juvenile and adult |
Generally, pre-canopy closure pest in farm areas with susceptible eucalypts
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Leaf beetles
(Paropsis spp. and Chrysophtharta spp.)
| Two | Larvae and adults (November to March) | E. viminalis
E. grandis
E. regnans
E. melliodora
E. globulus*
E. blakelyi | Juvenile and adult |
Attack lessens once trees achieve canopy closure; usually a problem near forest areas
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Brown basket lerp
Cardiaspina fiscella)
| Three to five | Nymphs and adults | E. botryoides | Adult |
Attack is concentrated adults on lower crowns
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Redgum basket lerp
(C. retator)
| Three to five | Nymphs and adults | E. camaldulensis | Juvenile and adult |
Whole crowns are susceptible
* Adult foliage only
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Leafblister sawfly
Figure 4. Leafblister sawfly damage
The eggs are laid into the upper palisade mesophyll tissue of the leaf through small passages sawn by the female. Following hatching, the larvae consume this tissue and the epidermis. As the leaf cuticle remains intact, each larva becomes surrounded by a conspicuous hollow blister which increases in size as the larva grows (4-5 mm) (Figure 4), and protects it from adverse weather effects. The larvae grow through four moults, and adjacent blisters on a single leaf may join (coalesce) to form an extended blister of necrotic tissue containing several larvae. Pupation occurs within a silken cocoon inside a blister, and adult wasps emerge up to two weeks later.
Approximately 4 to 5 generations are produced per year, although the actual number can vary according to local conditions with as many as eight being recorded. In north-central Victoria, four generations appear common, one between late summer and mid-winter, one from mid-winter to early summer and two short generations in the early to late summer. If the population level of the late summer/mid-winter generation is high and damage to foliage is severe, the subsequent generations are at much lower levels due to a lack of suitable foliage, giving the affected trees an opportunity to refoliate.
There are at least five primary host species of eucalypt (Table 1) but several other species have been recorded as susceptible (Table 2). Total defoliation has tended to be associated with exposed and level sites, while susceptible plantation trees in sheltered positions, especially near or within native forest areas, have not sustained much damage.
Table 2. Susceptibility levels to insect defoliators of various species of eucalypt in trial plantings in Victoria prior to canopy closure (L=low, M=moderate, H=high susceptibility, U=unknown).
Species | Autumn
gum moth | Leafblister sawfly | Steelblue sawfly | Christmas beetles | Leaf beetles | Brown basket lerp | Redgum basket lerp |
| E. blakelyi | U | M | M/H | H | H | U | U |
| E. botryoides | L | H | U | H | L | H | U |
| E. bridgesiana | H | U | U | H | U | U | U |
| E. brookerana | L/M | L/M | U | L/M | U | U | U |
| E. camaldulensis | L | L/M | H | U | U | U | H |
| E. dunnii | H | M | U | H | U | U | U |
| E. globulus | H | L/M | H | H | H | U | U |
| E. grandis | M | H | M | H | H | H | U |
| E. maculata | U | L | U | U | L | U | U |
| E. melliodora | U | U | H | M | H | U | U |
| E. muellerana | L | L | U | U | M | U | U |
| E. nitens | H | M | U | U | M | U | U |
| E. obliqua | U | U | U | L | L | U | U |
| E occidenalis | L | L | H | U | U | U | U |
| E. regnans | U | U | U | M/H | H | U | U |
| E. rubida | H | U | U | H | U | U | U |
| E. saligna | L | H | L | M | L | H | U |
| E. sideroxylon | L | U | L | H | U | U | U |
| E smithii | H | L | U | M | U | U | U |
| E. viminalis | M | L/M | H | H | H | U | U |
Note: Some provenances within species may vary in susceptibility from the above ranking.
Steelblue sawfly
Figure 5. Steelblue sawfly larvae cluster
One generation is produced per year with females laying their eggs within slits cut into the leaf surface during early autumn. Larvae emerge from late autumn onwards (Table 1), and group into distinctive clusters during the day (Figure 5). Feeding occurs at night and generally the whole leaf is consumed down to the midrib. The upper crowns are attacked first, but as the larvae increase in number and grow through to the final instar VI, foliage of the whole tree crown is destroyed. Following total defoliation, the larval cluster move in a column, usually at night, to neighbouring trees in search of additional foliage. Several eucalypt species are primary hosts, while others are secondary (Tables 1 and 2). The pupal period extends from late spring until early autumn, with pupae being confined to cocoons within soil adjacent to the roots of host trees. Adults emerge between early and mid-autumn to initiate a new generation.
Christmas beetles
Figure 6. Adult Christmas beetle
These insects pass through a 1 or 2-year-life cycle depending on climatic conditions with warm weather accelerating life cycles and cooler weather slowing them. Eggs are laid in the soil between early and mid-summer and hatching occurs within two weeks of oviposition. The soil-borne larvae usually pupate 9 or 21 months later during spring for one or two-year life-cycles respectively, with adults emerging between late spring and mid-summer for feeding, mating and egg laying (Table 1, Figure 6). Areas largely cleared of eucalypts for pasture development tend to favour increases in Christmas beetle populations due to a lack of natural predators. Plantations of susceptible eucalypts (Tables 1 and 2) established in such areas have often sustained severe defoliation by large swarms of Christmas beetles. First year plantings are generally not attacked with beetles prefering two to three-year-old trees.
Unlike most other defoliators, it is the adult rather than the larval stage that damages eucalypt foliage. Leaves of the current season’s growth in upper crowns are the preferred food source with damaged foliage having a ‘zigzag’ appearance (Figure 3c), and host trees showing a ‘brooming’ effect (Figure 7a). Christmas beetles are generally ‘light seekers’ and will usually not feed below 3 metres from the top of the tree.
Figure 7. Typical patterns of defoliation in young eucalypt plantations: a) the ‘brooming’ effect in the upper crown, b) lower crown defoliation and, c) severe damage leading to total defoliation.
Leaf beetles
Figure 8. Leaf beetle larvae
In the warmer areas of Victoria, two generations emerge annually (Table 1), one between spring and mid-summer, and the other between mid-summer and the following spring. Most damage to trees, caused by both adult and larval stages of the life-cycle, occurs during the summer and early autumn period when the two generations overlap.
The eggs are laid in batches of 30 to 80, either in rows on the upper surfaces of young leaves or around branchlets of shoots in a rosette pattern. The gregarious larvae grow through three moults and first feed on young leafy shoots in the upper half of the crown, then on the older and tougher foliage (Figure 8). Development is most rapid under sustained warm conditions coupled with a good supply of susceptible foliage (Figure 9). Fully-grown larvae are the most destructive.
Figure 9. Adult leaf beetle
Adults take semi-circular sections from leaf margins, in contrast to much larger and irregular damage, or total leaf loss, caused by the larvae (Figure 3d and 3e). Large populations of the spring/mid-summer generation may cause severe damage in the upper 50% of tree crowns by mid-summer, and subsequent severe attacks by the mid-summer/spring generation may maintain the defoliated condition until pupation in the soil during autumn. Observations in eucalypt plantations of north-coastal New South Wales have indicated that the destruction of apical buds and of foliage by large populations of leaf beetles causes severe checks to tree growth. Large damaging outbreaks have also been recorded in eucalypt plantations in Tasmania and in East Gippsland. Damage tends to be most pronounced in young eucalypt plantations aged 2 to 6 years and diminishes once trees achieve canopy closure. Eucalypt species vary in their degree of susceptibility (Tables 1 and 2).
Brown and redgum basket lerps
Figure 10. Basket lerp nymphs
These two species are recognised on leaves by purple/brown necrotic blotches and translucent basket-type lerp coverings below which nymphs suck the sap from leaves (Figure 10). The Brown Basket Lerp feeds on several eucalypt hosts, whereas the Redgum Basket Lerp appears to be restricted to foliage of E. camaldulensis (Tables 1 and 2). Eggs are laid by inserting their bases into the leaf surface. Hatched nymphs undergo four moults to form the winged adults. Three generations are usually produced between mid-spring and mid-autumn and a fourth by mid-spring. Outbreaks of the Brown Basket Lerp have occurred in coastal East Gippsland whereas the Redgum Basket Lerp has ravaged trees in central and north-eastern Victoria. Prolonged outbreaks in several successive years has led to severe defoliation and dieback.
Further reading
- Abbott, I., van Heurck, P. & Burbidge, T. (1993). Impact of frequency and intensity of defoliation on growth of Jarrah (Eucalyptus marginata)-an experimental study with saplings. Forest Ecology and Management 56: 175-83.
- Carne, P.B., Greaves, R.T.G. & McInnes, R.S. (1974). Insect damage to plantation-grown eucalypts in north-coastal New South Wales, with particular reference to Christmas beetles (Coleoptera: Scarabaeidae). Journal of the Australian Entomological Society 13: 189-206.
- CSIRO (1996). Insect Pests of Eucalypts on Farmland and in Plantations in southeastern Australia. CSIRO Australia Identification Leaflet Series, Leaflets 1-15.
- Elliott, H.J., Ohmart, C.P. and Wylie, F.R. (1998). Insect Pests of Australian Forests. Inkata Press Melbourne.
- Neumann, F.G. & Collett, N.G. (1992). The impact of insect pests on young eucalypt plantings in the Shepparton irrigation area. Report to the Trees for Profit Research Board, Department of Conservation and Natural Resources, Victoria,12 pp.
- Phillips, C. (1996). Insects, Diseases and Deficiencies associated with Eucalypts in South Australia. Primary Industries SA Forests, 160 pp.
- State Forests of New South Wales (1995). Forest Protection Leaflet Series. Leaflets E1 to E8, C1 and G1.
- Stone, C. (1991). Insect attack of eucalypt plantations and regrowth forests in New South Wales: a discussion paper. Forest Resources Series 17. Forestry Commission of NSW.
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Organisations and contacts
Australian Forest Growers (AFG)
PO Box E18
Kingston ACT 2604
Ph. 02 6285 3833
Email: afgnat@safetyweb.com.au
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