December, 2001 Insect pests - life histories and habits AG0800 Nick Collett, Forest Science Centre, Heidelberg ISSN 1329-8062 This Agriculture Note summarises the biology and symptoms Autumn gum moth of pests that are destructive to young eucalypt plantations. Wingless grasshopper 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 Figure 1. Adult wingless grasshopper from late summer to mid-autumn. In autumn, newly hatched larvae are approximately 3-4 mm long, and grow to about 4 cm These insects produce one generation per year with females in length following four moults by mid-winter. They are laying their eggs into the soil during late summer. With the onset characterised by a greenish brown colour with two distinct of cool winter conditions, the eggs enter diapause which prevents yellow spots on the mid-dorsal surface (Table 1, Figure 2). hatching until warmer conditions prevail in the following late Young larvae skeletonise the leaves (Figure 3a), while the older spring/ early summer (Figure 1). The nymphs moult four times stages consume the entire leaf down to the mid-rib (Figure 3b). and grow into wingless adults about 1.6 cm long. Plagues of The upper crowns are usually attacked first, but as the larvae grasshoppers occur generally during drought years when warm, increase in size and numbers, the whole crown is consumed. dry conditions accelerate hatching and enhance survival (Table Larvae feed mostly at night and shelter during the day in small 1). Once pasture and grasses have been either consumed or have groups in leaf fragments webbed together with silken threads, or desiccated in the dry conditions, grasshoppers turn to in rolled leaves attached to branch tips. The preferred hosts are predominantly eucalypt or pine seedlings and sometimes older eucalypts with glaucous, juvenile foliage, although many other trees as an alternative food source. When this occurs, they species of eucalypt are also susceptible (Tables 1 and 2). Larvae initially consume the lower leaves before stripping the entire enter a 5 to 7 month pupal stage within cocoons to a depth of 5 plant of foliage as the attack intensifies. Trees may subsequently cm in soil. Adult moths emerge between late summer and mid- die as a result of foliage loss and desiccation of the bare stems autumn. during hot and dry summer conditions. 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.) © State of Victoria, Department of Primary Industries Page 1 December, 2001 Insect pests - life histories and habits AG0800 Nick Collett, Forest Science Centre, Heidelberg ISSN 1329-8062 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. Damaging part Primary eucalypt Foliage Comments generations of life cycle host species attacked per year Wingless grasshopper One Nymphs and adults Most spp. of eucalypt at Juvenile Attack generally confined to (Phaulacriduium vittatum) (mid-summer to the seedling stage first year after planting during early autumn) drought years Autumn gum moth One Larvae (March to E. globulus Juvenile Attack ceases once trees have (Mnesampela privata) August) E. nitens adult foliage E. dunnii E. bridgesiana Leaf blister sawfly Four to five Larvae (mainly over E. botryoides Juvenile Attack ceases once trees have (Phylacteophaga froggatti) winter in north- E. grandis adult foliage central Victoria) E. saligna Steelblue sawfly One Larvae (April to E. camaldulensis Juvenile Attack declines once trees (Perga affinis affinis) September) E. globulus and adult achieve canopy closure E. occidentalis E. melliodora E. viminalis Christmas beetles One or two Adults (November E. grandis Juvenile Generally, pre-canopy closure (Anoplognathus spp.) to January) E. globulus and adult pest in farm areas with susceptible eucalypts E. blakelyi E. botryoides E. viminalis Leaf beetles Two Larvae and adults E. viminalis Juvenile Attack lessens once trees (Paropsis spp. and (November to E. grandis and adult achieve canopy closure; usually March) a problem near forest areas Chrysophtharta spp.) E. regnans E. melliodora E. globulus* E. blakelyi Brown basket lerp Three to Nymphs and adults E. botryoides Adult Attack is concentrated adults on Cardiaspina fiscella) five lower crowns Redgum basket lerp Three to Nymphs and adults E. camaldulensis Juvenile Whole crowns are susceptible (C. retator) five and adult * Adult foliage only © State of Victoria, Department of Primary Industries Page 2 Insect pests - life histories and habits AG0800 Leafblister sawfly 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. Figure 4. Leafblister sawfly damage The eggs are laid into the upper palisade mesophyll tissue There are at least five primary host species of eucalypt of the leaf through small passages sawn by the female. (Table 1) but several other species have been recorded as Following hatching, the larvae consume this tissue and the susceptible (Table 2). Total defoliation has tended to be epidermis. As the leaf cuticle remains intact, each larva associated with exposed and level sites, while susceptible becomes surrounded by a conspicuous hollow blister which plantation trees in sheltered positions, especially near or increases in size as the larva grows (4-5 mm) (Figure 4), within native forest areas, have not sustained much and protects it from adverse weather effects. The larvae damage. 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. 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 Leafblister Steelblue Christmas Leaf Brown Redgum gum moth sawfly sawfly beetles beetles basket lerp basket lerp E. blakelyi UMM/HHHUU E. botryoides LHUHLHU E. bridgesiana HUUHUUU E. brookerana L/M L/M U L/M U U U E. camaldulensis LL/MH UUU H E. dunnii HMUHUUU E. globulus HL/MH H HU U E. grandis MHMHHHU E. maculata ULUULUU E. melliodora UUHMHUU E. muellerana LLUUMUU © State of Victoria, Department of Primary Industries Page 3 Insect pests - life histories and habits AG0800 E. nitens HMUUMUU E. obliqua UUULLUU E occidenalis LLHUUUU E. regnans UUUM/HHUU E. rubida HUUHUUU E. saligna LHLMLHU E. sideroxylon LULHUUU E smithii HLUMUUU E. viminalis ML/MH H H U U Note: Some provenances within species may vary in susceptibility from the above ranking. Steelblue sawfly Christmas beetles Figure 5. Steelblue sawfly larvae cluster Figure 6. Adult Christmas beetle One generation is produced per year with females laying These insects pass through a 1 or 2-year-life cycle their eggs within slits cut into the leaf surface during early depending on climatic conditions with warm weather autumn. Larvae emerge from late autumn onwards (Table accelerating life cycles and cooler weather slowing them. 1), and group into distinctive clusters during the day Eggs are laid in the soil between early and mid-summer (Figure 5). Feeding occurs at night and generally the whole and hatching occurs within two weeks of oviposition. The leaf is consumed down to the midrib. The upper crowns are soil-borne larvae usually pupate 9 or 21 months later attacked first, but as the larvae increase in number and during spring for one or two-year life-cycles respectively, grow through to the final instar VI, foliage of the whole with adults emerging between late spring and mid-summer tree crown is destroyed. Following total defoliation, the for feeding, mating and egg laying (Table 1, Figure 6). larval cluster move in a column, usually at night, to Areas largely cleared of eucalypts for pasture development neighbouring trees in search of additional foliage. Several tend to favour increases in Christmas beetle populations eucalypt species are primary hosts, while others are due to a lack of natural predators. Plantations of secondary (Tables 1 and 2). The pupal period extends from susceptible eucalypts (Tables 1 and 2) established in such late spring until early autumn, with pupae being confined areas have often sustained severe defoliation by large to cocoons within soil adjacent to the roots of host trees. swarms of Christmas beetles. First year plantings are Adults emerge between early and mid-autumn to initiate a generally not attacked with beetles prefering two to three- new generation. 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 © State of Victoria, Department of Primary Industries Page 4 Insect pests - life histories and habits AG0800 generally ‘light seekers’ and will usually not feed below 3 metres from the top of the tree.