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S TAT E FOR EST S 0 F NEW SOU T.H W ALE S
FORESTPROTECTION RESEARCH DIVISION S E R I E S NUM B E R E5 ISSN 0158·3832 ISBN 0730556697
EUCALYPT SAWFLlES (PERGA DORSALIS AND PERGAGRAPTA SPP.)
Deborah Kent
INTRODUCTION
Sawflies (Hymenoptera: Pergidae) are not true flies
but belong to the group of insects which include the bees,
wasps and ants. Although many insects in this group are
beneficial insects, sawflies eat plant foliage. All damage
is caused by the larvae; adult sawflies are rarely seen and do not feed.
This leaflet provides information on the steelblue sa wfly,
Perga dorsalis , and several eucalypt-defoliating saw flies,
Pergagrapta spp. (i.e., more than one species). The larvae
of these sawflies often completely defoliate young
eucalypt trees, and could become serious pests in eucalypt
plantations. A wide range of eucalypt species, including
Eucalyptlls pilularis (blackbutt) and E. grandis (flooded
gum), are known food plants of the these sawflies.
LIFE HISTORY AND GENERAL BIOLOGY
Adult sawflies are large stout-bodied wasps, ranging
from 15-25 mm in length (Figs 1 and 2). They vary in
colour from shiny steelblue (P. dorsal is) to reddish brown
(Pergagrapta spp.), with both having yellow markings on
the head, body, and legs. The female, which is larger
than the male, has a saw-like apparatus (ovipositor)
beneath the abdomen which is used to cut the upper
surface of the leaf and push the eggs into the leaf tissue
(Fig. 1). The eggs are deposited along the midvein of the
leaf and form a raised blister, or pod (Fig. 2). Each pod
contains about 60-70 eggs. Adults are found in both
spring and autumn. The adults do not feed at all and
only live long enough (usually about a week) to find a
host tree and lay eggs.
The larvae pass through six stages which, in
Pergagrapta spp. lasts for three months and eight months
Figure 1. Female layillg eggs into leaf.
female lays eggs in leaf
] ~ 6 s: '1J
cocoons g in soil ~
i ui ~
" .:: .e ~ :.: vi ___ 0
Figure 2. Life cycle Perga dorsalis (insects actual size).
,
for P. dorsalis. The eucalypt sawfly larvae are caterpillarlike, with three pairs of stout legs. They lack the abdominal legs of most caterpillars, but all have a single sucker or uropod on the tip of the tail (Fig. 2). Both P. dorsalis and Pergagrapta spp. larvae have bodies covered with numerous short bristles. In P. dorsal is the bodies are black while Pergagrapta spp. range in colour from tan to dark brown or black, although the colour can vary with the host plant. The large mature larvae of P. dorsalis have yellow legs and a large yellow uropod, while Pergagrapta spp. tend to have a yellow/orange collar behind the head, and less yellow on the legs and uropod. Fully grown larvae range from 40-60 mm in length, depending on the species, P. dorsalis being the largest.
P. dorsalis has only one generation per year and, as the larvae take eight months to complete their development, they may be found throughout the year. Pergagrapta spp. on the other hand can have two generations per year as their larvae complete growth in only three months. Pergagrapta spp. larvae are found in both spring and autumn, with the autumn populations tending to be the more numerous.
The larvae of all species are highly gregarious and remain clustered together during the day. At night they spread out through the top of the tree to feed. After hatching from the pod, the young larvae cluster into a circular mass on the surface of a single leaf (Fig. 3). These "leaf" clusters feed together on the same leaf and point their heads outwards, which may be a defensive posture against predators and parasites. As the larvae grow the clusters become larger and group on twigs, then finally on the branches or trunks of trees (Fig. 4).
When the larval clusters are disturbed, individuals wave their abdomens around and regurgita te a thick yellowish fluid from their mouths. This smells strongly of eucalyptus and is used as a defence against predators. Although often called "spitfires", the larvae cannot 'spit' this fluid as is commonly believed and are harmless to humans. Another defensive behaviour adopted by the mature larvae is to drop to the ground when disturbed.
Fully grown larvae crawl to the ground and wander over the surface together (Fig. 5) until they find a suitable place to pupate, usually near the baseofa tree. They then burrow into the soil and form barrel-shaped cocoons, constructed from cemented earth, piled together in rows (Fig. 2). The emergence of adult wasps from the cocoons can extend over a long period, with wasps from the same group of larvae emerging up to one to two years later.
Figllre 3. YOllllg larvae all leaf.
Figure 4. Mature larvae all twig.
Figure 5. Matllre larvae all groulld.
2
DESCRIPTION OF DAMAGE .
Damage is caused only by the larval stages. Young larvae feed only op. one surface of the leaf. Older larvae feed on the whole leaf, eating up from the tip of the leaf and leaf margin, often only leaving the midrib. The mature larvae feed on different areas of foliage Elver successive nights until the ·entire 'Upper crown is defoliated. It is usually at this stage that the presence of thelarvae is neticed, as obvious larval clusters, After the upper crown has been defoliated, the larvae eat the foliage on the side branches. In heavy infestations, the larvae move down the tree, eating until they are fully
.. grown or the tree is ·def0liated,
If th~ saw flies an~ in lalig~ ,enough ntlmbers smaU trees " . a:r~ at extreme rIsk., Large populations 6f p, il6rsalis anq , · somespeciesofpergagl:aptaaie,:kJ;J.6wntooGcurseasonallY·
are not killed until they pupate. Although adult
populations are small, enough larvae still hatch to cause
significant damage to a tree. The larvae are also vulnerable
on and in the ground from reptiles and predatorybeetles,
It is possible to remove the larval clusters by hand when
the trees are small, However, this may not always be
practical in plantations.
As with any insect pest, the e.arlier they are found and
controlled, the less damage they ate likely to Cal,ise. The'
early stages of sawfl'ies are usually $mall and
inconspicuous and it will be up to the observer I grower
to learn to spot the early signs of damage, s1.].ch as egg
pods or "leaf" duster.s of very small larvae. Small t:re~s, less thaR f01.].r metres high, cap..h) spta:ved if .it is not
'pr~cfi~al toremQve and d,estr,oy larval Gluster~ l)y hand:
and the' subsequent large dusters(sometifnes mbie·than' S· T. £1' t Cl C"'t Z' if: t' . " Z t" f . C.·-th ' .. " . .,., '. .'. '. .: .. , .. ".: '" .:: , :. ee Lel'l. e '-" onro oJ lnfieC son euca YP. s, .or Uti ~r . ,200 mruv.lCluals) alie likely. to cause total defoUatioI1 of,· . , f • 't" . 'I'd' : h" : '1 ' d" . "':.J-l .' " .. . . .... . , m Ol'ma Ion mc u lllg ·c emlca san ,recommenl:.lel:!
· smalltrees. ThiS'may cause sfun~ing or e'v~:ti death, Fot' . ," .: :' :.', ;. . c . ". ; ..:,..,., .. ~ :' . , . , '.. ,. . ,'. . .,..' spraymg Ta:tes. . .. . ,'" " · thisreasonisawflle$mttstbe,];egan;led.aspelJ).gpot~hti~l1y: :. ': ' ' ' .. '. '
" . significant pests of pl?,ntafiG!rigrowttei;icalypts: : . . . !, .' '. , '" • • '. , • . . • . : : ,·PUR'tHER',INFORMA')':10N .... "~ ',:.
;.: .'. CONtROL : :' : .: ' 'qa~Pb~ri, ~.J: (i~9~):: fu~ec~,~esis.~f ~arm:tte~s. :Fa~ : I:, '" "" . , " ," :1)-~~$ Ne~:8;: NSW A~ku'ltur~'ancl-Fisheries, 16 Fp. . I . Some bh-ds~ will e~t the "lar~ae, inciu.ding cwrawohgs" '. " . " I andC:U~ko~~s1u:iKes,'butnlOStbirdsfindiherndist~stefuL 'StaJeFoie~ts 'of N:SW -(19.95); . '<::orl~ol bf insect~ on . r . : rhe'larva~ ~re highlypa~asi~i~ed·bY:flies.irnd' wasps/but' eu~aIYJ?ts. 'Foi:estProtectio.n,' Series'l'{o, q1:.4' pp .. ; 'I ' .' " ,.'., . . .'. "
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State Forests of New South Wales
Copyright ©: State Forests of New South Wales 1995
Additional copies may be obtained by contacting:
Publications Officer Research Division State Forests of NSW PO Box 100 BEECROFT NSW 2119
Phone (02) 872 0111
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