Weeds of National Signifi cance Willow Resource Sheet : 3 Willow sawfl y (Nematus oligospilus) What is it? Can willow sawfl y be controlled? Willow sawfl y is an insect which has recently On a large scale, it is not possible to protect arrived in Australia. The larval stage of the life willow trees from willow sawfl y with insecticide cycle feeds on willow leaves, and large populations sprays. It may be possible to protect individual of larvae can defoliate adult willow trees. trees - check with the relevant department in your State for registered insecticides. Where did it come from? At this stage it is not known if there are any Willow sawfl y is native to much of the northern natural enemies of willow sawfl y in Australia that hemisphere. It was fi rst recorded in South America may limit its population. in 1980, then in southern Africa in 1993 and New Zealand in 1997. Which willows does sawfl y prefer? How did it get here? Willow sawfl y prefer some types of willows, with It is unclear how willow sawfl y arrived in Australia, tree willows being more favoured than shrub but it was not introduced deliberately. It is possible willows. that adult sawfl ies were blown across from New Zealand or that cocoons were accidentally Tree willows: imported, for example on shipping containers. • crack willow (Salix fragilis) Where is it now? • black willow (S. nigra) Willow sawfl y was fi rst reported in Canberra in • matsudana (Peking) willow (S. matsudana) 2004 and, by April 2006, it had arrived in the ACT, NSW, South Australia, Victoria and Tasmania. • white willow (S. alba var. alba) golden willow (S. alba var. vitellina) Willow sawfl y adults can fl y 50-60 km, and the • insects can also hitch a lift with human couriers, • Chilean pencil willow (S. chilensis) so it is expected that willow sawfl y will soon spread to all suitable areas. • weeping willows (S. babylonica) What conditions suit willow sawfl y? Shrub willows: Rapid population increases seem to be associated • purple osier (S. purpurea) with warm, dry spring conditions. It is not known if high temperatures affect survival and reproduction of willow sawfl y. Willow sawfl y does not seem to attack grey sallow (Salix In ideal conditions, willow sawfl y can develop cinerea) or other shrub from an egg through its life cycle to an adult within willows. four weeks. Several generations can develop each season, from about October to April. Defoliated matsudana willow, ACT (DPI Victoria) Supported by the State Government of Victoria Weeds of National Signifi cance Willow sawfl y (Nematus oligospilus) Will the sawfl y affect native species? What does a sawfl y It is extremely unlikely that willow sawfl y will look like? attack native plants. Egg What is the impact of sawfl y? • 1-2 mm long oval or kidney-shaped Each willow sawfl y larva can eat 1-2 willow leaves • in its short lifetime, and suffi cient numbers of • bright green to yellow-green larvae can defoliate large willow trees. These trees • often found on upper leaf often grow new leaves, which are then eaten by surface (DAFF: www.insectimages.org) the next generation of willow sawfl y. • laid on fully expanded leaves This pattern of defoliation, new leaf production and subsequent defoliation may occur several times a season. Willow trees can die after 2-3 Larva years of repeated defoliation events. • grows to 20mm long • caterpillar-like body • yellow-green when young • green when older • green to brown stripes down body (DAFF: www.insectimages.org) • head cream-coloured, with dark eyes • brown stripes behind each eye to the top of the head Defoliated crack willow, NE Victoria (NECMA) • brown triangle on front of head Pupa Defoliation • up to 10mm long • initially larvae chew a key-hole along leaf • domed, with a fl at bottom margin • lime green (or sometimes • when all leaf blade eaten, only mid-rib yellow-brown) remains • found on willow leaves, bark • tree defoliation starts in and on ground at base of tree lower canopy, but total (DPI Victoria) tree defoliation can occur Adult • 7-8mm long, plus antennae • head and thorax yellow-orange/brown, shiny • green abdomen • wings transparent • prominent dark eyes Completely defoliated willow Partially defoliated willow leaves (DPI Victoria) leaves with new growth developing at top of branch (DPI Victoria) What does the sawfl y do over (DAFF: www.insectimages.org) winter? If you see willow leaves being chewed, it is Willow sawfl y forms a cocoon over winter which very likely willow sawfl y is present. are found on tree bark or in leaf litter at the base of the tree. Please report all sightings to: Willow Project For more information go to: Reply Paid 48 www.weeds.org.au/WoNS/willows/ Frankston Vic 3199 (no stamp required) www.hortnet.co.nz/publications/guides/willow_ Ph: 03 9785 0111 sawfl y/wsawfl y.ht fi [email protected].