The caterpillar-like larvae of two species of sawfly can in gardens, occasionally cause defoliation of pine (Pinus) trees.
Scientific name Diprion pini and Neodiprion sertifer
Plants affected Pine (Pinus)
Main symptoms Caterpillar like larvae defoliate plants
Most active Spring-Summer
What are pine sawflies?
Sawflies are a group of insects in the suborder (Symphyta) of the Hymenoptera (bees, ants and wasps). There are about 500 species of
Adult pine sawfly (Diprion pini) are 10mm long brown winged insects, The larvae reach up to 25mm long and are pale green in colour with a brown head and black markings.
Fox-coloured sawfly (Neodiprion sertifer) is 7-9mm long and pale orange-brown. The larvae reach 25mm in length are a dirty green colour with a black
The larvae of both species of sawfly feed in groups on the needles of pines during the spring and summer.
Control is only feasible on trees that are small enough to treat, on large trees these insects have to be tolerated.
Sawflies can be a part the biodiversity a heathy garden supports. Check pines frequently from spring onwards so action can be taken before a damaging infestation has developed. When choosing management options you can minimise harm to non-target animals by starting with the methods in the non-pesticide control section and avoiding pesticides. Within pesticides the shorter persistence products (that are usually certified for organic growing) are likely to be less damaging to non-target wildlife than those with longer persistence and/or systemic action. Pesticide treatments are likely to kill natural enemies and are only likely to be successful if the entire plant can be reached.
- Where possible tolerate populations of sawfly
- Encourage predators and other natural enemies of sawfly in the garden, such as birds and ground beetles.
- Check plants regularly from spring for the presence of larvae and remove by hand where practical
The RHS believes that avoiding pests, diseases and weeds by good practice in cultivation methods, cultivar selection, garden hygiene and encouraging or introducing natural enemies, should be the first line of control. If chemical controls are used, they should be used only in a minimal and highly targeted manner.
- If numbers of larvae are too high for hand picking, control may be achieved by spraying with pesticides. Spraying at dusk is likely to be more effective. Little can be done to deal with beetles on tall trees as treatment is only likely to be successful if the entire plant is sprayed
- Organic contact insecticides containing natural pyrethrum (e.g. Bug Clear Ultra 2, Neudorff Bug Free Bug and Larvae Killer). Several applications of this short persistence products may be necessary to give good control
- More persistent contact-action insecticides include the synthetic pyrethroids lambda-cyhalothrin (e.g. Westland Resolva Bug Killer), deltamethrin (e.g. Provanto Ultimate Fruit & Vegetable Bug Killer, Provanto Sprayday Greenfly Killer) and cypermethrin (e.g. Py Bug Killer)
- A systemic containing the active ingredient Flupyradifurone (Provanto Smart Bug Killer) is available for use on ornamentals and selected edibles
- The systemic neonicotinoid insecticide acetamiprid (e.g. Bug Clear Ultra) is also available
Plants in flower should not be sprayed due to the danger to bees and other pollinating insects.
Inclusion of a pesticide product does not indicate a recommendation or endorsement by RHS Gardening Advice. It is a list of products currently available to the home gardener.
Pesticides for gardeners (pdf document outlining pesticides available to home gardeners)
Pine sawfly adults are active in spring and the females lay eggs in slits they make with an egg laying organ (ovipositer) in the needles. The larvae hatch after a few weeks and feed in groups on the needles. These larvae will lift their abdomen off the plant in a group as a defensive posture when disturbed. The larvae are usually fully grown by July where they spin brown cocoons on the foliage or on the ground beneath the plant. New adults emerging in July or August and can produce a second generation of larvae that feed in late summer and autumn. The autumn generation spins cocoons in soil or leaf litter, pupating in the following spring.
Fox-coloured sawfly adults are active in late summer and early autumn and lay eggs on the needles. The eggs overwinter and hatch in spring. The larvae feed in groups which will raise their abdomens when disturbed. In late June the fully grown larvae drop to the soil to pupate in an oval cocoon. This species has one generation a year.
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