Pine sawflies

The caterpillar-like larvae of two species of sawfly can in gardens, occasionally cause defoliation of pine (Pinus) trees. 

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Pine sawfly larvae
Pine sawfly larvae

Quick facts

Common name Pine sawfly and fox-coloured sawfly
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

sawfly in Britain. They have caterpillar like larvae that feed on plant material and are named after the saw like egg laying organ used by females to lay eggs in plant material. Adults can come in a range of colours many are black, green orange or striped yellow and black. Most are small (< 1cm) but some species such as the Birch sawfly (Cimbex femoratus) can be over 2cm long. Several species can be found in gardens and are part of the biodiversity a healthy garden will support. More information can be found at The Sawflies of Britain and Ireland webpages.

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

lateral stripe and a black head.

The larvae of both species of sawfly feed in groups on the needles of pines during the spring and summer.

Symptoms

Large populations of pine sawfly larvae can cause considerable defoliation of trees, whilst this is unusual in gardens when it occurs it can affect the growth of the trees.

Management

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.

Non-pesticide

  • 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

Pesticide

The RHS recommends that you don't use pesticides. Most pesticides (including organic types) reduce biodiversity, including natural enemies, impact soil health and have wider adverse environmental effects.
 
Where you cannot tolerate sawflies, manage them using the information above as your first course of action.
 
Pesticide treatments are likely to kill natural enemies and so reduce the likelihood of natural control and can lead to resurgence of the target animal.

If you do decide to use 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.
 
The pesticides listed are legally available in the UK. This information is provided to avoid misuse of legal products and the use of unauthorised and untested products, which potentially has more serious consequences for the environment and wildlife than when products are used legally.
 
Always follow the instructions on the products. For edible plants, make sure the food plant is listed on the label and follow instructions on maximum number of applications, spray interval and harvest interval.

Homemade products are not recommended as they are unregulated and usually untested.
Be aware that products such as Neem oil are not registered for use in the UK and we cannot advise on their use.

Plants in flower must not be sprayed due to the danger to bees and other pollinating insects.
  • 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.
  • Organic contact insecticides containing natural pyrethrum (e.g. Bug Clear Ultra 2, Neudorff Bug Free Bug and Larvae Killer) are available and broad spectrum so will kill a wide range of insects
  • More persistent contact-action insecticides include the synthetic pyrethroids lambda-cyhalothrin (e.g. Resolva Bug Killer), deltamethrin (e.g. Provanto Ultimate Fruit & Vegetable Bug Killer, Provanto Sprayday Greenfly Killer) and cypermethrin (e.g. Py Bug Killer). These products have long lasting action against insects including those that are beneficial
  • Pesticides, with both systemic (absorbed and transported through plant tissues) and contact action, are available. These include  Flupyradifurone (Provanto Smart Bug Killer) for  use on ornamentals and selected edibles and the neonicotinoid insecticide acetamiprid (e.g. Bug Clear Ultra). These pesticides are widely considered to be the most environmentally damaging, remain active for a long time and will kill beneficial invertebrates

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.

Download

Pesticides for gardeners (pdf document outlining pesticides available to home gardeners)

Biology

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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