Sawflies are a group of insects suborder (Symphyta) of the Hymenoptera (bees, ants and wasps). There are about 500 species of

Sawfly are small winged insects, related to bees, wasps and ants. Their caterpillar-like larvae feed on the leaves or fruits of certain plants, including apples, gooseberries and Solomen’s seal.

Aruncus sawfly larvae feed in groups so defoliation can occur quickly. Keep vigilant for early signs from May onwards;

• Pale green caterpillar-like larvae with yellowish brown heads and up to 2 cm long
• Leaves can be reduced to a network of the larger leaf veins, plants often recover but repeated defoliation can affect the vigour host plants

Larvae can be found from May (first generation), with a second generation in July and August and a third generation in September.

Sawflies can be a part the biodiversity a heathy garden supports. Check Aruncus (goat's beard) frequently from spring onwards so action can be taken before a damaging infestation has developed. 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 aruncus sawfly, host plants often recover from defoliation and may not be affected every year
• Encourage predators and other natural enemies of sawfly in the garden, such as birds and ground beetles
• Check plants regularly from early may for the presence of larvae and remove by hand if required and where practical

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 aruncus sawfly, 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.

Within pesticides the shorter persistence products (that are usually certified for organic growing) are likely to be less damaging to non-target wildlife.

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 Ultra 2, Neudorff Bug Free Bug and Larvae Killer). Several applications of this short persistence products may be necessary to give good control

Download

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

Aruncus sawfly defoliates goat's beard (Aruncus dioicus), a plant that was formerly included in the genus Spiraea, so this insect is sometimes known as the spiraea sawfly. It occurs in gardens throughout Britain. 

The adult sawfly is 5-6mm long and has a black head and thorax with a yellow abdomen marked with dark bars on the dorsal surface. Larvae overwinter in the soil and, after pupation, adults emerge in May and lay eggs that hatch after about 7 days. Two or three generations of pale green larvae with brown heads feed gregariously on the foliage during the summer months, reducing the leaves to a network of the larger leaf veins. The pupal stage takes place within a silk cocoon in the soil.

This is a species that reproduces asexually and all the adults are female.