What is gooseberry sawfly?

Sawflies are in the same group of insects as bees, ants and wasps (the Hymenoptera). They have caterpillar like larvae that feed on plants the adults are winged insects that can appear fly-like. 

There are three common species of sawfly that can be found feeding  lon the leaves of gooseberry and some related fruit bushes.

Symptoms

• Defoliation of the bushes can be caused by the caterpillar-like larvae of one of three species of sawfly
• Larvae of the common gooseberry sawfly are up to 20mm (almost ¾in) long, pale green, with many black spots, and black heads  The adults are winged insects;  females are 5-7mm (up to ¼in) long and are yellow with black heads and black markings on the thorax; males are similar but more extensively marked with black, including the upper surface of the abdomen
• Larvae of the pale spotted gooseberry sawfly are slightly smaller than those of the common gooseberry sawfly and have pale green heads. It has one generation a year with larvae present in May and June 
• The small gooseberry sawfly can have up to four generations of pale green larvae from late April onwards
• The larvae of some moths may also eat the foliage of gooseberries and currants
• Plants will usually survive complete defoliation, however this may reduce yield

Control

Non-pesticide control

• Regularly check the plants from mid-April onwards for sawfly larvae and pick them off by hand
• A biological control (pathogenic nematode), sold as Fruit and Vegetable Protection, can be watered onto infested plants. The nematodes enter the bodies of the sawfly larvae and infect them with a bacterial disease. This nematode is available from some garden centres or via mail order. The nematode should be applied during cool damp weather

Pesticide control

• Spray when young larvae are seen, with an insecticide approved for use on the appropriate food plant. Make sure that the label instructions regarding maximum number of applications and harvest interval are followed
• Organic contact insecticides containing natural pyrethrins (e.g. Bug Clear Gun for Fruit & Veg, Ecofective Bug Killer). Several applications of these short persistence products may be necessary to give good control
• More persistent contact insecticides include the synthetic pyrethroids lambda-cyhalothrin (e.g. Westland Resolva Pest Killer), deltamethrin (e.g. Provanto Ultimate Fruit & Vegetable Bug Killer) and cypermethrin (e.g. Py Bug Killer)
• Follow label instructions when using pesticides
• Plants in flower should not be sprayed due to the danger to pollinating insects
• Inclusion of a pesticide product does not indicate a recommendation or endorsement by the RHS. It is a list of products currently available to the home gardener

Download

Pesticides for gardeners (Adobe Acrobat pdf document outlining pesticides available to gardeners)

Biological control suppliers (Abode Acrobat pdf)

Biology

• The common gooseberry sawfly is the most frequently found of the gooseberry sawflies. It can have three generations a year, with the larvae active in late April to June, July, and August to September
• The female sawflies lay eggs on the underside of leaves, low down in the centre of the bush, so the young larvae go unnoticed until they have eaten their way upwards and outwards, devouring the leaves as they go
• Defoliated plants are weakened and may produce a poor crop the following year
• When the larvae are fully fed, they go into the soil, where they spin silk cocoons and pupate
• The pale spotted gooseberry sawfly only has one generation a year with larvae present in May and June
• The small gooseberry sawfly has up to four generations a year with larvae present from late April