Geranium sawfly

The greyish green larvae of geranium sawfly larvae eat holes in geranium leaves during the spring and summer.

Geranium sawfly larvae

Geranium sawfly larvae

Quick facts

Common name Geranium sawfly
Scientific name Ametastegia carpini
Plants affected Geranium
Main symptoms Holes in leaves
Most active May to September

What is geranium 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. 

Geranium sawfly has greyish-green larvae that reach 12mm in length. The larvae feed on leaves of hardy geranium leaving a holed appearance. The larvae readily drop of the plants when disturbed and so are not often seen. The adult sawfly is a black fly-like insect 10mm long. 

Control

Although the damage on the foliage can be considered unsightly, it is generally not extensive enough to affect the plant’s growth or its ability to produce flowers and so this insect can be tolerated.

Non-pesticide control

The larvae can be removed by hand. One way of capturing for the larvae is to slide a sheet of newspaper underneath the foliage and then tap it and collect any larvae that drop off.

Pesticide control

  • If numbers of larvae are too high for hand picking, control may be achieved by spraying with pesticides. Spaying at dusk is likely to give the best results
  • 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)
  • The systemic neonicotinoid insecticide acetamiprid (e.g. Bug Clear Ultra) is also available
  • 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

Downloads

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

Biology

There are two generations a year of geranium sawfly with larvae present in May and September. Fully grown larvae pupate in the soil, the September generation overwintering in this state. Adults emerge in spring and lay eggs on the foliage.


Gardeners' calendar

Advice from the RHS

Find out what to do this month with our gardeners' calendar

Advice from the RHS

Did you find the advice you needed?

RHS members can get exclusive individual advice from the RHS Gardening Advice team.

Join the RHS now

Get involved

We're a UK charity established to share the best in gardening. We want to enrich everyone's life through plants, and make the UK a greener and more beautiful place.