Iris sawfly

The greyish-brown caterpillar like larval stage of iris sawfly can defoliate flag iris and other waterside iris in summer.

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Iris sawfly (Rhadinoceraea micans) on yellow flag iris (Iris pseudacorus)

Quick facts

Common name Iris sawfly
Latin name Rhadinoceraea micans
Plants affected Flag iris (Iris pseudacorus) and other waterside irises
Main symptoms The foliage is eaten by greyish-brown caterpillar-like larvae
Caused by Larvae of a sawfly
Timing April-July

What is iris 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. 

Iris sawfly has greyish-brown larva that reach 25 mm in length and eat the foliage of flag iris (Iris pseudacorus) and other waterside irises, including Iris spuria, I. versicolor, I. laevigata and I. ensata. The adults are similar in appearance to some other species of sawfly and have black heads and bodies up to 8mm long with smoky grey wings.

Symptoms

Iris sawfly larvae can feed in groups so damage can occur very quickly and defoliation can be extensive.

  • Greyish-brown caterpillar-like larvae with whitish spots brown heads and up to 25 mm long
  • Initially V-shaped notches from the leaf margins but later devour the foliage from the leaf tips downwards
  • Plants can be completely defoliated, affecting appearance 
  • Complete defoliation tends not to occur every season and plants can recover 

Control

  • Some defoliation from this sawfly can be tolerated and treated as part of the biodiversity a healthy garden support
  • Encourage predators and other natural enemies of sawfly in the garden, such as birds and ground beetles.
  • Regularly inspect plants during the growing season and where possible remove larvae from the leaves
  • Insecticides cannot be used against this sawfly because of the danger to fish, frogs, toads and other aquatic life in water bodies where irises grow

Biology

Iris sawfly adults are active in late April-May and soon lay eggs on the foliage of host plants. The greyish-brown caterpillar like larvae, speckled with small white spots and up to 25mm long, are present in June-July. The larvae initially eat V-shaped notches from the leaf margins but later devour the foliage from the leaf tips downwards.

There is one generation a year and larvae overwinter in the soil before pupating in the following spring.

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