Solomon's seal sawfly

The larval stage of Solomon’s seal sawfly can completely defoliate Polygonatum species and hybrids in early summer.

Solomon's seal sawfly

Solomon's seal sawfly

Quick facts

Common name Solomon’s seal sawfly
Latin name Phymatocera aterrima
Plants affected Solomon’s seal, Polygonatum species and hybrids
Main symptoms The foliage is eaten by whitish grey caterpillar-like larvae
Caused by Larvae of a sawfly
Timing May-July

What is Solomon's seal 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.  The larvae of Solomon's seal sawfly feed on the leaves of Polygonatum. 

Symptoms

Solomon's seal sawfly larvae feed in large groups so defoliation can occur very quickly. Keep vigilant for early signs;

  • Greyish white caterpillar-like larvae with black heads and up to 2cm (¾in) long seen on the underside of the leaves, eating elongate strips out of the foliage
  • Complete defoliation may occur
  • Purplish brown scars, up to 2cm (¾in) long, may be seen on the leaf stems where eggs were inserted

Control

Whilst the defoliation caused by the sawfly larvae can appear severe it normally occurs after flowering and the plants will usually put on healthy growth in the year following an attack. Therefore this insect can be tolerated and the plants will survive.

Non-pesticide control

Search for the larvae and remove them from the underside of leaves.

Pesticide

  • If deemed necessary and infestations are too heavy 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

Download

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

Biology

Adult Solomon’s seal sawfly are black-bodied insects, 8-9mm long, with two pairs of blackish grey wings. In appearance they are similar to medium sized flies but are in the same group of insects as the bees, ants and wasps, the Hymenoptera. They emerge in late spring at about the time when their host plant is coming into flower.

The female uses her saw-like eggs-laying organ to insert rows of eggs into the leaf stems. This causes vertical purplish brown scars to develop where the eggs were inserted.

The larvae feed together in small groups on the underside of the leaves. Initially they make small elongate holes but as the larvae increase in size, their appetite also increases. By mid-summer, the stems may have been stripped of foliage.

The fully fed larvae go into the soil where they overwinter and pupate in the following spring. Defoliated plants will survive but may produce reduced growth in the following year.


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