The Dreaded Lily Borer

CandideZA
Published on October 14th 2020
7
A close up of a green plant
The amaryllis borer (Brithys crini), is possibly the worst pest there is in any garden.
A hand holding a small piece of food
Brithys crini | Amaryllis / lily borer. Photo @johnmalan082.
These black and yellow caterpillars multiply rapidly and can cause total destruction to indigenous bulbous plants like Scadoxus, Clivia, Crinum, Cyrtanthus and Agapanthus species.

Appearance

The moth of this particular caterpillar lays its eggs at night on the underside of leaves - completely unnoticed. The eggs are small, almost the size of a pinhead, pearly-white-yellow in colour and are laid in clusters containing up to 40 eggs.
The amaryllis caterpillar itself is black with eleven transverse yellow bands, formed by dots with an almost chequered appearance. Their heads are reddish-brown and they can reach up to 40mm in length when fully grown.
Destruction of a clivia plant by the amaryllis borer
Destruction caused by the Lily borer. Photo @hanle.

Symptoms

If you see brown, dried out leaves on your bulbous plants like Clivia or Agapanthus during summer, be sure to know there is trouble! These caterpillars start feasting on the leaves and then work their way into the center of a plant where they will devour the entire core and bulb of the plant. They often feed in groups and you might even spot them inside the leaf tissue. Once they have reached a more mature size, they emerge from the leaves and find their way to the center of the plant as mentioned above. A heavy infestation can cause total destruction of leaves and even plant death.
A piece of cake sitting on top of a rock
Culprits found boring into the crown of a Clivia. Photo @Lorette.

Biological treatment

Act quickly if you suspect an infestation by the amaryllis borer! Keep removing the caterpillars by hand and squash them. Leaves that are heavily infested should be removed and destroyed.
Natural pests include parasitic wasps of the families Pteromalidae and Braconidae. Consider planting Crinum moorei which acts as a sacrificing plant, making the detection easier.

Chemical treatment

Contact insecticides control this problem and should be sprayed when the caterpillar is feeding outside the plant. Organic insecticides like Margaret Roberts Biological Insecticide, containing a pyrethrum-base can be used but should be applied more regularly.
Synthetic insecticides including either of the ingredients cypermethrin, phenothrin, lambda-cyhalothrin, and deltamethrin are thought to provide sufficient control of these insects. These can still be toxic to some wildlife and a pollutant to aquatic life if residues leach into water systems, so please take care to research products and read instructions carefully before using them.
In the words of one of our community members
You need eyes in the back of your head as these are fast movers! @lemon_assegai1

Have a look at the destruction caused by these caterpillars!

For more information on the lily borer dig into the pest profile below.

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