Q I had a failure with my feijoa bush last year, thinking that it had been hit by hail as it had shredded leaves. Upon trimming the bush back I discovered these interesting attachments. Can you enlighten me as to what they are and how to get rid of them please?
Question from K. Pearce, Rangiora
A This is a case made by the caterpillar of a bag moth, Liothula omnivora, which is common throughout the country. As the omnivora part of its name suggests, bag moth larvae feed on a wide variety of plants, seldom doing much harm though occasionally there are enough of them on a plant to cause noticeable leaf damage.
Bag moth caterpillars are interesting creatures; after hatching from the egg they crawl away and start building the tough ‘bag’ or case you have found by binding tiny pieces of bark and bits of leaves together with silk excreted from their mouthparts. The case is so tough it’s almost impossible to tear apart or penetrate. Each caterpillar lives inside its case, holding on with small hooks on its legs and sticking its head and upper body out to drag the case along as it moves around to feed. If it feels threatened the caterpillar retreats inside and pulls shut the front end of the case. When fully mature, the caterpillar anchors the front end of the case to a twig, branch or other suitable place then pupates into the adult moth stage.
While all bag moth caterpillars are virtually identical, there’s a significant difference between the adult stages of the species. The adult female is wingless, looks nothing like a moth at all and never leaves its protective case. The adult male is a grey, hairy moth with translucent wings and its only role in life is to mate with a female, which it does through her protective case. The female deposits her fertilised eggs in the case then dies. The eggs hatch and the new caterpillars escape through the end of the case, and so the life cycle continues.
Usually bag moth caterpillar numbers are controlled naturally by parasitic insects, including species of tachinid flies that lay their eggs on leaves to be consumed by bag moth caterpillars. The eggs hatch in the caterpillar’s gut where the maggots find a ready source of food, eventually destroying their host.
I think it unlikely bag moth caterpillars alone did all the damage to your feijoa, but it is possible. There are other caterpillars that may have also been involved. In future at the first sign of damage occurring, most likely in spring and early summer on the tender new growth, you could inspect the leaves and pick off any caterpillars you find, or spray with Yates Success Naturalyte or Kiwicare No Caterpillars Organic. Both are based on naturally occurring ingredients of low toxicity to humans yet very effective at killing caterpillars. Make sure to follow the label recommendations.
Answer by Andrew Maloy (The Plant Doctor)
