Case Moth
Bonsai For Beginners



Hi everone I know not everyone who recieves this newsletter lives in New Zealand but if you do you will understand why I haven't been spending much time at the computer. The weather has been great and I have been spending most of my evenings spraying our precious tank supply water all over my trees. We have had to buy water twice so far this summer, no matter. I kind of enjoy looking at the trees with a cool beer in one hand and the garden hose in the other.

The problem is it has been such a good summer the insect population seems to have exploded, so I thought it would be a good time to start on the pest section of the web site. The first pest I came across was the casemoth so I will have a practice on you guys with the first page.

Case Moth



Quite hard to see but it's here

Bit easier to see on close up but you still have to search to find them.

The cunning little bag moth, never seems to move and looks just like the bark of its host plant. As kids we would bring them inside and leave them overnight and then try to see where they had attached themselves the following morning. Believe me they do move. The bag moth loves ornamental conifers such as cupressus and larix they will also chew on your Manuka, elm or acacia bonsai given the chance.

When the bag moth eggs hatch the caterpillars weave themselves a tight little silk sleeping bag with small pieces of bark and leaf incorporated for camouflage. The sleeping bag even has a draw string in the top so when the caterpillar is disturbed it can pull the cocoon shut and wait out the danger.

The caterpillar will stay encased for many months by which time the cocoon will be several times larger than the one in the photo, sometimes up to 80mm long. The metamorphosis from caterpillar to pupa to moth all takes place in the relative safety of their carefully maintained bag and when the male moth hatches he crawls out the bottom of the case and shoots off in search of a female. The male is a small black furry moth with four quite small wings. The female moth has no wings and a grossly swollen abdomen supported by six stubby legs. She will lower her abdomen out through a hole in the bottom of her bag and wait for a passing male. Once fertilized she will crawl back into the bag and lay her hundred or so eggs and die. When the eggs hatch small caterpillars fall from the case and move off to spin their own sleeping bag.

On large specimen trees the bag moth will hardly be noticed with some browning on conifers and the odd hole on other trees. On a bonsai where aesthetics are important they need to be removed. It should be easy enough to keep an eye out and use digital control, just pick them off. I think they are quite cool and worth moving to another plant away from your trees, but that’s up to you. The only time they can disperse from a host plant is when the baby caterpillars drop out the bottom of the bag. Some will spin small lengths of silk which act as a parachute and catch the wind, otherwise they will stay put.

The other reason not to squish them is they are quite heavily preyed upon by a small parasitic fly. This fly lays its eggs on the edge of the previous nights feeding site, so when the caterpillar resumes feeding the following night it swallows them. The eggs hatch inside the caterpillar and eat it from the inside out, starting with the non essential parts first. So if you do catch one of these case moths after it has eaten a hole in your prize elm remember there are worse things than a quick squish under the heal of your boot.

I also mentioned in my last newletter that we would revisit some of the demonstrations for the past to catch up on progress. The first one we will go back to is the Air layering . The Air layer was started in the beginning of November last year, it has now had about four months to develop. The roots have formed and the tree has been pruned and fed several times. As it is now getting late in the summer I think I will let the roots develop over winter and cut the top off the tree in early spring next year. It could be cut now but the new growth would not have time to harden off before the cold weather and new buds could be damaged


The new roots showing through. They could still develop quite a bit more before the top section is removed

 I will be adding new pest pages to the site over the next few weeks. If anyone has a pest problem I would love to hear about it especially if you can get a photo.

Thanks Mark