In the past couple of years my greenhouse citrus collection has been plagued by an army of small caterpillars, causing considerable damage to foliage, flowers and fruit. Some years ago, I used the caterpillar-specific biological control Bacillus thuringiensis with considerable success, but it has recently been unavailable in the UK - at least for small scale users. I have now received a form of this control from the U.S. and hope to reduce the problem again.
page created 26th March 2008
In the meantime, I have been researching exactly what this pest is - and have come to the conclusion it is probably Epiphyas postvittana, known as the Light Brown Apple Moth. This member of the Tortrix moth family is an Australian native now widespread in the UK. It is unfussy about its host plant species.
The eggs seem to be always deposited on the upper side of a leaf. They are easily overlooked, appearing a bit like a scale insect. These pictures of an egg mass were on a leaf of the bitter orange, Citrus aurantium, in March 2008.
The larva, or caterpillar, is up to 2cms in length and is the damaging stage, feeding on leaves as it grows. It often pulls the leaf edges together with silken threads to form a protective canopy. Sometimes two or more neighbouring leaves or flower buds are sown together in this way. The larva eventually pupates hidden in the damaged or dying leaves, before emerging as an adult moth about 1cm long
After spraying with the biological agent Bacillus thuringiensis (sold as "Dipel"), any caterpillars which have eaten sprayed leaves stop feeding and soon die. However, it is difficult to coat every leaf especially where they have been curled together, so several repeat sprayings are required for effective control of this pest.