Caterpillar control: episode 1

Following the report of a box tree caterpillar infestation at reference 1 and following the suggestion on the RHS site that control was difficult and the best thing to do might be to replace the bushes with something else, the three box bushes concerned have now been cut back to around a foot off the ground. Maybe I will leave the stumps to sprout and then see how things go - but it is more likely that I will grub them up, on the grounds that the infestation is likely to return in the absence of serious chemical action. A pictorial record of the cutting back follows. Followed by a few remarks about the caterpillars.

First of the three bushes coming down

Unfenced compost heap at this stage

First bush down

The bushes from which the wood blocks used by my wood cutting uncle must have been a good deal bigger than this, even allowing that large blocks were composites, made up of several smaller pieces. Made by cutting across the grain, not with the grain, so these branches would not have been much good at all. Maybe there is also a distinction between heart wood and sap wood which needs to be taken into account.

Second bush down

Trying to escape the cataclysm

Third bush down

Terminal compost heap

Maybe I should have had the waste incinerated to make sure all the caterpillars, pupae and eggs were destroyed, but I decided, on balance, that this was not the way forward. In part because plenty of caterpillars, pupae and eggs would escape any such incineration.

Oddly, the loss of these three bushes, perhaps eight feet high, has made surprisingly little visual impact. The area is shady, surrounded by copper beech, regular beech and other trees and bushes, and does not look that different now than it did before.

Oddly also, while the infestation seemed to spread from the ground up, with freshly layered bushes (the bushes seem to layer quite freely) all being infested, the various juveniles (only a few inches high) in the vicinity do not seem to have been infested.

Escaped

This morning, near 48 hours later, I found one of the caterpillars making a bid for freedom, climbing up the study window, presumably towards the light. It must have fallen off my clothes when I came in.

From the references which follow, I find that the caterpillars are a major pest in China, Korea and Japan where box topiary is big business. They arrived in Germany in 2005 or so and got to England three or four years later. There is some infestation of the bushes of Box Hill, but not of the much larger collections of bushes to be found in the Chilterns. Parts of continental Europe have been badly affected.

While the caterpillars - which may go through three or four life cycles in a year - will spread themselves, most of the spread is put down to movement of infected plants from nurseries.

The caterpillars have also reached southern Ontario, in Canada, so it seems likely that despite fierce vegetable quarantine rules at the US border, it is only a matter of time before they jump across.

For those interested in the taxonomy of these caterpillars (and the moths they metamorphose into), see references 4a and 4b. A fascinating subject in its own right, involving, inter alia, careful inspection of the genitalia of the moths. For which purpose dissecting equipment and a microscope are helpful. While I have yet to see a moth.

Reference 1: https://psmv4.blogspot.com/2019/08/box-tree-caterpillar.html.

Reference 2: https://www.ebts.org/box-moth-and-caterpillar. A helpful introduction to the subject.

Reference 3: https://en.wikipedia.org/wiki/Cydalima_perspectalis. Wikipedia is on the case.

Reference 4a: http://www.eje.cz/artkey/eje-201003-0012.php.

Reference 4b: Phylogeny and nomenclature of the box tree moth, Cydalima perspectalis (Walker, 1859) comb. n., which was recently introduced into Europe (Lepidoptera: Pyraloidea: Crambidae: Spilomelinae) - Richard Mally - 2010.