Box Tree Caterpillar (1)

Gardeners are perpetually at war against a host of pests and viral and fungal diseases but, at least when it comes to pests, especially larger insects like the Box Tree Caterpillar, we have a fighting chance – we can see them and we have the means to kill them…
The Box Tree Caterpillar (Cydalima perspectalis) is a recent threat – the adult moth (yes, it is a moth not a butterfly) is a native of East Asia and was established in mainland Europe by 2007. It was first spotted over here in 2008 and its larvae first seen in private gardens in 2011. By the end of 2014, it was established in London and the Home Counties – and continues to spread. The main problem is that the adults are as abundant in their laying as its caterpillars are voracious. But they are just caterpillars and they can be stopped…
Vigilance
The main weapon is vigilance – just as you check your Hostas for slugs and your brassicas for Cabbage White Butterfly eggs, check your Box for the Box Tree Caterpillar. Fortunately, though the Box Tree Caterpillar is a fast and greedy eater, it is still just an ordinary caterpillar and has no in-built protection against pesticides and other counter-attacking measures…
What to look for
▫ Pale yellow eggs on the underside of the foliage from the beginning of spring. The eggs overlap, have a flat appearance and are laid like a  sheet
▫ On hatching, the caterpillars are greenish-yellow and have black heads. As they mature, reaching c. 4cm, they develop thin white and thick black stripes along their body
▫ •The pupae are cocooned in white webbing on the plant
▫ •The adult moth generally has white wings (and a wingspan of c.4cm) with a brown, slightly iridescent, edging. The wings can also be brown all over or even clear
▫ Identification, though, is not difficult as the Box Tree Caterpillar is the only caterpillar you will find on Box and the adult moths only ever lay their eggs on Box
▫ The Box Tree Caterpillar is most active from April to October and can lay eggs throughout spring, summer and, subject to the weather, early autumn. It survives winter as small caterpillars hidden between Box leaves that are spun together in autumn. Check for these and destroy as the first thing they’ll do when they emerge in spring is to start eating
In our next Post, we’ll look at counter-measures…