With surprise I noticed that the boxwood trees were defoliated within a few days by green caterpillars with black streaks. As an emerfence provision, I treated them with LARVITOX, a product I had at home, but what could I do to prevent the problem?
the caterpillars of which you speak seem to be really damaging box-borer pests; it is a small nocturnal butterfly, arrived in Europe from Asia in about 2007 (year of the first sightings of the insect in Germany) and in Italy the first cases date back to 2010; this insect, Cydalima perspectalis, lays its eggs beneath the leaves of the boxwood (attacks in Europe have been noted only on these plants, and rarely on rose plants); from the eggs come out the larvae, which are green caterpillars with black stripes: the worms are voracious, and can devour the crown of a small boxwood within a few days. They also produce canvas, and on the affected plants thin webs, and sometimes even small cocoons are noticed. Later, the larvae pupate, forming rigid chrysalises, green, 2-3 centimeters long, hidden among the leaves; the butterflies come out of the chrysalises, which begin to produce eggs; this cycle is repeated for 2-3 times in the spring and summer period; in the winter months these insects can survive the cold constituting cocoons on the foliage of the plant that hosts them, to resume the cycle when the heat arrives. In many areas of Italy the fight against the box borer is carried out promptly, as soon as the first specimens are seen, because this insect has caused very serious damage in the nursery areas, especially in Lombardy. The fight against pyralpids is not simple, because most of the insecticides that work against these caterpillars have effect by contact: therefore, to kill them with an insecticide, it is necessary to spray them, and then see them. In addition to this, usually eggs and chrysalises are not touched by insecticides, and therefore it is very important to repeat the treatments, at least 3-4 times, at the end of three or four weeks. We use insecticides based on pyrethrum, or pyrethrins; you will find various types of them in the nursery, some of which are also suitable for organic cultivation, thanks to short periods of shortage; I remind you that to function, these insecticides must be sprayed directly on the caterpillars, and therefore it is necessary to practice the treatment with great care, so as to hit any point of the foliage. There is also a variety of bacillus thuringensis suitable for corn borer, which kills the larvae, remaining on the plant for a certain period of time, after treatment. In addition to this, if it is a matter of a few plants, we also proceed to remove the chrysalises manually, to burn them.