The Pine processionary moth (Thaumetopoea pityocampa), is a major pest of pine trees around the Mediterranean Sea. It is most conspicuously damaging on pine plantations, or amenity pines.
Life cycle and appearance of Pine processionary moth
The female moth has a wingspan of 36-49 mm; the wingspan of the male is 31-39 mm. Both sexes have a hairy thorax. The forewings are dull ashen-grey; the veins, margins and three transverse bands are darker. The hindwings are white, grey-fringed, with a characteristic dark spot in the anal region.
The cylindrical egg masses range in length from 4 to 5 cm. They are covered with the scales of the female anal tuft, which mimics the pine shoots.
The larvae develop through five instars and the full-grown caterpillar is about 40 mm in length. The head capsule is black. The body of the first-instar caterpillar is dull apple-green. After the second moult, the caterpillar assumes its definitive appearance and the reddish dorsal urticating hair patches on each body segment appear, arranged in pairs. The integument and hairs that clothe the body vary considerably with different provenances. In general, the integument is darker in colder areas and varies from dull bluish-grey to black.
Pupation takes place in the soil in an oval, ochreous-white silken cocoon. The pupae are about 20 mm in length, oval, and of a pale brownish-yellow colour that later changes to dark reddish-brown
The life cycle of T. pityocampa is normally annual but may extend over 2 years at high altitude or in northern latitudes. Development lasts 6 months under the most favourable conditions, but the fourth and fifth instars may be prolonged in the winter. The pupal stage can be prolonged considerably by diapause.
A few hours after emergence and mating, the females oviposit on the nearest pines. The eggs are laid in cylindrical masses around pairs of needles; most eggs masses are laid on the peripheral shoots of the crown and contain 70-300 eggs.
After 30-45 days, the eggs hatch. The larvae aggregate in colonies and spin silken nests, which enlarge until the fourth instar when the definitive winter nest is built. In general, this is situated at the branch tips in the upper part of the crown. At the third instar urticating hair patches appear.
The pupation 'processions' occur in late winter and early spring. The caterpillars move in a file searching for a suitable site to tunnel underground and pupate in the soil. Pupation takes place at a depth of about 10 cm and the pupae enter diapause. Some pupae may not yield adults in the year of pupation, the diapause period extending until the following year or longer.
The nests of caterpillars on infested trees are clearly visible. Defoliation damage is extremely serious in young reforested areas where it may lead to death of trees, directly or as a consequence of attack by bark beetles or other wood-boring insects. In mature forests, trees are rarely killed but significant losses occur in volume growth. Defoliation damage and the presence of caterpillars are important on amenity trees in recreational and residential areas
The caterpillars have urticating hairs from the third instar onwards, which may cause allergies. Domestic and farm animals may also be affected. These effects occur not only when the caterpillars are present, but also during the following summer because of the persistence of allergenic hairs in the remains of winter nests
The larvae of the Pine processionary moth cause severe defoliation, reducing the viability of oak trees.