Classification and host plants
Species: C. cossus L.
“Phytopathology, agricultural entomology and applied biology” – M.Ferrari, E.Marcon, A.Menta; School edagricole - RCS Libri spa
Host plants: Pome fruit, Stone fruit, other fruit, forest, ornamental and landscape interest.
Identification and damage
Cossus cossus is a particularly polyphagous insect; the larvae are xylophages and produce very serious damage to a large number of cultivated species. The adults are large butterflies (70-100 mm wingspan) with the front wings of gray-brown color finely streaked with dark. The larvae are pinkish or dark red on the back, depending on the age, with yellowish-ocher areas and dark head; the length of the larvae is about 80-100 mm, when ripe. The eggs, which are hazel-brownish or reddish in color, have a diameter of about 1-1.5 mm and are laid in the ravines of the rind, generally at the base of the plants. The damage consists in the trophic activity of the larvae which dig deep tunnels in the trunk and branches; these organs weaken both mechanically and because a slow and progressive general deterioration of the plant begins. Furthermore, the deep wounds, due to the excavation of the tunnels, are an excellent entry and settlement point for pathogenic fungi, cancer and caries agents, or other parasites (Sesidi). For wood plants (e.g. Walnut and Poplar) the damage is much more serious than for other plants. The insect can act both as a primary phytophagous, on fruit trees, and as a secondary, on ornamental and landscape plants, especially by attacking plants that are already weak or that present other pathological problems.
Cossus cossus is an insect that completes its development cycle in two or three years; it therefore carries out one generation every 2 or 3 years. The adults appear in late spring from the third decade of May until August, with a wide flicker interval; the peak attendance is in July.
The adults mate and the females lay their eggs in groups, especially at the base of the plants or at the scaffolding of the large branches. The newborn larvae, which are gregarious, dig, after about 10-12 days, small sub-circular tunnels, destroying the promissory zone. If these tunnels are dug in young plants or in relatively small branches it is easy to notice, in the affected area, typical protrusions or swellings, due to the reaction of the tissues. Furthermore, if the plants have a clear bark, it is possible to notice, even at a distance, the exit of a dense blackish mucilaginous fluid which is made up of altered lymph and mixed with the catabolites of larval activity and rosure. The 1st year larvae spend the first winter in these galleries. In the following spring, the larvae resume their activity by digging deeper and larger diameter single tunnels; these tunnels generally have vertical direction both upwards and towards the roots, in some cases they have oblique directions or initial transverse niches. These tunnels are kept clean by eliminating outside rosure and excrement in the form of a red-brownish pulp (with an intense smell of altered leather) which represents an evident signal of the presence of Cossus. Generally the whole 2nd year is spent at the larval stage, digging tunnels in the wood. The flickering will occur in the summer of the 3rd year, after an incralidation occurred in the outermost layers of the tunnel or in the soil at the base of the affected plant. In some situations (due to late oviposition or colder climates) the Cossus can flicker in the spring / summer of the 4th calendar year making 1 generation every 3 years.
Red Rodilegno adult - Cossus cossus L. (photo http://home.scarlet.be/entomart)
Red Rodilegno larva - Cossus cossus L. (photo Pavel Krasensky)
The fight against Cossus has evolved in recent years following new guided and integrated fight technologies; however, still today it is a set of different practices that are applied, from time to time, as appropriate.
Specific treatments during the oviposition period do not always give satisfactory results, in consideration of the large flicker interval; to overcome this drawback, it is possible to carry out environmental monitoring, through the use of sexual traps.
The traps are to be installed approximately in the first half of May.
In this case, the treatment must be performed on the woody organs in the period of maximum capture; the products to be used are the phosphorganic insecticides possibly mixed with white oils, to improve persistence and penetration.
Fight against ongoing infestation
This fight is carried out with attacks already in place and with evident signs of the tunnels; it consists in the elimination of the larvae with mechanical means (iron wires that go up the tunnel until the larva is reached) or with chemical means, blowing insecticides into aerosol state in the tunnels, saturating the tunnels themselves, and closing them with putty. These methods do not always have the desired success both because of the difficulty in reaching the larvae and because, however, the damage has already occurred. Their application is often limited to ornamental plants.
Biological and biotechnological struggle
In recent years, new methods of biological and biotechnological control have been developed which consist in the use of microorganisms, the former, and pheromones for mass capture traps, the latter. The mass capture is carried out by capturing, in special traps triggered with sexual pheromones, the males who do not fertilize the females make them ovide the unfertilized eggs: in this way the population is gradually sterilized. The traps must be set at a density of about 5-10 or 10-20 per hectare according to the environment and the type of plants. As regards the microbiological struggle, the good results obtained by using the Neoaplectana Nematodes (Steinernema) carpocapsae and feltiae are to be recorded; these, sprayed with special tools in the tunnels or simply put in cotton wool on the edges of the same, are able to actively search for xylophagous larvae and attack them (even if they are less active on Cossus). On an experimental basis, entomopathogenic fungi are being tested, such as Beauveria bassiana; this is very active, also for natural parasitizations, against rodile wood. Among the natural enemies we can remember the Larvevorid Diptera (gen. Phorocera) and some parasitoid Hymenoptera.