The goat moth is a parasite of tree crops that can cause many problems. It is a lepidopteran considered a wood insect, as it lives and develops at the expense of the wood of trees. It has a very peculiar life cycle, which differs significantly from lepidopterans like the pine processionary, the cavolaia, and the tomato leafminer. To keep it under control and preserve the lives of our fruit or ornamental trees, fortunately, there are various techniques of organic defense. Therefore, it is possible to implement multiple strategies together.
Let’s get to know this parasitic insect better and see how to eliminate it from our trees.
The Characteristics of the Goat Moth
The goat moth (Cossus Cossus) is an insect of the order Lepidoptera, family Cossidae. This species should not be confused with another similar one, the leopard moth (Zeuzera pyrina). The latter has differences both in its life cycle and the damage it causes to crops. The Cossus Cossus, in its adult stage, appears as a large butterfly with a wingspan of 70-100 mm. Its color is very distinctive and resembles the bark of trees. Thanks to this characteristic, these butterflies can perfectly camouflage themselves on tree trunks. The wings are gray-brown with fine black streaks. The head, from which two long black antennae protrude, is of a more uniform color (brownish), with regular stripes and spots (white, black, gray, brown). The larvae have different colors depending on their age. When young, they are pink, while as adults, they become dark red. The head is always dark, while the abdomen is lighter, yellow-ochre. When fully mature, goat moth larvae reach a considerable size, about 80-100 mm. The eggs are laid by adult moths in the crevices of tree bark, usually at the base. They are rather large, about 1.5 mm, and have a reddish color.
Damage to Trees Caused by the Cossus Cossus
The Cossus Cossus causes serious damage to trees through its larvae. These larvae, with their trophic activity, i.e., feeding, dig deep galleries in both the trunk and the secondary branches of the tree. It is a highly polyphagous species of lepidopteran and, therefore, causes damage to numerous tree crops. The most affected species are pome fruits (apple, pear, medlar, service tree, hawthorn), stone fruits (cherry, almond, walnut, peach, plum, apricot). Some forest and ornamental plants are also damaged. The damage caused by goat moth larvae primarily affects the mechanical structure of the plant. The affected tree typically suffers from general decline. If the infestation is at an advanced stage, even by observing the bark from the outside, you can see the damage. In the damaged areas, the wood shows passage holes and significant crumbling. Cutting the trunk would reveal the galleries. This is the primary damage caused by the goat moth. However, secondary damage can also occur. The wounds that the larvae create are an excellent entry point for fungi, diseases, and other pathogens.
Life Cycle of the Goat Moth
The biological cycle of the goat moth is quite unique compared to other lepidopteran species of agricultural interest. While the cavolaia, the tomato leafminer, and the pine processionary complete multiple generations in a year, the goat moth completes only one every 2 or 3 years. Adult emergence occurs in late spring and lasts throughout the summer. During this period, adults mate, and females lay eggs. The preferred location for egg deposition, as mentioned, is at the base of host plants. Young larvae exhibit gregarious behavior and immediately begin to create the famous galleries.
Another way to detect the presence of larvae in wood is to observe the exudation of sap. During the first year, the larvae spend the entire winter in the galleries, hibernating. In the following spring, they resume their trophic activity by widening the galleries and going deeper into the tree. The goat moth spends the entire second year in the larval stage. It is during this period, with the mature larvae, that this species causes the most serious damage. At the end of the third year, adult emergence resumes, following a pupal stage that occurs in the outer layers of the gallery or in the soil at the base of the affected plant. Once the adult emergence is complete, the life cycle starts again.
Biological Defense Against the Goat Moth
Given the long life cycle of the goat moth, if a tree is attacked by this lepidopteran, it is necessary to limit the damage as soon as possible. This can be done in different ways.
The simplest but also the most effective biological control against goat moth larvae is the wire method. It is sufficient to pass a common metal wire (like this) through the galleries until reaching the larvae, which, when struck, die. If the infestation is in the initial stage, this can be a conclusive method. However, if it is advanced, the method is often too laborious and ineffective. It becomes difficult, with this manual method, to reach all the larvae in their deep and convoluted galleries.
Mass Trapping with Pheromones
An effective system, ideal for preventing larval damage, is the mass trapping of adult goat moths. This system should be implemented during the adult emergence period when mating and oviposition occur. To implement it, you only need specific traps that are activated using specific sexual attraction pheromones. These pheromones attract and trap the male specimens, preventing them from fertilizing the females. The females still lay eggs, but these are not fertilized. With this method, over time, the population becomes sterile. Pheromone traps should be placed in the orchard or arboretum at a density of about 10 per hectare. In a family orchard, therefore, one trap may be sufficient.
Entomopathogenic nematodes are microorganisms that we have already encountered when discussing the weevil. These are tiny, cylindrical-shaped worms that are not visible to the naked eye. They are considered obligatory parasites of lepidopteran larvae and are very effective against those of lepidopteran species. In the case of the goat moth, entomopathogenic nematodes are inoculated directly into the galleries created by the larva. The nematode reaches it and inoculates it with symbiotic bacteria that cause its death within 72 hours. The nematode species useful for combating the goat moth are:
- Steinernema feltiae
- Steinernema carpocapsae
These nematodes are among the remedies permitted in organic farming. Furthermore, they do not require a license for purchase, as is the case with phytosanitary products, and are easy to find online (available here).
Another method of microbiological defense that can be used against the goat moth is Beauveria bassiana. This is an entomopathogenic fungus that can be considered a true bio-insecticide. It is a natural pathogenic agent that acts on contact, inoculating the fungus and causing the larva’s death. We have already discussed this fungus when talking about the potato beetle. The use of Beauveria bassiana is permitted in organic farming. The organic product can be easily found in online stores (you can purchase it here).