The Capnodis tenebrionis is a sizable beetle that wreaks havoc on fruit trees. It’s also commonly referred to as the stone fruit flatheaded woodborer because it primarily affects trees such as apricots, plums, almonds, peaches, and cherries. This pest is widespread in all Mediterranean countries and is particularly prevalent in the southern regions of Italy, where drought phenomena are pronounced. However, in recent years, it has been expanding its range, causing significant damage to apricot orchards in the Emilia-Romagna region. Due to the insect’s characteristics, biological control measures are quite complex and require careful implementation.
In this article, we explain the long life cycle of Capnodis tenebrionis, the damage it causes to trees in its various stages, and successful strategies for its elimination.
Description of Adult Capnodis tenebrionis
Capnodis tenebrionis is an insect belonging to the order Coleoptera, family Buprestidae. As an adult, it has a distinctive appearance and reaches significant dimensions, measuring up to 3 cm in length! The body is compact, thickened in the middle, and tapering towards the rear. Its exoskeleton is exceptionally tough, with a blackish color and whitish shades on the head. It possesses two long antennae and three pairs of legs. It’s not very mobile, but its hard exoskeleton provides protection against predators.
Description of Stone Fruit Flatheaded Woodborer Larvae
The larvae of the stone fruit flatheaded woodborer are quite conspicuous. They go through several life stages and can reach lengths of up to 7 cm at full maturity. These larvae are legless, meaning they lack legs. They are cream-white in color and have distinct segments. The prothorax is more colorful, featuring a darker coloration and a typical inverted “V” pattern. They live inside the wood of trees, where they feed by eroding woody tissues. They create tunnels, often folding them into a “U” or “S” shape.
Life Cycle of the Flatheaded Woodborer
The beetle Capnodis tenebrionis has a very long life cycle, lasting up to 3 years, including the adult phase. Adults overwinter in soil crevices, in shallow natural shelters. In spring, from April onwards, they emerge from the ground and appear on plants. Until September, they feed on tree vegetation, consuming leaves and tender young branches. During the hottest hours of the day, they may move from one plant to another.
Mating and Egg Laying
In summer, mating rituals begin, followed by egg-laying. A female flatheaded woodborer can lay up to 600 eggs, which are deposited around the plants or in typical crevices in the bark at the base of the trunk.
After about 10-12 days from egg-laying, the larvae hatch. This is the most critical time for the insect. Newly hatched larvae are unable to make significant movements, so they try to reach a host plant immediately. If they fail to do so within 24 hours, they die. Once they reach a host plant, they settle in, beginning to create tunnels beneath the bark. Their activity primarily focuses on the underground portion of the stem, below ground level and where the roots originate. As they grow, they dig progressively deeper tunnels, often reaching the root system.
Mature larvae are relatively easier to spot, as they tend to return to the surface wood layers to pupate. The stone fruit flatheaded woodborer completes its larval cycle in 1-2 years, and new adults reappear outside in the 2nd or 3rd subsequent solar year.
Damage Caused by Capnodis tenebrionis to Fruit Trees
Both adults and larvae of Capnodis tenebrionis inflict damage on trees. The damage caused by adult beetles is limited to the erosion of foliage, leading to leaf drop, and damage to non-lignified young branches. Larvae, on the other hand, are more destructive, as they can seriously harm the wood and roots of the tree with their tunnels. Plants affected by the stone fruit flatheaded woodborer larvae deteriorate relatively quickly, especially if they are young trees. In cases of high infestation levels, the tree may die.
Limiting or Predisposing Environmental Factors
The number one enemy of the stone fruit flatheaded woodborer is moisture. If the soil is wet after egg-laying, i.e., with high humidity, it is highly likely that the eggs will not hatch. Even after egg hatching, if the soil remains damp, the newly hatched flatheaded woodborer larva cannot move and reach the host plant. If this environmental factor limits the spread of the pest, it is evident that drought favors it. Orchards located on arid hillsides are the most susceptible to its attacks.
Preventing Capnodis tenebrionis
Given these factors, it’s easy to understand that regular irrigation is the best natural remedy to avoid the damage caused by Capnodis tenebrionis. Soil that is consistently moist prevents egg hatching and the mobility of newly hatched larvae. Unfortunately, regular irrigation is not always possible and, in the case of mature trees, not always necessary.
Wide planting distances, with ample space between plants, also make it more challenging for the beetle to act.
Reducing Capnodis Infestations
To limit flatheaded woodborer infestations, one option is to apply physical barriers at the base of plants, around the collar. These barriers, made of layers of non-woven fabric material, are simple and cost-effective. The physical barrier prevents the stone fruit flatheaded woodborer from laying eggs near the collar. Consequently, the larvae have a harder time reaching the host plant. These protections should be placed around newly planted trees and should be renewed over time. Mulching can also help maintain soil around the tree collar consistently moist.
Of course, if you happen to spot adult Capnodis tenebrionis individuals on the plant’s vegetation, gently dislodge them and crush them vigorously underfoot or with a stone. This is worth emphasizing, as this beetle species has a highly durable protective exoskeleton.
Eliminating Capnodis tenebrionis
Remarkable results in biological defense against Capnodis tenebrionis have been achieved through the use of entomopathogenic nematodes. These are microscopic parasites of beetle larvae. Nematodes are released into the soil along with water and seek out the flatheaded woodborer larvae for parasitization. The larva dies within 72 hours, and the nematodes can reproduce independently. This is an intriguing frontier in microbiological control that has yielded excellent results.
The most effective entomopathogenic nematodes for eliminating Capnodis tenebrionis are Steinernema carpocapsae (available here). Their effectiveness is associated with high humidity conditions, as mentioned earlier, a limiting condition for Capnodis itself. The nematodes should be administered to the soil using at least 30 liters of water per tree. It’s advisable to begin this biological treatment in spring and repeat it a couple of times during the season.