The Peach Rootborer (Capnodis tenebrionis) is another one serious up to – under certain circumstances – completely destructive pest of the Stone Fruits trees, Pome Fruits and some of the Ornamental plants.
It is found mainly around the Mediterranean basin countries, although recently it has expressed its intention to move further north, taking advantage of global warming.
With this unstoppable destroyer, who also proves to be an excellent publicist, since he manages in practice not to have natural enemies, the reader of ‘Kalliergeia’ is invited to co-exist in this article.
A pupa and a larva of Capnodis tenebrionis on a dead peach tree trunk.
Peach Rootborer is classified in the Kingdom of animals (Animalia – syn. Metazoa) and the subkingdom of Bilateria ( animals with bilateral symmetry). The full taxonomic shape of the coleopterous is listed directly below.
● Domain: Eukaryota
● Kingdom: Animalia
● Subkingdom: Bilateria
● Phylum: Arthropoda
● Subphylum: Hexapoda
● Class: Insecta
● Subclass: Pterygota
● Order: Coleoptera
● Suborder: Polyphaga
● Family: Buprestidae
● Subfamily: Buprestinae
● Genus: Capnodis
● Species: C. tenebrionis
➤ Capnodis tenebrionis (Linnaeus, 1758)
Peach Rootborer (Capnodis tenebrionis)
The basic morphological elements refer to the main biological forms that the coleopterous Peach Rootborer, takes in the various stages of its life, including eggs, larvae, pupae and adults insects.
The egg of the Peach Rootborer has oval shape, color white opalescent and hard shell. Its dimensions usually range from 1.4 to 1.5 mm in length, and from 1.1 to 1.2 mm in diameter.
However, larger dimensions are also mentioned, where the length is between 5.6 and 5.7 mm, and the diameter is between 3.5 and 3.6 mm.
This difference is due to the prevailing temperatures and the incubation period of the egg, since it has been observed that temperature affects the incubation period and after long periods of incubation produced larger eggs.
The form of the larvae of Capnodis tenebrionis is identical at all ages – what changes is size.
Their color is whitish, their body elongated and flattened, they have strong maxillae and mandibles and are practically legless.
Their head is small and brown, and although they share with many other species of the family Buprestidae, the naming of flatheaded rootborers, this is due to the fact that they have prothorax obviously wider in relation to the rest of the body, which can easily be confused and considered as a head.
Characteristic of the dorsal part of the prothorax is that it is traversed by a central shallow groove which shape a narrow inverse V, while its color is pale yellow to brown.
In the abdominal segment of the larvae, the lateral-flattened segments that constitute the larvae can be seen clearly – the abdominal rings.
In terms of size, the neonate larva is about up to 3mm long, while the last larval instar is 80 mm in length and about 13 mm wide.
The larval instars are 9.
The pupa is whitish-grey, with dimensions of 14 to 30 mm in length and 7 to 12 mm in width.
The adult of Capnodis tenebrionis has elongated shape and color generally black or blurry black, with the exception of the dorsal part of the thorax and specifically the pronotum, the color of which when the temperature exceeds 24 °C becomes whitish-grey.
The head of the insect is relatively small, and has about half the width of the pronotum, from which it is largely covered.
Its eyes have brown color and shape ellipsoid, while it has short filamentous type antennae, which when the insect is at rest fold below the prothorax.
The pronotum is the widest part of the Peach Rootborer’s body, and is varied with black dots and spots of varying size and shape – almost imperceptible increases of skin products.
The anterior wings of the adult, the elytra, are black in colour and display arranged in rows crowd reentrant dots as well as whitish-grey spots sparse and scattered.
The elytra typically narrowed resulting in slightly acute posterior apex, more rounded in females and tends to the trapezoidal shape in males.
In terms of dimensions, the length of the adult is almost twice its width, the first being between 14 and 30 mm and the second being between 7 and 12 mm.
The female adult of the Peach Rootborer is larger than the male – the length of them rarely exceeds 20 mm.
Difference is detected and the width of the pronotum, where in females this is between 9 and 10 mm, whereas in males it is between 8 and 9 mm.
Peach Rootborer (Capnodis tenebrionis)
The Peach Rootborer for the insect world it is an extremely long-lived, thermophilic species, and in addition to infesting fruit trees and commercial orchards, it adapts – within its distribution zone – to a wide range of ecosystems. All this, and more, is discussed immediately below.
The Capnodis tenebrionis has 1 generation per 1 to 2 years.
Rising temperatures in the spring, adults who passed through the winter diapause stage leave their shelters and go to the initial hosts. If their shelter is outside the orchard, then they go to the trees of the first 3 to 4 rows to feed with buds, the cortex of twigs and young branches, as well as with the petiole of the leaves.
This activity takes place during the day with full sunshine and no wind. The night leaving the foliage and find shelter at the base of the tree, any weeds, as well as in soil cracks.
Initially their mobility is not great, due to relatively low temperatures. But then, by the end of March to early April, which in the Mediterranean regions the temperature is ranging between 20 and 22 °C, and the photoperiod is LD 13:11, the adults of the Capnodis tenebrionis intensify their activity, eating more and dispersing and to new hosts.
The sexual maturation of the adult is being completed in May. Then comes the period of mating and oviposition, which is extremely long, since it can last from late Spring until the Autumn – as the days continue to remain warm.
Mating takes place at temperatures between 19,5 and 37 °C, wile the oviposition at temperatures between 25 and 40 °C.
The Female Adult of the Peach Rootborer are extremely productive, since they can each laying 1000 or more eggs.
When the average daily temperature reaches 25 °C and above starts the laying of the eggs, within an area of approximately 50 cm around the base of the trunk of the tree (rarely, in cracks of the bark of the base) and a depth of from 3 to 12 cm – that sometimes can reach up to 20 cm.
If the soil is light, the females shall lay their eggs directly on the surface; if medium-textured or heavy they shall lay them in soil cracks. It is not uncommon, however, that the eggs laying takes place even in sheltered spots under stones.
Regardless of specific choice, the females of the Peach Rootborer will lay eggs only to those places that are sunny, warm and dry, and will avoid both soils that moisture of dry weight exceeds 10%, as well as those that have received insecticidal formulations in the form of powder.
In such cases, the laying of the eggs will only take place in clean areas and up to the distance of 120 cm or more from the base of the trunk of the tree.
When the females adults completing the eggs laying, after 3 to 4 days in good repute they end their lives.
The Peach Rootborer eggs are directly affected by the relative humidity. In low relative humidity conditions egg hatching is favoured, whereas in high relative humidity conditions hatching becomes difficult to impossible.
The hatching period of eggs depends on the temperature. Thus with temperatures of 20 °C the neonate larvae appears within 30 days, while at 35 °C it takes only 7 days. No hatching shall take place below 18 °C and above 45 °C. As regards egg hatching rates, this amounts to around 80%.
After hatching eggs, the larvae move towards the roots of the host, having the ability to to locate the root at distances of 60 cm from the hatching site.
To move use and the peristaltic muscle contractions of their body, but, above all, the hairs that surround each body ring, and which are discharged with the first ecdysis, which means that until then they should have made the entrance in the host.
The period from hatching of larvae until the occurrence of the infestation does not exceed 3 days, otherwise the neonate of the Peach Rootborer dying.
Of all hatched larvae, it is estimated that only 1 to 2% actually manages to penetrate the roots of the host trees – roots that the more shallow they are, the more they favour survival.
After the larvae are established, they begin to forming long galleries as they eat, having the possibility while being still small to move from one root to another. But from then on they remain in the one they chose, which may initially be thin, but as they grow they are obliged to move forward through it to increasingly thicker areas of the tree.
The galleries that the larvae burrow begin beneath the bark, in cambium, and reach the wood, filling with the compressed frass – products of their action.
The galleries and tunnels are directed both upwards and downwards, the central roots, progressively become more and more wide, and on each host there may be more than one, which develops a corresponding number of larvae.
It is not uncommon, the length of the galleries exceeds 1.5 m, while within each gallery the larva is found mostly folded, with its body appearing under the shapes U or S.
The development of the larvae of Peach Rootborer is extremely slow, reaching up to the period of 10 to 12 months, and always takes place in the same host.
Within the latter, at any given time of the year, larvae of various sizes and therefore of age occur – a fact that is evidently directly related to when and how they mature, as well as the duration of the biological cycle of the insect.
On the above mentioned, it has been found that larvae which hatched in July, can reach in February, the length of 60 mm, which means that they will be adults before reaching one year.
On the other hand, larvae that hatched at the end of August, found at the end of December to have reached just 10 mm, which means that they will be adults in the second year, and so the biological cycle will be two years.
For the rest and the Peach Rootborer in order to reach adulthood initially needs to pass all the larval instars.
And once this is done, immediately after it will be found in the phase of pupa, where it will pass the pupal stage in the lower trunk or principal roots, within a cell, length of about 3 cm.
Finally, 3 to 5 weeks later, the pupae will be transformed into adults, which will emerge after penetrate the bark of the host’s trunk.
Movements and dispersion of the adults begin for males with temperatures ranging between 21 and 25 °C, and for females with temperatures ranging between 26 and 30 °C.
On the other hand, with regard to the flights, these are generally carried out at midday, and since the Peach Rootborer is a large and robust insect, they have a characteristic loud buzz.
The ideal conditions for the execution of adult flights, and for the nutrition activity, is when temperatures are above 30 °C and the wind speed does not exceed 4 m/s (approximately 2 Beaufort).
The maximum of adult flying is located at temperatures between 31 and 35 °C, while the temperature limits for feeding and moving are between 15 and 45 °C.
At 15 °C the Peach Rootborer does not move and does not feed, as at 45 °C – although here there can be a few hours movement.
The Peach Rootborer overwinters either as a larva or as an adult: when the biological cycle is completed in two year, then overwinters as a larva within the gallery, on the trunk of the affected tree, while the annual biological cycle, the overwintering takes place in the form of the adult.
The adult finds shelter in or out of the orchard. In the orchard take shelter in soil cracks near weeds, or if is clean then take shelter in protected places near weeds that are located around the perimeter of the orchard, in areas where there are snakes holes, or in appropriate positions in the irrigation canals, or even farther.
The survival rate of adults during winter is about 50%.
Peach Rootborer (Capnodis tenebrionis)
The References of this flat-headed article of ‘Kalliergeia’, entitled ‘Peach Rootborer (Capnodis tenebrionis)‘, are presented alongside by The Fratellis, with their song Flathead.
With Pomp and Circumstance
A flathead song about a flatheaded insect.
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