PESTS - Paysandisia archon
The butterfly Paysandisia archon is a lepidoptera palms pest belonging to the family Castniidae, subfamily Castniinae.
This palm-eating insect is native from Argentina and Uruguay.
In Argentina, P. archon attacks local palms and exotic species.
Until recently, this insect was little studied because it was doing few damages on the South American continent.
During the 1990s, Paysandisia archon was accidentally introduced into Spain and France by imports of adult palms from Argentina.
Since its introduction, the butterfly has spread in Europe through both adult flight (natural dispersal) and the transport of infested palms, ensuring the spread of the pest over long distances.
In addition to species originating from South America, the known hosts in Europe and the Middle East of P. archon include the following species:
Chamaerops humilis, Livistona chinensis, L. decipiens, L. saribus, Sabal spp. , Phoenix canariensis, P. dactylifera, P. reclinata, Trachycarpus fortunei, Washingtonia filifera et Washingtonia spp.
The species Trachycarpus fortunei (or Chamaerops excelsa, Chinese palm) and Chamaerops humilis (dwarf palm) are particularly sensitive because they have a soft heart and the fibers of their stipe facilitate egg laying.
PAYSANDISIA ARCHON CYCLE
The female lays eggs in the hundreds (between 100 and more than 500), which she deposits at the level of the central palms of the heads of the palms. The larvae feed on the living tissue of the base of the fins and dig galleries to finally reach the terminal bud causing the death of the palm.
In a year, a female, can theoretically produce 4 generations and generate nearly 4,000,000 individuals!...
The female lays her eggs at the base of the palm leaves.
Each female, after fertilization, has the capacity to lay 140 eggs, as many new potential larvae parasitizing palms...
Opposite: part of the abdomen of the female from which emerges the ovipositor organ, at its base chemo-tactile hairs make it possible to guide egg-laying inside the fiber of the palm tree.
Each egg laid has up to 12 days to hatch and give birth to a larva, which must then penetrate through the first tender tissues of the palm tree, for more than 11 months (or 2 years for biannual larvae), the latter not will stop feeding in the head of the palm tree by drilling galleries on their passages.
Here in situ: the larvae of Paysandisia archon housed in their galleries.
Every day, the larvae perforate the tissues of the palm tree by transforming them into sawdust, product of their digestion, this sawdust provoking a rot and a fermentation inside the palm tree.
At the heart of the infestation, the palm becomes a 'fermentor' where the internal temperature remains high even during the winter period.
Here is an example of a larva at the end of the cycle (L9): with an average size of 6 cm its color turns from white to yellow before winding in its cocoon.
A palm tree, heavily infested with the palmivorous butterfly, may contain more than one hundred larvae in the case of Phoenix canariensis.
From the month of April the end-of-cycle larvae migrate towards the periphery of the stipe to make their cocoon by winding in the fiber of the palm tree, from then on they stop feeding and they will use the energy stored during the months before to become an imago (butterfly) and for the breeding phase.
The hatching of the cocoon and the exit of the imago (butterfly) is a function of the temperature (> 25 ° C) and hygrometry (< 40 %), from May to the end of September.
Just after the exit of the cocoon, the butterfly must spend 20 minutes of immobility to breathe, the necessary time of blood supply for the deployment of the wings.
At the end of its development, the adult butterfly is released from the envelope at the end of the cocoon located next to the exit of the gallery and takes off to go to reproduce.
DURATION OF THE CYCLE
Studies leaded in France show that this butterfly has a development cycle of 11.5 months.
The absence of natural predators in Europe and the Middle East has allowed a very rapid development of this parasite.
QUANTITY OF LARVAE IN INFECTED PALM
The number of larvae depends both on the diameter of the palm and the date of the first infestation. In fact, each year brings its batch of new generations emerging from the palm, palm butterflies laying their eggs preferentially on their palm as long as there are still living tissues suitable for future larvae, until the total dieback of the palm tree.
Thus, the number of larvae irretrievably increases with each generation, especially since part of the larval "pool" adopts a biannual cycle.
For small section palms such as Trachycarpus:
we find in the last stages of infestation => 30 larvae on average.
For large section palms such as Phoenix canariensis and Phoenix dactilifera (the most planted):
it is found in the last stages of infestation => up to 130 larvae, which makes this species of palm a true incubator to pest.
As many hill Phoenix represent so many "infestation bombs".
Even 1 year after their death, the ability to spread their parasites in the environment persists...
DAMAGES SPREAD BY THE PAYSANDISIA ARCHON
Damages observed on the palm tree is characteristic of the passage of P. archon:
. sawdust on the base of the crown and / or stipe
. perforated or nibbled palms
. presence of axial and transverse galleries in the stipe
. abnormal development of axillary buds
. abnormal deformation or twisting of the stipe
. abnormal drying of palms, including central leaves
The decline of the palm occurs within a variable period of time, which depends on the number of larvae.
When these are numerous, death can occur in the relatively short term (8 months to 2 years).