The Asian hornet
The Asian Hornet is an invasive species (recognized as such for a year and a half). It was introduced in France by accident in the region of Bordeaux more than 10 years ago. Below is the current distribution map drawn up by the National Museum of Natural History.
The presence of the Asian Hornet has devastating consequences on the species from which it takes the place and hunt them away. Regarding the bee, when an Asian hornets nest settles near a hive it is generally depleted in a few weeks.
There is currently no effective means of control: the existing methods are either too dangerous (nest destruction with a gun) or ineffective (traps) or prohibited (pesticides). Beekeepers are now powerless to Asian hornets, but we have developed a system that overcomes these difficulties.
Pollinis works alongside the association L’Arbre aux abeilles (The bee’s Tree), to finance the development of a prototype of unprecedented struggle against this scourge that is decimating hives and threatens the economic balance of beekeepers.
Inventory of control methods
Natural defenses of asian bees
In Asia, the bee species Apis Cerana has developed an effective defense strategy: bees create a compact mass around the hornet and increase the temperature by vibrating their wings inside the « ball » they have formed. After five minutes, the temperature reaches up to 45° C, making the hornet succumb to hyperthermia.
In Europe, only the bees raised in Asia use this strategy with a lower efficiency. The only solutions of defense for bees raised in Europe involve the fled and not the death of the hornet.
The products mainly used are Fipronil or other insecticides, very often based on sulfur. The main disadvantages are:
– Toxicity, which makes the use of Sulphur Dioxide illegal.
– The lack of selectivity inherent to the toxicity of the product, responsible for significant environmental damages (other insects, predators of the hornets…).
– The flight of the nest by a portion of the colony if fumigation is used, because the time for action is too long.
– Sleeping individuals are not necessarily affected since they do not breathe at the moment of the treatment.
Physical destruction of the nests
The methods usually employed are shooting with a rifle, the water lance or even the flamethrower. The main disadvantages are:
– The survival of a part of the colony, which then shows aggressive towards the close vicinity, including manipulators. In addition, the colony can build a new nest nearby.
– The risk of fire, given the dryness of the environment in question at the time of proliferation of hornets.
Capture of founders
During spring, the founders are getting out of wintering with a high energy need to move and choose the location of the nest. Resources in sugar are scarce in this season. Such a situation is favorable to the action of trapping.
Selectivity is far from perfect and other species are caught. In particular, the action during spring affects many other insect species.
The effectiveness of such methods is highly questionable (eg the Rhône-Alpes region where only one hornet was captured on 16 trapped nests). Only 10% of the founders from a nest manage to start a new nest. Therefore it is sufficient that some founders escape trapping for the action to be ineffective.
The HDM system meets the main elements of following specifications:
– Setting up a remote containment chamber of microwaves around the nest to generate a stream of microwave power of 3kW at a frequency of 2.45GHz inside the containment chamber;
– Bring the deployable containment device and production of microwaves near the nest;
– Enable the emergency stop system with a button;
– Secure the ignition system (to prevent unintentional start).
The system consists of three main part interconnected mechanically and each providing a separate function:
– The positioning subsystem consisting mostly of a telescopic aluminum pole which role is to place other subsystems near the hornet’s nest. It is expected to reach nests up to 25 meters high and to pass through flexible branches and rigid branches if they are spaced more than 20 cm. So it can reach almost all nests.
– The inflatable subsystem containment is composed of several “petals” capable of enclosing a nest which is 90 cm high and 70 cm in diameter, which are the largest nests encountered. Lined with a layer of braided bronze (product of the Gantios company), it realizes the electromagnetic sealing in the manner of microwave walls. This, in addition to protecting the users, allows an increase in efficiency by a factor of 100.
– The “microwave” subsystem is composed of three magnetrons of 1kW each positioned in “triskele”. Provided with output waveguide to avoid interactions between them, they provide power to blast in a few seconds hornets present inside the nest. Thanks to the thermal insulation of the nest by the containment chamber and the structure of the nest (layers of dried cellulose) the best protected hornets will die in a few minutes as a result of the increase in temperature.
To these three major subsystems will be added components allowing a better ease of use and protection of the user. Including a secure power supply and a light pump for the pumping of the system. It is also intended to provide the system with a high tripod to facilitate its deployment in larger height.
Research and experiments conducted
Noting the temperature sensitivity of Asian hornets, we developed the idea of using microwaves to increase the internal temperature of hornets.
A partnership with the ONERA and the generous expert collaboration with Dr. François Lemaître (ONERA Toulouse) and Dr. François Isaac allowed us to perform several tests on the Asian hornets subjected to the microwaves. In short we explored through the facilities of ONERA Toulouse the frequencies that give the best efficiency of the system. Subsequently we determined precisely the required microwaves power to achieve the rapid and systematic death of a hornet. We ensured that the power supply was not harmful to the natural environment, or for manipulators – in addition to be produced easily.
We also conducted behavioral tests proving that the Hornets do not become aggressive when exposed to microwaves. Instead, they fall in a few seconds into a state of lethargy.
These tests show that microwaves can be used to eliminate realistically the Asian hornets. Microwaves, unlike chemical controls, leave no trace in the environment after the destruction of the nest. Even if the nest is abandoned and the birds eat the dead hornets. The problem of sizing the system still existed: it was necessary to ensure achieve the necessary power to guarantee the death of hornets.
To address this problem we worked on the concept of deployable reverberation chamber. The principle of a reverberation chamber is the Faraday cage. It is a closed chamber which walls are reflective to prevent microwaves from escaping and to conserve energy. The energy confinement with the nest allows to be more than 100 times more efficient. We have determined that our system requires a maximum power of 3 kW.
In short, the advantages of this system are many:
– Clean system: no pollution because no pesticides or chemicals;
– Selective system: no other animal or plant species affected by the destruction;
– Secure system: remote handling from the operators, no risk of further abuse;
– Legal system: containment of microwaves used: no emission permits, no environmental or operators exposure to radiation;
– Exhaustive system: death of the entire colony, including the sleeping individuals which are not affected by pesticides;
– Quick System: a few minutes to destroy a nest;
– Ergonomic system: system controlled from the ground for the inflation and activation of the microwave;
– Economic and sustainable system: affordable final cost of the system (cost of the final materials below €2,000), no mechanical usury: you can destroy many nests with a single device, very low cost of use (only energy is required).
Beyond the prototype
Early research suggests that standards for domestic microwave ovens are 5mW/cm² measured 5cm of the microwave oven. The magnitude calculations indicate that our device should widely meet these standards. In addition, the standards for agricultural tools are certainly larger than the domestic standards. We have to do more research to get an idea of how to proceed to achieve an approval or certification of the device. However, in the views of recognized standards for home devices, we can easily verify that our device is not more dangerous than a commercial microwave oven once it is built.
The location of the nests remains a problem: even if we have an effective method of destruction. Indeed, leaves and branches often hide nests in the trees and their detection is difficult by the nude eye.
We have studied many ways to facilitate the detection of nests. We considered the use of a thermal camera that would reduce the natural camouflage of the nests. There are also ways to locate nests by the sound signature of the flight of hornets. We are focused on the use of a method similar to radar called modulated diffusion.
A conventional radar would not work in the forest environment due to the presence of insignificant echoes. Instead, with the modulated spread and once a hornet is caught, a transponder attached to his back provides an exploitable radar echo even through dense vegetation. The components of this transponder weigh less than 200 mg and its total cost is of a few euros.
It is relatively easy to build and test the method in a research context. However, the construction of a system usable beyond the research stage will take longer.