This “double blow”, in the laboratory, at least, proved effective. “Coupled with gas chromatography (NB: enabling the quantification and identification of the odorizing molecules), a system of odor sampling enabled us to establish that the alginate beads, following a quite brief initial peak, released the two semiochemicals in a very constant manner for seven consecutive days which was conclusive. In other words, our beads released doses very close to what a typical population of ladybird beetles would release in nature in the form of pheromones. We could certainly have increased the released dose a little to increase the attraction but this would be to run the risk of unnecessarily disturbing the male ladybird beetles and induce an undesired behavior. During these manipulations, we also tested the attractiveness of our encapsulated alginate beads on hoverflies (Episyrphus balteatus), a diptera that travels a lot more by flying than the ladybird beetles. Here too, the experiment proved very conclusive”. At this stage, Bérénice Fassotte had therefore perfectly reached the two objective of her doctorate: identification of the sex pheromone of the Asian ladybird beetle and the design of an efficient odor distributor. It should be added briefly that she also completed an international bibliographic review on the ladybird beetle reproduction which was successfully published in the “bible” of this subject area: The Journal of Pest Sciences (2)… It remained at this point to show that this alginate distributor was efficient in the field and not only in the laboratory.  

"Paintball" to the rescue

This is where things went downhill, mainly due to the weather conditions of the summer in 2015. “Based on our inventory experiment with aphidophagous insects (consumers of aphids) in large cultures, we knew that sooner or later we ran the risk of encountering a season where the aphids would be low in numbers and therefore the ladybird beetles as well. This is exactly what occurred! Installed on several wheat and bean plots of the Gembloux Agro-Bio Tech experiments farm, our distributors were only able to yield sparse results which were statistically insignificant. Then in 2016, due to lack of finance, the in situ experiment was unable to be renewed”. Was this the end of the road? Thankfully it was not. The alginate beads are currently being tested in China by my colleague Frédéric Francis with the help of Belgian and Chinese financial aid. There, in the dryer regions, there is scope for hope. It must be acknowledged that the ladybird beetles do not seem to be adapted to the humidity of our regions: when near oils, the terpenes are not water-soluble”. It would take more than this to calm the enthusiasm of François Verheggen who, as we speak, is working on other forms of matrix likely to make good odor distributors. One of these, based on a polymer encircled with a rubber membrane, well-known in the world of integrated pest control, has the disadvantage of not being biodegradable: a solution to this drawback needs to be found. Another idea, developed in collaboration with a French company, consists in designing bigger beads (two or three centimeters in diameter) in which the molecules would be encapsulated and released to keep walnut grove pests away. By means of propellants inspired by “paintball” games, “snipers” placed on the ground could propel them into the treetops thus ensuring homogenous release throughout the targeted arboriculture. 

Unfounded fears

If the experiment conducted in the fields had been able to be done as planned, it would have been interesting to observe the real behavior of the male beetles. It is not enough merely to be attracted to the aphid-infested areas are. They also need to devour the aphids in great numbers which is the aim of the “game”! Another question remains, linked to the interspecificity of species: is the sex pheromone identified in Harmonia axyridis more or less identical to that which is found in other species of ladybird beetles? This is the case with aphids. “We hope to have the answer to this question within two years thanks to the work of Pauline Legrand, who has just begun a doctoral thesis dealing with these questions. 

The question remains as to whether if by “feeding” the Asian ladybird beetle which is already affecting our ecosystems, we are running a non-negligible risk: Will Harmonia axyridis individuals that have been well fed on aphids not have a better chance of reproducing in great numbers thus increasing their chances of survival during winter? Faced with these questions, François Verheggen refuses to give up. “It must be understood that our entire strategy involves displacing already existing ladybird beetles. And this means moving them from places where they live in perfect conditions already (for example in nettle patches) to environments which are less suited to them such as cereal crops. This “forced” displacement is likely to weaken them and to interfere with them. In addition, it will be necessary to attract them to the wheat (for example) as soon as the very first aphids arrive while they are still only present in small numbers. They are therefore not being offered abundant nourishment. Finally, we can reasonably expect that, by heading for the cereal crops due to the odors released, the Asian ladybird beetles will leave more room for the indigenous ladybird beetles whose larvae, it should be remembered, are a prey for the Asian ladybird”! The researchers at Gembloux are far from finished with Harmonia axyridis and with the other ladybird beetles present in nature...

(2) The scent of love: how important are semiochemicals in the sexual behavior of lady beetles?, Journal of Pest Science, jui 2016.