« Tree injection » The effect of Cinnamomum cassia’s essential oil on the rosy apple aphid (Dysaphis plantaginea) and the crop auxiliaries.

Synthetic pesticides are usually used against the rosy apple aphid Dysaphis plantaginea, a pest of apple crops. The "Tree injection" project in which this master thesis is included, attempts to control this aphid in an innovative way: via the injection of essential oil emulsions into the tree. A prototype of biopesticide based on essential oil of cinnamon (Cinnamomum cassia) was tested during this thesis. The main experiment took place in an apple orchard on 15 years old trees of the Jonagold variety. Five different treatments were administered to the 40 trees in the experiment. A blank treatment (no injection), an injection of saline solution (water only), an injection containing an emulsifier, an injection of an emulsion of 1% cinnamon essential oil and an injection of an emulsion of 2% cinnamon essential oil. Measures on the quantity of aphids, the biodiversity present in the orchard and on the volatile organic compounds were carried out. In addition to these measures, the general health of the tree was assessed by analyzing the chlophylian fluorescence and by measuring the cracks that appeared after the injections. The second experiment consisted of a semi-controlled environment. It tested the effect of 4 treatments (a blank and injections of essential oil emulsion at 1, 2 and 4 %) on a specific number of aphids placed in nets on 2-years-old apple trees of the Jonagold variety. The last experiment studied the behaviour of pollinators (here bumblebees) in relation to essential oil injections under laboratory conditions. This was possible thanks to a wind tunnel in which an injected plant and a blank plant were placed (Jonagold 6 months old). Results on aphids, biodiversity and crack size were analyzed via generalized linear models (GLM) with Fisher or Chi-square tests. Volatile organic compounds were analyzed via PCA and PermANOVA. Chlorophyll fluorescence measures were analyzed via repeated measures ANOVA. Finally, bumblebees behaviours were analyzed via binomial test, paired T-tests and linear model (LM). The results showed a treatment effect whereby an aphid peak occurred only on the blank treatment. No effect on crop auxiliaries in the orchard but a possible repellent effect on bumblebees in the laboratory when a tree received a large amount of treatment. Significant results for the presence of cinnamon compound and volatile organic compound emissions were observed but could not be specifically linked to any of the treatments. The general health of the trees did not appear to be impacted other than the appearance of cracks.