Diogo Gonçalves

Control of the pinewood nematode (PWN), the causal agent of pine wilt disease, can be achieved through the trunk injection of nematicides; however, many pesticides have been linked to environmental and human health concerns. Essential oils (EOs) are suitable alternatives due to their biodegradability and low toxicity to mammals. These complex mixtures of plant volatiles often display multiple biological activities and synergistic interactions between their compounds. The present work profiled the toxicity of eight EOs against the PWN in comparison to their 1:1 mixtures, to screen for successful synergistic interactions. Additionally, the main compounds of the most synergistic mixtures were characterized for their predicted environmental fate and toxicity to mammals in comparison to emamectin benzoate, a commercial nematicide used against PWN. The mixtures of Cymbopogon citratus with Mentha piperita and of Foeniculum vulgare with Satureja montana EOs showed the highest activities, with half-maximal effective concentrations (EC₅₀) of 0.09 and 0.05 µL/mL, respectively. For these, complete PWN mortality was reached after only ca. 15 min or 2 h of direct contact, respectively. Their major compounds had a higher predicted affinity to air and water environmental compartments and are reported to have very low toxicity to mammals, with low acute oral and dermal toxicities. In comparison, emamectin benzoate showed lower nematicidal activity, a higher affinity to the soil and sediments environmental compartments and higher reported oral and dermal toxicity to mammals. Overall, uncovering synergistic activities in combinations of EOs from plants of different families may prove to be a source of biopesticides with optimized toxicity against PWNs.

The pinewood nematode (PWN), Bursaphelenchus xylophilus, the causal agent of pine-wilt disease (PWD), is a threat to Pinus forests in Asia and Europe. Bursaphelenchus mucronatus and B. fraudulentus are closely related non-pathogenic pine-wood nematodes. In the present work, four medium-chain aliphatic alcohols (C10 to C13) were evaluated in direct-contact bioassays against B. xylophilus, B. mucronatus and B. fraudulentus. The compounds showed high nematicidal activity against the species tested. The lowest values for half-maximal effective concentrations (EC₅₀) were determined in B. xylophilus and B. fraudulentus, suggesting a higher sensibility to these compounds. Further bioassays will include compounds with different chain lengths and functional groups to explore the diversity in the activity of oxygen-containing aliphatic compounds for a more targeted sustainable-control strategy for the PWN.

The pinewood nematode (PWN) Bursaphelenchus xylophilus is a major threat to pine forests. Research on sustainable pest management strategies is now a priority. Essential oils (EOs) are biodegradable, complex mixtures of volatiles that can show low toxicity to mammals and powerful nematicidal activities depending on their chemical composition. In the present work, the EOs of four plants were screened against the PWN, solely and in combination to identify possible synergistic interactions. The combination of Cymbopogon citratus and Mentha piperita EOs (1:1) resulted in higher activities than those of each tested solely, suggesting the occurrence of synergistic interactions between the compounds of these EOs. Research on the combination of synergistic EOs may lead to the development of plant based biopesticides with optimized activities against the PWN.