| Sumario: | Increasingly, plant essential oils (PEOs) are being shown as an alternative to
synthetic chemicals to fight against pests and diseases. PEOs might have a direct effect by being
toxic and repellent to pests and even attractive to natural enemies. In addition, several PEOs
have recently been described as elicitors of plant defenses, which could indirectly affect pests
and diseases. This work describes the effectiveness of five commercial PEOs (Achillea
millefolium, Allium sativum, Rosmarinus officinallis, Tagetes minuta, and Thymus zygis) on
controlling the South American tomato pinworm Tuta absoluta and the beneficial effect on the
predator Nesidiocoris tenuis. Therefore, a Y-tube olfactometer was used to test the behavioral
response of T. absoluta and N. tenuis to PEO-sprayed tomato plants and intact tomato plants.
The PEOS of Achillea millefolium and A. sativum, when sprayed on tomato plants, were found
to be significantly repellent to T. absoluta but attractive to N. tenuis; thus, these two PEOs were
selected for further studies in a greenhouse experiment. The spray of tomato plants with either
A. millefolium or A. sativum PEOs significantly reduced the number of T. absoluta eggs, larvae,
and infested leaflets. Additionally, both PEO sprays did not affect the establishment and
reproduction of the predator N. tenuis compared to the control. Interestingly, the spray of
A. millefolium and A. sativum upregulated the expression of the defence genes related to abscisic
acid (ABA), jasmonic acid (JA), and salicylic acid (SA) pathways. Plant defence activation
triggered the release of herbivore-induced plant volatiles, mainly Z-3-hexen-1-ol, heptanal,
1-octanol, (Z)-3-hexenyl propanoate, nonanal, 2-nonenal and (Z)-3-hexenyl butyrate. Our
results suggest that A. millefolium and A. sativum oils could play a significant role in T. absoluta
management. The potential of these oils as elicitor agents in tomato crops is discussed.
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