Different population densities and continuous feeding by Oligonychus yothersi (McGregor) (Acari: Tetranychidae) affect the emissions of herbivore-induced plant volatiles on avocado (Persea americana Mill. cv. Hass) shoots under semi-field conditions

Plants attacked by insects and mites release blends of herbivore-induced plant volatiles (HIPVs), which act as chemical cues that attract predators and/or repel herbivores alongside alerting neighbouring plants. The chemical profiles of avocado (Persea americana Mill. Cultivar Hass) shoots infested with the foliar mite Oligonychus yothersi (Acari: Tetranychidae) were analysed using a gas chromatograph coupled to a mass spectrometer (GC-MS); the different collections of volatiles were performed under semi-field conditions in summer. Four infestation treatments were applied to the avocado shoots (uninfested plant or control; low, medium and high mite-infestation levels). The chemical profiles collected in situ changed qualitatively and quantitatively after infestation, increasing the emissions of (Z)-β-ocimene, (E)-β-ocimene, β-linalool, α-farnesene, farnesyl cyanide and methyl salicylate (MeSA) as opposed to those of the uninfested shoots. The amount of HIPVs emitted by the avocado shoots with the highest O. yothersi population density (250 ± 10 mites per leaf) were greater than those of the shoots infested with the lower population density (60 ± 10 mites per leaf); to the emissions of (E)-β-ocimene, sesquiterpenes and MeSA at higher amounts even after seventeen days of continuous infestation. Likewise, the emissions of HIPVs increased with each infestation level; also fluctuating between collecting dates, which indicates that environmental conditions maximized or constrained those emissions. In addition, the damaged foliar area increased with higher O. yothersi population densities after seventeen days of infestation. These results indicate that higher mite-population densities and continuous O. yothersi-feeding increases the amounts of HIPVs emitted by O. yothersi-infested shoots in summer.