Herbivore-induced plant volatiles emitted from avocado shoots infested by Oligonychus yothersi (Acari: Tetranychidae) increases the attraction of micro-coleopterans

Tommy Rioja1, 2, Ricardo Ceballos3*, and Loreto Holuigue4
The avocado red mite, Oligonychus yothersi (McGregor) (Acari: Tetranychidae), is a polyphagous pest that causes damage to a wide range of plants. In Chile, is commonly found in avocado (Persea americana Mill.) orchards, and the plant damage is expressed as a reduction of photosynthetic activity in leaves, causing defoliation of trees under severe attack conditions. Oligota pygmaea (Solier) (Staphylinidae) and Parastethorus histrio (Chazeau) (Coccinellidae) micro-coleopteran predators are found on ‘Hass’ avocado orchards, infested by O. yothersi. This study investigated the role of volatile compounds released by avocado in response to O. yothersi infestation in the tritrophic interaction avocado-O. yothersi-O. pygmaea-P. histrio. Plant volatiles were collected from live plants by headspace technique on Porapak Q traps and analyzed by gas chromatography coupled to mass spectrometry (GC-MS). In the chemical analysis, several chemical groups were identified including terpenes, aromatic compounds, and green leaf volatiles. Eight chemical compounds were detected only in the infested plants volatile profile, and differences were observed in the emission of 10 compounds between infested and uninfested plants (P < 0.05). The behavioral responses of the insects to plant volatiles were evaluated in a choice-test using a Y-tube as olfactometer. Uninfested plant volatiles were significantly attractive to O. yothersi, while infested plants volatile extract repelled the mites. Two compounds, R-limonene and α-pinene, elicit an attractant behavioral response from O. yothersi. Oligota pygmaea and P. histrio females registered a strong attraction to volatiles from infested plants, and the compounds (Z)-β-ocimene and methyl salicylate detected only in infested plant also were attractive to predators.
Keywords: Avocado red mite, Coccinellidae, methyl salicylate, monoterpenes, olfactory responses, Persea americana, Staphylinidae.
1Pontificia Universidad Católica de Chile, Facultad de Agronomía e Ingeniería Forestal, Av. Vicuña Mackenna 4860, Santiago, Chile.
2Universidad de Tarapacá, Facultad de Ciencias Agronómicas, Campus Azapa km 12 Arica, Chile.
3Instituto de Investigaciones Agropecuarias, INIA Quilamapu, Av. Vicente Méndez 515, Chillán, Chile.
*Corresponding author (rceballos@inia.cl).
4Pontificia Universidad Católica de Chile, Facultad de Ciencias Biológicas, Av. Libertador Bernardo O’Higgins 340, Santiago, Chile.