Infestation of the gall midgeDasineura oleaeprovides first evidence of induced plant volatiles in olive leaves

Abstract

In this study, we present the first characterization of herbivore-induced plant volatiles (HIPVs) released from infested olive leaves. The gall midge Dasineura oleae is a specific pest of Olea europaea and endemic of the Mediterranean Basin, an area in which severe outbreaks currently occurred. Little is known about the damage caused by the pest and the relationship with its host. Since gall formation and larval feeding activity may lead to the release of specific plant volatile compounds, we investigated the volatile profiles emitted from infested plants compared with healthy plants under both laboratory and field conditions. Additionally, the volatiles emitted from mechanically damaged plants were considered. A blend of 12 volatiles was emitted from olive trees infested by D. oleae. Of these, β-copaene, β-ocimene, cosmene, unknown 1 and unknown 3 were found to be exclusively emitted in infested plants. The emission of germacrene-D, (E,E)-α-farnesene, and (Z,E)-α-farnesene, α-copaene, (E)-4,8-dimethylnona-1,3,7-triene, (E)-β-guaiene and heptadecane significantly increased in infested trees. Linalool, β-copaen-4-α-ol, β-bourbonene, β-cubebene, β-elemene, β-copaene and δ-amorphene were found only in the field trial and showed differences depending on the level of infestation and the plant stage. (Z)-3-Hexenol, (E)-4-oxohen-2-enal, and 2-(2-butoxyethoxy)-ethanol, were exclusively emitted from the leaves after mechanical damage. In a field trial in Italy, we also demonstrated spring synchronization between adults of D. oleae and O. europaea trees. Analyses of morphoanatomical malformations of gall leaves showed that tissue alterations occur at the spongy parenchyma causing an increase of the leaf blade thickness. We speculate that tissue alterations may lead to HIPV release, in turn potentially attracting D. oleae natural enemies.

Electroantennographic and olfactory responses of Quadrastichus mendeli to eucalyptus volatiles induced by the gall‐forming insect Leptocybe invasa

“…2 To date, plant volatiles that attract parasitoids to gall-forming insects have barely been reported. 8 Gall-forming insects live within plant tissues and induce tumor-like growths that provide the insect with food, shelter and protection from parasitoids. 9 To date, more than 2000 species of gall-forming insects belonging to 20 families in Hemiptera, Diptera and Hymenoptera have been found.…”

“…However, studies focused on leaf‐eating, trunk‐boring and piercing‐sucking insects, 4,6,7 and chemical cues facilitating host location have been described in only a few parasitoid species 2 . To date, plant volatiles that attract parasitoids to gall‐forming insects have barely been reported 8 …”

The Cuticular Hydrocarbons of Dasineura Oleae Show Differences Between Sex, Adult Age and Mating Status

“…Insect Collection Shoots with galled leaves by D. oleae were collected during March and April 2021 from an infested olive orchard located in Gavorrano (Grosseto, Italy) (42°54'28.30'' N, 11°00'10.65''E) considering the timing of the emergence of D. oleae reported by Caselli et al (2021b) at the same place in 2020. After collection, shoots with a maximum of 2 leaves having 5 galls each were selected and placed in plastic transparent containers (diameter 87 mm, length 115 mm) closed at one extremity with a chiffon fabric (mesh size 0.04 mm) to allow aeration.…”

Metabolic Responses in Leaves of 15 Italian Olive Cultivars in Correspondence to Variable Climatic Elements

“…Therefore, climatic conditions represent potential factors in changing the pathways of several secondary metabolites from different families, such as volatile organic compounds (VOCs) and the green leaves volatiles (GLVs), largely spread in higher plants. However, except for that which has been reported by some authors [ 2 , 3 , 4 ], a lack of information exists on the VOCs emission by olive leaves and, in particular, on the comparison of the emission among different olive cultivars. Likewise, the studies on biophenols (BPs) in olive tree leaves are focused on the different factors (biotic and abiotic) influencing the amount, the concentration, and the pharmacological proprieties of these antioxidant compounds, although climatic conditions are still scarcely investigated [ 5 , 6 ].…”