Aceria oleae (Nalepa)
Common name: Olive gall mite.
Taxonomic placing: Acari, Prostigmata, Eriophyoidea Eriophyidae.
Geographical distribution: Of East Mediterranean origin, the pest has also invaded other Mediterranean countries and South Africa.
Host plants: Olive (Olea europea Linnaeus)
Morphology: The body of the adult mite is yellow, about 0.13 mm in length, cylindrical, with a similar number (50-60) of dorsal and ventral opisthosomal rings. The prodorsum has an obscure pattern with lines that are discernible only towards the rear and bears two long backwards-pointing setae; the featherclaw is four-rayed.
Life cycle: The olive gall mite prefers young olives growing in warm and humid conditions, thus thriving in nurseries and well-irrigated young plantations, and infesting mainly the peripheral growth. It passes the winter hidden on the lower sides of the leaves, the populations moving to the flower clusters in spring. In Greece the pest raised 12-15 annual generations in the field, and its populations peaked during June-July, with a smaller rise in late September. The mite reproduces by arrhenotoky, each female depositing up to 40 eggs. When reared in the laboratory on olive leaf disks at 21-24ºC, its life cycle (egg to egg) required about a forthnight.
Economic importance: By feeding within the growing points of the olive, the mite causes the emerging leaves to be deformed and twisted. In severe cases this leads to withering and death, and even total lack of blossoming (and thus prevents fruit formation). Overall tree development (especially of saplings) and yield may be seriously affected. Greenish spots develop on infested mature leaves which become distorted. Infested young fruit turns silvery and may be deformed by protuberances; more than half the fruit may drop or be damaged. Mature fruits are not attacked.
Due to the fact that several eriophyids may live side by side on olives and infest the olive organs together, the particular injury attributed to A. oleae may actually be due to one or more species that affect the host together.
Management
Cultural control: Some olive varieties seem to be tolerant to the pest. In addition, horticultural practices, such as pruning or topping, induce new growth and thus the formation of more susceptible buds. The mite may spread to new areas by infested seedlings, which should be suitably treated prior to transportation.
Chemical control: In the past the mite was often controlled with wettable sulfur, usually applied early in the season. Nowadays either amitraz or abamectin will control the pest when applied before olive blooming, in order to prevent damage to fruit, or given several times during the season if leaf damage is to be avoided.
Biological control: Several predatory mites of the family Phytoseiidae are associated with the olive gall mite, the most abundant species in Italy being Typhlodromus athena Swirski and Ragusa. Although the quantitative effect of the phytoseiids has not been resolved, it is commonly believed that eriophyid olive pests are held below their economic injury threshold by the predators.
References
Abd Elhadi, F. and Birger, R. 1999. A new approach to the control of the olive mite Aceria (Eriophyes) oleae in olive trees. Acta Horticulturae 474: 555-557.
Castagnoli, M. and Oldfield, G.N. 1996. Other fruit trees and nut trees. In: Eriophyoid Mites, Their Biology, Natural Enemies and Control (edited by Lindquist, E.E., Sabelis, M.W. and Bruin, J.), pp. 543–559. Elsevier, Amsterdam.
Harpaz, I. 1955. Notes on the eriophyid mites of Israel. Bulletin of the Research Council of Israel (Section B) 5: 61-69.
Hatzinikolis, E.N. 1973. A contribution to the study of Aceria oleae (Nalepa, 1900) (Acarina: Eriophyidae). Proceedings of the 3rd International Congress of Entomology, Junk, The Hague, pp. 221-224.