Επιλογη Του Φυτου-Ξενιστη Απο Το Εντομο Eurytoma Amygdali Enderlein (Hymenoptera: Eurytomidae)

Abstract

HOST-PLANT SELECTION IN THE INSECT EURYTOMA AMYGDALI ENDELREIN (HYMENOPTERA: EURYTOMIDAE)This dissertation deals with the behaviour of the almond seed wasp, Eurytoma amygdali Enderlein (Hymenoptera: Eurytomidae), and especially the process of host selection and certain factors influencing it.Field observations on the distribution and location of adult activity on almond trees of the Retsou variety showed that during the early morning and late afternoon hours, females mostiy rested or walked on fruit or on the upper surface of leaves.Oviposition began at about 10:00 in the morning and continued until dark. Only a limited number of males was observed walking or resting on fruit or leaves. Between 09:00 and 13:00 a high number of males was observed in flight, close to the tree canopies. Only a few adults of both sexes fed on fruit, leaves, pedicels, or stems.Laboratory experiments with an olfactometer showed that females are attracted to odours from almond flowers and unripe fruit and to a lesser extent to odours from leaves, whereas males are not. Using a bioassay it was found that extracts of almond flowers, leaves and fruit with ethanol, methanol and acetone, stimulate aggregation and oviposition of females and also attract them.Ovipositional behaviour exhibited by individual females in the presence of unripe almonds in a laboratory cage can be distinguished into the following phases: search for a fruit, visit of a fruit and location of an oviposition site, ovipositor insertion, oviposition, withdrawal of the ovipositor, deposition of a host-marking pheromone by dragging the tip of the abdomen on the fruit surface, and grooming of various body surfaces. The percent of failing oviposition attempts and the duration of oviposition ix were positively correlated with the thickness of the pericarp and the hardness of the endocarp.In fruits of the soft-shell Retsou variety, both in the laboratory and in the field, eggs were uniformly distributed when the mean number of eggs per almond was 2.5 or lower, and randomly when it was higher. The main factor contributing to this uniformity is a host-marking pheromone deposited by females. Laboratory tests revealed that this pheromone enables females to discriminate between the infested and uninfested fruit and to select the latter for oviposition. The pheromone can be perceived by the females on direct contact and, when at high concentrations, also at a short distance. It was present inside the abdomen, thorax and faeces of females but not of males, and, although water soluble, could not be entirely removed by water-rinsing heavily infested almonds. Its activity persisted for at least eight days under laboratory conditions. j Examination of infested fruit, that were collected from the field throughout the period of oviposition and larval development, showed that even when more than one egg is deposited in each fruit only one larva attains maturity. This elimination of competing larvae within the same fruit was found to be through cannibalism.The practical value of certain resul...