The rate at which infested olives drop was related to the developmental stage of D. oleae and to natural fruit abscission. Partial life-tables concerning the survival of eggs and larvae were obtained from sleeve cages in which the olives had been infested over a short period of time. Fruit drop under these conditions was then compared with fruit drop of uninfested and infested olives in the field. Also, resistance values for olive detachment were measured.



Olives with exit holes dropped at a rate 2.5 and 3.3 times higher than those containing a larva, in the Koroneiki and Tsounati varieties respectively. Olives containing larvae were found less frequently among the dropped olives than on the tree because, from autumn onward, female D. oleae preferred to oviposit in the less ripe olives with their lower rate of natural drop. In fact, resistance to detachment of infested olives in comparison to equally ripe uninfested ones diminished slowly as the larvae matured; it decreased mainly after the larvae had left the olives. From summer up to harvest, olives containing dead larvae dropped at double the rate of uninfested ones.



Finally, the risk of freshly infested olives for dropping before harvest was tabulated for different values of physiological fruit drop and for each month. Because of high egg and larval mortalities, this level is low in the summer; it then increases to a maximum one month prior to harvest. It is concluded that most fruit loss in Crete is likely to occur in October. Furthermore, damage attributed to D. oleae often appears to be overestimated.



Zusammenfassung

Der von Dacus oleae (Gmel.) (Diptera, Tephritidae) verursachte Fruchtfall von Oliven



Der Fruchtfall von befallenen Oliven wird vom Entwicklungsstadium von D. oleae und von der Starke des physiologischen Fruchtfalls beeinfluβt. Fur Eier und Larven von D. oleae wurden deshalb an Hand von Kafigdaten partielle Lebenstafeln errechnet. Fruchtfall in diesen Kafigen wurde dann mit dem Fruchtfall von befallenen und gesunden Oliven im Feld verglichen. Ferner wurden Resistenzwerte fur die Loslosung einzelner Oliven gemessen.



Oliven der Koroneiki- und Tsounati-Varietat fielen 2,5- resp. 3,3mal haufiger, wenn sie Ausschlupflocher aufwiesen als wenn sie Maden enthielten. Oliven mit Fliegenlarven waren aber weniger zahlreich unter den gefallenen Oliven als auf dem Baum, weil die Fliegenweibchen vom Herbst an die weniger reifen Oliven mit ihrem geringeren Fruchtfall fur die Eiablage bevorzugten. Ein Vergleich der Resistenzwerte gleich reifer befallener und unbefallener Fruchte dagegen zeigte, daβ diese Werte mit dem Heranwachsen der Larven abnahmen. Die Abnahme war besonders deutlich, nachdem die Maden die Oliven verlassen hatten. Vom Sommer bis zur Ernte war der Fruchtfall von Oliven mit toten Larven etwa zweimal so stark wie derjenige unbefallener Fruchte.



Endlich wurde noch die Wahrscheinlichkeit dafur errechnet, daβ Oliven, welche zu verschiedenen Zeiten von D. oleae befallen worden waren, vor der Ernte zu Boden fallen. Dabei wurden den Berechnungen verschiedene Werte fur den physiologischen Fruchtfall zugrunde gelegt. Wegen der hohen Ei- und Larvensterblichkeit ist dieses Risiko fur vorzeitigen Fruchtfall im Sommer klein, nimmt dann aber bis zu einen Monat vor der Ernte zu. Es wird geschlossen, daβ der groβte Fruchtverlust in Kreta im Oktober erfolgt. Ferner scheint der Schaden, welcher D. oleae zugeschrieben wird, oft uberschatzt zu werden.

Olive fruit drop caused by Dacus oleae (Gmel.) (Dipt. Tephritidae)

Materials for the determination of economic thresholds for Dacus oleae (Gmel.) on oil olives in western Crete.

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Materials for the determination of economic thresholds for Dacus oleae (Gmel.) on oil olives in western Crete.