No abstract

An attempt was made to determine, mathematically, the point at which a significant reduction occours in the yield of mandarins at different levels of infestation by the red scale, Aonidiella aurantii (Maskell). Such point is commonly referred‐to as the economic threshold of damage. For this purpose, counts were taken during each of the main three annual peaks of this insect's infestation over two years (1968 and 1969). Twenty two trees provided the necessary data for the statistical analysis. The results indicated that the economic damage‐threshold lies around an average infestation level of 0.24 alive adult females per leaf occurring during June. The October and December infestation peaks played lesser roles in this respect. Zusammenfassung über die Schadensschwelle der Roten Schildlaus, Aonidiella aurantii (Mask.) auf Mandarinen‐Bäumen in ägypten Es wurde versucht, die Schadensschwelle, bei welcher eine wesentliche Verminderung der Mandarinen‐Ernte durch Befall von A. aurantii eintritt, festzulegen. Zu diesem Zweck wurden 1968 und 1969 Zählungen während der 3jährigen Befallsspitzen bei 22 Mandarinenbäumen durchgeführt. Die Ergebnisse zeigten, daß die Schadensschwelle bei 0,24 lebenden Weibchen pro Blatt im Juni gegeben ist. Die Oktober‐ und Dezember‐Zählungen lieferten keine brauchbaren Werte.

The kairomonal effect of hexane extract of the larvae of Ostrinia nubilalis and Sesamia cretica on Bracon breuicornis adults was evaluated through olfactometer tests. The parasitoid males showed no definite response to any kairomone. Females were attracted to the kairomone of S. cretica more than to that of 0. nubilalis. Highly significant effect of the sex pheromone of 0. nubilalis on the females of B. breuicornis was recorded. Kairomones (hexane extracts of larvae) varied in their effect on the released B. brevicornis parasitoids. The kairomone of S. cretica increased the parasitisation from 7.74 to 17.05%, while the kairomones of 0. nubilalis and of Spodoptera littoralis were not significantly effective. Spraying molasses solution (10%) on the corn stalks before releasing B. brevicornis parasitoids increased the rate of parasitism from 7.74 to 28.21%. The concentration of 5% gave insignificant increase in the parasitisation rate.

Aphytis lepidosaphes proved to be the most common and efficient parasitoid on Lepidosaphes beckii. % parasitism was estimated by dissecting hosts collected from the field, and also by rearing the parasitoids to emerge from the hosts, using a trapping box. Results obtained by dissecting the scale hosts, directly, supported and proved to be parallel to those obtained by rearing the adult parasitoids from the hosts. Two periods of high activity of these parasitoids were found to occur throughout the year of study, the first from middle of August until the middle of December, whereas the second period lasted between the middle of March until the middle of June. The rate of parasitism reaches 58.5% in April, 66.5% in June and a peak of 84% in October. Thus, it could be concluded that parasitism plays a major role in controlling populations of the purple scale in Menofia Provience, Egypt. Zusammenfassung Zur Rolle der Parasitoiden bei der Regulierung der Schildlaus Lepidosaphes beckii (New.) in Ägypten Aphytis lepidosaphes erwies sich als häufigster und wirksamster Parasitoid von Lepidosaphes beckii. Die Parasitierungsquote wurde sowohl mittels Sezierung der gesammelten als auch mittels Aufzucht der in Fallen gefangenen Wirte festgestellt. Die Sezierungsergebnisse stimmten mit jenen der Aufzuchten überein. Es zeigten sich zwei Perioden hoher Aktivität der Parasitoiden im Jahresverlauf: Mitte August bis Mitte Dezember sowie Mitte März bis Mitte Juni. Die Parasitie‐rungsrate erreichte im April 58.5%, im Juni 66.5% und eine Spitze von 84% im Oktober. Aus den Untersuchungen geht hervor, daß der Parasitismus durch Schlupfwespen bei der Schildlaus L. beckii im Untersuchungsgebiet eine große Rolle spielt.

The number of progeny of Bracon brevicornis was greatly affected by the number of deposited eggs of Bracon females per host larva. The increase in the egg clutch size from 5 to 25 eggs/larva increases the progeny production. On the other hand, the increase in the egg clutch size of the parasitoid decreases the body size of produced female progeny. The ratios of parasitoid females‐host larvae and time of parasitization which leads to optimal parasitism were studied. The most appropriate crowding level of B. brevicornis females to O. nubilalis full grown larvae was studied. The sex ratio of produced parasitoid progeny was significantly affected by changing the sex ratio of parent parasitoids, while there was no effect on the number of deposited eggs per host.