The Damage Threshold of the Red Scale, Aonidiella aurantii (Maskell) Infesting Mandarin Trees in Egypt

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.

Estimate the Annual Field Generations of Lepidosaphes tapleyi (Williams) Infesting Guava Trees and Predicting its Expected Peaks Using Thermal Units Accumulation under Luxor Governorate Condition, Egypt.

“…The simple regression value indicates the average rate of change in insect activity due to a one-unit change in accumulated heat units during the whole year. The equation of linear regression was calculated according to the following formula of Fisher (1950) and Hosny et al (1972):…”

Economic threshold and economic injury levels for the two spotted spider mite Tetranychus cucurbitacearum (Sayed) on soybean

“…The effect of the population density of the mite, T. cucurbitacearum on the yield of soybean could be obtained through a preliminary analysis. According to Hosny et al, (1972) and Hassan (1998) using the partial regression formula "C-multiplier" (Fisher 1963). Three independents were considered in the regression process (x1, x2 and x3).…”

Assessment the Damage on Sugar Beet Plants Caused by the Infestion with Beet Fly, Pegomyia mixta (Vill) in Sharkia Governorate

“…Data were subjected to statistical analysis of assessment damage threshold under field conditions according to (Hosny et al 1972, Salem and Zaki. 1985, Sherief.…”