Fluctuation of populations of certain predators on flowers of cotton in Egypt

Abstract

The Egyptian cotton is one of the most important crops in Egypt. This resulted in an attention towards the predators belonging to orders Diptera and Neuroptera which play an important role in biological control of insects attacking cotton. The experiment was conducted in Quesna (Menofia Province) at reclaimed lands. In this experiment a study on fluctuations of populations of predators belonging to family Syrphidae and Chrysopidae occuring daily during the flowering period of cotton (from June until August), was conducted, in order to know the time of occurrence of these predators in large numbers on cotton flowers in order to avoid the harmful lethal effect of the used insecticides sprayed for control of cotton insects on these predators. From family Syrphidae, Sphaerophoria flavicauda Zett. and Eristalis sp. were recorded while of Chrysopidae, Chrysopa vulgaris Schm. was registered. The activity and abundance of these three species was studied in relation to weather factors as temperature and relative humidity. The periodicity and abundance was investigated in relation to times and periods of the day from 9 am to 5 pm. Also the abundance and frequency of the population of these insects was correlated to the period of flowering. The maximum activity of Eristalis sp. was early in the day while that for Sphaerophoria flavicauda occurred between 9 to 11 am and for Chrysopa from 9 am to 1 pm. Spraying against harmful cotton insects should be conducted before 9 am or after 5 pm. Zusammenfassung Populationsbewegungen einiger räuberischer Insekten auf Baumwollblüten in Ägypten Bei Quesna (Prov. Menofia) wurden 2 Arten Syrphiden und 1 Neuropteren‐Art hinsichtlich ihrer Populationsbewegung während einer Blüteperiode der Baumwolle (Juni bis August) untersucht. Ziel war es, die Zeit des maximalen Auftretens der Predatoren kennenzulernen, um sie bei den chemischen Bekämpfungsaktionen berücksichtigen zu können. Die Erscheinungszeiten der Schwebfliegen Sphaerophoria flavicauda Zett. und Eristalis sp. sowie des Netzflüglers Chrysopa vulgaris Schm. wurden in Beziehung zur Jahreszeit, Tageszeit und Blühperiode der Baumwolle registriert. Ihre maximale Aktivität entfalteten: Eristalis früh morgens, Sphaerophoria gegen Mittag und Chrysopa von früh bis nachmittags. Demgemäß sollten chemische Bekämpfungsmaßnahmen gegen Baumwollschädlinge zur Schonung der Predatoren vor 9 Uhr früh, bzw. nach 5 Uhr nachmittags durchgeführt werden.