Abstract
Studies were conducted in cucumber fields to evaluate the standard and reduced dosage rates of 5 insecticides for control the cotton whiteflyBemisia tabaci (Genn.) and melon aphidAphis gossypii Glov. and effect of insecticide application on associated parasites and predators. Eggs of whitefly appeared to be less susceptibility to all treatments (max. 66% reduction) than larval and pupal stages. Populations of larval and pupal stages of whitefly were significantly reduced in all treated plots. For example (larvae on day 10 after treatment with ethiofencarb, diafenthiuron, and chlorpyrifos methyl 67, 50, and 68% pupae 68, 69, and 75%). Two aphelinid parasitoids,Eretmocerus mundus Mercet andProspaltella lutea Masi, were the most primary important parasitoids of the whitefly pupae in all test plots. Percent parasitism, in most treated plots, were slightly affected as a result of insecticide application. However, all tested insecticides and dosage rates caused severe suppression of emergence of adult parasitoids. Moreover, longevity of adult parasitoids were highly decreased.
Populations of the melon aphid were extremely reduced, especially by ethiofencarb and diafenthiuron. Populations of predator species (Chrysopa carnea Steph.,Coccinella undecimpunctata Reiche andSyrphus spp.) were reduced in all treated plots. However, ethiofencarb applied at rates as low as 208.4g a.i./1001 provided equally effective aphid control and conserved numbers of insect predators in the treated plots. Also, the prothiofos and chlorpyrifos methyl applications at rates as low as 166.7 g a.i./1001 kept aphid numbers below than those in control and caused a smaller reduction in the combined populations of insect predators.
Zusammenfassung
Untersuchungen an Gurkenpflanzen sollten die Wirkungen von 5 gebräuchlichen Insektiziden in normaler und reduzierter Dosis auf die MottenschildlausBemisia tabaci (Genn.) und die BlattlausAphis gossypii Glov. sowie auf deren wichtigste parasitische und episitische Feinde klären. Die Eier vonB. tabaci erwiesen sich als weniger empfindlich (max. 66% Reduktion) als die Larven und Puppen. So waren z. B. unter dem Einfluß von Äthiofencarb, Diafenthiuron und Chlorpyrifosmethyl 10 Tage nach Applikation die Larven um 67,50 und 68% sowie die Puppen um 68,69 und 75% gegenüber Kontrolle reduziert. Zwei parasitische Feinde der Puppen, die AphelinidenEretmocerus mundus Merc. undProspaltellus lutea Masi, wurden durch die Insektizide in ihrem Parasitierungs-Prozent kaum, jedoch in ihrer Schlüpfquote und Lebensdauer erheblich beeinträchtigt. Die Populationen der BlattlausAphis gossypii wurden in allen Fällen, besonders aber durch Äthiofencarb und Diafenthiuron reduziert. Die Dichte der räuberischen Blattlausfeinde (Chrysopa carnea Steph.,Coccinella undecimpunctata Reiche undSyrphus spp.) sank nach allen insektiziden Behandlungen. Doch blieb nach Äthifencarb-Applikation, bei guter Wirkung gegen die Blattläuse, ein erheblicher Teil der Raubinsekten am Leben. Auch bei den Behandlungen mitProthiofos undChlorpyrifosmethyl in Dosen von 166,7 g/1001, durch welche die Blattläuse erheblich reduziert wurden, blieben wesentliche Teile der Raubinsekten-Populationen verschont.
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El-Sayed, A.EG.M., El-Ghar, G.E.S.A. The influence of normal and low-rate application of insecticides on populations of the cotton whitefly and melon aphid and associated parasites and predators on cucumber. Anz. Schadlingskde., Pflanzenschutz, Umweltschutz 65, 54–57 (1992). https://doi.org/10.1007/BF01905830
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DOI: https://doi.org/10.1007/BF01905830