Effects of neem preparations on Plutella xylostella L. and its natural enemies of the genus Trichogramma
1993
Klemm, U. (Giessen Univ. (Germany). Inst. fuer Phytopathologie und Angewandte Zoologie) | Schmutterer, H.
Plutella xylostella (Lepidoptera: Yponomeutidae) is one of the most important cabbage pests in tropical agriculture. To combat this pest, effects of neem seed kernel water extracts 25 g of 30 g seed kernels/liter of water, on the pest and its natural enemies Trichogramma pretiosum ans Trichogramma principium (Hymenoptera: Trichogrammatidae) were studied by laboratory- and a field experiment in Taiwan. Surprisingly, treated cabbage plants were more attractive for egglaying by P. xylostella (1073.25 eggs/plant) than untreated plants (351.75 eggs/plant) in the laboratory as well as in the field (treated = 33.40 eggs/plant; untreated = 9.47 eggs/plant). In the field study, the number of larvae were significantly reduced by application of neem to 4.98 and 5.92 larvae/plant at the end of the experiment compared to the other treatments: 18.57 larvae/plant (control) and 25.17 larvae/plant (release of T. pretiosum). Development of P. xylostella pupae was generally low and about zero on neem-treated plots. Parasitization of the eggs of P. xylostella by T. principium was not affected by neem treatment (99.75 parasitized eggs/plant) compared to control (78 parasitized eggs/plant) in the laboratory, as well as in the field (Trichogramae pretiosum). Natural parasitism of T. chilonis was evident but low in the field. The effectivity of release of T. pretiosum on parasitism was high in all variants and replications and reached an average of 47.03% of P. xylostella eggs after two releases on neem-treated and untreated plots, respectively. Parasitism (%) was not sufficient because of a relatively low number of released parasitoids (50/square metres). There was a positive correlation (r = +0.62) of parasitization to high egg densities
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