Economic-injury levels and economic thresholds of Aphis craccivora Koch on faba bean in Egypt (Homoptera: Aphididae).

摘要

The economic injury levels of A. craccivora on faba beans [Vicia faba] cv. Giza 2 were evaluated during the 1994-96 growing seasons in the Beni-Suef Governorate, middle Egypt. Ten levels of A. craccivora infestation (5, 10, 20, 30, 50, 60, 70, 80, 90 and 100%) were maintained by Pirimor [pirimicarb] application at 0.75 g/litre whenever the given infestation level was reached or exceeded. The resulting seed yields from various infestation levels were significantly higher than that of the untreated control. Significant differences in yield were obtained between the different infestation levels. The overall mean increase in yield ranged from 0.081 t/feddan at 100% infestation to 1.308 t/feddan at 5%. The initial number of aphids which might cause detectable losses in seed yield was 23.6 aphids at 2.5% plant infestation. The economic injury level was 50.9 aphids per plant shoot and the economic threshold was 34.3 aphids per shoot. The implications of spraying insecticides at lower levels of aphid infestation are discussed. [1 feddan = 0.42 ha]