Abstract
The behavior of Aphidius sp. and B. brassicae populations on cabbage cultivars Kobayashi, Roxo, Chato de Quintal, Coracao de Boi and Matsukase were studied in natural field conditions. Monthly samples were collected from August to December 1995. Leaf discs measuring 6.1cm2 were taken from sites showing higher aphid concentration from each most infected leaf. The percentage of parasitized insects was determined by the number of mummified aphids among the total on each leaf disc. Although Roxo and Kobayashi cultivars showed the highest aphid infestation, they were the least parasitized by Aphidius sp. , with 23.3% and 25% parasitism, respectively. Coracao de Boi and Chato de Quintal cultivars were the least infested by the aphid, but showed the highest parasitoid populations, as 51.7% and 67.5% respectively. The lower aphid and parasitoid populations were observed on Matsukase cultivar. Chato de Quintal, Coracao de Boi and Matsukase cultivars presented a high aphid and parasitoid populations in August, which decrease in September and December and rose in October and November. On Kobayashi and Roxo cultivars both populations increased until November and decreased in December. Generally, higher B. brassicae and Aphidius sp. populations were found during August, October and November. The average parasitism in all cultivars was 36%. The highest parasitism level was 55.8, observed in August. KEY-WORDS: Aphidius ; Brevicoryne brassicae ; comportamento; parasitism; behavior.
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