Contribuição para o controle biológico da broca da cana de açúcar

Abstract

During the period of 5 months and 20 days, we obtained 4 generations of Metagonistylum immense Towns, with a total number of 662 adults individuals. The complete life cycle, varies from 31 days to 51 days, with an average of 38 days at 18,9 C. The percentages of natural parasitism in sugar cane and corn fields, was 23,1% and 37,3% respectively. - 526 filies were released and, a parasitism of 48,3% was found in sugar cane against a parasitism of 61,1% in corn. During the period of 12 months, 10 generations of Lixophaga diatraeae Towns have been reared at the laboratory with a total number of 915 adultes individuals. The complete life cycle, during the period from September through April was found to be from to 30 days to 39 days, with an average of 32,5 days at 21,4°C. During the period from May through August the complete life cycle was found to be from 33 days to 43 days with an average of 36 days at 16,9°C. A total of 262 adults individuals of Lixophaga, was released. From this total, 139 individuals were scattered in a corn field (plot A) and, the rest of the individuals was scattered in a sugar cane field (plot B and C). We recuperated 76 alived pupae and 38 empty ones. The total percentage of parasitism verified was 28,7%. One year after first releasing (1951, we recuperated several pupae, which shows that Lixophaga has be come established in this region. During the period from May through August, the larval capacity is reduced, due to low temperatures. During this period, the individual adults have to be maintained at a temperature from 22°C to 25°C, in order not to paralyze reproduction. During the gestation period Lixophaga is more resistant than the other two native species. The potential of reproductivity of Metagonistylum and of Paratheresia is larger than that of Lixophaga. For rearing and maintaining of the parasitized borer, the apical part of a shoot of sugar cane was kept in a container with water, since the whole shoot would remain alive only during a short period. The average life cycle of Lixophaga is of 32,5 days, thus being shorter than the one of Metagonistylum (38 days) and Paratheresia (47 days). The sugar cane parasites suffer in nature a hyperparasitism of about 5%, however this takes place in the pre-pupae fase, after the destruction of the sugar cane borer. By rearing the parasites in large scale and, making periodic distributions in sugar cane fields, the infestation of sugar cane borer is greatly reduced.