Biological aspects of Oncideres saga (Dalman) (Coleoptera: Cerambycidae) and effects of its damages on Acacia mangium Willd / Aspectos biológicos de Oncideres saga (Dalman) (Coleoptera: Cerambycidae) e efeitos de seus danos em Acacia mangium Willd
DATA DE PUBLICAÇÃO
The present study was performed to obtain information on the biology of Oncideres saga (Dalman, 1823) and to evaluate the effects of its girdling of branches and trunks of Acacia mangium Willd. trees in terms of increase in diameter and height . The study on the biology of this insect pest was performed in a plantation of A. mangium located in Coimbra- MG, between September/2006-November/2007. Damage was assessed by collecting fallen branches and adults of this insect. The laboratory activities were performed in the Casa dos Cupins/UFV, in Viçosa-MG. The eggs of O. saga were of white coloration, of elongated shape, with length being approximately three times greater than the width average length of 3,540,03 mm and width 1,050,02 mm. The incubation period of eggs varied from 8 - 14 days and the viability was 52,89%. First instar larvae are whitish and semi- transparent, they have no legs, they have a prognathous head that is retracted in the prothorax, the antennae are short, and the mandibles are robust and short. The larvae average length was 2,920,04 mm, while the average widths of the body and of the head capsule were 1,020.01 mm and 0,620,01 mm, respectively. Sex of adults can be distinguished by total length of the antenna, with emphasis on the eleventh antennal segments. The occurrence period of O. saga was from January-April 2007 and the period of adult activity was 4 months. Adults of O. saga fed on the bark, on the epidermis of the leaf petiole (leafstalk) and also on the phyllode. Oviposition by O. saga in the branches of A. mangium was always close to the incision, with the egg being deposited between the bark and the xylem. There was only one egg per incision, rarely two and the average number of incisions for a girded branch was 80,3316,81; the lower third had the largest amount of incisions (64,73%). It was found that 77,78% (n=9) of the girdle were made in the shaft. The average diameter of the girded branches was 6,680,70 cm and the average length of these branches was 3,450,16 m. With only one girdle, O. saga caused an average leaf loss of 135.069,424,354.4 cm2, which corresponds to a loss of 14,79% of foliar area of the tree. This beetle can therefore be considered an important defoliator of forests. The presence of one Scolytidae species was verified in branches of A. mangium girdled by O. saga, and four cerambycid species also emerged from these branches, which were identified as Engyum quadrinotatum Thomsom, 1864; Eburodacrys sexmaculata (Olivier, 1790); Achryson surinamum (Linnaeus, 1767) and Neoclytus pusillus (Laporte &Gory, 1838). Another experiment was carried out in May 2007 in order to evaluate the effect of sawing the main shoot of A. mangium. Blocks were randomized, and portions were subdivided according to ages of trees (from 40 - 46 months). Fifty-four trees were examined monthly in three blocks, in which three experimental treatments were applied, with six replicates for each one. The applied treatments consisted of "No damage" (T1= Control), "Artificial defoliation of the main shoot (T2) and "Artificial cut of the main shoot (T3). I also measured for each tree the total height (H) and the diameters with bark at 1,30 m (Breast diameter) and 20 cm (Base diameter) from the ground. It was concluded that the artificial cut of the main shoot (equivalent to girdling by O. saga) affected growth in diameter and in height. The effect on height was equivalent to the effect due to defoliation of A. mangium by O. saga. Thus, we conclude that this beetle can be considered as a serious defoliator in this forest system.
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