Ecologia de Bruchidae na predação pré-dispersão de sementes de Albizzia lebbeck (L.) Benth. em arborização urbana

Abstract

The pre-dispersal seed predation by insects has great importance for seed production. The germination is affected due to damage caused by insects in larval development inside the seed. If this damage occurs in the cotyledons, it mainly affects the performance and survival of seedlings, otherwise, if it occurs directly in the embryonic axis, the seed mortality is unavoidable. There are few studies about species of Albizzia lebbeck (L.) Benth. in urban trees, especially when it comes to ecology and behaviour of insect predators of their seeds. In this context, this study aims to evaluate and quantify the damage in seeds, the occurrence and population fluctuation of insects on pods and seeds with emphasis mainly on the stage of pods ripening at different levels of human disturbance and air pollution caused by motor vehicles. The samples of pods were carried out on mother trees of A. lebbeck located on the campus of UFRRJ (Seropédica), km 32 of old road Rio-São Paulo (Nova Iguaçu) and km 47 (Seropédica), Rio de Janeiro and the pods analyzed at the Laboratory of Forest Entomology, DPF, IF, UFRRJ. It was observed low levels of insect infestation in prematurely ripening pods which should be linked to the low number of specimen in oviposition on the first pods. However, for late ripening pods, especially those collected at sites with high levels of human disturbance and influence of air pollution, it was observed an increase in insect infestation. The same was observed in the final processing of seeds in pods of quarantine. In general, 9% of the seeds presented intact (healthy), 31% aborted and 60% damaged. 83% of damaged seeds were from the mother trees located in central reservation of Highway (Km 32), 43% of its margin (km 47) and 42% in the conservation area of Universidade Federal Rural do Rio de Janeiro Botanical Garden. Percentage of 92.68 was found of insect seed predators distributed in the following species: Bruchidius sp. (57.39%), Merobruchus paquetae (33.98%), Stator limbatus (0.27%), an unidentified species of Lepidoptera (1.04%) and the rest of emerging insects (7.32%) belonging to Order Hymenoptera. Specimen of Bruchidius sp. presented emergency period with well-defined peak in mid-September (approximately 135 days after observation of the first ovipositions in the field) and species M. paquetae average occurrences rather homogeneous, with low numbers of specimen and few variations throughout the period of emergency quarantine on pods. The largest number of bruchids was recorded in an area of high human disturbance, being the species Bruchidius sp. predominant in pods of trees placed in central reservation of the highway and the species M. paquetae on mother trees located beside of the highway. The number of bruchids in seeds of A. lebbeck was reduced with decreasing levels of human disturbance in urban trees which resulted in a lower percentage of damaged seeds and higher number of healthy seeds