CEPAVE   05420
CENTRO DE ESTUDIOS PARASITOLOGICOS Y DE VECTORES
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
71. Dendrochronological methods applied to study ambrosia beetle (Megaplatypus mutatus (Chapuis)) population dynamics in poplar (Populus spp.) plantations of Argentina
Autor/es:
ACHINELLI, F.; DELGADO, M.R.; JOUANNY, M.; LILJESTHROM, G.
Lugar:
Beijing, China
Reunión:
Congreso; International Poplar Commission, 23rd Session; 2008
Resumen:
Ambrosia beetle (Megaplatypus mutatus (Chapuis)) is the most important insect pest in poplar plantations (Populus spp.) in Argentina, producing losses in both wood yield and quality. Despite the various research projects being carried out on the biology of this beetle, some aspects of its population dynamics are still unclear. Field work needed to monitor the density and dynamics of the insect is time- and labour-consuming, and the results we have obtained to date showed marked fluctuations from year to year in relative density fro unknown reasons.             In order to reconstruct in time the previous density of this beetle in a poplar plantation, we applied dendrochronological techniques to 208 trees from 16 permanent sample plots (PSP), located in a commercial poplar plantation al Alberti, Buenos Aires, Argentina (34° 50´ S Lat;  60° 30´ W Long; 55 m elevation). Dendrochronological techniques may be applied in this situation as these poplar clones produce wood rings which can be dated, and also stand ages are recorded in each case. This 1,945 ha plantation can be considered an isolated forest situation because it is completely surrounded by agricultural crops such as cereals and soybeans. The PSPs were representative of intermediate (9-10 years old; eight PSPs) and mature (11-12 years old; eight PSPs) stands.             Selected trees were felled to obtain four logs from each main stem: a basal logs 2.6 m long, and second, third and fourth logs 2.2 m long each. This permitted study of the first 9.2 m of trunk of each tree. Logs were then split lengthwise with an axe  into two of approximately equal parts to expose the interior of the wood. The pieces were carefully examined in the field to mark all beetle galleries, and the discs of wood were obtained with a chainsaw for each marked gallery. Wood discs were processed in the laboratory to determine: number and dating of tree rings, age of section, type of gallery (imaginal gallery made by male individuals; larval galleries, a nest that reached reproductive state) and years of formation of the gallery (season when the attack was produced).             First attacks were very early in some cases, when stands were three years old, but in other plots initial attacks occurred one to four years latter. Relative density of the beetle, expressed as the cumulated number of imaginal galleries · ha-1 during the rotation varied between 3,710 and 8,584 galleries · ha-1, but was not related to the age of the stand. The presence of the beetle in all mature PSPs were characterized by density peaks al 9-10 years old, followed by pronounced declines at the end of the rotation. Most importantly, this pattern determined that plantations with the highest average diameter at breast height (DBH) had minimal ambrosia beetle activity prior to harvest. This behavior could be related to possible detrimental influence of natural enemies on the population growth rate of the beetle.