Dimorfismo sexual em Heilipodus naevulus (Mann.) (Col.: Curculionidae) e impacto do ataque no desenvolvimento inicial de clones de eucalipto.

Abstract

Adults of Heilipodus naevulus (Mannerheim, 1836) when they attack the pointers intensely, main and the lateral ones, of the eucalypt, they can cause the shoot proliferation, with consequent loss in the final production, mainly when the damage happens in the initial phase of planting. Due to its night habit, reduced size, grayish coloration and for sheltering in the litter area during the day, its detection is hindered, being its presence detected just because the presence of tumbled pointers. For the integrated management of insect-pest populations it is necessary to know basic aspects of its biology and behavior. Therefore, this work aimed to study the external morphologic characteristics that allow the sexual differentiation between males and females; knowing the species distribution across the planting areas, along the first year of eucalypt clones growth; and, knowing the effects of the damages caused on the growth of eucalypt clonais plantings. The work was carried out in the municipal district from Barão de Cocais, MG, from October/2008 to January/2009. Two evaluation plots were stratified in slope, hillside and top, being three parcels in each stratum, of 10 x 10 trees, with total of nine parcels per plot. The collections of insect adults happened during the night period, out of the evaluation areas. For the sexual differentiation the characteristic that was shown more reliable was the presence of the premucro of the medium leg with the thin tip in the females and round in the males. In order to calculate distribution, the aggregation indexes of the Variance/Mean Ratio were used, Morisita Index, Parameter k, Green’s Coefficient, Poisson Distribution and the Law of Taylor potency. In all the calculated indexes, along the period of presence detection of damaged pointers, these attacks presented a aggregated pattern of occurrence. That indicates that the species presents a aggregated pattern of distribution, even in low occurrence. For the evaluation of the effect of the attack it was collected the total height data of the tree and the diameter in the height of 20 cm of the ground (DA20). The evaluation period was from October/2008 to January/2009. The occurrence of H. naevulus in the planting areas was observed from october to march, coinciding with the rainy period. In the DA20 just the trees of the Hillside did not present significant difference on the growth (p = 0,01), in the other areas significant difference was observed, with the injuried trees presenting larger growth, which can be attributed to retention of the inferior branches that causes a thickening of the trhunk close to the ground. In the Ht significant difference was observed in the growth (p = 0,01) just in the trees of the slope, in the other areas there was not difference in the growth, with the injuried trees presenting greater initial growth. When it compares the growth between areas, it was observed that the development of DA20 (p = 0,01), of the no injuried trees, from the Slope and from the Top, they showed themselves similar, the other comparisons showed different amongst themselves. For Ht all of the comparisons between the areas showed significant difference (p = 0,01). The greates growth of DA20 observed in the injuried trees can be attributed to loss of apical dominance and to emission of lateral shoot, causing the lateral branches retention.