Efeito do estresse hídrico na qualidade nutricional de Eucalyptus camaldulensis DEHN (MYRTACEAE) e no ataque de Glycaspis brimblecombei MOORE (HEMIPTERA: PSYLLIDAE

Abstract

This study aimed to test the plant stress hypothesis (PSH) in a system consisting of the herbivorous Glycaspis brimblecombei Moore (Hemiptera: Psyllidae) and the plant Eucalyptus camaldulensis Dehn (Myrtaceae) in northern Minas Gerais, Brazil. From PSH, three predictions were derived: 1) Plants in xeric habitats are under greater water stress than plants in mesic habitats; 2) Plant water stress have better nutritional quality for herbivores that plants not stressed; 3) The density of eggs and nymphs of G. brimblecombei is greater water stress in plants. Furthermore, it was assessed whether the rates of parasitism of nymphs G. brimblecombei by parasitoids and fungi vary depending on the nutritional quality of individuals of E. camaldulensis. The study was conducted from February to December 2008, in 60 individuals E. camaldulensis (30 in xeric habitat and 30 in mesic habitat) and the statistical analysis conducted in the month of August. This was evaluated the percentage of soil water and water relative content (WRC) to verify the water stress in plants. It was subsequently evaluated the nutritional quality of individuals of E. camaldulensis through measures WRC and chlorophyll content of leaves. The attack of G. brimblecombei was determined considering the average density of eggs and nymphs per cm2 of leaf. The individuals of E. camaldulensis with lower percentages of water in the soil showed lower WRC. In this system the chlorophyll content of plants was significantly influenced by the WRC of the leaves. The density of eggs and nymphs of G. brimblecombei was higher in individuals with lower WRC and lower chlorophyll content. There was a significant relationship between the average density of eggs and nymphs of G. brimblecombei and all variables related to water stress in plants, as predicted by the PSH. The rate of parasitism of nymphs by P. bliteus and fungi was also higher water stress in plants, indicating a possible dependence on the density of nymphs of G. brimblecombei. The parasitism by fungi was also related with the chlorophyll content. Our results corroborate the PSH, indicating that host xiv plant nutritional quality may be the most important regulatory factor in determining herbivore attack the rates and parasitism in this system.