Silício no crescimento populacional de Melanaphis sorghi (Theobald) (Hemiptera: Aphididae) e na biologia de Aphidius platensis (Brèthes) (Hymenoptera: Braconidae: Aphidiinae)

Abstract

Silicon (Si) induced resistance is an important tool for pest management, by reducing the growth rate of phytophagous populations. However, the same effects of Si can be effective at higher trophic levels, such as in parasitoids, negatively interfering with the biological control of pests. Thus, the objectives of this work were to evaluate the effect of soil application of Si in the induction of resistance by antibiosis in sorghum plants on the population growth of Melanaphis sorghi (Theobald) and on the biology of the parasitoid Aphidius platensis (Bréthes). Rhopalosiphum maidis (Fitch) was used in the experiments because it is known to be a species that has reduced populations in sorghum plants fertilized with Si and because it is a good host for A. platensis. The experiments were conducted in the greenhouse with the two aphid species on forage sorghum plants of the Volumax hybrid, protected by 3 L PET bottle cages, covered with organza. A single dose of 800 kg ha-1 of soluble Si or dolomitic limestone was applied to the soil as a control without Si. To evaluate the population growth of M. sorghi and R. maidis each sorghum plant was infested with four fourth-stage nymphs of each species, and the number of aphids was evaluated 17 days after infestation. To evaluate the effect of Si on parasitoid biology each plant was infested with thirty third instar nymphs of one of the aphid species and released a female parasitoid. The population growth of M. sorghi was 48.8% higher than that of R. maidis in plants without Si, but in plants with Si there was no difference in the population size of the two aphid species. The application of Si reduced the population of M. sorghi by 50.7% and R. maidis by 51.1%. The addition of Si to the soil reduced the number of eggs per female and the size of the tibiae of A. platensis, respectively, by 28.37% and 12.68%, when the parasitoid developed on M. sorghi, and by 46.21% and 15.95%, when it developed on R. maidis. Si induced antibiosis resistance in sorghum plants by reducing the population of both aphid species and negatively interfering with parasitoid biology, but the negative effect of Si was greater on M. sorghi population growth than on the reproductive potential of A. platensis, indicating compatibility between Si induced resistance and biological control.