ABSTRACT
Supplementation with Silicon (Si) is well-known for increasing resistance of grasses to insect herbivores. Although the exact underlying mechanism remains unknown, Si accumulation interacts with the jasmonic acid-signalling pathway, which modulates herbivore-induced plant defences. We examined whether Si supplementation alters direct and induced indirect defences in maize plants in ways that deter the initial infestation by the fall armyworm Spodoptera frugiperda (JE Smith). We assessed the herbivore's oviposition preference, neonate and third-instar larval performance as well as the recruitment of a predator of young larvae, the flower bug Orius insidiosus (Say), by herbivore-induced plant volatiles (HIPVs). In choice tests, S. frugiperda deposited about two times more eggs on -Si than on +Si maize. The mortality of neonate S. frugiperda larvae was about sixfold higher in +Si compared to -Si plants, even though they consumed similar leaf area on both treatments. Although there were no mortality differences, Si supplementation also impacted third-instar larvae that gained about twofold less weight than those fed on -Si maize. In olfactometer assays, O. insidiosus was not attracted to volatiles of uninfested maize plants with or without Si supplementation, but it was attracted to those emitted by fall armyworm-infested plants, irrespective of whether plants received Si supplementation. However, when the flower bug could choose between the volatiles released from -Si and +Si fall armyworm-infested plants, it preferentially oriented to +Si fall armyworm-infested plant. Our results show that Si supplementation in maize may deter fall armyworm colonization because of greater direct defences and attractiveness of HIPVs to the flower bug.
Subject(s)
Herbivory , Silicon , Spodoptera , Zea mays , Animals , Dietary Supplements , LarvaABSTRACT
ABSTRACT The objective of this research was to determine the survival, reproduction and predaceous capacity of Orius insidiosus on cotton aphid Aphis gossypii. Cotton plants of Antares, CNPA7H and Acala 90 cultivars (respectively, without tricome, medium tricome density and high tricome density) were individualized and infested with 15 third/fourth instar nymphs ofA.gossypii, and then first-instar nymphs ofO. insidiosus were released on the plants. The evaluations were made daily, quantifying survival and nymphal development; the number of cotton aphids A. gossypii per day and total; the number of eggs and the population of the predator (number of insects by female); and the conversion efficiency ofA. gossypii predaceous. The nymphal development did not differ according to the cotton cultivars. The Antares cultivar favored a higher daily predation rate for the 1st, 2nd and 4th instars and adults of O. insidiosus. The number of eggs and nymphs was smaller when. O. insidiosus females were confined on the Acala 90 cultivar. According to the predation rate of O. insidiosus, the efficiency of alimentary conversion was determined for the Antares, CNPA7H and Acala 90 cultivars, being respectively, 4.28, 3.00 and 2.75 cotton aphid predation for each egg of the predator.
RESUMO Estudou-se a sobrevivência, a reprodução e a capacidade predatória de Orius insidiosus (Say) sobre o pulgão do algodoeiroAphis gossypii Glover. Plantas de algodoeiro das cultivares Antares, CNPA7H e Acala 90 (respectivamente, glabra, de média pilosidade e pilosa) foram individualizadas e infestadas com quinze ninfas de terceiro/quarto estádio de A. gossypii e, em seguida, liberadas ninfas do predadorO. insidiosus a partir do primeiro estádio ninfal.As avaliações foram realizadas diariamente, quantificando-se sobrevivência e desenvolvimento ninfal; o número de pulgões predados por dia e total; o número de ovos e a população do predador (total de indivíduos gerados pelas fêmeas) e determinada a eficiência de conversão alimentar através da taxa de predação de O. insidiosus. O desenvolvimento ninfal não foi afetado pelo cultivar de algodoeiro. O cultivar Antares favoreceu maior taxa diária de predação para os dois primeiros e quarto estádio ninfal e fase adulta de O. insidiosus. O número de ovos e de ninfas foi menor quando as fêmeas de O. insidiosus foram confinadas no cultivar Acala 90. A eficiência de conversão alimentar nos cultivares Antares, CNPA7H e Acala 90 foram, respectivamente, 4,28; 3,00 e 2,75 pulgões predados para cada ovo gerado pelo predador.