Multiple infestations induce direct defense of maize to Tetranychus urticae (Acari: Tetranychidae)
Abstract
Plants present constitutive or induced defense mechanisms against herbivory. In addition, studies show that there are interactions between these different defense mechanisms when multiple species infestations occur. This study investigated the interaction between maize defensive mechanisms to control two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae) under single and double species infestations with this spider mite and fall armyworm, Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae). The experiment was carried out in a greenhouse with the following treatments: uninfested Bt (Bacillus thuringiensis Berliner; Bacillaceae) and conventional maize, single infestation with spider mite on Bt and conventional maize, and both maize types with infestations of spider mite and fall armyworm. Two d after infestation, all treatments were re-infested with spider mite. The number of eggs, immatures, and adult females (alive and dead) were recorded for re-infested populations. In addition, a leaf sample was taken from all maize plants for spectrometric analysis. There was no significant difference of biological variables of spider mite between Bt and conventional plants, as well as the ones from pre-infested and non-infested plants. The same chemical pattern of ions was observed on plants in these 4 groups. In the conventional pre-infested plants with spider mite and fall armyworm, the population of re-infested mite showed reduced survival and fertility. Defensive compounds detected were HMBOAGlc, Linoleoyl-GPI, and kaempferol rutinose. It was suggested that there is direct induced defense against spider mite in conventional maize in multiple infestations with spider mite and fall armyworm.
Resumo
As plantas podem apresentar mecanismos de defesa constitutivos ou induzidos contra herbivoria. Estudos mostram que há interações entre esses diferentes mecanismos de defesa quando ocorrem infestações múltiplas. Este estudo investigou a interação entre os mecanismos de defesa do milho contra o ácaro-rajado Tetranychus urticae Koch (Acari: Tetranychidae) sob infestações de uma e várias espécies com este ácaro e lagarta-do-cartucho, Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae). O experimento foi conduzido em casa de vegetação, com os seguintes tratamentos: milho Bt não infestado e milho convencional, infestação única com ácaro em milho Bt e convencional e milho com infestações de espécies de ácaro-rajado e lagarta-do-cartucho. Dois dias após a infestação, todos os tratamentos foram infestados com ácaros. O número de ovos, indivíduos jovens e fêmeas adultas (vivas e mortas) foram registrados para populações reinfestadas. Além disso, foi retirada uma amostra de folhas de milho de todas as plantas para análise espectrométrica. Não houve diferença significativa de variáveis biológicas entre ácaros, e plantas Bt e convencionais, bem como de plantas pré-infestadas e não infestadas. Nas plantas convencionais pré-infestadas, com ácaro-rajado e a lagarta-do-cartucho, a população de ácaros reinfestada mostrou redução na sobrevivência e fertilidade. Os compostos de defesa observados foram HMBOA-Glc, Linoleoyl-GPI e kaempferol rutinose. Foi sugerido que há defesa induzida direta contra T. urticae em milho convencional em infestação múltipla com ácaro-rajado e lagarta-do-cartucho.
Key Words: plant resistance; plant defense mechanisms; constitutive defense; Spodoptera frugiperda
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