The greenbug Schizaphis graminum (Rond.) (Hemiptera: Aphididae) is one of the principal pests of Triticum aestivum L. and may be responsible for the injection of toxins, the transmission of viral infections and, ultimately, plant death. The aphid can be controlled by the use of selective insecticides or with the application of silicon. The objective of the present study was to investigate the influence of imidacloprid and silicon on the feeding behaviour of S. graminum on wheat plants. Aphids collected from and reared on sorghum plants were maintained in a growth room at 25 ± 2°C; 12 h photoperiod. Seeds of the wheat cultivar EMBRAPA 22 were planted in plastic pots containing a commercially available soil substrate and thinned out 8 days after sowing to leave two vigorously growing seedlings in each pot. Four treatments (each replicated 25 times) were applied: (i) seeds were treated with imidacloprid (36 g/100 kg) 1 day prior to sowing; (ii) silicon (50 ml of 1% silicic acid; equivalent to a dose of 1000 kg of silicon/ha) was applied directly to the substrate 10 days after plant emergence; (iii) the described treatments with imidacloprid and silicon were applied jointly; and (iv) neither seeds nor substrate were treated (untreated controls). Electrical penetration graph assays were performed 15, 30 and 45 days after plant emergence. The results showed that wheat seed treatment with imidacloprid and/or the application of silicon to the substrate reduced both the feeding time of S. graminum and the percentage of insects that fed on phloem sap. Moreover, this study provides further support that the action of silicon may not be restricted to physical resistance (constitutive or induced) but may also involve induced plant chemical defence.
First report on the parasitoid Trichospilus diatraeae of the genus in Eulophidae found in the field parasitizing pupae of the eucalyptus defoliating looper Melanolophia consimilaria. This opens new perspectives for the use of this parasitoid in biological control programs against caterpillars of forestry importance.
The greenbug Schizaphis graminum (Rond.) (Hemiptera: Aphididae) is one of the main pestinsects of wheat (Triticum aestivum, L.). Resistance inducing agents as silicon (Si) and acibenzolar-s-methyl (ASM) can provide some protection against insects and diseases. The effect of Si and/or ASM on the development and probing behaviour of S. graminum in wheat plants was evaluated. Wheat plants (cultivar Embrapa 22) were treated with Si (silicic acid at the rate of 1%) and acibenzolar-S-methyl (ASM) at the rate of 0.5%. The effects of these treatments on greenbugs were analyzed by development parameters, honeydew excretion and probing behavior monitored by Electrical Penetration Graphs (EPG). The development and honeydew experiments consisted of ten replications each and EPG experiment was replicated 25 times. The application of both resistance inducing agents reduced fecundity, prolonged the duration of pre-reproductive period, and decreased honeydew production. Induced resistance was localized mainly at phloem level and caused a strong reduction of phloem sap ingestion, but some effect of ASM at parenchyma/mesophyll level could not be discounted as far fewer aphids reached the sieve elements. Key words: S. graminum, EPG, ASM, silicon, induced resistance Agentes indutores de resistência na biologia e no comportamento alimentar do pulgão-verde em trigoRESUMO: O pulgão-verde Schizaphis graminum (Rond.) (Hemiptera: Aphididae) é um dos principais insetospraga da cultura do trigo (Triticum aestivum, L.). Agentes que induzem resistência como silício e acibenzolars-methyl (ASM) podem fornecer proteção às plantas contra insetos e doenças. Avaliou-se o efeito do silício e/ ou ASM no desenvolvimento e comportamento alimentar de S. graminum em plantas de trigo. Plantas de trigo cultivar Embrapa 22 foram tratadas com silício (ácido silícico a 1%) e acibenzolar-S-methyl (ASM) a 0.5%. Os parâmetros estudados foram biologia, excreção de honeydew e comportamento alimentar (de prova) monitorado por meio da técnica Electrical Penetration Graphs (EPG). Para o estudo de biologia e excreção de honeydew foram usadas dez repetições e 25 para EPG. A aplicação de agentes indutores de resistência reduziu o número de ninfas, prolongando a duração de período de pré-reprodutivo e o número de gotas de honeydew. O efeito de resistência foi localizado principalmente no floema, com redução de ingestão de seiva elaborada.
RESUMO Objetivou-se avaliar a toxicidade de alguns fungicidas aplicados em cultura de pepino (Cucumis sativus L.), em função das formas de exposição, por contato ou ingestão de presas contaminadas, para larvas de primeiro ínstar de Chrysoperla externa (Hagen) alimentadas com Aphis gossypii Glover (Hemiptera: Aphididae) e os efeitos sobre as fases subseqüentes de desenvolvimento do predador. Os experimentos foram conduzidos em condições controladas a 25 ± 2o C, 70 ± 10% UR e fotofase de 12 horas. O delineamento experimental foi inteiramente ao acaso, com quatro tratamentos e seis repetições, sendo cada parcela composta por quatro larvas. Os compostos utilizados e suas respectivas dosagens de aplicação em g i.a.L-1 foram: enxofre (Kumulus 800PM 1,6), mancozebe (Manzate 800PM 1,6) e oxicloreto de cobre (Recop 840PM 1,49). A testemunha foi composta por água destilada. No bioensaio de contato, larvas de primeiro ínstar de C. externa receberam os produtos via pulverização, por meio de torre de Potter e, em seguida, foram individualizadas em tubos de vidro, as quais foram alimentadas diariamente com ninfas de A. gossypii. No bioensaio via ingestão, as ninfas de A. gossypii tratadas via pulverização com os compostos foram oferecidas como alimento para larvas de primeiro estádio de C. externa. O efeito total dos fungicidas para C. externa foi estabelecido conforme as classes de toxicidade preconizadas pela IOBC, em que oxicloreto de cobre mostrou-se inócuo (classe 1) via contato ou ingestão. Enxofre e mancozebe por ingestão foram inócuos, e quando aplicados via contato foram levemente nocivos (classe 2).
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