Abstract
The salicylic acid analog BTH (benzo-(1,2,3)-thiadiazole-7-carbothioic-acid S-methyl ester) induces systemic acquired resistance by promoting plant resistance against numerous plant pathogens and some insect pests. The objective of the research was to evaluate the activation of plant defenses with BTH on melon (Cucumis melo L., Cucurbitaceae) and its effects on the herbivore Aphis gossypii Glover, 1877 (Hemiptera: Aphididae) and on the aphid predator Chrysoperla carnea (Stephens, 1836) (Neuroptera: Chrysopidae). Under laboratory conditions, plants were sprayed with BTH (50 g/ha) zero (B0), four (B4), and seven (B7) days prior exposure to insects. B0 treatment resulted in 100% mortality of aphid nymphs and disrupted adult feeding behavior (recorded by electrical-penetration-graphs technique), by prolonging the time to reach the phloem, requiring more probes to first salivation and reducing ingestion activities. There were no effects on feeding behavior of A. gossypii fed on B4 plants but on its life history because fewer nymphs were born, intrinsic rate of natural growth decreased, and mortality increased. There were no effects on biological parameters of aphids reared on B7 plants. Prey consumption by C. carnea larvae when predated A. gossypii fed on BTH-treated plants was not different among treatments. Therefore, BTH enhances the suppression of A. gossypii in the short term, without negative effects on the predatory larva C. carnea, which makes this plant strengthener a useful tool to be considered in integrated pest management programs.
Highlights
Plants respond to herbivores and pathogens with a wide range of physical and chemical defenses [1,2]
The induction of Systemic acquired resistance (SAR) is signaled by the phytohormone salicylic acid (SA) and it is associated with pathogenesis-related proteins
The effects of BTH applied at fresh residue could be due to a direct toxicity of the product on the aphid that undermines its fitness and feeding behavior, causing total mortality of A. gossypii nymphs
Summary
Plants respond to herbivores and pathogens with a wide range of physical and chemical defenses [1,2]. Chemical defenses involve complex processes with cascading reactions that use molecules, signals, and regulators with an initial short-term response at membrane level when the plant receptors detect the presence of phytophagous pests and the subsequent trigger of induced direct and indirect defenses [4]. Systemic acquired resistance (SAR) is a type of induced long-lasting defense response [5], very effective against biotrophic and hemibiotrophic pathogens and some insect herbivores [6]. Elicitors are conserved molecular patterns of pathogens and pests recognized by plant transmembrane receptors that activate defense events termed pattern-trigged immunity (PTI)
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