Abstract
In this study we report the effects of fungal metabolites isolated from cultures of the fungus Trichoderma citrinoviride ITEM 4484 on the feeding preference of the aphid Rhopalosiphum padi, a major pest of cereal crops. Different phagodeterrent metabolites were purified by a combination of direct and reverse phase column chromatography and thin-layer chromatography. Chemical investigations, by spectroscopic and chemical methods, led to the identification of different long chain primary alcohols (LCOHs) of the general formula R-OH, wherein R is a long, unbranched, unsubstituted, linear aliphatic group. LCOHs have been reported as components of lepidopteran pheromone blends, but their phagodeterrent effect to aphids is herein reported for the first time. The effects of LCOHs on R. padi were studied by behavioral and electrophysiological bioassays. Feeding preference tests that were carried out with winged and wingless morphs of R. padi showed that LCOHs had high phagodeterrent activity and restrained aphids from settling on treated leaves at a concentration as low as 0.15 mM (0.036 g/l). The results of different electrophysiological analyses indicated that taste receptor neurons located on the aphid tarsomeres were involved in the LCOHs perception. Behavioral assays carried out with some commercial agrochemicals, including azadirachtin A, pyrethrum and a mineral oil-based product, in combination with 1-hexadecanol, the LCOH most abundantly produced by T. citrinoviride ITEM 4484, showed that these different active principles could be applied together, resulting in a useful increase of the phagodeterrent effect. The data shown indicate that these compounds can be profitably utilized for novel applications in biotechnical control of aphid pests. Furthermore, the tested LCOHs have no chiral centers and therefore can be obtained with good yield and at low cost through chemical synthesis, as well as from natural sources.
Highlights
Aphids are insect pests of great economic importance for agriculture and represent one major cause of damage and loss of both quantity and quality of produce in horticultural, cereal and tree crops (Blackman and Eastop, 2007; Dedryver et al, 2010)
In this paper we report the chemical and biological characterization of one more group of phagodeterrent metabolites obtained from T. citrinoviride ITEM 4484, which consists of primary alcohols of the general formula R-OH, wherein R is a long, unbranched, unsubstituted linear aliphatic group
The organic extract obtained from the solid culture of T. citrinoviride 4484 was purified by combined column chromatography (CC) and thin layer chromatography (TLC) on silica gel as described in detail in the Materials and Methods section, yielding the already known compounds citrantifidiene (acetic acid 4-acetoxy-6-hydroxy-1-(2-diydroxyethyl)-hexa-1,3-dienyll ester and citrantifidiol (1,2,3-trimethyl4-(4-methylpent-3-enyl)-cyclohexane-1,3-diol (Evidente et al, 2008), trichodimerol, dihydrotrichodimerol, bislongiquinolide, and dihydrobislongiquinolide (Evidente et al, 2009) and a homogeneous oily mixture of metabolites which were identified as long chain primary alcohols (LCOHs) as below reported
Summary
Aphids are insect pests of great economic importance for agriculture and represent one major cause of damage and loss of both quantity and quality of produce in horticultural, cereal and tree crops (Blackman and Eastop, 2007; Dedryver et al, 2010). Aphids use their piercing sucking mouthparts to feed on host plants causing damage by subtraction of sap, injection of saliva which has phytotoxic effects, and spread of insect-transmitted virus diseases (Hull, 2002; Ng and Perry, 2004; Katis et al, 2007). There is a growing interest in the development of innovative control strategies that may lead to a progressive reduction of chemicals, with the aim to minimize the environmental impact of pest management and improve the safety of the agro-food chain
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