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In the tritrophic system consisting of tomato, Solanum lycopersicum (L.), the aphid Macrosiphum euphorbiae (Thomas) and its natural enemy, the parasitoid Aphidius ervi (Haliday), it has been shown that the release of volatile organic compounds following aphid attack is responsible for attracting aphid parasitoids in wind tunnel experiments. The main compounds involved in these multitrophic interactions have been characterized and quantified. In this work, the possible activity of such compounds on plant direct defences against the aphid M. euphorbiae was assessed in laboratory tests. The selected compounds were applied to uninfested tomato plants, either by evaporation or contact, and performance of aphids, in terms of plant acceptance, fixing behaviour and aphid development, calculated in standard conditions. The results showed that two compounds, namely methylsalicylate and cishex3en1ol, alter aphid performance. These two compounds have been reported to be those eliciting the best response by A. ervi in terms of flight behavior (wind tunnel bioassay) and antennal stimulation (EAG bioassay).

Bacillus thuringiensis Berliner toxins are highly specific in terms of insect pest targeted. For example, Cry3Bb is active against Coleoptera. As a consequence, in the framework of using genetically modified plants expressing different Bt toxins in sustainable agriculture, there is a growing interest about the impact of these crops on the environment and on non-target organisms. The effects of genetically modified Bt-tomato plants expressing the toxin Cry3Bb on the aphid Macrosiphum euphorbiae (Thomas) and its natural enemies, the generalist predator Macrolophus caliginosus Wagner and the endoparasitoid wasp Aphidius ervi Haliday, were assessed under laboratory conditions. No significant differences between performance of M. euphorbiae were observed on genetically modified tomato plants (line UC82Bt) with respect to their near-isogenic control line (line UC82). Immunoassays did not detect Cry3Bb protein in M. euphorbiae developing on Bt-expressing tomato plants. Similarly, no significant differences were found on the longevity and prey consumption of M. caliginosus when fed aphids reared on UC82Bt or on UC82. Moreover, the genetic modification did not affect the attractiveness of uninfested tomato plants toward A. ervi. It is therefore concluded that Cry3Bb-expressing tomato plants did not show any acute adverse effects on the biological parameters of the non-target herbivore M. euphorbiae or its natural enemies, M. caliginosus and A. ervi, under laboratory conditions. © 2012 Copyright Taylor and Francis Group, LLC.

Below ground and above ground plant-insect-microorganism interactions are complex and regulate most of the developmental responses of important crop plants such as tomato. We investigated the influence of root colonization by a nonmycorrhizal plant-growth-promoting fungus on direct and indirect defenses of tomato plant against aphids. The multitrophic system included the plant Solanum lycopersicum ('San Marzano nano'), the root-associated biocontrol fungus Trichoderma longibrachiatum strain MK1, the aphid Macrosiphum euphorbiae (a tomato pest), the aphid parasitoid Aphidius ervi, and the aphid predator Macrolophus pygmaeus. Laboratory bioassays were performed to assess the effect of T. longibrachiatum MK1, interacting with the tomato plant, on quantity and quality of volatile organic compounds (VOC) released by tomato plant, aphid development and reproduction, parasitoid behavior, and predator behavior and development. When compared with the uncolonized controls, plants whose roots were colonized by T. longibrachiatum MK1 showed quantitative differences in the release of specific VOC, better aphid population growth indices, a higher attractiveness toward the aphid parasitoid and the aphid predator, and a quicker development of aphid predator. These findings support the development of novel strategies of integrated control of aphid pests. The species-specific or strain-specific characteristics of these below ground-above ground interactions remain to be assessed. © 2013 The American Phytopathological Society.

The blend of volatile compounds emitted by tomato plants (Solanum lycopersicum) infested with the potato aphid (Macrosiphum euphorbiae) has been studied comparatively with undamaged plants and aphids themselves. Aphid-infested plants were significantly more attractive towards Aphidius ervi than undamaged plants and aphids themselves. Oriented response towards host-damaged plant, from which aphids were removed just before running the bioassay, did not differ from that recorded for infested plants. Collection of the volatiles and analysis by gas chromatography revealed only quantitative differences between uninfested and aphid-infested plants. Nine compounds, agr-pinene, (Z)-3-hexen-1-ol, agr-phellandrene, limonene, (E)-β-ocimene, p-cymene, methyl salicylate, (E)-β-caryophyllene and an unknown compound, were emitted at higher levels from aphid-infested plants than from undamaged control plants, whilst no differences were noted for hexanal, 6-methyl-5-hepten-2-one, and humulene (=agr-caryophyllene). Synthetic standards of these compounds were tested in wind tunnel bioassays and all elicited a significant increase in oriented flight and landings on the target by the aphid parasitoid Aphidius ervi. (E)-β-caryophyllene resulted the most attractive towards female wasps. These results corroborate the hypothesis that the volatiles produced by the plant in response to aphid attack derive from both jasmonic and salicylic acid pathways, and are exploited by A. ervi as olfactory cues to locate its hosts.