Plant volatile emissions for sustainable pest control

The bioeconomy objective with regards to agriculture is to strengthen sustainable agricultural production and processing. Nevertheless, agriculture has to face the destructive activities of numerous pests like fungi, weeds and insects, leading to radical decrease in yields and products quality. The control of these pests often relies on chemical pesticides, however, the over dependence on these compounds raises environmental concerns. Besides, pesticide residues can also affect food safety with negative effects on consumers health and trade impediments for export crops. A large number of commercialized biocontrol products such as biopesticides, plant-growth regulators and biofertilisers have been tested in the last years. Biopesticides include substances that interfere with growth or mating or substances that repel or attract pests. In this context, plants exhibit a variable ability to communicate with consumer or beneficial insects through constitutive or induced volatile organic compounds (VOCs). In the last years the tomato pinworm Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) has become one of the most harmful pests of tomato in the Mediterranean Basin, both in greenhouse and outdoor.[1] This study aimed to develop a sustainable control tool against this tomato pest promoting predator presence throught alternative noncrop plants as banker plants. Among natural enemies of T. absoluta the omnivorus predator Nesidiocoris tenuis (Reuter) (Hemiptera: Miridae) was chosen and Dittrichia viscosa L. (W. Greuter) (Asteraceae) and Sesamum indicum L. (Pedaliaceae) were used as alternative plants.[2] A Y-tube olfactometer was used to test the olfactory preference of the predator in dual-choice bioassays comparing S. indicum, D. viscosa, healthy tomato plants, and tomato plants infested by eggs and larvae of T. absoluta, revealing a marked preference of N. tenuis for S. indicum. The headspace solid-phase microextraction combined with gas chromatography-mass spectrometry (HS-SPME-GC-MS) was performed to characterize the volatile substances emitted by the tested plants. Analysis of the volatiles highlighted a lower complexity for S. indicum compared with the other plants. Sesame plants emitted the lowest amount of hydrocarbon monoterpenes but the highest rate of oxygenated terpenes. Green leaf volatiles, known for attracting mirids, were emitted at higher levels by sesame plants compared to D. viscosa and tomato plants, both healthy and infested. The use of S. indicum as banker plant, thanks to its VOCs emission, could favor the presence of predators from the first phase of pest attack providing a useful tool in the bioeconomy strategy in order to reduce the use of pesticides and to improve the productivity and quality of tomato. Besides, ther study offers a chemical basis for the higher attractiveness of sesame, allowing to understand the ecological mechanisms and to set up integrated pest management strategies using synthetic volatiles on the basis of the identified natural ones.