Bioactivity of neotropical plant compounds to agricultural and vegetable pests and selectivity to non-target insects

Abstract

The demand for new products to control pests is growing. The number of environmental issues stemming from the use of synthetic pesticides to control agricultural pests is also increasing. Accordingly, natural pesticides, particularly those of plant origin, are now considered to be promising alternatives. This study aimed to evaluate the effects of plants on important agricultural pests and several non-target insects. An initial bioassay screening with hexane and ethanol extracts from 23 plants was performed. The hexane extract from Acmella oleracea (L.) R.K. Jansen exhibited the highest activity of all extracts, and the structure of its bioactive compounds was identified. The following three alkamides were isolated from the hexane extract of the aerial parts of A. oleracea: spilanthol, (E)-N-isobutylundeca-2-en-8,10-diynamide and (R,E)-N-(2-methylbutyl)undeca-2-en-8,10-diynamide. We analyzed the insecticidal activity of these compounds on Tuta absoluta Meyr. (Lepidoptera: Gelechiidae), Ascia monuste Latr. (Lepidoptera: Pieridae), Diaphania hyalinata L. (Lepidoptera: Crambidae), Plutella xylostella L. (Lepidoptera: Plutellidae), the predator Solenopsis saevissima Smith (Hymenoptera: Formicidae) and the pollinator Tetragonisca angustula Latr. (Hymenoptera: Apidae: Meliponinae). We also evaluated the effects of extracts and compounds present in A. oleracea on the aphids Myzus persicae (Sulz.) and Lipaphis erysimi (Kalt.) (Hemiptera: Aphididae), the aphid parasitoid Diaeretiella rapae McIntosh (Hymenoptera: Braconidae), and the predator Orius insidiosus (Say) (Hemiptera: Anthocoridae). The extracts and alkamides of A. oleracea showed high insecticidal activity against pest insects and were selective to non-target insects. Another objective of this research was to assess the lethal and behavioral effects of plant extracts on the leaf-cutting ants Atta sexdens rubropilosa Forel, Atta laevigata Smith and Acromyrmex subterraneus molestans Santschi (Hymenoptera: Formicidae). All extracts showed some insecticidal effect on the ants, and the A. oleracea extract was the most toxic to all ant species studied. No extract affected the walking behavior of the ants.