Insect attraction to synthetic herbivore-induced plant volatile-treated field crops

Abstract

1 Plants produce natural enemy-attracting semiochemicals known as herbivore-induced plant volatiles (HIPV) in response to herbivore damage. Deployment of synthetic HIPV in crops could enhance the biological control of pests. To test this, six HIPV [methyl salicylate (MeSA), methyl anthranilate (MeA), methyl jasmonate (MeJA), benzaldehyde (Be), cis-3-hexenyl acetate (HA), cis-hexen-1-ol (He)] in three concentrations (0.5%, 1.0% and 2.0% v/v) mixed with a vegetable oil adjuvant, Synertrol® (Organic Crop Protectants Pty Ltd, Australia), were sprayed onto winegrape, broccoli and sweet corn plants. 2 The relative abundance of insects within treated plots was assessed with non-attracting, transparent sticky traps at varying time intervals up to 22 days after spraying. 3 In the vineyard experiment, Trichogrammatidae responded to Be and MeA (0.5%) and Be (1.0%); Encyrtidae and Bethylidae responded to MeA (1.0%); Scelionidae responded to all compounds at 1.0% and 2.0%; and predatory insects responded to MeA. In sweet corn, parasitoids as a group and Encyrtidae responded to MeA (0.5%); Braconidae responded to all compounds at 0.5% and Synertrol-only; thrips responded to all compounds at 0.5% and 1.0%; while all parasitoids responded to all compounds at 0.5% and 1.0% and Synertrol-only. In broccoli, parasitoids as a group and Scelionidae responded to Be, HA, He and Synertrol-only; Trichogrammatidae responded to Be (0.5%), He (0.5% and 1.0%), MeJA (1.0%) and MeSA (0.5%); and thrips responded to all compounds at to 0.5% and 1.0%. 4 Significant attraction of insects occurred up to 6 days after the HIPV application, suggesting that plants may have been induced to produce endogenous volatiles that attracted insects over an extended period. 5 The results obtained are discussed in relation to the potential utility of synthetic HIPV to enhance the biological control of pests.