Identication of semiochemicals from four major insect pests of Eucalyptus and Pinus species in South Africa

Abstract

The chemical ecology for key insect pests in South Africa's commercial Pinus and Eucalyptus plantations are explored in this thesis. The main aim was to discover and characterize semiochemical compounds that explain certain behaviours of the insects involved, and that could potentially be exploited in future for the manipulation of the insects' behaviour. Such formulations are sought after because they can be applied in environmentally friendly pest management techniques. Semiochemical interactions were studied in four di erent biological systems. These included the sex pheromone communication system for the Cossid moth, Coryphodema tristis; allelochemical interactions between the Eucalyptus weevil Gonipterus spp. and their Eucalyptus host; allelochemical interactions between Sirex noctilio's, symbiotic fungus, Amylostereum areolatum and its biological control agent Ibalia leucospoides; and allelochemical interactions between the egg clutches of Thaumastocoris peregrinus and its biological control agent Cleurocoides noackae. Semiochemical compounds were found and identi ed through analysis techniques that included gas chromatography coupled to electroantennography (GCEAD) and gas chromatography coupled to mass spectrometry (GC-MS). Some of these semiochemical interactions were complex involving combinations of di erent chemical cues, such as the host recognition cues identi ed for Gonipterus species and potential cues between T. peregrinus females and their egg clutches. Other speci c interactions were found to be simpler and relied on a few speci c chemicals. These included the sex pheromone communication between C. tristis adults and the interaction occurring between female I. leucospoides wasps and the mutualistic fungus of their prey, namely A. areolatum. Biological activity was investigated only for compounds with con rmed identity and included the sex pheromones of C. tristis and some of the chemicals identi ed from the egg clusters of T. peregrinus. These tests were conducted in laboratory and eld conditions. Biological activity was proven for the identi ed sex pheromone of C. tristis during eld trials conducted in 2011 and 2013. One of the chapters was published and another submitted for publication in a peer reviewed journal. Two provisional patents were also registered from this work.