Abstract
The eucalyptus bronze bug, Thaumastocoris peregrinus, is an exotic pest of eucalyptus crops that has spread worldwide. The objective of this study was to evaluate the toxicity of aqueous plant extracts at 5% of Matricaria chamomilla, Echinodorus grandiflorus, Punica granatum, Maytenus ilicifolia and Origanum majorana on T. peregrinus. For this, choice and no-choice tests were performed. Eucalyptus leaf disks were treated with 5% aqueous extract and two experiments were conducted: (1) the leaf disks were put inside a tube with T. peregrinus adults and their longevity was evaluated. Each repetition was one leaf disk/tube (no-choice test); (2) one leaf disk of each treatment was put inside a Petri dish, and offered to T. peregrinus. Faecal deposits on each leaf disk were quantified (choice test). In addition, high performance liquid chromatography (HPLC) was carried out to verify phenolic compounds present in the plant extracts. All plant extracts reduce the survival of T. peregrinus adults up to nearly 50%. Regarding the choice experiment, T. peregrinus fed with eucalyptus disk leaves containing E. grandiflorus, M. chamomilla and Maytenus ilicifolia extracts produced less faecal deposits when compared wiht the other plant extracts and the control group. In addition, HPLC detected gallic, ferulic, caffeic, coumaric and vanillic acid in the extracts samples. These results suggest that these three plant extracts had a repellent effect on T. peregrinus adults, aside from reducing its survival, and the phenolic compounds may have contributed to these results. Key words: Bronze bug, phenolic compounds, Eucalyptus.
Highlights
IntroductionSevere infestations may lead to canopy thinning and decreased tree growth due to the reduced photosynthetic area (Nadel et al, 2010; Wilcken et al, 2010)
T. peregrinus fed with eucalyptus disk leaves containing E. grandiflorus, M. chamomilla and Maytenus ilicifolia extracts produced less faecal deposits when compared wiht the other plant extracts and the control group
high performance liquid chromatography (HPLC) detected gallic, ferulic, caffeic, coumaric and vanillic acid in the extracts samples. These results suggest that these three plant extracts had a repellent effect on T. peregrinus adults, aside from reducing its survival, and the phenolic compounds may have contributed to these results
Summary
Severe infestations may lead to canopy thinning and decreased tree growth due to the reduced photosynthetic area (Nadel et al, 2010; Wilcken et al, 2010) This insect reaches not more than 4 mm when in adult stage. It has a short life cycle (an average of 35 days) and the female can lay up to 60 eggs during her lifespan (Jacobs and Neser, 2005; Noack and Rose, 2007; Soliman et al, 2012) This high biotic potential enables T. peregrinus to have several generations per year, and to have the potential to spread and rapidly establish into new environments (Nadel et al, 2015; Saavedra et al, 2015)
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