Toxicity and repellency of plant extracts on Thaumastocoris Peregrinus (Carpintero Dellap) (Hemiptera: Thaumastocoridae)

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.