Insecticidal Effect of Cry Toxins Produced by Bacillus thuringiensis on Diceraeus melacanthus (Dallas, 1851) and Euschistus heros (Fabricius, 1798) (Hemiptera: Pentatomidae)

Abstract

Some species of the Heteroptera (Hemiptera) suborder are of great agricultural importance, mainly as pests, and their control is often necessary. The use of Bacillus thuringiensis, an entomopathogenic bacterium normally extracted from the soil and used in biological control, is an alternative to the chemical control of these insects. Mortality tests must be carried out in order to select and determine a viable toxic strain, but currently there is no validated methodology for conducting those tests. In this context, this research aimed to develop and improve a selective bioassay methodology to assess the toxic effect of B. thuringiensis Cry toxins on Diceraeus melacanthus (green-belly stink bug) and Euschistus heros (neotropical brown stink bug) nymphs. A bioassay methodology consisting of tubes and artificial diet was proposed. Bioassays with D. melacanthus and E. heros nymphs were performed incorporating Cry toxins (Cry1Aa, Cry1Ab, Cry1Ac, Cry1B, Cry1C, Cry1F, Cry1G, Cry1Ia, Cry2Ab, Cry2A, Cry2Ae, Cry4A, Cry4B, Cry10, and Cry11Aa) into their liquid diet. The artificial feeding system developed in order to carry out the stink bug mortality tests was conducted. Among the toxins tested, we can highlight 2 causing 80-85% nymphal mortality on D. melacanthus, and 4 toxins causing 90-100% nymphal mortality for E. heros after 7 days of incubation. Both species are susceptible to different Cry toxins, with emphasis on Cry2Ab and Cry4B for D. melacanthus and Cry1B, Cry1G, Cry1Ia and Cry2Ab for E. heros.