Persistence of the pesticidalBacillus thuringiensisprotein expressed in Bt maize plant materials in two soils of the Central Eastern Cape, South Africa

Abstract

Environmental effects of genetically modified plants are not yet fully u~derstood. Experiments were conducted to determine relative amounts of the bioactive Bt protein in roots, leaves and stems of Bt maize and persistence of the protein in two soil forms (Shortlands and Oakleaf). The Bt protein activity was bioassayed using 2 nd to 3 rd instar larvae of diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae). Bioassay results showed that the extracts from different parts of Bt maize plants were equally toxic and caused overall larval motility of over 70%. It was also found that two years' storage of dried Bt maize material af room temperature, did not reduce the pesticidal activity of the protein toxin. When Bt maize plant materials were incubated' in soils for two weeks under glasshouse conditions, the extracted toxin caused 20% larval mortality and within 7 weeks of incubation in both soils, the extracts obtained caused <10% larval mortality. However, extracts obtained from Bt maize plant materials incubated in the field showed decreased. larval mortality, from 60% to 30% in two weeks and remained >25% after 12 weeks of incub.ation in the Shortlands soil and from 55% to 15% within four weeks and eventually down to 10% in 23 weeks of incubation in the Oakleaf-soil. The findings suggest that Bt maize plant parts contribute comparable amounts of Bt protein toxin to the soil, and toxin persisten'ce in the soil appears to depend on soil type, and temperature and moisture conditions.

Bt‐maize as a potential trap crop for management of Eldana saccharina Walker (Lep., Pyralidae) in sugarcane

“…The persistence and activity of Bt toxin in completely dead Bt-maize plant material (stalks, leaves and roots), which was stored for 2 years, was demonstrated in a recent study (Muchaonyerwa and Waladde 2007) where it produced 80% larval mortality of diamond back moth, P. xylostella. The activity of the toxin in completely senesced maize would potentially allow the trap crop to be left standing without the need to harvest and replant new seed, providing an important advantage over trap species (crop or wild hosts) that do not kill stem borer larvae feeding on them [e.g.…”

Carbon and nitrogen mineralisation and inactivation of the Cry1Ab protein in Bt maize (MON810) residues during composting

“…Bt maize may contribute up to 650 g Cry1Ab protein ha -1 compared to about 0.25 g ha -1 produced naturally (Blackwood and Buyer 2004). Cry proteins have been shown to adsorb to soil particles resulting in their persistence in the soil (Tapp et al 1994, Crecchio and Stotzky 2001, Muchaonyerwa and Waladde 2007, which could lead to its increased exposure to soil biota. However, Head et al (2002) and Dubelman et al (2005) reported that the Cry1Ab and Cry1Ac proteins did not accumulate in soil as a result of continuous cultivation of Bt corn (MON810 and BT11) and cotton, respectively.…”