Expression of Bacillus thuringiensis Cry1Ac protein in cotton plants, acquisition by pests and predators: a tritrophic analysis

Abstract

1 Studies have shown that Cry proteins of the bacterium Bacillus thuringiensis expressed in transgenic plants can be acquired by nontarget herbivores and predators. A series of studies under field and controlled conditions was conducted to investigate the extent to which Cry1Ac protein from Bt transgenic cotton reaches the third trophic level and to measure the amount of protein that herbivores can acquire and expose to predators. 2 Levels of Cry1Ac in Bt cotton leaves decreased over the season. Among herbivores (four species), Cry1Ac was detected in lepidopteran larvae and the amount varied between species. Among predators (seven species), Cry1Ac was detected in Podisus maculiventris and Chrysoperla rufilabris . 3 In the greenhouse, only 14% of the Cry1Ac detected in the prey ( Spodoptera exigua larvae) was subsequently found in the predator P. maculiventris. Detection of Cry1Ac protein in Orius insidiosus , Geocoris punctipes and Nabis roseipennis was probably limited by the amount of prey consumed that had fed on Bt cotton. 4 Purified Cry1Ac was acquired by the small predatory bug G. punctipes but at much higher concentration than found in plants or in lepidopteran larvae. 5 Bt protein was shown to move through prey to the third trophic level. Predatory heteropterans acquired Cry1Ac from prey fed Bt cotton, but acquisition was dependent on the concentration of Cry1Ac conveyed by the prey and the amount of prey consumed. The type and availability of prey capable of acquiring the protein, coupled with the generalist feeding behaviour of the most common predators in the cotton ecosystem, probably constrain the flow of Cry1Ac through trophic levels.In the laboratory, a study of ingestion of various dosages of Bt protein was conducted using adult G. punctipes to verify the ability of this predatory heteropteran to ingest Cry1Ac 194 J. B. Torres et al.

Biologia comparada e comportamento de Tetranychus urticae Koch (Acari: Tetranychidae) e Phytoseiulus macropilis (Banks) (Acari: Phytoseiidae) em algodoeiro bollgardTM e Isolinha não-Transgênica

“…O material congelado foi pesado e misturados à solução PBST 1:10 (peso/volume), sendo essa concentração utilizada para as folhas de algodoeiro. Dada a alta concentração da toxina esperada a ser quantifi cada no ácaro rajado (Dutton et al 2002, Torres et al 2006, nesse caso empregou-se diluição 1:40 (peso/volume) para a extração da toxina. O produto sobrenadante foi centrifugado a 4000 rpm por um minuto em centrífuga 80-2B Centribio, com rotor de ângulo fi xo (45º) e raio de 7 cm.…”

“…Essas toxinas são produzidas constitutivamente pela planta, mas predominantemente nas folhas. Ao serem expressas continuamente, as toxinas fi cam expostas aos demais herbívoros não-alvos e, consequentemente, aos seus inimigos naturais (Dutton et al 2002, Obrist et al 2006a, Torres et al 2006, Torres & Ruberson 2008. Entretanto, nenhum dos trabalhos realizados até o momento avaliaram os possíveis efeitos subletais das toxinas Cry ao longo de gerações ou indiretos, através da planta e comportamentais, na biologia e comportamento de T. urticae, praga não-alvo do algodoeiro Bt, mas que apresenta considerável exposição à toxina.…”

Direct and Indirect Effect of Bt Cotton and No Bt Cotton on the Development and Reproduction of the Predator <i>Podisus nigrispinus</i> (Dallas, 1851) (Hemiptera: Pentatomidae)

“…Predators of the genus Podisus (Hemiptera: Pentatomidae) are often found in several agricultural systems, where they act by feeding on various insect species on immature and adult forms [12] [13]. This group of predators can be directly affected by plants that express Bt proteins, when they have the habit of sucking parts of these plants to obtain water and minerals or even indirectly, by feeding on those prey that have previously developed in these transgenic plants [14] [13].…”

Environmental Risk Assessment of Genetically Modified Crops: General Principles and Risks to Non-target Organisms

“…For risk assessment, one may wish to know the highest concentration of a substance that elicits no adverse effect on an organism; this is the no observable adverse effect concentration or NOAEC. If no organism were Raybould et al 2007 3 E.g., Head et al 2001;Raps et al 2001;Dutton et al 2002;Howald et al 2003;Obrist et al 2005;Obrist et al 2006a;Obrist et al 2006b;Torres et al 20064 Babendreier et al 2004 5 Westgate et al 2003;Depuis et al 1987 6 E.g., Khan & Afzal 1950;Thies 1953;Sidhu & Singh 1961;Llewelyn & Fitt 19967 Crocker et al 2002 exposed to concentrations of a substance greater than its NOAEC, then that substance would pose minimal risk to non-target organisms. Thus a third hypothesis can be tested to determine the safety of exposure to a transgenic protein, or to any other potential toxin detected in a GM crop:…”