Evaluation ofBt-toxin uptake by the non-target herbivore,Myzus persicae(Hemiptera: Aphididae), feeding on transgenic oilseed rape

Abstract

As consequence of the concern about the biosafety of genetically modified plants, biological and ecological studies are considered crucial for environmental risk assessment. Laboratory experiments were carried out in order to evaluate the transfer of the Cry1Ac Bt-toxin from a transgenic Bt-oilseed rape to a non-target pest, Myzus persicae Sulzer. Cry1Ac protein levels in plants and aphids were determined using a double sandwich enzyme-linked immunosorbent assay. Phloem sap from (Bt+) and (Bt-) oilseed rape plants was collected from leaves using a standard method of extraction in an EDTA buffer. Bt-toxin was present in phloem sap, with a mean concentration of 2.7 +/- 1.46 ppb, corresponding to a 24-fold lower level than in oilseed rape leaves. Toxin was also detected in aphid samples, with a mean concentration in the positive samples of 2.0 +/- 0.8 ppb. The evidence that Bt-toxin remains in herbivores, in this case an aphid, could be useful to clarify functional aspects linked to possible consequences of Bt-crops on food chains involving herbivore-natural enemy trophic systems. Further studies are needed in order to improve the knowledge on the functional aspects linked to the transfer of the Cry1Ac Bt-toxin from GM-oilseed rape to aphids and their possible consequence.

Interactions betweenBt-expressing tomato and non-target insects: the aphidMacrosiphum euphorbiaeand its natural enemies

“…The possible effects of Bt toxins on organisms at higher trophic levels delivered via GM plants and aphids have been described in several plantÁCry toxin systems, but the results are sometimes contrasting (Head et al 2001;Raps et al 2001;Dutton et al 2002;Lumbierres et al 2004;Liu et al 2005;Burgio et al 2007;Ramirez-Romero et al 2008;Zhang et al 2008).…”

“…Burgio et al (2007) obtained mixed results in the detection of Bt toxin in different strains of M. persicae (Sulzer) (Hemiptera: Aphididae) on oilseed rape reared under different conditions. More precisely, the aphids reared in the greenhouse were heavier than those reared in a growth chamber and were shown to contain the Cry1Ac toxin, while only in one sample out of eight aphids reared in the growth chamber was the toxin detectable.…”

“…The actual presence of Cry toxin in the vascular tissues of transformed plants clearly depends on the promoter used, but whether the toxin is translocated into phloem sap is controversial: it appears that the toxin is not detected when methods based on microcapillary techniques (Raps et al 2001) or stilectomy are used (Faria et al 2007), while, when leaf extraction (Raps et al 2001;Dutton et al 2002) or petiole exudation (Burgio et al 2007) are performed, the presence of the toxin can be revealed. Since in one case, when Cry toxin was administered via artificial diet, activity against aphids was demonstrated (Porcar et al 2009), it seems reasonable to expect a similar activity, should the same concentration of toxin be presented via the phloem sap.…”

“…Assays to determine the presence of the Cry3Bb toxin in aphid whole bodies were performed using kits designed for the detection of the Bt toxin in plants (Burgio et al 2007). Aphids were reared on UC82-Bt plants for several generations, and M. euphorbiae samples were regularly collected, weighted and frozen.…”

“…Aphids were reared on UC82-Bt plants for several generations, and M. euphorbiae samples were regularly collected, weighted and frozen. Before extraction, the samples were pooled, to reach weights that are considered above the detectability level of the assays (Burgio et al 2007 and references therein). The pooled samples were homogenized with a pestle with 100 ml of extraction buffer (as indicated in the kit's instructions) and centrifuged, and the surnatant was assayed either with Envirologix QuickStix (Catalogue No.…”