Proceedings of the XLVI Italian Society of Agricultural Genetics - SIGA Annual Congress

Giardini Naxos, Italy - 18/21 September, 2002

ISBN 88-900622-3-1

Poster Abstract - 3.18

MEASURING ARTHROPOD BIODIVERSITY IN Bt-EXPRESSING TRANSGENIC CROPS IN EXPERIMENTAL FIELDS

FIORE M. C.*, SCHMIDT J.**, CLEMENTE A.***, SCARDI M.****, ARPAIA S.*****

*) Metapontum Agrobios, Metaponto (MT), Italy

**) ETH Zurich, Geobotanical Institut CH-8044 Zurich, Switzerland

***) Università degli Studi di Bari Dipartimento di Zoologia, I-70125 Bari, Italy

****) Università degli Studi di Roma “Tor Vergata”, Dipartimento di Biologia, I-00133 Roma, Italy

*****) ENEA C.R. Trisaia, I-75026 Rotondella (MT), Italy

insect resistance, Bacillus thuringiensis, environmental impact, biosafety, genetically modified plants

Whereas transgenic insect-resistant crops (TIRC) expressing Bacillus thuringiensis (Bt)-derived toxins are ever growing in importance in countries outside the EU (James C., ISAAA Brief 2001), in Europe there is deep concern about the environmental safety of such crops. Most of the field studies so far, have addressed TIRCs particularly for their resistance capability we therefore know that most likely target insects will almost disappear and therefore changes into the agroecosystem complex might be induced. Apart from this obvious major effect, more subtle mechanisms might also induce changes in the agroecosystem: some non target herbivores may also transfer the toxin to higher trophic levels, predators may be exposed to toxin ingestion via pollen, parasitoids may suffer for an unbalanced development in non optimal prey. Moreover, it has never been investigated if the genetic modification in plants may bring an unexpected change of plant volatiles that are important in host plant finding by herbivores and prey searching behavior of parasitoids and predators as well. Most of these assumptions are only theoretical, as very little is known about multitrophic relationships in transgenic agroecosystems. In order to gather pluriannual field data and to find out good ecological indicators for measuring insect biodiversity in transgenic fields, we setup field studies with TIRC expressing either lepidoptera specific Cry1 toxin (canola and potato) or coleoptera specific Cry3Bb toxin (eggplant). Transgenic and control plants were seeded in experimental fields with a completely randomized design with three replications per treatments. Three kind of sampling methods were adopted for quantitative and qualitative data collection: 1) visual observations on plants; 2) sweepnetting; 3) pitfall traps. The “quasi-holistic” approach of our observations was pursued also by choosing ad hoc statistical indexes: Corrispondence Analysis, Multi Response Permutation Procedure (MRPP), Indicator Species Analysis.

No differences in species assemblage were found between control and transgenic plots. Particularly, Correspondence Analyses results for the three crops gave the following eigenvalues for the three axes considered: canola 0,36, 0,094, 0,083; potato 0,19, 0,11, 0,079; eggplant 0,48, 0,44, 0,38. Even graphical representations shows how observations are evenly distributed and no differences can be seen between the two treatments. MRPP analysis during the season also confirmed the results, statistics for the three experimental fields are the following: 1) Canola 17/4/2001 expected d = 4.347 observed d = 4.358, T = 0.644 p = 0.699; 2) Potato 30/7/2001 expected d = 17.671 Observed d = 17.377 T = -1.068 p= 0.126; 3) Eggplant 4/9/2001 expected d = 18.811 Observed d = 18.528 T = -2,997 p= 0.019. Similar results are available for several different dates. Indicator Species Analysis is a particularly useful index when all the taxa are given a similar significance in ecological terms (i.e. no “key species” has been chosen beforehand). When used for our data it proved to be very sensitive, no differences were found for any date for both canola and potato fields. In two occasions Indicator Species Analysis found a different assemblage for the two treatments in the case of transgenic and control eggplants, the taxa differentially aggregated were the Alticinae beetles and spiders. While the first group represents a potential target for Cry3B toxins, the second is not and therefore further investigations are worth for these arthropods involving a more thorough taxonomic discrimination within this group of species.