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ANNO 3 Numero 1
Donato Tesoriero [1], Fabio Sgolastra [2], Sara Dall’Asta [2], Francesca Venier [2], Anna Gloria Sabatini [1], Giovanni Burgio [2], Claudio Porrini [2]

Effects of Bt-oilseed rape on the foraging activity of Apis mellifera in confined environment and Osmia cornuta in laboratory

[1] CRA - Istituto Nazionale di Apicoltura , Bologna, Italy
[2] DISTA - Area Entomologia, Università di Bologna, Italy

Genetically modified (GM) plants may have direct or indirect effects on bees. Direct effects are those that arise when a bee ingests a novel protein expressed by a GM plant. Indirect effects may arise if the process of introducing the transgene into the plant results in inadvertent changes to plant phenotype that affects its attractiveness or nutritive value to bees. The direct and indirect effects of transgenic oilseed rape (Brassica napus cv. Westar) expressing the Cry1Ac protein on the foraging activity of Apis mellifera and Osmia rufa were investigated.

To determine if genetic modification results in an unexpected change in the plant’s phenotype, the quantitative and qualitative analyses of pollen and nectar were conducted. Significant differences between isogenic and transgenic plants were recorded at 18°C: GM flowers produced significantly less nectar than isogenic ones (p=0.006), and also the sugar content of the nectar was lower in transgenic flowers (65.7%) than in isogenic flowers (82.2%). At 26°C, nectar production was again higher on isogenic plants, but differences were not significant. Concerning pollen production, transgenic plants contained 8.94±0.31 ppb of Bt-toxin, but no differences were revealed in pollen quantity between transgenic and isogenic plants.

The foraging activity of honeybees on flowering transgenic oilseed rape plants were investigated under semi-field conditions in a 6 x 3 m net cage. Foragers from a three-frame nucleus of A. mellifera (approx. 2,000 workers) were given a choice between GM oilseed rape plants and untransformed plants at the same flowering stage. The number of each plant type varied during blooming. The frequency of bee visits, the mean duration of the bee visits, and the frequency of bees moving among flowers were recorded.

The observed frequencies of bee visits to isogenic and transgenic flowers (average: 0.41 and 0.59, respectively) did not differ significantly from expected frequencies, and also the duration of bee visits on isogenic flowers was comparable to that on transgenic flowers (means: 10.80 s and 10.77 s, respectively). The frequencies of the bee movements from one flower phenotype to the same phenotype or the other phenotype did not significantly differ from expected.

A related study using O. rufa was conducted at 26°C in laboratory conditions with 14 newly emerged females. Each bee was put in a covered glass cylinder (19 cm diameter x 10 cm high) with six oilseed rape flowers in an alternating 3 iso- and 3 transgenic flower array inserted into a polystyrene base. The behaviour of the bees was recorded for 30 minutes and analyzed by Program Observer®.

No significant differences between transgenic and isogenic plants were observed in respect to the mean time spent on each flower and the total duration of visits in the first, in the second, and in subsequent visits. However the bees spent, on average, always more time on isogenic flowers.

Also the times that bees visited the same oilseed rape flowers was similar during the experiment, with an average of 2.8 times for the isogenic flowers and 3.0 times for the transgenic flowers.