6. Potential Impacts of GM Plants on Bee Health
Although not directly related to the presence of GM material in bee products, there may be impacts of GM plants on bee health that could affect on the bees' ability to produce honey, pollen and propolis.
There is a growing body of published research on the impacts of GM plants and novel proteins on bee health. This research has recently been reviewed (Malone and Pham-Delègue, 2001; 2002; Pham-Delègue et al., 2002). These reviews are summarised below.
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 affecting its attractiveness or nutritive value to bees.
6.1 Direct Effects of Novel Proteins on Bees
Potentially, the ingestion of a novel protein expressed in pollen or perhaps occurring in nectar, resin or honeydew from a GM plant may affect bee behaviour, development or survival, or it may have no effect. As pointed out above (Section 2), pollen represents the most likely vehicle for the expression of novel proteins. Adult bees consume significant quantities of pollen during their first week after emergence and they have received the most research attention to date. Bee larvae also ingest pollen, especially during the later instars, but their food is composed in large part of glandular secretions from nurse adult bees.
Many experiments have been conducted in which bees are fed with purified novel proteins at concentrations estimated to approximate or to exceed likely pollen expression levels. Novel proteins with insecticidal properties aimed at making GM plants pest resistant have been the most thoroughly tested. There have also been trials conducted with small colonies of bees and potted flowering GM plants in glasshouses or under mesh in the field. Tests have assessed food consumption by adult bees, adult bee survival, olfactory learning and foraging behaviour in adult bees, larval bee development and survival. Results to date are briefly summarised in Table 3. Supporting references may be found in reviews by Malone and Pham-Delègue.
6.2 Indirect Effects of GM Plants on Bees
Indirect effects of transgenic plants on bees may occur when genetic modification results in an unexpected change in the plant's phenotype. Insertional mutagenesis is one such change. In this case, the random positioning of the transgene in the plant's genome interferes with a gene or suite of genes needed for a "normal" phenotype. For example, an insertional mutagenesis event that resulted in plants without flowers would have a definite negative impact on bees. Less obvious changes, such as alterations in nectar quality or volume would be harder, but not impossible, to detect. Effects due to insertional mutagenesis will vary among different lines of plants derived from separate transformation events and can easily be eliminated by line selection. Pleiotropic effects represent a second type of inadvertent phenotypic change. In this case, it is not the position of the transgene, but its product, which interferes unexpectedly with a biochemical pathway in the plant to create a phenotypic change. Such changes would occur in all lines of the transgenic plant and could not be remedied by line selection.
Nectar analyses of GM oilseed rape plants have suggested that some modification events may lead to phenotypic changes that could influence bee behaviour (Pham-Delègue et al., 2002). One line of GM oilseed rape expressing a chitinase produced more nectar of higher sugar concentration than the corresponding control line, as did one herbicide-resistant line compared with its control.
6.3 Current and Future Research
There are a number of research teams continuing to investigate the effects of GM plants on honey bees. In New Zealand, HortResearch in collaboration with AgResearch has a programme of work looking at non-target effects of GMOs, including effects on honey bees. Current research aims to determine whether feeding young adult bees with a Bt toxin, a protease inhibitor or a biotin-binding protein affects their ability to develop hypopharyngeal glands. (These glands are important because they secrete food for larval bees.) Similar work is being conducted with Bt-corn pollen and bees in Switzerland (J. Romeis, pers. comm.). In France, the effects of Bt-corn on bee larvae are being determined and an assay of bee defensive behaviour (stinging) is being developed (M. Pham-Delègue, pers. comm.). In Denmark, the effects of protease inhibitors on bee larvae are being assessed (H. Brødsgaard, pers. comm.). In Canada, the effects of Bt-sweetcorn pollen on bees are being determined and work on impacts of GM plants on bumblebees and wild bees is planned (C. Scott-Dupree and M. Winston, pers. comm.).
In New Zealand and overseas, many molecular biologists developing GM plants are moving their emphasis away from "input traits", such as herbicide tolerance, insect resistance, disease resistance or drought tolerance, and towards "output traits", such as altered nutritional qualities, improved processing traits, altered flowering and plant form and the production of valuable proteins in GM plants ("biopharming") (Christey and Woodfield, 2001). The potential effects of these new traits on bees will need to be tested. For example, altering the nutritional qualities of plants could well affect the attractiveness of pollen to honey bees, since lipid profiles have been shown to be important in determining the phagostimulatory and antibacterial properties of some pollens (Singh et al., 1999; Manning, 2001).
Contact for Enquiries
Dr Sharon Adamson
Manager,
Innovation Policy
Ministry of Agriculture and Forestry
PO Box 2526
Wellington
NEW ZEALAND
Phone: +64 4 894 0618
Fax: +64 4 4 894 0741
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