ACRE Advice

A Report on a Paper Concerning the Effect of
Genetically Modified Bt Maize on Monarch Butterflies

Advice of the Advisory Committee on Releases to the Environment
under Section 124 of the Environmental Protection Act 1990

29 September 2000

ACRE was asked to review the study by Hansen & Obrycki, (2000)^[1] concerning the effect of pollen from genetically modified Bt maize on Monarch butterflies. The maize lines used in this study were genetically modified for resistance to larvae of the European Corn Borer moth which is an important pest of maize crops. Resistance to the corn borer is achieved by inserting a gene into the maize from the soil bacterium Bacillus thuringiensis. The gene codes for an insecticidal protein (Bt toxin) that is preferentially toxic to insects of the order Lepidoptera, which includes butterflies and moths.

In this study, milkweed plants in pots were positioned in maize fields where 'natural' densities of maize pollen accumulated. Leaf discs from these plants were then used in laboratory tests as food for the larvae of Monarch butterflies. The report concludes that Monarch larvae reared on Bt pollen dusted leaves had a higher mortality than larvae reared on leaves with non-genetically modified maize pollen. ACRE considered whether these results altered the Committee's previous advice on Bt pollen and whether there are any implications for the risk assessment of genetically modified plants for release in the UK.

ACRE's advice:

ACRE agreed that the research by Hansen & Obrycki represents a step in the right direction, but it does not add greatly to work done previously by Losey et al., (1999) nor to the body of work that is accumulating elsewhere.

Although the Committee recognised that Hansen and Obrycki used densities of pollen accumulated under field conditions it was nonetheless still essentially a laboratory based study. Therefore, as ACRE has advised previously, important factors that would effect the exposure of the larvae to the Bt toxin in the field need to be verified in the field situation. These include the timing and period of pollen release, possible photodegradation of the Bt toxin, rain washing away settled pollen, food plant choice and feeding behaviour of the larvae, and location of milk weed plants near fields. All of these could affect the exposure of larvae to the toxin.

ACRE will continue to monitor closely this area of research. Bt maize or other insect resistant GM crops are not being grown in the UK nor are any expected to be grown commercially within the next three years. If this situation were to change, then ACRE would review its current advice in the light of the GM crops concerned and the scientific understanding at that time. ACRE reminds applicants wishing to release GM plants, in particular those modified for insect resistance, that they will need to give more prominence in the risk assessment to any effects of GM pollen on non-target invertebrates.

ACRE considers that laboratory studies are an important first step in investigating non-target effects and may indicate issues for further study, but they must not be used in isolation. Confidence in the environmental safety of GM plants can best be gained by proper evaluation in the field. More research is required to investigate the possible non-target effects of GM crops and how harm is to be measured and compared.