Research suggesting that butterflies could be poisoned by eating genetically engineered maize pollen caused quite a stir when released two years ago. It was seized upon by environmentalists and the media as an example of science gone dangerously out of control.
It now seems that the original research was wrong. The laboratory conditions as applied were too far removed from what happens in the natural environment to be an accurate indication of what to expect in the field.
It wasn't the first time, and won't be the last, that new research has overturned an earlier study. It is part of what science is all about, the pursuit of truth and knowledge with new information overtaking old and new discoveries invalidating earlier theories.
The research involving the Monarch butterflies was special, however, because it involved genetic engineering, a particular flash point between those for and against the use of the advanced genetic technologies. The original conclusion, that the Monarchs were at serious risk from a transgenic product, also carried much popular emotive power.
It is difficult to find people indifferent to something as beautiful as a Monarch and any threat to it is tantamount to an assault on nature.
The apparent risk to the butterflies indicated by the early work from entomologists at Cornell University in Ithaca, New York, struck a chord with people. It also provided significant ammunition for those opposed to the use of the genetic technologies.
The initial Nature report was followed by a string of research projects attempting to move away from the laboratory approach and look at the reality of what actually happens in the fields. This new study by researchers in the Department of Environmental Biology at the University of Guelph in Canada should really bring the debate to an end.
Engineered corn is in widespread use in the US and Canada. It carries a gene originally taken from a bacterium, Bacillus thuringiensis. The gene produces a substance that is toxic to the dreaded European corn borer, a significant threat to maize. Those promoting the new BT corn heralded it as an environmental breakthrough. Borers eating the corn would be killed off by an insecticide inside the plant which supposedly meant that there would be much less need for chemical crop spraying.
The Cornell team decided to see whether unexpected "collateral damage" might be caused to other non-harmful insect species who encountered either the corn plant or its pollen. The BT toxin is released inside the plant but also in the pollen.
They looked at the Monarch butterfly, Danaus plexippus, more particularly its early larval or caterpillar form. Monarchs are migratory, wintering in central Mexico but then travelling beyond the US/Canadian border during the summer. The US mid-west corn belt is home to about half the total US population of the insect each summer.
The caterpillars dine exclusively on the leaves of the milkweed plant, a weed which, conveniently for the bugs, grows in profusion along the roadsides and around the edges of cultivated fields. In these mid-western fields maize is the principal crop.
The Cornell report when released caused consternation. The researchers dusted milkweed leaves with BT corn pollen and fed them to larvae in the lab. It killed 44 per cent of the caterpillars that fed on it and those that survived grew less than a control group.
The researchers noted that corn pollen could be carried on the wind and spread for more than 50 metres from the maize fields, extending the danger zone for the Monarchs. The Cornell group, led by Prof John E Losey, urged more research so that the preliminary results could be assessed.
In fact, later work showed that the risks were much less when larval activity, pollen dispersal and other "real world" factors were taken into account. The Guelph study by Dr M K Sears, Dr D E Stanley-Horn and Dr H R Mattila was prepared for the state-funded Canadian Food Inspection Agency and Environment Canada.
The team assessed the level of pollen necessary to kill or sicken the larvae. It also established methods to predict the level of BT toxin exposure to Monarch larvae, work carried out at a test area in southern Ontario.
The researchers found that 90 per cent of the pollen fell within five metres of the maize fields and beyond this range, pollen levels fell to almost zero. The pollen levels detected on milkweed leaves had, on average, less than the amount found to be toxic to the larvae, although the leaves with the highest levels came close to this limit.
Most milkweed plants available to the insects were growing along the road or in conservation areas and not adjacent to cultivated fields, the researchers said. The Guelph team also found that there was no evidence for a strong overlap between the critical period when Monarch larvae were most active and the eight to 10 day period when most of the maize pollen was shed.
The team did not find conclusive evidence for a delay in larval development if BT pollen was on their menu. Exposure to low levels did, however, result in decreased weight gain and if BT pollen was present the larvae ate less leaf material than if there was no pollen.
This episode is not an example of science going wrong, it is an example of science going right. Scientists are continually reassessing what has gone before, trying to find exceptions to what appear to be invariable rules.
They like nothing better than to disprove an existing theory or research claim. For this reason they take nothing for granted and keep existing science under constant scrutiny. The Guelph researchers do not say their results are absolute, describing their results as "extremely preliminary" and saying they "should be interpreted with caution".
This level of self-scrutiny means that there are no absolutes in science. You never know when a long-standing theory might suddenly and unexpectedly fall. It also means that science becomes a consensus-driven undertaking.
Eventually enough research is done to allow scientists to accept that a theory is correct. And so it has gone for the Monarchs who, despite the introduction of BT corn, are likely to continue bringing beauty and grace to the countryside they populate.