One of the major agricultural pests of the African continent — the Busseola fusca caterpillar — has now developed resistance to the Bt-toxin that GMO corn relies on for its productivity. While the relatively fast emergence of resistance in the caterpillars is notable in its own right, what’s most interesting is that the resistance is being inherited as a dominant trait — in complete contrast to expectations, and to the great disadvantage of those relying on current management strategies.
As it stands now, the management strategies in use have all been designed with the expectation of resistance being passed down solely as a “recessive” trait, and thus the emergence of resistance could be delayed significantly with the use of “refuges for Bt-susceptible moths”. But if the resistance is being passed down as a dominant trait (as it now is in Busseola fusca) than these strategies are completely ineffective. Which no doubt is why genetic resistance to GMO corn/Bt-toxin has experienced such a rapid geographical expansion over the past few years in the region.
The Institut de Recherche pour le Développement (IRD) provides background and more information:
Genetically engineered maize is created by introducing a gene into the plant genome that expresses a toxic protein from a bacterium, i.e. Bacillus thuringiensis (Bt). Both the leaves and stems of Bt maize produce this toxin which destroys the gut of any moth larvae eating the plant. However, sooner or later, insect species may be able to develop a mechanism of resistance against any pesticides. Bt maize is not fundamentally different in this regard and in order to delay the evolution of resistance in pest populations, the concept of maintaining refuges for Bt susceptible moths was developed.
The refuge strategy consists of planting a small proportion of land with non-Bt maize; the aim being to maintain pockets of insects that remain susceptible to the toxin. In line with other known cases of Bt-resistance, resistance in Busseola fusca was expected to involve modification of the cells in the gut wall, which prevents the toxin from binding. Crucially, this type of adaptation is inherited recessively: both parents must be resistant to produce fully resistant offspring. Since the probability of resistant individuals arising in the field is low, any resistant insects surviving on Bt maize will mate with one of the many Bt-susceptible individuals originating from the refuge area and their progeny will not survive in the Bt-maize field. This tactic has been successful, especially in North America where the first Bt maize has been planted since 1995 with resistance yet to develop among lepidopteran pests.
However, about seven years after Bt maize was introduced to South Africa in the late 1990’s, scientists observed resistant Busseola fusca caterpillars and, more importantly, these resistant insects seemed to reproduce and spread rapidly. To explain this phenomenon, scientists in South Africa, together with IRD researchers, crossed resistant South African moths with susceptible moths imported from Kenya, where Bt maize is not yet commercialized. The offspring developed perfectly on Bt maize and were as resistant as the South African resistant parents. Unlike everything known so far, this resistance evolved in the field was inherited as a dominant trait.
Yet another example of the actual reality of implementation falling far short of the often wild claims made by those who are in support of GMO crops — not only have GMO crops not “solved world hunger and poverty”, but they can not even maintain modest crop yield increases for more a couple of years in many cases.
What the new research has shown, for the first time, is that resistance to GMO Bt corn can be inherited via dominant pathways rather than recessive ones. And also that such resistance can spread very rapidly once established. As the researchers put it: “The moth does not seem to have followed the expected pattern of adaptation.” Which is exactly what many opponents of GMO crops have been saying all along — the incredible complexity present in the organisms of common agricultural crops, their pests, and the wider biosphere that they exist in, can not accurately be reduced down to a simple conceptual framework, potential consequences can not accurately be predicted. With something as vital to modern human life/civilization as agriculture, why the rush into dangerous territory and unpredictable consequences?
As it stands currently (while there are several hypotheses) the exact nature of the mechanism conferring resistance is still unknown. As the researchers word it: “It is very likely that Busseola fusca has developed an unconventional resistance mechanism yet to be identified.”
The new research was just published in the journal PLoS ONE.
For more information on GMOs see: GMO Cotton Loses Its Natural Defenses As A Result Of Less Competition With Their Primary Natural Pests; The Economic Argument Against GMOs: a Top Ten List; and Monsanto Protection Act Signed By Obama, GMO Bill Written By Monsanto Itself Signed Into Law.