Researchers Vale´rie Lemesle, Ludovic Mailleret and Maurice Vaissayre have investigated a means to slow the evolution of pests that become evolutionarily resistant to genetically altered, toxic crops. In agriculture it is common practice to use crops that have been genetically altered to produce a toxin in order to keep certain pests from destroying farmer’s crops. Pests are progressively becoming more and more resistant to these modified crops. Continually modifying these plants is becoming economically unfeasible and so new practices must be considered.
A particular cropping system was considered during this study. The use of only toxin producing crops causes accelerated resistance in these pests so cycling between the use of toxin producing crops and non toxic producing ones is the main argument of this article. The hypothesis was that if every season farmers alternatively cycle between a field composed of a mixture of toxic and non toxic crops and a field of purely non toxic crops that the effects on the evolution of resistant pest would be slowed. It was found that, controversially, the increase in the portion of non toxin producing plants does not necessarily mean a lesser frequency of toxin resistant pest for the generations to come. An optimal ratio of the two crops which yields the best results was established during the study.
In this study the time that it takes to produce the next generation of pest was considered negligible. This means that this study although it shows evidence that this practice could help from evolving toxin resistant pests it can be practically applied only to a small variety of these pests. These results fit for pests like aphids. Aphids reproduce through parthenogenesis meaning that they bear offspring that are adult like constantly through the season. In order for this study to apply to most other species of pests new models would have to be made in order to account for the length of time that it requires generating the next generation of offspring.
It was deduced that although this practice can reduce the increase of toxin resistant pest, there is an optimal ratio of non toxic and toxic plants. The reason behind this is that there are two general categorizations of pests in this study. Pests that are susceptible to the toxins and those that are not. If the ratio of non toxic plants to toxic ones is too high, the entirety of the population will thrive more because both the susceptible pests and the unsusceptible ones have a more equal chance of surviving and procreating. With the right ratio, the susceptible pest’s numbers dwindle leaving the unsusceptible ones with fewer mates and thus the population declines.
Models illustrated in this study suggest that for certain species of pests the increase of evolutionary resistance to these toxins could be nearly halted. As previously stated this would only apply to small variety of pests that rear offspring witch are nearly mature upon being born and which are constantly giving birth to the next generation throughout the whole season.
A similar study was conducted during 2007 by Mohammed Awel. In this study he deduced the same result, that there is an optimal ratio of the crops that must be met to obtain the best results. Although this would seem counted intuitive it has a logical underpinning. This work used a hypothesis of immigration of susceptible pests into the system. It is said that in a further investigation it would be wise to include this immigration phenomenon into the study.
This study shows that there are environmentally friendly alternatives by witch the agricultural society is able to both maintain a field of crops and slow development of evolutionarily unsusceptible pests. Although this study is not entirely conclusive because it neglects a key aspect of most pest species, (the time between the maturation of the next generation of pests) it has cast light on new way of controlling those pests. The models produced by this study have deduced an optimal ratio of toxic and non toxic plants in order to slow the increase of there resistant pests and that it is possible to slow it to a near stop.
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