Modelling the Potential Pressure of Fall Armyworm in Key Corn Markets

The fall armyworm, Spodoptera frugiperda, is a lepidopteran species of insect that is indigenous to the tropical and subtropical regions of the western hemisphere covering South America, Caribbean Islands, Mexico, southern United States, and southern Canada. However, the insect has now spread to further regions. The fall armyworm was first reported in Africa in 2016, in Nigeria, Sao Tomé, Benin, and Togo. At the time of writing, the insect has been reported in more than 30 countries on the continent. The insect was first reported in India in 2018, spreading further to over 20 countries on the Asian Pacific continent, particularly China and more recently Australia.

The fall armyworm feeds in large numbers on leaves, stems, and reproductive parts of more than 350 plant species. The insect damages several economically important crops including corn, wheat, sorghum, cotton, rice, sugarcane, and soybeans.

The fall armyworm has four stages in its life cycle: egg, larval, pupae, and adult. The insect damage crops in its larvae stage, at its adult's stage it will only reproduce and migrate. The insect can tolerate a wide range of ecological conditions, but development is dependent on the cumulative energy it obtains from temperature variation. For the insect to transform to another stage of its life cycle, it must be able to accumulate a certain number of degree days (a measure of energy via heat over time). If the temperature is below a certain threshold, the fall armyworm will not accumulate degree days and will die. Unlike some other insect species, the fall armyworm will not enter diapause (period of suspended development). Conversely, during its adult stage, all adults will die after accumulating degree days surpassing its upper threshold. At this stage, longevity is negatively correlated with temperature and subsequent accumulation of energy will only accelerate metabolism. Due to the insect's tropical origin, the fall armyworm is not able to survive extended periods of low temperature. A new generation will form when adults lay eggs according to an oviposition (expulsion of the egg) probability and can produce 4 to 6 generations per year in tropical climates.

Intermittent outbreaks of the fall armyworm on corn crops can lead to significant economic losses for farmers. The insect is expected to remain ever-present in the coming years because it has a high reproductive rate, a relatively short generation period, a high dispersal ability, it prefers a wide range of host plants, and it can produce multiple generations within a year. Climate change will likely affect the fall armyworm's geographical distribution, abundance, growth rate, survival, mortality, and its number of generations per year. The fall armyworm will benefit from rising temperatures because of the insect's preference for tropical climates. Hence, it will be able to establish itself in new regions, further exacerbating the insect's population.

Moreover, there is a growing Bt toxin-resistant fall armyworm population. This variant of fall armyworm will reduce the effectiveness of transgenic crops and will make crops more susceptible to infestations. Furthermore, the insect has developed resistance to certain insecticides, including pyrethroids, again potentially leading to further crop damage.

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This article was published by S&P Global Commodity Insights and not by S&P Global Ratings, which is a separately managed division of S&P Global.