Effects of Drought Stress on Maize Susceptibility and Response to Fall Armyworm Infestation

In the fields of sub-Saharan Africa, maize is more than just a crop; it is the foundation of food security for millions. Yet, this vital plant faces a double threat that is becoming increasingly common as the climate shifts. On one side, the land is suffering from drought, a lack of water that slows growth and shrinks harvests. On the other, a voracious insect known as the fall armyworm is tearing through crops, devouring leaves and burrowing into the corn cobs. For decades, scientists have understood that plants under stress often become more attractive to pests, or that pests might struggle when their food source is dry and tough. But the reality of how these two forces interact when they strike at the same time has remained unclear. Does a thirsty plant become an easier target for the hungry insect, or does the lack of water somehow protect the crop by making it less nutritious? Understanding this relationship is critical for farmers who need to know if their crops can survive a season where rain is scarce and bugs are plentiful.

To answer this, researchers at the International Maize and Wheat Improvement Center set up a controlled experiment in Kenya to watch how maize behaves when it is forced to deal with both water shortage and insect attacks simultaneously. They grew a popular commercial variety of maize in large plots, carefully managing the water supply to create two distinct environments: one group of plants received plenty of water, while another group was subjected to a strict drought regimen where irrigation was withheld for weeks at a time. Within these wet and dry zones, the scientists introduced the fall armyworm in different ways. Some plots were left alone to serve as a baseline, some were infested by planting rows of a highly susceptible maize variety nearby to let the insects wander in naturally, and others were directly infested by placing the larvae onto the plants by hand. This setup allowed the team to compare exactly how much damage the insects caused under wet conditions versus dry ones, and how the plants' growth and final harvest were affected by the combination of stresses.

The results revealed a harsh reality for the maize crop. When the plants were dry, they became significantly more vulnerable to the fall armyworm. The researchers found that the insects caused roughly forty-six percent more damage to the leaves and fifty percent more damage to the corn cobs on the drought-stressed plants compared to those that were well-watered. It appears that the water deficit did not make the plants tougher or less appetizing; instead, it weakened their ability to defend themselves or recover from the feeding. The dry plants simply could not replace the tissue the insects ate as quickly as the healthy, watered plants could. This lack of resilience meant that the damage was not just cosmetic; it translated directly into a loss of food. The plants that were both dry and infested by the armyworms produced the smallest harvests, yielding less than one ton of grain per hectare. This was a drastic drop compared to the healthy, watered, and pest-free plants, which produced more than two and a half tons per hectare.

The study also showed that the impact of the insects depended entirely on how much water the plants had. Under ideal watering conditions, the fall armyworm infestation reduced the grain yield by about thirty-two percent. However, when that same infestation hit the drought-stressed plants, the yield loss jumped to forty-three percent. The combination of the two stresses was far worse than the sum of their individual parts. The plants that were dry and then attacked by insects grew much shorter and produced smaller ears of corn than those that were only dry or only attacked. In fact, the shortest plants and the smallest ears were found in the plots where the drought and the artificial insect attack happened together. The researchers also noted that the insects caused more ear rot, a fungal disease that spoils the grain, particularly when the plants were well-watered, suggesting that the entry wounds created by the insects allowed fungi to take hold more easily in the moist environment.

Ultimately, this work demonstrates that drought does not protect maize from the fall armyworm; it makes the situation much worse. The stress of a lack of water leaves the plant too weak to fight off the insects or to bounce back from the damage they cause. For farmers and breeders, this means that looking for maize varieties that can resist insects is not enough if those same varieties cannot also handle dry spells. To ensure food security in a changing climate, new crops need to be developed that can withstand both the thirst of the soil and the hunger of the pest at the same time. The findings suggest that testing crops under these combined pressures is essential to find the varieties that will keep producing food when the weather turns against them.