Comparative Toxicological and biochemical Effects of Seed and Leaf extracts of Azadirachta indica and Jatropha curcas on the Fall armyworm (Spodoptera frugiperda) Under Laboratory Conditions

In the vast fields of sub-Saharan Africa, maize stands as a cornerstone of food security and economic stability. Yet, this vital crop faces a relentless threat from the fall armyworm, a moth whose larvae consume leaves with voracious efficiency. These young caterpillars begin by feeding in groups on the surface of leaves, creating window-like holes, before burrowing into the heart of the plant to destroy its growing point. As they mature, they attack the reproductive parts of the maize, damaging the ears and reducing the harvest. For decades, farmers have relied on synthetic chemicals to stop these pests, but the armyworm is learning to resist these poisons, and the chemicals themselves pose risks to the environment and the people who depend on the land. This has driven scientists to look back to nature for solutions, investigating whether extracts from common plants might offer a safer, effective way to protect crops without the heavy toll of industrial pesticides.

Researchers in Nigeria set out to test two such plants: the neem tree and the physic nut. They focused on the seeds and leaves of both species, asking a simple but critical question: which part of which plant works best to stop the fall armyworm, and how does it actually kill the pest? To find the answer, they gathered fresh seeds and leaves from a botanical garden, dried them, and ground them into a fine powder. They then soaked this powder in water to create liquid extracts, filtering out the plant matter to leave behind a solution rich in the plant's natural chemicals. These solutions were applied to fresh maize leaves, which were then fed to third-instar fall armyworm larvae in a controlled laboratory setting. The team watched closely to see how many larvae died, how long it took for the poison to work, and what happened inside the bodies of the surviving insects.

The results revealed that both plants contain a complex mix of natural compounds, including phenols, tannins, and alkaloids, which are known to interfere with insect biology. However, not all extracts were created equal. The researchers found that the seed extract of the neem tree was the most potent weapon in their arsenal. When exposed to this specific extract, the larvae died faster and in greater numbers than with any other treatment. In fact, a concentration of just under eight percent of the neem seed solution was enough to kill half of the larvae within a single day. The seed extract of the physic nut was also effective, though it required a slightly higher concentration to achieve the same result. The leaf extracts from both plants worked as well, but they were less powerful than their seed counterparts, with the leaf extract of the physic nut showing the weakest effect of all. Over the course of four days, the most effective treatments killed nearly every larva, matching the performance of a standard synthetic pesticide used as a benchmark in the study.

Beyond simply counting the dead, the scientists wanted to understand the mechanism of death. They examined the surviving larvae that had been fed leaves treated with the most effective concentration of each extract. What they found inside the insects told a story of biological collapse. The treated larvae showed a severe depletion of their energy reserves. Their bodies contained significantly less protein, carbohydrate, and fat compared to the healthy, untreated larvae. It is as if the plant extracts had cut off the insect's fuel supply, leaving it unable to grow or sustain itself. Furthermore, the chemical processes that insects use to break down toxins were shut down. The activity of key enzymes, which normally help the insect survive by neutralizing harmful substances, was drastically reduced. Without these defenses, the larvae could not cope with the plant chemicals, leading to a buildup of toxic effects that ultimately proved fatal.

The study also observed how the extracts affected the growth and development of the larvae. Those that survived the initial exposure took much longer to reach the next stage of their life cycle. While untreated larvae completed their development in roughly thirteen days, those exposed to the neem seed extract took nearly seventeen days to finish. This delay suggests that the plant chemicals act as a growth regulator, confusing the insect's internal clock and preventing it from shedding its skin and moving forward. This disruption of the life cycle is a crucial advantage, as it slows the population's ability to reproduce and spread. The researchers concluded that these plant extracts do not rely on a single method of attack; instead, they strike the insect from multiple angles, starving it of energy, disabling its detoxification systems, and halting its growth.

These findings suggest that the seeds of the neem tree and the physic nut offer a promising, eco-friendly alternative to synthetic pesticides. The study demonstrates that these botanicals are not just mild deterrents but powerful tools capable of killing the fall armyworm and disrupting its life cycle through natural biochemical pathways. While the research was conducted in a laboratory, the results provide a strong foundation for developing these plant extracts into practical biopesticides that farmers can use to protect their maize. By harnessing the chemistry of plants that are already available in the region, there is a clear path toward managing this destructive pest in a way that is safer for the environment and sustainable for the future.