Changing colour of crop mosquito nets scares away insects: they don't like red

Developing advanced pest control methods that do not rely on insecticides is crucial for sustainable agriculture. This becomes especially critical when dealing with micropests that exhibit high resistance to conventional insecticides. As our options for combating these pests dwindle, the economic impact worldwide becomes substantial.

Researchers from the University of Tokyo (Japan) conducted a study revealing that the effectiveness of mosquito nets, commonly used to protect crops, can be significantly enhanced by changing their color—specifically to a shade that insects dislike.

By altering the color of these nets, we can reduce the need for pesticides. For instance, the study demonstrated this “red effect” using onion thrips (Thrips tabaci), a major vector responsible for spreading iris yellow spot virus and tomato spotted wilt virus, both of which cause severe damage to various vegetables.

Red nets effectively suppressed invasion rates and minimized damage (such as white spots on leaves) in a Kujo leek (Kujo Negi) greenhouse, also known as Welsh onions. Remarkably, this outcome was achieved with minimal pesticide use. Researchers emphasize that “red nets are compatible with sustainable, labour-saving agriculture and hold promise for the future of ‘optical pest control’ based on insect colour vision and behavioural responses.”

Up to 50% less pesticide

The study involved experimenting with red, white, black, and mixed-colour nets to deter onion thrips from feeding on Kujo leeks. Notably, red mosquito nets outperformed other colours significantly in both laboratory and field tests. In practical field trials, onion crops partially or completely covered by red netting required 25% to 50% less insecticide compared to completely exposed fields.

The researchers’ conclusion emphasizes that changing agricultural nets from white or black to red could significantly reduce pesticide use and mitigate the related negative environmental impact. This shift supports more sustainable and effective agricultural practices.

In the world of gardening and horticulture, insect pests pose a constant challenge. As soon as fresh buds emerge, they become targets for aphids, beetles, and other unwelcome insects. While synthetic insecticides are commonly employed to control pests in gardens and crops, their use often comes at a cost to the natural environment. These chemicals can leach into soil and water supplies, harming plants, wildlife, and beneficial insects.

Adding to the complexity, some pests have developed resistance to chemical treatments. Consequently, farmers find themselves with dwindling options and an increasing need for frequent applications.

Enter agricultural nets—a practical solution for safeguarding crops while minimizing reliance on insecticides. Similar to mosquito nets over beds, these nets physically block insects from reaching crops.

The study explored the impact of different net colors on pest deterrence. Surprisingly, red nets, despite having a mesh size larger than the insects’ bodies, outperformed conventional white or black nets with smaller mesh sizes. This innovative approach demonstrates the potential of “optical pest control,” leveraging insect color vision and behavioral responses to enhance crop protection.

Insects without red photoreceptors

“Optical pest control” capitalizes on the unique color vision of insects to deter them," explains Professor Masami Shimoda, co-author of the study. “Most insects lack red photoreceptors in their eyes, making it challenging for them to perceive the color red. Intriguingly, an invisible color can effectively influence their behavior.”

The research team specifically targeted onion thrips—an insect notorious for its resistance to insecticides and its ability to wreak havoc on various essential crops worldwide by feeding on them and transmitting harmful viruses.

To explore the impact of color, the scientists tested three red net combinations (red-white, red-black, and red-red) across three mesh sizes (2 millimeters, 1 millimeter, and 0.8 millimeters). They also evaluated conventional black-white-black-white nets of the same size, both in controlled laboratory settings and out in the field.

Remarkably, all nets containing red fibers outperformed black or white nets in deterring onion thrips.

In a subsequent outdoor trial, the researchers assessed the effectiveness of red nets at different coverage levels: no coverage, full coverage, top-only, and side-only. Given an onion thrips outbreak in the area, insecticide was used.

The fully covered plot required minimal insecticide and yielded high-quality onions. In contrast, plots partially covered by nets (roof or sides only) necessitated additional insecticide applications compared to the fully protected plot.

The "dream" of a scientist

Compared to completely uncovered plots, the use of red nets resulted in a remarkable 25% to 50% reduction in the need for insecticide applications.

Professor Masami Shimoda emphasizes the economic viability of these new red nets. Although they are initially more expensive than pesticides, their long-term usability makes them cost-effective. Moreover, they effectively control pests without the labor-intensive process of pesticide spraying.

Shimoda envisions a future where red nets—while still functionally effective—may not appear red to the human eye. This innovation could reduce manufacturing costs and enhance durability.

Beyond pest control, red nets offer additional benefits. Because they rely on color rather than mesh size, they can have larger holes. This enhances breathability, reduces the risk of fungal infections, and allows better sunlight penetration. Additionally, improved airflow inside greenhouses keeps temperatures manageable, facilitating farmers’ work.

Shimoda concludes that if consumers embrace sustainable agriculture and seek alternatives to chemical pesticides, this straightforward yet powerful solution will undoubtedly gain widespread adoption.

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