Arachnophobes may never consider having spiders protect their farms, but new research says that these particular creepy crawlies can eat pest moths of important crops like tomato and potato worldwide.
Tuta absoluta, another name for the tomato leafminer moth, has evolved to resist chemical insecticides, wreaking havoc on humans and the environment.
Therefore, researchers from the University of Portsmouth suggested that different, natural approaches like using natural predators are essential to tackle such infestations.
People who are afraid of spiders may not want to go with this option, but there’s a good reason for bringing these arthropods. Tropical tent-web spiders, Cyrtophora citricola, are non-cannibalistic spiders that form groups and create large webs to capture prey.
How the spiders act
in the study, the researchers tested these spiders with different types of prey, namely the small tomato leafminer, flightless fruit flies (Drosophila hydei) and larger black soldier flies (Hermetia illucens).
The prey insects were introduced to colonies of spiders with different sizes. During observation, researchers found that larger spiders built larger webs and caught more prey in general, being able to catch and eat the tomato leafminer and fruit flies more easily. Meanwhile, the larger black soldier flies could get away more often.
Lead author Dr. Lena Grinsted, Senior Lecturer in Zoology in the School of Biological Sciences, said that this discovery showed how tropical tent-web spiders have the prospect to be a great natural control agent of flying insect pests—although they should grow bigger first in order to be effective.
These spiders have also evolved to live in groups, making them more suitable for biological control. They’re the better alternative when compared to the more aggressive, solitary spiders which tend to eat one another.
“Spiders that can form groups of hundreds, or even thousands, of interconnected webs can provide large surface areas of capture webs capable of intercepting high frequencies of airborne insects.
“Spider colonies also provide a substrate for other spider species, further increasing the number of predators and therefore, potentially increasing pest insect capture capability within colonies,” Dr. Grinsted said.
Tropical tent-web spiders are widely spread across the globe. In fact, their range overlaps with regions of moth infestations, including Mediterranean Europe, Africa, Asia, and the Middle East—areas that may benefit from this natural and sustainable agricultural approach.
Per the researchers, since the spiders have inhabited those regions, their job as a control agent won’t likely damage native biodiversity, at least not significantly.
When spiders may not work
After the lab test, researchers investigated the varying web sizes in different seasons in southern Spain. They found that the spiders are most effective in the tomato planting and growing season in May and June.
Unfortunately, wasps will be a problem. Surprise, surprise.
The researchers found that a wasp species that lives in the region called Philolema palanichamyi eats spider eggs in its larvae form. In southern Spain, researchers discovered that about half of the spider egg sacs were infected with zero surviving spiderlings. So, these wasps will negatively affect the spider colony.
Dr. Grinsted said that if the wasp infections are kept in check, the spiders could become an important part of an integrated pest management system, and they might lead to a decline of chemical pesticides dependence.
In turn, all of that could result in reduced pollutants in soils, waterways, and food chains in the future.
The lead author also added that there should be a further examination to determine if the spiders could leave a negative impact on crop pollination due to their consumption of bees and other key pollinators.
One thing for sure: if you’re an arachnophobe but you want to have natural pest management by using spiders, then you might want to overcome your fear of arachnids.
That said, you may find relief that other natural measures of protecting your crops are actually achievable, like using fungus.
Fungi that help plants to repel pests
Thanks to never-ending research that scientists do, we don’t have only one or two pest-controlling alternatives that are safer for local habitat and ones that utilize nature.
As we know, more farmers have sought agricultural solutions that include less to no chemical elements so that they can contribute positively to reducing environmental impact in agriculture.
Well, they may be able to fully depend on entomopathogenic fungi in the future; that is, if they’re not on board with deploying spiders.
Entomopathogenic fungi are microorganisms with the ability to make pest insects ridden with disease, which make them on par with spiders as an effective control agent.
Researchers from Agricultural Entomology Unit at the University of Córdoba (UCO) have explored the potential of these fungi on olive fruit fly. What they found was, the fungi don’t just get rid of pests, they also help plants when they’re experiencing nutritional deficiencies, like iron.
All in all, Entomopathogenic fungi are beneficial to the plants they’re protecting.
In their experiment, researchers with the Department of Agronomy at the UCO (DAUCO) found how strains of fungi were able to make the most iron available to the plant. Then, they wanted to know which iron deficiency responses were induced by the fungus.
One of the researchers María José García explained, “We verified that it induces the two main iron acquisition genes. We could say that it makes plants more efficient at absorbing iron from the soil.”
Entomopathogenic fungi help plants get iron both directly and indirectly. “The direct mechanisms are the part at the molecular level, the changes made by the genes that induce these microorganisms to provide the plant with more iron,” another researcher Meelad Yousef noted.
Yousef also added that indirectly, the process happens in the soil. So, the fungi’s effects don’t affect the response of the plant due to the fact that being in the soil makes iron more available to the plant.
In the UCO study, researchers tested the fungi on cucumber and melon. They learned that from the first day they applied entomopathogenic fungi solution, the plants have started to induce responses to iron deficiency.
This is important because in Spain, many soils are calcareous—the type that isn’t easily absorbable for plants.
With these findings, there will be more value added to bioinsecticide developed from this strain.
Repelling pervasive pests such as aphids and whiteflies is highly feasible with the use of these fungi. Firstly, they’re effective, made from natural microorganisms, and not harmful to the environment.
Secondly, they provide additional advantages because they have the right properties to make plants acquire more iron. As a result, farmers can reduce chemical fertilization, which in turn may also reduce costs and damage.
What we should remember about studies from UCO and University of Portsmouth is that the plants they’re testing are not the same. We don’t yet know for sure if the fungi will work on tomatoes and potatoes or if the spiders will be effective for aphids and whiteflies.
And although the spider one delivered promising results in the test; the authors stated their limitations still.
Nonetheless, I still believe that these findings are important and will be useful for future scientists who want to develop natural pest repellent.