Spiders can protect tomatoes from invasive pests

Spiders could provide an environmentally-friendly option to protect crops against pests. New research led by the University of Portsmouth suggests that web-building groups of spiders can control a pest moth that is known to devastate important crops like tomatoes.

The tomato leafminer moth, Tuta absoluta, has developed resistance to chemical insecticides that are also known to cause human and environmental damage. Natural approaches, like using predators such as spiders, are needed to combat infestations. 

Climate change is facilitating the spread of invasive pests that attack agricultural crops by expanding their habitable environment ranges.

To explore natural options, the researchers used tropical tent web spiders, Cyrtophora citricola, which form groups and create large webs to trap prey. In lab settings, different types of prey were introduced to colonies of spiders of varying body sizes. Larger spiders were found to build larger webs that caught more prey.

These findings suggest that the tropical tent web spiders could provide an effective alternative to controlling pests. 

“Because they have evolved the ability to live in groups, these spiders might be better suited for biological control than more aggressive, solitary spiders that are prone to cannibalism,” said study lead author Dr. Lena Grinsted.

“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.”

Tropical tent web spiders are found around the world and their global range overlaps with regions of moth infestations, including Mediterranean Europe, Africa, Asia, and the Middle East. In these regions, environmental health and economic stability could greatly benefit from this sustainable approach. Since the spiders are already found in these regions, using them as pest control would not likely damage the native biodiversity.

The researchers further investigated the seasonal variations in web sizes in southern Spain, and found that pest control would be most effective in the tomato planting and growing season in May and June. 

However, a wasp species (Philolema palanichamyi) found in the region, whose larvae eat spider eggs, could be detrimental to the spider colony. About half of the spider egg sacs were infected with zero surviving spiderlings.

“If wasp infections are controlled, these spiders could form an important part of an integrated pest management system,” said Dr. Grinsted. “This could potentially lead to a reduction of reliance on chemical pesticides, resulting in reduced pollutants in soils, waterways, and food chains in the future.”

“Future studies are now needed to investigate whether the spiders may negatively impact crop pollination by also catching and feeding on bees and other key pollinators.”

The study, published in the journal Insects, involved researchers from the Universities of Portsmouth and Nottingham, and Ben-Gurion University of the Negev in Israel.

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By Katherine Bucko, Earth.com Staff Writer

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