Using swarms of spiders to protect crops from agricultural pests could be beneficial to the environment. Tuta absolute, the tomato leafminer moth, has developed resistance to chemical insecticides, which cause human and environmental harm, so alternative approaches, such as using natural predators such as spiders, are required to combat infestations.
The researchers looked into using tropical tent web spiders, Cyrtophora citricola, as pest control because they form groups, are not cannibalistic, and build large webs to catch prey. Different types of prey were introduced to colonies of spiders of varying body sizes in lab settings, including the small tomato leafminer, flightless fruit flies (Drosophila hydei), and larger black soldier flies (Hermetia illucens). Larger spiders built larger webs and generally caught more prey, and they easily caught and ate tomato leafminer and fruit flies, whereas larger black soldier flies were rarely caught.
"Our findings suggest that tropical tent web spiders have the potential to be an effective biological control agent of flying insect pests, at least after growing to medium-sized juveniles," said Dr. Lena Grinsted, Senior Lecturer in Zoology in the School of Biological Sciences at the University of Portsmouth and lead author of the study. "Because they have evolved the ability to live in groups, these spiders may be better suited for biological control than more aggressive, solitary spiders that are prone to cannibalism."
"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 serve as a habitat for other spider species, increasing the number of predators and, potentially, pest insect capture capability within colonies." Climate change, caused by human overpopulation and reliance on fossil fuels, is facilitating the spread of invasive pest species of agricultural crops, such as the tomato leafminer, by broadening their habitat ranges.
Tropical tent web spiders live in colonies all over the world, and their global range overlaps with moth-infested regions such as Mediterranean Europe, Africa, Asia, and the Middle East, all of which could benefit greatly from this sustainable agricultural approach. Furthermore, because these spiders are already present in these areas, the introduction of pest control spiders is unlikely to have a significant impact on native biodiversity.
The researchers looked into seasonal variations in web sizes in southern Spain and discovered that pest control would be most effective during the tomato planting and growing seasons in May and June. They discovered, however, that a wasp species (Philolema palanichamyi) found in the area, whose larvae eat spider eggs, could be harmful to the spider colony. The researchers discovered that approximately half of the spider egg sacs were infected and had no surviving spiderlings.
"If wasp infections are controlled, these spiders could form an important part of an integrated pest management system," Dr. Grinsted added. This could lead to less reliance on chemical pesticides in the future, resulting in less pollution in soils, waterways, and food chains. Future research is needed to determine whether the spiders have a negative impact on crop pollination by catching and feeding on bees and other key pollinators.
