How can you encourage ladybugs to your garden?
Unwanted pests can cause a lot of damage to crops. Pesticides can be a solution, but they can cause problems of their own and can be expensive. It would be helpful if nature lent a hand. Coccinellid beetles, known as ladybugs, ladybirds or lady beetles, can certainly help – but they have been in decline in many places. John Losey and colleagues at Cornell University have examined plants to see what traits the beetles find most attractive. Their results, published in a forthcoming issue of Biological Control, reveal that they prefer plants in the Apiaceae, Asteraceae, and Rosaceae families.
The scientists identified a few factors that attracted the ladybugs. Open flowers helped make nectar accessible. This made Apiaceae, a family including carrots and parsley, and Asteraceae, the family containing daisies and sunflowers, popular with ladybirds. They also like convenient aphids as prey, so they like Rosaceae, the rose family, as well as Asteraceae. A third factor is protection.
Ladybugs like plants with certain defensive trichomes, as they help defend the eggs against predators. Another problem for ladybugs can be herbivores. While herbivores don’t hunt ladybugs, a large herbivore could accidentally eat them while eating the plant. Protection from herbivores can also help defend the beetles.
Finally, the beetles have an eye for colour. They find yellow flowers particularly attractive, and some plants in the Apiaceae, Asteraceae, and Rosaceae produce yellow flowers.
The results come from a combination of site surveys and a citizen science project, the Lost Ladybug Project. The Lost Ladybug Project produced over 38,000 images between 2008 and 2018, allowing the identification of plants occupied by ladybugs. These were whittled down to 1,948 unique observations identifiable to at least the plant family level from all 50 US states, 12 Canadian provinces and 10 Mexican estados.
While ladybugs are an asset to any garden, Losey and colleagues argue that their work has potential commercial benefits. Crops like alfalfa and soybean can suffer from pests but lack the attractive features that the entomologists have identified. Planting suitable plants near the crops could help bring in natural defences to aid farmers in their fight against pests. Once the ladybugs find the crop fields, the natural abundance of prey should keep them there, say the scientists.
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Losey, J., Allee, L., Gill, H., Morris, S., Smyth, R., Wolleman, D., Westbrook, A. and DiTommaso, A. (2022) “Predicting plant attractiveness to coccinellids with plant trait profiling, citizen science, and common garden surveys,” Biological control: theory and applications in pest management, (105063), https://doi.org/10.1016/j.biocontrol.2022.105063