Attracting beneficial insects
Showy milkweed attracted the greatest number of beneficials.
A sticky trap monitors beneficial insect abundance near flowering yarrow plants.
After evaluating more than 40 flowering perennial plant species, Dr. David James found that while virtually all the plants attracted beneficial insects, some plants attracted more groups of insects than others.
The evaluation was in preparation for James’s research project launched this year called Beauty with Benefits. All of the plants chosen for his study were growing wild in natural sage steppe landscapes in the Yakima Valley. He assessed the plants’ attractiveness to beneficials by placing sticky yellow traps on or adjacent to the plants during spring and late summer and analyzing trap catches.
The trap results have helped him narrow down the list of plant species that warrant further study to about 25, although there are a few more he didn’t evaluate last year that he would like to look at. He noted that there’s been no published data on the attractiveness of Pacific Northwest indigenous flowering plants to beneficial insects.
The Washington State University entomologist ranked the top 20 plants that have beneficial insect potential based on the number of total beneficials caught in the traps. Showy milkweed, ranked number one, attracted the greatest number of beneficials and was the only plant that averaged more than 100 beneficials per trap per week.
He found that different plants had varying attraction to different groups of beneficials. For example, mite-eating ladybeetles were strongly attracted to rock buckwheat and Columbia Basin prickly pear, while minute pirate bugs were most attracted to yellow sweet clover (the one nonnative in the study), gray rabbitbrush, tall buckwheat, and showy milkweed. Munro’s globemallow was the most attractive to the Anagrus wasp, an important leafhopper predator.
James looked for plants attracting a wide variety of beneficial insects because they’re likely to have value as refugia or ground cover plants. But he’s also interested in plants that attract certain species or insect families of beneficial insects that are key players in the biological control of grape pests, such as leafhoppers, cutworms, mites, thrips, and mealybugs. Such plants could be selected components of “farmscaping” (manipulating the agricultural ecosystem to enhance biological control) and be used to target specific pest problems. For example, luring mite-eating ladybeetles into the vineyard by planting rock buckwheat could help control spider mite populations.
Gray rabbitbrush was found to be highly attractive to late-season beneficial insects and could serve to concentrate populations for overwintering.
Many of the buckwheat species have potential as beneficial insect attractors and are low growing and could tolerate mowing, he said. “The buckwheat species are extremely hardy, really tough plants, and they’re well adapted to this environment. I have a lot of hope for the buckwheats.”
James plans to include a few nitrogen-fixing plant species in the study, including yellow sweet clover and the native Astragulus species.