Plant geraniums to kill off Japanese beetles

Some insect pests are very specialized—usually feasting on one crop. Many are named after that one particular crop that they ingest most—like pickleworms, melonworms, and sweetpotato weevils. Unfortunately for growers of ornamentals, soybean, maize, fruit, and vegetables, the Japanese beetle is not a picky eater. It feeds on nearly 300 plant species in almost 80 plant families.

The beetle, Popillia japonica, is by far the most destructive pest of ornamental and turf plants in the eastern United States, with more than $450 million spent each year to control it and replace damaged plants.

But there is hope, since there is one plant that the hungry little critter may want to avoid—the geranium, Pelargonium zonale. Though its lovely, colorful flowers are very attractive for all and profitable for growers, the flowers are deadly to the beetles. Within 30 minutes of consuming the petals, the beetle rolls over on its back, its legs and antennae slowly twitch, and it remains paralyzed for several hours. When paralyzed under laboratory conditions, the beetles typically recover within 24 hours, but they often die under field conditions because predators spot and devour them.

Technicians prepare geranium leaves for grinding, extracting, and filtering, while entomologist (background) separates and purifies the active phytochemicals: Click here for full photo caption.
Technicians Gerald Hammel (left) and Alane Robinson prepare geranium leaves for grinding, extracting, and filtering, while entomologist Christopher Ranger (background) separates and purifies the active phytochemicals. (D1585-4)

The poisoning effect of geranium flowers on beetles is not a new discovery; it has been reported in scientific papers dating back to the 1920s. But the phenomenon has not been studied in depth—how or why it happens—until recently, when Agricultural Research Service scientists in Ohio picked up where scientists left off more than half a century ago.

Currently, Chris Ranger, an entomologist in the ARS Application Technology Research Unit in Wooster, is working on a natural, botanical formulation for controlling the beetles based on paralytic compounds isolated from geraniums. Patent rights are being pursued. Ranger is collaborating with Ajay Singh, a natural products chemist from Rutgers, The State University of New Jersey.

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