It is Western Jimson Weed (Datura wrightii) season.

Some of you may know this beautiful plant as sacred datura, just another common name for it. The wide low-growing annual shrub has wide velvety leaves and large white trumpet-shaped flowers that open at night and twist shut during the day.

Understandably, nighttime pollinators love datura. But during the day, you can still find visitors such as a few bees or flies that will take advantage of a flower that stays open a little longer than usual. Your chance of also running into a three-lined potato beetle or two is pretty high.

As its Latin name, Lema daturaphila, indicates, this beetle has a particular affinity for the plant. While it will also feed on many other plants in the nightshade family (Solanaceae), the preferred snack is Western Jimson Weed. The beetle will gladly spend its entire life cycle on it. The adult is a small yellow oblong beetle with, you guessed it, three black lateral lines on the elytra.

After mating, the female will lay a cluster of orange eggs under a leaf. When the larvae hatch, they will start ferociously feeding on the leaves and stems as seen in this observation on iNaturalist posted by Peter Thomas (docprt): inaturalist.org/observations/33861984.

Now you may have heard that some plants in the nightshade family are toxic, and some are not.

For example, potatoes, tomatoes, peppers, and eggplants are quite delightful. But our datura is among the most harmful cases. All parts of the plant are toxic, containing tropane alkaloids. Most herbivores are deterred by them, but not our potato beetle. In fact, quite to the contrary, the larva uses the plant to its advantage. Nothing is wasted, including waste. The larva will use its own feces on its back to deter predators. Captain America’s got nothing on this “fecal shield”.

When the larva is ready, it will pupate after falling to the ground and burying in the soil. It emerges later in the summer as an adult and mates, securing a second generation for the season. When that second generation reaches adulthood and temperatures drop, the adult beetle will overwinter in the soil and re-emerge the next spring. One thing I find fascinating is that in different parts of the country, where temperatures drop sooner, the second generation overwinters as a pupa, not as an adult.

Since three-lined potato beetles feed on a variety of nightshade family plants, they occasionally find themselves in domestic gardens and can be a bit of a pest. In this case, crop rotation is recommended as a control. Since the beetles spend their entire life cycle on one plant, moving that plant around can be disruptive enough.

For some nice visuals, check out this short video: youtube.com/watch?v=T-DBzeeTyD0

Photo credit: Peter Thomas

Editor’s note: Patricia Simpson is a trail guide with Mission Trails Regional Park.