Bagrada bugs, which were first confirmed in California six years ago, have been steadily expanding their range to the east and north.

They now have been confirmed as far north as Yolo County and have taken up residence in counties stretching from Santa Clara and San Mateo west to Fresno and Inyo counties, according to a University of California news release.

The university has tracked the pest's expansion using citizen scientists.

Bagrada bugs, which have also hit crops in Arizona's Yuma Valley, prefer cruciferous vegetables, such as cabbage, kale, cauliflower, brussels sprouts and broccoli.

In home gardens, they also have been found on green beans, cantaloupe, corn, peppers, potatoes, tomatoes and sunflowers.

In addition, the bugs have been found on ornamentals, including sweet alyssum, stock and candytuft.

Pesky bagrada bugs expand northward in CaliforniaAdult bagrada bugs are about the size of a watermelon seeds with black backs and white and orange markings.

Immature nymphs are more round with red, black and white markings. They can be mistaken for ladybird beetles.

Both adults and nymphs have piercing and sucking mouth parts. As they feed, they remove plant sap and cause dead spots plant leaves and stems where they feed.

Under severe infestations, especially with young transplants, the pest can stunt, deform and even kill plants.

Originally it was hoped that Northern California's colder winter temperatures would help prevent their northerly march.

But bugs simply take up refuge in the top layer of soil around the crops and appear to survive.