The bagrada bug (Bagrada hilaris), an African native, was first found in California in 2008. By 2010, it had spread to southern New Mexico and was found in Santa Fe County in 2012. Adults and nymphs pierce leaves, stems, flowers, and seeds with their needle-like mouthparts, inject digestive enzymes, and suck plant juices. Starburst-shaped, brown lesions form on leaves and stems. Other damage includes “scorched” leaves, stunted growth, and forked or multiple heads on cauliflower, broccoli, and cabbage. Bagrada bugs may kill seedlings.
Bagrada bugs prefer to feed on members of the Brassicaceae family, which also includes kale, mustard, and arugula; and ornamental plants such as sweet alyssum, stock, and candytuft. However, they may eat many different crops, among them corn, potatoes, tomatoes, asparagus, melons, carrots, peppers, roses, and cotton. The bugs feed on both cruciferous plants (wild mustards, shepherd’s purse, London rocket) and non-cruciferous weeds (lambs quarters, purple nutsedge, field bindweed). The adults are shield -shaped and 3/16- to 1/4-inch long and are black with orange markings. The first instar nymph is bright orange and the second through fifth nymphs are red with dark markings.
Bagrada bugs overwinter as adults in leaf litter or topsoil. In the spring, females lay their eggs (singly or in small batches) on the soil surface or on the leaves of host plants. Each female lays about 100 eggs in her life. The eggs hatch in four to nine days. Larvae progress through five stages. The egg-to-egg cycle depends on the temperature, generally taking 38 to 65 days. In New Mexico, two or three generations per year are possible. They become locally abundant in mid-July and may reach high densities with hundreds of bugs feeding on a single plant.
Control of the bagrada bugs is difficult. They are not easily seen until the infestation is out of control. Feeding damage is easier to spot earlier in the summer than the insects themselves; they are more active (and more easily spotted) when the temperature is above 75 degrees.
In a home garden, the bugs can be removed by hand (wear gloves — they stink) and drowned in soapy water. Large numbers of bugs can be shaken onto a sheet and vacuumed. The trapped bugs should then be bagged or killed since they can survive vacuuming. Pyramid traps baited with crushed sweet alyssum can destroy bugs, particularly when numbers are high. These traps can be made from soda bottles or adapted from commercially available stink bug traps. (Chemical lures that attract other stink bugs will not work.)
Currently there are no effective biological controls in the USA. Birds find their taste to be unpleasant. The adult bugs usually escape pesticides by flying away only to return later. Until there are approved pesticides, home vegetable growers need to use manual methods or bag the plant (including the stem) to exclude the bugs.
Terry McGuire was a professor of genetics at Rutgers University for 36 years. He was also a senior fellow of the National Center for Science and Civic Engagement, helping educators connect science to civic issues. He moved to Santa Fe in 2014. He is a Master Gardener and a Master Composter.