The red-headed flea beetle (RHFB), Systena frontalis, also known as the cranberry flea beetle has been emerging in the last week. RHFB is native to the United States with a range from Maine to Florida to Texas and Montana. It is an important pest in nurseries, greenhouses and agricultural crops, including cranberry and, in the last decade or so, it has become more of a problem in these systems.

In cranberry, RHFB larvae feed on cranberry roots and adults feed on foliage and occasionally fruit. RHFB has likely always been present in cranberry marshes in Wisconsin but was probably historically controlled by broad-spectrum insecticides. The pest is now reappearing in higher numbers, which we suspect is due to the use of more selective insecticides.

Appearance.  Adult RHFB are shiny, black beetles with a reddish head. They are about 1/10” – 1/4” long with antennae nearly half as long as their body and enlarged hind legs used for jumping when disturbed. Adult females are slightly larger than males.  Larvae are 1/5” – 1/4” long with a fleshy projection at the tip of the last abdominal segment.

Life Cycle. Female RHFB deposit single eggs into the soil in late summer to early fall. RHFB overwinters in the egg stage which requires a cold period for optimal egg hatch. In the laboratory optimal hatch occurs following a 15-week period at 41˚F (Jaffe et al. 2021). Eggs are found predominantly at 15-30 cm from the soil surface (Jaffe et al. 2021). Eggs will hatch into white larvae in the spring and larvae will develop through three instars before pupating approximately three weeks later. Larvae feed on roots from June through August in Wisconsin. RHFB pupae have not been formally described but are likely present in Wisconsin from late June to early August. Adults begin to emerge in early to mid-July and are present through September in Wisconsin. There is one generation of RHFB per year in Wisconsin.

Host Range.  RHFB is an occasional pest of cranberry and is also found on cranberry weeds including marsh St. John’s wort, Joe-pye weed, smartweed, jewelweed, and hardhack. Overall, it has a very broad host range of over 50 plant species that include many woody and herbaceous plants. RHFB is shown to prefer feeding on weeds near cranberry beds but will switch to feeding on cranberry foliage and sometimes fruits if weeds aren’t present or are mowed. RHFB is also an occasional pest of other commercial crops, including alfalfa, beans, beets, blueberries, cruciferous vegetables, eggplant, horseradish, potato, grapes, and sweet potatoes.

Symptoms and Effects.  RHFB larvae feed on plant roots and underground cranberry runners. Severe infestations can cause girdled roots and vine death.  Adults feed on the upper and lower surface of foliage, skeletonizing leaves, and may also feed on the surface of cranberry fruit. The skeletonization of leaves leads to the leaf browning, which may result in the individual uprights dying. Heavy feeding can impact bud development and yield in the following year. Since adults prefer areas of lush growth, adult RHFB populations and damage are usually patchy. Adults prefer feeding on new leaves rather than older mature leaves (Jaffe et al. 2021).

Scouting.  Monitoring for RHFB focuses on adult beetles, since finding larvae in the soil is difficult. Sweep nets can be used to monitor for RHFB adults, but it is important to sample thoroughly across different areas to account for the patchiness of adult infestation. There is no firm action threshold for RHFB in cranberry due to how patchy infestations can be. However, it is recommended to take action if you find more than ~15 RHFB per 20 sweeps averaged across representative areas of a cranberry bed.

Control.  If sweep net samples yield enough adult beetles to warrant an insecticide spray, there are several products that are effective against RHFB adults.

These include neonicotinoids (such as thiamethoxam, acetamiprid, dinotefuran, imidacloprid), diamides (such as chlorantraniliprole, cyantraniliprole) spinosyns (such as spinetoram, spinosad), pyrethroids (such as bifenthrin, fenpropathrin), organophosphates (such as phosmet, diazinon) and carbamates (such as carbaryl). Soil chemical applications targeting the larvae have been tested but were not very successful with the products allowed around bloom time. Please check with your handlers before using a new product as handlers may have restrictions on certain products for domestic and/or foreign markets. Handlers may extend PHIs beyond the number of days stated on the label to reduce residues, so please always check with your handler. And as always, make sure to read the labels before using any pesticide.

As always, it is recommended to rotate chemical classes to delay insecticide resistance, and to consider the effects on non-target and beneficial insects. Please check the Cranberry Pest Management in Wisconsin Guide A3276 for full product recommendations.

Little work has been done to develop alternative management strategies for RHFB. Since RHFB tends to prefer some weed species, trap crops could be effective but may be difficult to implement in cranberry. Biocontrol may be a promising way to control RHFB larvae and research from UW-Madison showed that native Wisconsin entomopathogenic nematodes significantly reduced RHFB populations in small scale experiments (Foye, 2019). Since RHFB is an emerging pest, there is still little information regarding other natural enemies that may help control the pest.

Happy growing season!

This article was posted in Cranberry, Insects and tagged Christelle Guédot, Cranberries, cranberry, Cranberry Flea Beetle, Hanna McIntosh, insects, red-headed flea beetle.