Despite the frigid weather that recently swept across the United States, gardeners are busily planning for the growing season. In the Adirondacks, the stakes are high for gardeners; a shorter growing season is made more urgent by frequent flea beetle attacks. The purpose of this article is to discuss these insects, share information about control measures, and reflect on one potentially positive aspect of living with these insects.
Flea beetles are members of the insect family Chrysomelidae, and the subfamily Alticinae. The name Alticinae is derived from the Greek ‘haltikos,’ which means good at jumping. Due to powerful hind legs, flea beetles can evade predators by hopping. They can also fly, because they have two pairs of wings. The top pair, called the elytra, is hardened and shiny. The bottom pair is membranous, clear, and malleable. Globally, there are approximately 6,000 flea beetle species. An extensive survey of the Adirondacks has not been done, but scientists have found hundreds of species in the northeastern United States. One Adirondack species of interest is the red-headed flea beetle Systena frontalis Fabricius (Coleoptera: Chrysomelidae).
The red-headed flea beetle (pictured) is named in part due to the red coloration on its head. Spanning several millimeters in length, this shiny, fragile-looking beetle may seem cute to the neophyte horticulturalist. Unfortunately for professional farmers and homesteaders alike, the red-headed flea beetle is highly polyphagous, and feeds on hundreds of plant species. Corn, soybeans, alfalfa, potatoes, and cranberries are all susceptible to this pest. Efforts to control it will make more sense when understood in the context of the beetle’s life cycle.
The red-headed flea beetle begins life as an egg, laid singly in the soil, near the roots of plants. Eggs are laid in the fall, and hatch into larvae around April. The grubs are small, translucent-to-creamy in coloration, and are difficult to tease out of the roots that they use as food. Larval feeding can damage the roots badly enough to stop the plant from absorbing nutrients. As the summer progresses, the larvae pupate, and emerge as adults. The adults feed on foliage, leaving a “buckshot” feeding pattern on the leaves that they damage. Adult activity begins in July, and lasts as late as October. In the Adirondacks, one generation is typically observed; however, reports of multiple generations have been made in Georgia, where warm weather allows the insect to proceed through its life cycle faster, and remain active during a wider window of time.
Gardeners take control
Flea beetles can damage plants above and below ground, so control strategies have been developed to protect plants in both locations. For conventional growers, neonicotinoids, arsenical pesticides, and carbamates have all been deployed against flea beetles. Both foliar sprays and soil soaks are available. Foliar sprays are targeted at adults, so they have to be repeatedly sprayed, because adults slowly emerge throughout the summer. Soil soaks only have to be deployed once or twice in the early summer or late in the spring, but this approach is tricky because the pesticide has to get past the detritus on the ground, down into the soil where the larvae are present. An example of a pesticide that often works against flea beetles is cypermethrin. Although it can rapidly kill a wide variety of flea beetles quickly, some growers don’t want to use it, or other insecticides. Here’s why.
According to Scitable, “a collaborative learning space for science” that is affiliated with Nature Education, there are several noteworthy risks of pesticide use. One such risk is volatilization, which occurs when sprayed pesticides evaporate after they’ve been sprayed. Pesticides can then travel away from the land to contaminate nearby areas, potentially harming wildlife and farm workers. Leeching is another problem with pesticides that are sprayed near the ground. Leeching occurs when pesticides move through the soil into groundwater. According to Samantha Jakuboski, of Scitable, pesticides are related to cancer, Alzheimer’s, ADHD, and birth defects. The details can be found in Jakuboski’s article, “The Dangers of Pesticides,” published July 25, 2011. These risks represent some of the reasons why people are interested in organic agriculture.
Organic growers have tried a variety of methods to control the adult stage of these beetles. Row cover can provide a barrier to flea beetles that may try to hop into crops. Trap crops, such as some mustard plants, can be planted before beetles arrive, so that the beetle chooses not to attack vulnerable seedlings. Furthermore, some farmers are waiting longer to plant seedlings, because larger plants are allegedly less vulnerable to adult flea beetle attack. Yellow sticky traps are sometimes used to capture adults, but there is little peer-reviewed evidence that stickies alone will protect crops. The corn flea beetle is a vector of Stewart’s wilt, and a single beetle is all it takes to transmit the disease. Therefore, trapping and exclusion are often not enough to protect a corn crop from this pest.
Bring on the nematodes
Some organic growers rely on soil management to control larvae. Farmers who are willing to till use their machines to kill or disrupt larvae. Aside from tilling, applying beneficial nematodes to the soil is another option. These small, translucent roundworms are naturally found in the soil. They crawl through pore spaces, in search of larvae, then enter the insect through the spiracles (breathing holes), mouth, or anus. Some species possess a tooth-like structure that can help the nematode burrow through the insect’s cuticle. Once inside the insect, the nematode releases a symbiotic bacterial species to kill the insect. The bacterial species consumes the flesh of the dead grub. While feeding on the cadaver, bacterial cells serve the nematode by secreting antifungal substances that preserve the cadaver, protecting it from invading fungi and scavenging insects. The nematode can then reproduce within the dead insect, grazing on the very bacteria that protect it from intruders. When the cadaver is depleted, the nematodes gather their microbes by storing them in pouches along their digestive tract, and seek new insect hosts. This process is animated in the video, “Life Cycle of Entomopathogenic Nematodes: Remastered and Extended Edition,” by the YouTuber Maxwell Helmberger. It should be noted that the nematodes are not known to be harmful to humans, livestock, or crops.
Growers may wonder if the nematodes are reliable enough to control pests, and if they are as good as chemical controls. There are several recent studies that evaluate the effectiveness of entomopathogenic nematodes against flea beetles. For example, Antwi and Redi showed that entomopathogenic nematodes are comparable to the synthetic pesticide imidacloprid for the control of crucifer flea beetle in canola crops grown across the Great Plains of North America. Their work was published in the Journal of Economic Entomology, volume 109, issue 4, during the year 2016. Another paper about the effectiveness of nematodes against flea beetles was published in 2018, in the journal Biological Control. This document was produced by the Steffan Laboratory at the University of Wisconsin – Madison. These scientists found that native Wisconsin nematodes were comparable to neonicotinoids and organophosphates for the control of red-headed flea beetles in cranberry farms.
But what about beetles in New York? Dr. Elson Shields and Tony Testa of Cornell University are two experts in the field of entomopathogenic nematology. The duo is perhaps most famous for their control of alfalfa snout beetles with nematodes native to New York. Their nematodes differ from store-bought roundworms because the NY nematodes are raised anew each year from native nematode populations that have survived and thrived outside, so they are hardy enough to survive in the wild. Laboratory specimens are raised continuously in sheltered conditions, so they do not survive outdoor conditions for more than a season. Shields and Testa spray the persistent, native nematodes into fields that have apparently lost their natural nematode communities, thus restoring the balance of the ecosystem. Due to the multi-year persistence of the Shields and Testa nematode strains, the roundworms provide control after one application for years to come. This treatment is the only option alfalfa growers have, as chemical controls have not been shown to reliably control alfalfa snout beetle.
In recent years, Shields and Testa chose to take on the western corn rootworm, known to pest control professionals as the “billion-dollar bug.” This pest is in the same family as the flea beetles, so it’s possible that the nematodes can control flea beetles too. If you would like to try entomopathogenic nematodes on your property, consider contacting Mary DeBeer, of DeBeer Seeds and Spraying ([email protected], (518) 812-8565). She can sell you the nematodes that Shields and Testa evaluated. If you do use these nematodes, please consider sharing your experiences with Cornell Cooperative Extension – Essex County, as they are interested in spreading information and awareness of these beneficial nematodes. Be advised that the nematodes will target the larvae in the soil, and adults may move into your crop to attack the leaves. Exclusion measures may be needed to stop the intrusion of adults. More information about the collaboration between DeBeer, Shields, and Testa can be found in the article, “Persistent Biocontrol Nematodes: What, Why, How, When and Where to Get Them,” by Kara Lynn. For information about other commercially available strains, consider this product description by Arbico Organics, titled “NemAttack™ – Sc Beneficial Nematodes.”
Although gardeners lament the presence of flea beetles, there are some silver linings to the existence of the pests. When cabbage is attacked by the flea beetle Phyllotreta nemorum L. (Coleoptera: Chrysomelidae), it produces more ascorbic acid to deter the insect. This substance is also known as Vitamin C, which is a helpful nutrient in humans.
Share your tips
Flea beetles play major roles in the gardens of the Adirondack region. They can be controlled by a variety of conventional and organic means, although vigilance is required if any approach is to be successful. Please comment below, if you have any special tips and tricks for dealing with these insects, or if you’d like to learn more about the nematodes used to control them!
Caption: This picture shows a red-headed flea beetle adult that is alive, and another adult that has been killed by the nematode Oscheius onirici. The trial took place in the summer of 2018 in Madison, Wisconsin, although this beetle is present throughout the United States, including the Adirondack region. The nematodes are the small, threadlike worms in next to the beetle, which was placed in a drop of water, so that the nematodes could be made more visible.