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Southern Chinch Bug Update
By David Held, Ph.D.
Southern chinch bugs (Blissus insularis) were recently introduced into Europe (Portugal) and are spreading especially in areas where St. Augustine lawns are common. This spread into Europe prompted my review of the literature and an update of any new knowledge on this pest. A literature search for new research on southern chinch bugs revealed relatively few new publications since 2020, despite the importance of this pest and damage potential in southern lawns. In my experience, industry support for insecticide research and not federal funding drives new information on many key pests. With relatively few new active ingredients being released for use in turfgrass in the last 5-10 years, this has limited support for applied research. This article will highlight three areas of importance relative to management of southern chinch bug in lawns.
Diagnostics and Lookalikes
Damage (yellowing or stunted grass that may also appear wilted) in St. Augustine or zoysia is most likely chinch bugs. Similar damage in bermudagrass could be chinch bugs but is more likely broad-headed bugs. Damage to bermudagrass from broad-headed bugs often shows up in August to September. Overwintering adult chinch bugs could begin feeding in spring and continue through summer. A close inspection where you part the grass should reveal these active pests and predatory true bugs. Turfgrass stands have many related insects with sucking mouthparts that look alike, yet not all are bad (Figure 1). Chinch bugs and broad-headed bugs are the most common pests, and minute pirate bugs and bigeyed bugs are common beneficials associated with these pests. The head and eyes of all life stages of chinch bugs are not wider than the body. Chinch bugs most resemble minute pirate bugs in coloration and size, but minute pirate bugs have a thickened, wider first segment to their beak (mouthparts). The heads and especially the eyes of bigeyed bugs and broad-headed bugs are wider than the body. The eyes of the predatory bugs are also large occupying almost the entire lateral sides of the head. These characteristics are easily seen with a hand lens.
Chinch bug basics
Chinch bugs are one of several important sap-sucking bugs in turfgrass. They are in the same order as ground pearls, mealybugs, and most things with ‘bug’ in the common name. These insects insert their thin mouthparts (stylets) into plant tissue as adults or immatures and feed on primarily phloem. While feeding, they also inject saliva which causes a range of symptoms from stunting and discoloration to death.
Chinch bugs are a complex of species in a single genus (Blissus) that runs from Canada to the Gulf of Mexico. Cool season grass managers up north struggle with hairy chinch bug while our foe is southern chinch bug. Southern chinch bugs are grass specialists so all grass including many weedy grasses can support populations. St. Augustine and zoysia varieties will support reproducing populations that most often results in an outbreak.
Chinch bugs overwinter as adults and begin feeding early in spring. They occur in aggregations of adults and immatures. Grass quality can impact survival, life span, and reproduction. Females, for example, on a good host can produce 10–30 eggs over a 10 week life span. A generation (nymphs to adults) is about 30 days, and 3 or more generations are expected in Alabama.
Chemical Control and Insecticide Resistance: Real but Most Products Still Work
Insecticides are the primary way to manage southern chinch bug outbreaks of lawns. About 15–20 years ago, there was a considerable amount of data published on insecticide resistance among populations of southern chinch bugs in Florida. Although the potential for insecticide resistance is high, a recent test from Georgia suggests that pyrethroid insecticides are still working to control chinch bug populations. Insecticides for chinch bug management can be categorized by active ingredients, use restrictions, and residuals or systemic activity. First, the older chemistries (Dursban, Carbaryl, Acephate) are only labelled for use on sod farms. Pyrethroids (examples, bifenthrin, zeta-cypermethrin) are common in many professional and homeowner products. This group of products provide good contact activity with some extended (4 week) residual under lower chinch bug populations. Resistance to pyrethroid insecticides has been commonly reported for populations in Florida. Fortunately, those insecticide resistant populations can still be managed by changing the mode of action to another group like the neonicotinoids (imidacloprid, thiamethoxam, dinotefuran) or anthranilic diamides (e.g., chlorantraniliprole). Products in these two groups of active ingredients have systemic activity and produce the highest mortality when ingested during feeding. Because of the systemic activity, they may have longer residual control than products with contact only activity. However, not all systemic insecticides have good knockdown activity for large populations.
Misinformation on Non-insecticide Controls, Fertilizer, and Irrigation
The internet and now AI driven apps seem to abound with outrageous or impractical solutions (ex. dish soap, vacuuming the lawn, diatomaceous earth) to chinch bug problems. It is useful to review some cultural practices evaluated in published research studies.
Cultivars of St. Augustine grass vary in susceptibility. Common cultivars in Alabama (Common, Raleigh, Palmetto) are among the most susceptible cultivars to chinch bugs. Palmetto is often used in greenhouse and lab experiments to maintain colonies of these insects! This variety in lawns has a very high probability of being infested and damaged. Captiva, Floratam, and Bitterblue have resistance factors for chinch bugs. Thickened and lignified cell walls in resistant grasses prevent the thin stylet mouthparts of chinch bugs from penetrating cells around the phloem. All zoysia varieties in controlled experiments support about 5–10% of the populations produced on St. Augustine grass. Among the tested zoysia varieties, Cavalier supports the lowest (resistant) populations of chinch bugs and Palisades supports the most.
Irrigation, at even low levels, does not positively or negatively change chinch bug damage to turfgrass. A two-month research study from Florida found no impact on grass roots or clipping weight under the three irrigation regimes they evaluated. Chinch bugs density, more than drought, drives the severity of damage symptoms (wilting, etc) in infested St. Augustine. Irrigation can drive outbreaks of insect fungal pathogens among chinch bugs. This is more widely reported for hairy chinch bugs. Coupling high irrigation with fungal pathogens (like Beauveria bassiana) may be a strategy where insecticide use is limited.
Fertilizer applications, as low as 1 lb N per 1000 ft2, can increase populations or damage from chinch bugs. Populations of southern chinch bugs in St. Augustine grass plots that received 0.5 lb N per 1000 ft2 were similar to untreated plots. Nitrogen sources like ammonium nitrate that are faster to release have higher densities of chinch bugs relative to unfertilized and Milorganite-treated plots. The severity of damage in the same study was inconclusive. Damage was more severe early in plots with higher fertilizer rates. High fertility plots (1 or 2 lb N per 1000 ft2) were 100% damaged in 2–3 weeks, then those chinch bugs moved into and damaged the lower fertility plots. Low fertilizer rates will not prevent damage if chinch bugs are present, but it can delay the onset of damage or keep population densities lower.
De-thatching and proper mowing heights in lawns are other ways to reduce chinch bug populations. Why? It is unclear, but papers speculate the removal of eggs or laying sites (dethatching) or changing the microclimate for chinch bugs to develop as reasons. Lawn damage from chinch bugs is also correlated with increased weediness.
Natural enemies, particularly the predatory bugs mentioned earlier, are important to regulate populations of chinch bugs. If you look carefully into a chinch bug infested lawn, you likely see these fast-moving predators chasing their chinch bug prey like a lion after a gazelle. In a perfect world, these predators would increase in response to a chinch bug infestation and eventually greatly reduce or eliminate the population. However, we add fertilizer which allows chinch bugs populations to outpace their predators. And insecticides, like pyrethroids, can reduce chinch bugs but they are also broadly toxic killing most or all of the natural enemies. This is one advantage to newer chemistries like Acelepryn; they have lower toxicity to generalist predators than pyrethroids.
Managing chinch bugs is not impossible, but damage can occur more rapidly and extensively than most other turfgrass pests. This article outlined the key factors (proper diagnosis, understanding inputs) needed to be successful. If you apply these ideas, you will have fewer callbacks or losses due to chinch bugs.
Dr. David Held (david.held@auburn.edu) is an entomologist with Auburn University’s Department of Entomology and Plant Pathology. He has 30 years’ experience as a turf and landscape entomologist, and 22 years as both a faculty researcher and Extension specialist.
