Active Beetles in Turfgrasses
Predatory ground beetles and billbugs were two groups of beetles commonly collected from pitfall traps in 2011 in northern Utah turfgrasses. Both are active beetles that rarely fly; however, predatory ground beetles are beneficial insects and billbugs are pests of turfgrasses.
PREDATORY GROUND BEETLES
Predatory ground beetles are common predators in the family Carabidae that frequent lawns, parks, and golf courses. In Cache County, Pterostichus melanarius was the most abundant predatory ground beetle. This beetle was introduced to the U.S. from Europe and is widely distributed. These beetles are generalist predators that actively search for a wide variety of prey including caterpillars and other insect larvae, aphids, beetles, and snails. Pterostichus is highly mobile, nocturnal, and both the larval and adult stages are predatory. Although these beetles do not fly, they are occasionally found in plant and tree canopies searching for food. With their high abundance and ground activity it is not surprising that these beetles are found scurrying across floors in homes from time to time. In 2011 in northern Utah, activity of adult beetles started in May, peaked in August, AND declined drastically in October. Pterostichus overwinters in the larval stage in the soil. The benefits of this predator have been especially recognized in agricultural systems. The conservation and enhancement of predatory ground beetle populations has been achieved by using “beetle banks” which are strips of grasses or perennial refuge within agricultural crops. The impact of predatory ground beetles against turfgrass pests, however, is less understood.
Billbugs are weevils (or snout beetles) whose larval stages can be damaging to turfgrasses. Often billbug larvae are overlooked as major turf pests because damage resembles drought stress and larvae are small. Larvae feed in grass stems and move down through the thatch layer and then feed on turfgrass roots. Adult billbugs are not fast, but rather meander and “play dead” when disturbed. Monitoring of adult billbugs in 2011 revealed a complex of three billbug species in northern Utah: the hunting, bluegrass, and Denver (aka Rocky Mountain) billbugs. This year the most common billbug collected was the hunting billbug. Typically adult activity for hunting and bluegrass billbugs is low during June and July. The cool and wet spring of 2011 pushed adult emergence back about a month in northern Utah, starting around late May, so the peak was in July. Adult billbugs will move to sheltered sites (e.g., in weedy areas, debris, or perennial shrubs) to overwinter. Hunting and bluegrass billbug larvae that have not become adults before freezing temperatures occur may not survive through the winter. It is thought that only Denver billbugs can overwinter as adults or larvae. Chemical control for billbugs is ineffective in the fall season and only a few insecticides have curative properties against turf insects. Those insecticides, however, have had mixed results.
Beetles make up a large component of the turf insect community in Utah. In addition to predatory ground beetles and billbugs, other beetle pests such as white grubs, and other predators including some rove beetle species can be present. Monitoring these predatory and pest beetles is important to maintain beneficial services (i.e., biological control) from the good guys and to make an informed decision about early treatment of damaging larval stages of turf pests.
-Ricardo Ramirez, Entomologist