Glowing on the Golf Course: Fluorescent Imaging Reveals Turfgrass Pest’s Most Active Period

A new step forward in managing a pernicious pest of golf course putting greens comes with an assist from an unlikely source: marine biology.

Researchers at Penn State University’s Center for Turfgrass Science have been seeking to improve management methods for the annual bluegrass weevil (Listronotus maculicollis), but a key challenge is to determine when the insects are most active in the grass canopy. Mowing putting greens can remove some of the weevils, and timing the mowing for the weevils’ active foraging period might remove more of them. But the weevils are small (at most 4.5 millimeters long) and difficult to monitor, says Benjamin McGraw, Ph.D., associate professor of turfgrass science at Penn State. So McGraw and then-Master’s student Benjamin Czyzewski needed a way to make the weevils easier to see, during both night and day.

Their first attempt ran into trouble. They marked weevils with fluorescent ink and placed them in cages with a UV light and a time-lapse camera. “No matter how hard we tried to exclude other insects, nocturnal insects would somehow get in, be attracted to the UV light, and block the time-lapse images,” McGraw says.

So, they went searching for solutions. On the tradeshow floor of the 2015 Entomological Society of America Annual Meeting, McGraw came across NightSea, which makes tools for fluorescent photography and whose founders originally created their equipment for exploring coral reefs and underwater sea life at night. NightSea’s flashes and camera filters block white light and allow fluorescence—whether natural or, in this case, via human-marked ink) to shine.

This led to a new experimental set up, using still photography taken at one-hour intervals instead of time-lapse video, and this time it worked. The results offered a new understanding of the weevils’ daily behavior patterns and are reported in a new article published in October in the Environmental Entomology.

Researchers at Penn State University monitored activity periods of annual bluegrass weevil (Listronotus maculicollis) with an experimental setup in which 30-by-30 centimeter arenas were used to contain weevils within the putting grass surface. A custom-made camera box holding a digital camera with filters and an external flash was used to excite a mark placed on adult weevils using a neon marker. (Image originally published in Czyzewski and McGraw 2018, Environmental Entomology)

Researchers at Penn State University monitored activity periods of annual bluegrass weevil (Listronotus maculicollis) with an experimental setup in which 30-by-30 centimeter arenas were used to contain weevils within the putting grass surface. A custom-made camera box holding a digital camera with filters and an external flash was used to excite a mark placed on adult weevils using a neon marker. (Image originally published in Czyzewski and McGraw 2018, Environmental Entomology)

Previously, research had suggested that L. maculicollis behavior was driven by light cycles, but Czyzewski and McGraw’s study showed temperature is the stronger factor. They found that the weevils’ activity was greatest when temperatures were between 14 and 17 degrees Celsius (57-63 Fahrenheit) and declined as the temperature rose. The researchers conducted their tests during April, May, and June, and the progression of the seasons meant that the weevils’ prime activity period occurred during the day in the spring but during early morning, right after sunrise, in the summer.

McGraw says the findings will help golf course managers better time their monitoring efforts to detect annual bluegrass weevil infestations and their insecticide applications for the pest’s most active periods. Shifting mowing times may be trickier, though, as course mangers typically want to keep mowers out of the way of golfers, but the knowledge about the weevils’ active periods will allow them to make more informed decisions.

“I am just glad that we didn’t find that annual bluegrass weevils were most active on top of the canopy during the middle of the night,” McGraw says. “That would have made implementing mechanical removal extremely difficult. I wouldn’t want to have to tell turfgrass managers that they need to work in the middle of the night. They already work really long hours, and if anything, I hope our research would make their lives easier, not more challenging.”