Annapolis, MarylandHanging a cluster of twigs on a tree might sound like a pointless exercise, but Heather Disque, a forest pest entomologist for the state of Maryland, isn’t hanging just any sticks in Martinak State Park.

Hundreds of immature parasitic wasps are hidden in Disque’s bundle, and when these Spathius galinae mature in several days, they’ll be driven by a single need: to lay their eggs on the larvae of the emerald ash borer, an invasive beetle that has over the past few decades ravaged many species of ash trees across the United States.

Scientists have been using parasitic wasps for 10 years, with some success, but this particular species, originally from the Russian Far East, is the best