In keeping with our Halloween tradition of visiting bugs in orange and black like monarch butterflies, milkweed bugs, and milkweed leaf beetles, this week we present a spooky story of a garden pest, Colorado potato beetle, and its nemesis, the two-spotted stink bug. Anyone who has grown potatoes or related crops such as tomatoes has likely encountered the Colorado potato beetle as both larvae and adults shredded the leaves of your plants. You may not have known that this traveler originated in Mexico where its aboriginal host was a member of the potato family called buffalo bur. When Spanish colonists arrived in Mexico with cattle, herds were driven from Mexico northward to markets in Texas. As cattle moved north, buffalo bur and the beetle moved with them. The weed and beetle continued to expand their range north and east during the 18th century. Potatoes were introduced from Europe to North America in the late 1700’s and by the 1800’s they too had expanded their range from New England westward. Sometime around 1860 the beetle acquired a taste for potato and made the jump from buffalo bur to its delectable new host. It has since spread to many places where potatoes grow, including the Washington metropolitan region.
Although potato is common in their diet now, Colorado potato beetles first fed on other members of the potato family, like buffalo bur.
This summer while visiting a potato patch, I witnessed droves of Colorado potato beetles eating the tops of plants into nubbins. Prowling around the vegetation were gorgeous nymphs and adults of the native two-spotted stink bug, Perillus bioculatus. Like their cousins wheel bugs, which we met in a previous episode, predaceous stink bugs actively hunt and kill their prey. On a potato plant loaded with beetles, I watched a two-spotted stink bug stealthily approach an unsuspecting potato beetle larva. The actual attack was much less an energy-charged pounce and kill and more of a seemingly gentle poke with the stink bug’s beak. Before the hapless beetle larva could attempt to escape, the proboscis of the stink bug hit pay dirt. After spearing the beetle larva with its beak, the stink bug injected digestive enzymes into its victim. These enzymes help liquefy tissues in the body of the beetle. A muscular pump in the head of the stink bug enables the bug to suck the nutrient rich broth from its prey.
Whether it’s dining on eggs of Colorado potato beetles or contemplating an attack on a Colorado potato beetle larva, the two-spotted stink bug is an awesome predator of garden pests.
As I wandered around the potato patch, I noticed that only a few plants had potato beetles and an attendant complement of stink bug assassins. Many healthy plants lacked beetles and stink bugs. How do stink bugs locate plants with potato beetles in a vast field of potatoes where many plants have no potential prey? Clever researchers discovered that as potato beetles eat potato plants, the leaves of the plants release volatile compounds into the atmosphere. Hungry two-spotted stink bugs on the prowl for prey are able to detect the compounds from beetle-wounded plants and use them as an olfactory beacon to find the beetle infested plants that house their prey. Sometime before the killing frost annihilates the remnants of your potato patch, pay one last visit to spot predator and prey dressed in orange and black.
The following fascinating studies were used to prepare this Bug of the Week: “Identification of Volatile Potato Sesquiterpenoids and Their Olfactory Detection by the Two-spotted Stinkbug Perillus bioculatus” by Bernhard Weissbecker, Joop J. A. Van Loon, Maarten A. Posthumus, Harro J. Bouwmeester and Marcel Dicke, and “Comparison of Perillus bioculatus and Podisus maculiventris (Hemiptera: Pentatomidae) as Potential Control Agents of the Colorado Potato Beetle (Coleoptera: Chrysomelidae)” by Judy Hough-Goldstein and D. McPherson. The great reference “Invasive species” was also consulted for this episode.