Ten-Lined June Beetles

Has a largish beetle with stripes ever hissed at you? It was probably a ten-lined June beetle. Ten-lined June beetles (Polyphylla decemlineata), also known as watermelon beetles, can kill mature trees outright.

Male ten-lined June beetle (Amanda Townsend) CC BY-SA 3.0

Ten-lined June beetle description​

The stripes are a giveaway for this relatively large beetle. Averaging 1.5 inches or longer, male ten-lined June beetles have distinctive antennae made up of overlapping scales, called lamellate plates. When these pests feel threatened, those plates are closed up and air is forced between the back and wings to create a hissing sound. Adult females do not fly. Eggs are 1/16" long, oval and cream-colored. Larvae have a white body and a brown head. They can grow to 2” in length with 3 pairs of legs.

Male ten-lined June beetle (Junkyardsparkle) CC0

Damage caused by ten-lined June beetles

Almond, apple, cherry, and plum trees are susceptible to damage caused by larval feeding of ten-lined June beetles. Trees may simply not thrive, at first. By the time the damage is significant, it is usually too late to save the tree. Adult ten-lined beetles feed on leaves, but that damage is insignificant.

​Ten-lined June beetle lifecycle

​Ten-lined June beetles are relatively long-lived insects.  It takes 2 years to complete one generation of ten-lined June beetles. They can exist in the larval stage for up to 4 years. Larvae are found in the top 14” of soil where they feed on roots. Each summer and early autumn, adult females emerge from the soil and release pheromones to attracts males. Males fly from dusk until midnight or so. After mating, the females return to the soil where they lay eggs.

Canadian ten-lined June beetle (Alex of Canada) CC BY-SA 4.0

Ten-lined June beetle open (Amanda Townsend) CC BY-SA 3.0

Ten-lined June beetle controls

Heavily infested trees must be removed and the surrounding soil fumigated to prevent infestation of nearby trees. Luckily, that is rarely necessary in a home garden. Because female ten-lined beetles do not fly, populations spread slowly. Commercial growers use soil insecticides to kill beetles in the larval stage. Aboveground insecticides are not effective. 

Tachinid flies parasitize these pests, but not significantly. Because male ten-lined June beetles are attracted to light, you can capture them on your porch with a butterfly net and feed them to your chickens, or simply squish them whenever you see them.