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Tenlined June Beetle

Tenlined June Beetle

R. Rodstrom, GreenWood Resources, Portland, Oregon, J. Brown, Department of Entomology, Washington State University
Grown as a monoculture for biofuel, pulp, and non-structural saw timber, hybrid poplars suffer serious insect pest infiltration. Depending on location, hybrid poplar crops can be attacked by 40 different identified species of insect pests. These pests consume foliage, burrow into stems and bole, and destroy roots. Each publication in this series focuses on an individual identified insect pest of hybrid poplars. The publications are designed to aid poplar growers and insect pest managers by characterizing an insect pest, discussing the damage it causes, and suggesting strategies for managing it.
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Polyphylla decemlineata Say (Coleoptera: Scarabaeidae: Melolonthinae)


Immature grubs of the tenlined June beetle are establishment pests of poplar. Cuttings used to propagate and establish hybrid poplars on land used previously for pasture or irrigated crops often fail due to grub feeding behavior. Loss of one cutting is of no consequence because adjacent trees will fill in the canopy; however, grub populations are grouped, and loss of nine or more adjacent trees can cause an opening in the canopy for years or the entire length of the rotation.


There are 36 species of Polyphylla in the US (Pinto n.d.). Polyphylla decemlineata and P. sobrina (Johnson et al. 2012) are both found in California and Nevada, whereas P. decemlineata has a more extensive range. Common names include watermelon beetle, hissing beetle, or June bug.


Feeding of tenlined June beetle larvae (grubs) has been reported on almonds, apples, cherry, poplar, prune, walnut, and stone fruits in California (Johnson et al. 2012), apples and poplars in Washington, and various cane fruits, vegetables, berries, and row crops throughout its range (Beers et al. 2016).


Populations of tenlined June beetles are widely dispersed in sandy soils west of (Beers et al. 2016) and near the eastern slopes of the Rocky Mountains in the US and Canada (Myers 2017).

Life History

Two most noticeable life stages are the adult males that are attracted to lights at night and the late instar grubs found in association with roots. Generally females have limited ability to fly and are rarely captured in light traps.

Females emit a sex pheromone allowing the male to locate them shortly after eclosion. Often females mate and subsequently lay approximately a dozen eggs in the soil near where they emerged. Therefore, the rather large (4 mm) oval-shaped, cream-colored eggs are seldom noticed. There are three larval instars. Larval development requires multiple years depending on latitude and site. In California two or three seasons are required, while in some northern sites the life span can be four years. In California the first instar hibernates. The following growing season the grub (Figure 1) completes its second instar and again overwinters as a third instar during the second year (Van Steenwyk and Rough 1989). Pupation and adult eclosion occurs in the third growing season. Pupation occurs within subterranean cells, so only adult males, near lights in June through September, are evidence of an existing population. Males use sense cells on their large tongue-shaped lamellate antennae to locate a female by following her sex pheromone (Lilly and Shorthouse 1971).

Figure 1. Second and third instar tenlined June beetle grubs (Photo by R. Andrew Rodstrom).
Figure 1. Second and third instar tenlined June beetle grubs (Photo by R. Andrew Rodstrom).


Belowground damage to newly planted poplars is often caused by the tenlined June beetle, P. decemlineata (Rodstrom 2013). This damage to the belowground portion of the stem is characterized by the stripping of the bark down to the woody part of the cutting (Figure 2). This damage is also visible aboveground with shriveled shoots and yellowing leaves (Figure 2).


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