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).
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.
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).