Seeds, insects, earthworms, parasitic worms, mushrooms and more can be found in soil. It is for this very reason that Guam law prohibits the importation of soil into the territory, in order to keep out unwanted invasive plants and animals.
The College of Natural and Applied Sciences Extension and Outreach personnel at the University of Guam have received many complaints from clients finding beetle grubs in bags of potting soil purchased at stores on island. “These complaints prompted us to investigate by visiting the garden center of a local hardware store franchise that imports soil from the US mainland,” said Dr. Aubrey Moore, UOG extension entomologist. “We noticed several unopened bags of potting soil with multiple holes in the plastic. After selecting one and opening it we discovered five large coconut rhinoceros beetle (CRB) grubs. Unfortunately for Guam’s coconut trees, this is a really good way to spread rhino beetles around the island.”
Garden centers very often keep bags of potting soil stacked outdoors making them easily accessible to any interested insect. Coconut rhinoceros beetles seek out high-density organic material, as decaying organic matter is the preferred place to find a mate and lay their eggs. With the alluring high organic matter content of packaged potting soil, coconut rhinoceros beetles make holes in the thin plastic bags and deposit their eggs. When unsuspecting gardeners buy potting soil for use in their home gardens they are getting more than they paid for and are helping the invasive rhino beetles move around the island.
“Rhino beetle larvae are excellent decomposers, which is why dead standing coconut trees and fallen logs are a hotbed of rhino beetle breeding activity. There is plenty of food to support development from egg to adult,” warned extension agent Roland Quituqua.
A scientific note on these observations will be published in the next issue of the Proceedings of the Hawaiian Entomological Society. Banning the outdoor storage of bags of potting soil would be one way to help curtail the spread of coconut rhinoceros beetles throughout the island.
For more information on coconut rhinoceros beetles and the work UOG researchers are doing to control this invasive insect, please visit, http://cnas-re.uog.edu/crb/.