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Heat treatment -A potential approach of killing Megastigmus larvae in imported conifer seeds

The production of Nordmann fir and Turkish fir Christmas trees is increasing, particularly in the Pacific Northwest where they now account for approximately 10% of the total trees grown. Domestic conifer nurseries mostly rely on the importation of seeds from natural stands in the Republic of Georgia and Turkey to produce the planting stock of these species.

Insect pests currently threaten the consistent supply of imported seeds, and none are more common than conifer seed wasps from the genus Megastigmus. These chalcid wasps lay eggs within premature seeds while still in the cone, and the larvae nourish themselves on resources meant for the seed embryo. They can lie dormant within seeds for several years even after the cone has matured. Within the past few years, APHIS PPQ has returned or destroyed considerable numbers of imported seed shipments at U.S. plant introduction stations due to the x-ray detection of live Megastigmuslarvae in infested seed. APHIS PPQ currently has records of 15 species/subspecies of Megastigmusthat are considered to bequarantine pests and there are currently no APHIS approved treatments for Megastigmus-infested conifer seeds, so importers have no recourse.

Previous research on the native Megastigmusstrobiloviushas shown that exposing infested Douglas-fir seed to 45C for 27 to 33 hours was effective in killing larvae in infested seed. This heat treatment also had no adverse effect on seed germination and subsequent growth of seedlings. If heat treatment of Nordmann and Turkish fir seed was shown to be effective in killing larvae and haaveno adverse effects on seed germination and seedling growth, it would provide seed importers and regulatory agencies with a technique that could be used to treat infested seed.

  • Project ID17-01-WSU
  • CategoriesInsect Management
  • Growing Region(s)Pacific Northwest
  • Tree SpeciesFir
  • Investigator(s)Chastagner
  • Institution(s)The Davey Institute, Washington State University
  • Research Year2017
  • Publication Year2022
  • ReportDownload 📁