Results of the 2011-12 campaign

This post summarizes the results of our 2011-12 campaign.

Let’s start with the visual examination of the cones and berries:

  • As reported earlier, Western Red Cedar (Thuja plicata) cones received from the Saanich Forestry Centre (British Columbia) showed insect damage. Papery cocoons between the scales, in places where the seeds should have been are likely traces of the red cedar cone midge, Mayetiola thujae (Diptera, Cecidomyiidae). This insect is the most serious pest of Western red cedar in BC, Washington and Oregon. Mayetiola larvae feed inside the cones from May through late summer. The cones were collected mid-August. By that time, mature larvae have constructed a cocoon within which they will overwinter. We didn’t get any emergence from these cocoons so we can’t confirm that it was indeed M. thujae.  One bag of cones also contained a metallic green chalcid that resembles Torymus azureus, a parasite of the galling midge Kaltenbachiola rachiphaga in spruce cones. Could this be a parasite of M. thujae?
    The same cones had also holes previously described as “exit holes” but could also be puncture holes from pentatomid feeding, as suggested by our colleague Ward Strong.
  • Other traces of infestation in the form of almost perfectly circular holes (see picture) were found on cones of Juniperus virginiana, J. horizontalis and J. communis from British Columbia (Shorts Creek Canyon), Ontario (Guelph Arboretum) and Northeastern US (Boston, MA). This damage looks like exit holes of a seed chalcid, possibly Eurytoma juniperina. In their review, Chambers et al (1999) listed several insect species affecting Juniperus seed production in Western North America including the chalcidoid wasp Eurytoma juniperina on J. horizontalis. This insect is also found on the Rocky Mountain juniper (J. scopulorum).

J. horizontalis from Guelph showing exit hole

J. communis from Shorts Creek Canyon (BC) showing exit holes

  • Several insects were also found in the bags containing the juniper berries collect by Ward Strong at the Shorts Creek Canyon (BC). The determination of these insects is in progress.

After visual examination, all samples were processed for seed extraction, cleaning and x-raying. In total, more than 51.000 seeds from 34 species sampled in 35 locations over 2 sampling dates were treated last year. Seeds that were identified as potentially infested on the x-rays were picked from the samples and put in rearing in emergence boxes outside in Great Lakes Forestry Centre (Sault Ste Marie, ON) insectarium. Reading x-rays can be challenging, particularly for smaller seeds, so a conservative approach was taken and seeds were picked out even when there was only the smallest indication of a possible infestation. No emergence had occurred by mid-July so we decided to dissect some seeds from each sample to confirm the presence of larvae in the seeds. We will present the results by host species:

  • Chamaecyparis obtusa: infested seeds were found at the Arnold Arboretum (28/345 infested seeds) and the Morris Arboretum (359/1842 infested seeds). Samples from the New York botanical garden were not infested. The dissection of the Arnold and Morris samples confirmed that the seeds were infested. Seeds of C. obtusa are infested by Megastigmus chamaecyparidis  and Megastigmus cryptomeriae in Japan but to our knowledge, these Megastigmus species have never been recorded in North America.
  • Chamaecyparis thyoides: infested seeds (4/250 on x-rays, 3/251 confirmed after dissection) were found in samples collected at the University of North Carolina Botanical Garden. Interestingly, none of the other C. thyoides samples collected at the Atlanta Botanical Gardens (GA), Arnold Arboretum (MA), New York Botanical Garden (NY), Cornell Plantations (NY), and Morris Arboretum (PA) were infested. Dissection confirmed that 3 seeds were infested, the other was empty. Infestation is likely due to Megastigmus thyoides. This chalcid was first found in seeds of C. thyoides collected in 1994 in North Carolina (Turgeon et al., 1997).
  • Cryptomeria japonica: among all the C. japonica seed samples we received from the Arnold Arboretum (MA), Atlanta Botanical Gardens (GA), the UC Davis Arboretum (CA), and the Morris Arboretum at UPenn, the latter was the only one showing some level of infestation (29/413). The presence of larvae in these seeds was confirmed by dissection. Cryptomeria japonica seeds are known to be infested by Megastigmus cryptomeriae in Japan, China and Taiwan but this species has never been recorded in North America.
  • Juniperus communis or horizontalis: only one seed out of 664 collected by Ward Strong at the Shorts Creek Canyon (BC) appeared on the x-rays as being infested. The dissection of this seed confirmed the presence of a larva.

In summary, without being able to attribute any infestation to a species or even a genus at this point, we can confirm that we have found seed infestation in 4 species of Cupressaceae: Chamaecyparis obtusa, Chamaecyparis thyoides, Cryptomieria japonica and Juniperus communis or horizontalis.

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