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ARS Home » Pacific West Area » Reno, Nevada » Great Basin Rangelands Research » Research » Publications at this Location » Publication #334430

Research Project: Invasive Species Assessment and Control to Enhance Sustainability of Great Basin Rangelands

Location: Great Basin Rangelands Research

Title: Impacts of granivorous and frugivorous arthropods on pre-dispersal seed production of western juniper (Juniperus occidentalis)

item Dimitri, Lindsay - University Of Nevada
item Longland, William - Bill
item Tonkel, Kirk
item Rector, Brian
item Kirchoff, Veronica - University Of Nevada

Submitted to: Arthropod-Plant Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/16/2018
Publication Date: 6/28/2018
Citation: Dimitri, L.A., Longland, W.S., Tonkel, K.C., Rector, B.G., Kirchoff, V.S. 2018. Impacts of granivorous and frugivorous arthropods on pre-dispersal seed production of western juniper (Juniperus occidentalis). Arthropod-Plant Interactions. 12:465.

Interpretive Summary: Western juniper is a native tree that has been expanding its range into shrub lands and thereby reducing the amount of forage plants available for wildlife and livestock. New juniper seedlings must establish for this expansion to progress. However, even though it is known that most of a crop of juniper seeds can be heavily damaged by seed-feeding insects, there have been no comprehensive studies of insects and other minute seed-eaters that feed on western juniper seeds, and may thus play an important role in combating its ongoing expansion. Here, we document that 4 different groups – 3 insects and a species of mite – can cause substantial damage to western juniper seed crops. We describe characteristics of juniper trees that seem to influence the degree to which their seeds are vulnerable to damage by juniper seed and juniper berry feeders. We also describe symptomatic damage that can be seen on juniper seeds and juniper berries to indicate the presence of these insects and mites.

Technical Abstract: Western juniper (Juniperus osteosperma) forests have been expanding into adjacent shrub lands across the species’ range. Community-level effects of pre-dispersal seed predation have not been studied for arthropod species that feed on seeds and berries of western juniper. From 2009-2013, we quantified impacts of three arthropod granivores or seed predators and a frugivorous insect species on seed production by western juniper trees at two N. California field sites – Madeline and Shinn Peak. The proportion of juniper seeds damaged by each of the four arthropod taxa varied significantly among years and often differed seasonally (spring versus fall) as well as between sites. Arthropod taxa also generally differed significantly in their impacts on seed production; granivorous juniper berry mites (Trisetacus quadricetus) had a much greater effect on reducing seed production at Madeline than any other arthropod, and granivorous cosmopterigid moths (Periploca spp.) had the greatest effect at Shinn Peak. Estimated berry production of western juniper trees had significant negative effects on seed damage across sites by a granivorous chalcidoid wasp (Eurytoma juniperina) and by Periploca at Shinn Peak. Number of seeds per berry positively affected damage attributable to a frugivorous tortricid moth (Henricus infernalis) at Madeline and inversely affected seed damage by Trisetacus at Shinn Peak. Distance to neighboring trees had positive, site-specific effects on damage by Periploca and Henricus, perhaps due to distance limiting movement of parasitoid insects that attack these two moths. Arthropods, in turn, affected morphology of western juniper berries; Periploca, Eurytoma, and Henricus, had negative effects on the mass and/or diameter of berries.