Progressive restriction of host plant exploitation along a climatic gradient: the willow psyllid Cacopsylla groenlandica in Greenland

• Published in: Ecological Entomology
• Main Author: HODKINSON, IAN
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1997
• Subjects: Arctic; Greenland
• Online Access: http://dx.doi.org/10.1046/j.1365-2311.1997.00039.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1046%2Fj.1365-2311.1997.00039.x; https://onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-2311.1997.00039.x

1. Host plant selection by the endemic willow psyllid Cacopsylla groenlandica was studied at eight sites in three locations along a N–S climatic gradient in west Greenland. 2. C. groenlandica oviposited and developed on four willow species: Salix glauca, S. arctophila, S. uva‐ursi and S. herbacea. Development took place on female catkins of all species and on leaf shoots of S. glauca . 3. At sites in southern Greenland, C. groenlandica fully utilized all four willow species. However, there was progressive reduction of host plant species and tissues exploited as latitude increased, such that towards the northern limit of its range the psyllid became highly specialized, feeding only on female catkins of S. glauca , despite the presence of alternative hosts. Where plant growth was tightly constrained within a restricted growing season, the demands of synchronizing with more than one species may have become too great, resulting in specialization on a single host. 4. The probable mechanisms producing specialization were between‐species differences in host plant phenology, linked to variation in the growing season, set against the partially non‐overlapping geographical distribution patterns of the host willows. 5. A small degree of phenological asynchrony between host plants can be advantageous for the insect. Under favourable conditions the reproductive season can be extended by using a series of host plants with staggered phenologies. Some ‘early’ hosts also create predator‐free space. However, as asynchrony increases, the advantages disappear as the insect becomes unable to exploit the full range of host options. 6. The importance of host plant synchrony in the life histories of arctic insects is discussed.