Pollination and herbivory treatments
For the pollination treatments, all flowers on a plant were either
exposed to ambient pollination conditions (control) or received
supplemental hand pollinations every ca. 5 days for the full flowering
period. Only three plant genotypes were used as pollen donors to control
for pollen quality effects. Herbivory was manipulated through the
addition or removal of an ecologically important herbivore; the
strawberry leaf beetle, Galerucella tenella L. (Coleoptera:
Chrysomelidae). This oligophagous herbivore feeds on leaves and flowers
of several Rosaceae plants (Stenberg & Axelsson 2008). For woodland
strawberry this can reduce fitness both directly and indirectly, via
pollinator limitation (Muola et al. 2017; Muola & Stenberg
2018). The plantation in which the herbivore treatments were applied was
fenced with a 2 m fine mesh to exclude herbivory from small and large
browsing vertebrates, including deer and digging rodents. For the
‘herbivore addition’ treatment, several hundred adult individuals of the
strawberry leaf beetle were collected in early May soon after their
emergence on their main host plant meadowsweet (Filipendula
ulmaria (L.) Maxim.) (Stenberg & Axelsson 2008). Further details of
these collection localities are provided in (Weber et al. 2020b).
The beetles were released onto plants at a density of 0.4 individuals
per plant. Adult and larval feeding damage were apparent within one and
five weeks of release respectively. Most feeding damage in the
‘herbivore addition’ treatment was hence caused by the strawberry leaf
beetle. However, damage from larvae of two species of leaf‐ and
flower-feeding Lepidoptera – Cnephasia asseclana Denis &
Schiffermüller (Tortricidae) and Ceramica pisi L. (Noctuidae) –
was also observed on experimental plants. The former is a pest of
cultivated strawberry (Sigsgaard et al. 2014), whereas the latter
is a generalist moth that feeds on genera including Rubus andSalix (Robinson et al. 2010). As a common practice for the
experimental removal of insect herbivores (Siemann et al. 2008),
the ‘herbivore removal’ treatment was made through application of low
doses of an insecticide. For this we employed foliar applications of
Calypso (Bayer CropScience); a systemic insecticide based on the active
substance thiacloprid. All manufacturers’ recommendations were followed
concerning dosage concentration and frequency of application. Three
rounds of application were made every ca. 4 weeks between early May and
mid-July. Spraying took place when conditions were dry and windless so
as to avoid cross-contamination. Virtually no damage to plants in the
‘herbivore removal’ treatment was observed.