Statistical analysis
Data were analyzed using SAS v. 9.4 (SAS Institute, Cary, NC). Samples
that comprised fewer than 10 fruits were excluded from the analysis.
Week represents time after the first sample was collected and held
constant for both years. Cultivation type denotes whether the berry was
wild-grown or cultivated. Eggs per berry are the mean number of eggs per
fruit while eggs per gram were calculated using the number of eggs per
berry divided by the average per berry weight of each sample group. The
eggs per gram value was log transformed to adjust for assumptions of
normality. Unless noted otherwise, we used a generalized mixed model
(GLIMMIX) with a log normal distribution. Adjusted means were compared
using the Tukey-Kramer adjustment.
In order to examine average infestation by cultivation type and ripeness
stage, ripeness stage and cultivation type were considered fixed
effects, and year, elevation nested within year, location, and week
nested within year as random effects. For weekly infestation rates, eggs
per gram was used as the dependent variable, week, ripeness stage and
cultivation type were considered fixed effects, and year, location, and
berry nested in location by week were random effects.
The effect of elevation was assessed for JKWA samples from 2018 with
elevation, ripeness stage and week as fixed effects. The proportion of
infested fruit at each sampling point (ripeness stage/location/week) was
calculated as the number of berries with one or more eggs divided by the
total number of berries in that sample group. Data were fitted to a
normal distribution via Proc GLIMMIX with cultivation type, ripeness
stage, and their interaction as fixed effects and location, year, and
elevation nested within location as random effects.
Oviposition preference was calculated as the proportion of eggs laid in
either the wild or cultivated berries divided by the total number of
eggs laid in each replicate. These proportion data were then evaluated
with a paired Student t-test; replicates with non-responding flies
(those which did not lay eggs during the experimental period) were
removed from analysis.