In this trial, there were significant effects of the
chemical treatments on damage and parasitism, and
a marginally non-significant effect on numbers of
L. huidobrensis (Table I). The farmer chemical treatments
reduced parasitism in the two treated fields
compared to the three control fields, whereas damage
levels and L. huidobrensis numbers were relatively
higher in the unsprayed treatments (Figure 1).
Chemical treatments were therefore ineffective in
controlling the leafminers, but may have harmed or
repelled the parasitoids. Repeated measures ANOVAs
indicate a linear increase in damage levels with
time, whereas there were quadratic components for
leafminer numbers and parasitoid effects (Table II).
Leafminer numbers increased initially to peak at 9
weeks after planting, whereas the percentage parasitism
peaked earlier to a maximum of 60% in one of
the control plots (Figure 1). Chemical treatments
were therefore antagonistic to parasitism but less
effective in controlling leafminers, presumably due to
the detrimental effects of the treatments on parasitoids
and other beneficials.