The levels of parasitism in larval populations of
leafminers were assessed by direct sampling of larvae.
Every week, 30 leaves containing leafminer larvae
(second or third instar) were randomly collected
from each plot and placed in an ice box. In the
laboratory, each leaf was confined in a separate
transparent plastic cup (diameter 6 cm, height 5 cm)
with paper towel to absorb excess leaf moisture and
thereby prevent fungal growth. Cups with leaves were
covered with plastic film and held at room temperature
for 3 – 4 weeks. The numbers of emerging
L. huidobrensis adults and parasitoids were recorded.
The level of parasitism was estimated as the number
of parasitoids divided by total number of flies and
parasitoids that emerged.
Crop damage was measured weekly beginning 7
w.a.p. From each plot, 32 potato plants were
randomly selected. Every plant was scored on a
validated damage scale as follows (Raman et al.
1994): 0 = no leaf damage; 1 = leaf damage restricted
to basal half of plant (1 – 25% damage); 2 = leaf
damage restricted to middle and basal half of plant
(26 – 50% damage); 3 = entire plant damaged except
terminal leaves (51 – 75% damage); 4 = most of the
plant damaged (76 – 100% damage).
Potatoes were harvested on 5 October 1999, and
tubers from each plant sample were weighed to assess
yield effects.