Results
- Specific leaf area and plant protein and carbohydrate content
Five days after fertilization, there was no difference in specific leaf
area (SLA) or protein content among treatments (control, moderate, and
high fertilization), but carbohydrate was marginally higher in the
control millet relative to the high fertilization millet (Figure 1,
Table 1). After 12 days, plants from the high fertilization treatment
had higher SLA than plants from the control. SLA for plants from the
moderate fertilization treatment was not different from the control nor
the high fertilization treatment (Table 1).
Without fertilization, plant protein content declined over time, but
carbohydrate content remained constant. In both fertilizer treatments,
carbohydrate content decreased through time and protein content remained
constant or increased (Figure 1, Table 1). The magnitude of changes in
plant nutrient contents yielded three different protein:carbohydrate
ratios that were increasingly protein-biased as N input increased
(Figure 1, Table 1).
- Preference: choice experiment
Five days after applying fertilizer, locusts did not show preference
when given the choice between unfertilized plants (control) and plants
that received the medium level of fertilizer (medium-N). However, when
given the choice between unfertilized plants (control) and plants that
received high level of fertilizer (high-N), female locusts preferred
control plants. Males did not show any preferences (Figure 2, Table 2).
- Performance: survival and egg mass
More female locusts survived on the control treatment than on the high
fertilization treatment (Figure 3, Table 3). Survival for males was
identical on all treatments. Male wet mass, but not female wet mass, was
a good predictor of total egg mass, regardless of treatment. Females
laid the same average number of eggs on all treatments; however, eggs
were smaller on the high fertilization (high N) treatment (Figure 4,
Table 3).