Results
  1. 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).
  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).
  1. 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).