Moving to Keep Fit: Feeding Behavior and Movement of Helicoverpa armigera (Lepidoptera: Noctuidae) on Artificial Diet With Different Protein: Carbohydrate Ratios

Abstract

Insect herbivores can modify their foraging behavior to obtain a balanced food intake, and they tend to move between food sources with different nutrient values. We investigated this movement in early instar larvae of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) using a putative optimal artificial diet (OP) and high protein (HP) and high carbohydrate (HC) artificial diets based on protein (p) and carbohydrate (c) ratios. Larvae were allowed to choose between the same kind of diet cubes (effectively no-choice), or diet cubes with different p: c ratios. In no-choice tests, we found that first instar larvae remained longest on OP diet and spent the least time on HC diet, while third instar larvae remained longest on HC diet and spent least time on OP diet. First instar larvae moved the most when provided with HC diet, while third instar larvae moved most when provided with OP diet. However, both stages moved the least when allowed to choose between diet cubes with different p: c ratios. The relative growth rate decreased when larvae increased their movement, but this influence was not evident when larvae fed on HC diet. Larvae that fed only on HC diet had the highest relative growth rate, followed by larvae with access to all diets simultaneously, indicating a behavior to mix nutrient intake. We relate these findings to behavior of this major pest species under field conditions.

Keywords: choice; instar; larva; nutrient; relative growth rate.

Fig. 1.

Probability that first instar and third instar Helicoverpa armigera larvae were observed on diet (A, B) and the mean number of moves larvae made between diet cubes (C, D). Asterisks represent significance between groups when tested in GLM (*P < 0.05; **P < 0.01; ***P < 0.001). OP, HC, HP represent optimal, high carbohydrate and high protein diet, respectively; First represents first instar larvae; Third represents third instar larvae.

Fig. 2.

Larval weight and developmental time when fed on different diets in first (A) and third (B) instars; effect of diet on RGR of (C) the first instar larvae, and (D) the third instar larvae; instar effect on RGR in both first and third instar larvae (E). OP, HC, HP represent optimal, high carbohydrate and high protein diet, respectively. Means with different letters were significantly (P < 0.05) different.

Fig. 3.

Scatter plot of individual larval RGR versus the number of moves in the first 2 d. Data from the first instar larvae (A) and the third instar larvae (B) were showed with different shapes and colors to represent different diets. OP, HC, HP represent optimal, high carbohydrate and high protein diet, respectively. Lines indicate regression lines of the same colored data.

Fig. 4.

Proportion of times that first instar (A) and probability of third instar (B) H. armigera larvae were observed on diet in choice experiment and the mean number of moves larvae made per dish between diet cubes across different dish types (C, D). OP, HC, HP represent optimal, high carbohydrate, and high protein diet respectively (A, B). OP, HC, HP, MIX represent optimal diet, high carbohydrate diet, high protein diet, and mixed-diet dish types respectively (C, D). Asterisks represent significance between groups (*P < 0.05; **P < 0.01; ***P < 0.001).

Fig. 5.

The influence of dish types (A) and instar (B) on RGR over 2 d. Asterisks represent significance between groups. OP, HC, HP, MIX represent optimal diet, high carbohydrate diet, high protein diet and mixed-diet dish types respectively (*P < 0.05; **P < 0.01; ***P < 0.001).