Crowding as a possible stress factor in food choice of aphidophagous ladybird beetle, Propylea dissecta (Mulsant)

Abstract

Crowding induces behavioral and lasting morphological and chromatic changes in insects. This study examined how larval rearing density of Propylea dissecta (Mulsant 1850) affected food choice and development duration, hypothesizing that larvae under stress will opt for lower quality food as larval density increases. Larvae were reared at various densities under three crowding treatments: direct physical, indirect physical, and chemical tracks. In each treatment, larvae experienced crowding at densities of 0, 2, 4, 6, 8, 10 and 12 individuals per arena. Fourth stage larvae were provided with food choice of aphids, heterospecific eggs and conspecific eggs. Significant effect of crowding on total development duration, first consumption time and first food consumption were observed. Decrease in development duration at densities of 4 and 6 and increase in development duration at low and high densities were observed in direct physical crowding. Indirect physical and chemical crowding yield the shortest development duration at densities of 8, 10, and 12, when compared to low and moderate crowding. First encounter time increased with increasing chemical tracks concentration, while first consumption time decreases with crowding across all groups. First consumed food was also significantly influenced by crowding, suggesting a negative impact on larval food choice. Our results indicate that crowding among larvae leads to a longer development duration and show less selectivity in their food choices.