Influence of fourth-instar larval nutrition on ovariole development in Harmonia axyridis (Coleoptera: Coccinellidae)

Abstract

Ovariole number is one of the key determinants of reproductive potential in insects, yet the developmental factors influencing its variation remain unclear. This study examined how feeding conditions during the fourth instar affect body size, weight and ovariole number in the ladybird beetle Harmonia axyridis. Thirty-five adult females collected from the field were used to establish laboratory lines. Newly hatched fourth-instar larvae were reared individually under two feeding regimes: high-food and low-food conditions. Adults raised under high-food conditions were significantly larger and heavier, and females had 1.25 times more ovarioles than those reared under food-limited conditions. Ovariole number was affected only by larval feeding condition, not by maternal line or their interaction. Ovariole number significantly influenced daily fecundity; however, its contribution was small. These results demonstrate that food availability during the fourth instar plays a critical role in shaping reproductive capacity and maintaining natural variation in ovariole number and body size in H. axyridis.