Born in crowds: How larval density shapes gonadal development in a ladybird beetle

Abstract Interactions among conspecific insects generate social cues that can influence development and reproductive physiology. Larval crowding is common in insects, including ladybird beetles, yet its effects on reproductive traits under abundant food conditions remain poorly understood. However, separating the effects of crowding itself from those of food limitation remains challenging, as these factors often co‐occur in natural and laboratory settings. In this study, we examined how larval crowding affects growth and reproductive physiology in the ladybird beetle Cheilomenes sexmaculata (Fabricius) under laboratory conditions with ad libitum food supply. We hypothesized that larval crowding would negatively influence growth and reproductive investment despite food limitations. Larvae from an experimental stock were reared either singly (control) or under crowded conditions (six larvae per Petri dish). Development time, body weight, gonadosomatic index (GSI) and gonadal traits (weight, area and number of testicular lobules/ovarioles) were measured. Larval crowding significantly increased development duration and body weight in both sexes. Crowded individuals also exhibited larger gonads, accompanied by sex‐specific changes in reproductive allocation: Males showed reduced GSI, whereas females showed increased GSI. Such differences suggest that early crowding has lasting effects on how reproductive traits develop. Examination of gonadal morphology showed that beetles reared under crowded conditions developed fewer but larger testicular lobules and ovarioles. Overall, these results demonstrate that larval crowding alone, independent of food limitation, influences growth and gonadal development in a sex‐specific manner. The study highlights density as an important developmental factor shaping reproductive physiology in ladybird beetles.