Mating Behavior of the Black Soldier Fly (Hermetia illucens): Diel Rhythm, Mating Frequency Distribution, and the Lack of Effect of Multiple Mating

Mating behavior is critical for the reproduction of Hermetia illucens, but the effects of multiple mating on female fecundity remain poorly understood. This study systematically investigated mating and oviposition behavior, mating diel rhythm, mating frequency distribution, and the effects of different mating histories on female egg production and the egg hatching rate in H. illucens under controlled conditions. The behavioral sequence of courtship, copulation, and oviposition was described. To evaluate the reproductive consequences of mating frequency, females with different pre-pairing mating histories (unmated vs. once-mated) were paired with males with different mating histories (unmated vs. once-mated vs. twice-mated), and the egg mass per female and egg hatching rate were compared among treatments. Mating peaked on day 2 after emergence (77.3%), with two daily activity peaks at 09:00–11:59 and 14:00–16:59. Most individuals mated once or twice, with a maximum of four matings. Notably, 30.0% of males remained unmated, a proportion significantly higher than that of unmated females (10.6%). Mating history had no significant effect on egg mass per female or the egg hatching rate (p > 0.05): neither female mating frequency (unmated vs. previously mated once) nor male mating frequency (unmated vs. previously mated once vs. previously mated twice) significantly affected these reproductive outcomes. These results indicate that one successful mating can meet female fertilization requirements, with no additional reproductive advantage from multiple mating under unfed, single-oviposition-event conditions. The higher unmated rate in males than in females suggests that the proportion of males in production colonies can be appropriately reduced without compromising reproductive efficiency under the tested cage conditions; validation under larger-scale, higher-density production systems is still required.