Effects of mating habits of Carposina sasakii on reproduction

【Objective】This study aimed to investigate the effects of male multiple mating and female delayed mating on the reproductive capacity of Carposina sasakii (Lepidoptera: Carposinidae), in order to provide scientific evidence for evaluating the efficacy of male annihilation using sex pheromones in orchard management.【Methods】Laboratory experiments were conducted to investigate the effect of male mating frequency and female delayed mating of C. sasakii on reproductive ability. A newly emerged virgin male was paired with two virgin females (1- day- old) in a Petri dish. Mating behavior was observed at 24-hour intervals. After each successful mating, the male was paired with two new virgin females. If the male did not mate within 24 hours, the observation was continued, and if it did not mate within 3 days, two new 1-day-old females were replaced to mate with it. Observations continued until male death (n=23 replicates). Mated females were transferred individually to new Petri dishes for oviposition. Mating timing and duration were recorded. The pre- oviposition period, oviposition duration, amount of oviposition, and egg hatching rate of females were also counted to study the effect of male mating frequency on mating rates, female egg production and egg hatching rate. A total of 56 females were tested. Furthermore, the study investigated the effects of delayed female mating on mating rate, egg production and egg hatching rate. Virgin females of different ages (1-4 days old) were paired with 1-day-old virgin males (n=16 females per age group). The mating behavior was observed every 24 hours. If the female did not mate, a new 1- day- old male was replaced to mate with it. The mated females were transferred individually into new Petri dishes to lay eggs. The mating rate, the amount ofeggs laid and the egg hatching rate of each day-old female were counted to study the effect of female delayed mating on fecundity. A total of 16 females were tested.【Results】The female of C. sasakii were strictly monandrous, while males were polygynous, with an average of 2.4 females per male and a maximum of 4 females per male, but a maximum of 1 female per male in a day. Adults mating began from 0:00 to 3:00, and the average mating duration of the adults was 75.6 minutes. The minimum duration of mating was 46 minutes and the maximum duration was 196 minutes. The mating rate of 0:00—1:00 was the lowest (8.9%), that of 1:00—2:00 was 37.5%, and that of 2:00—3:00 was the highest (53.6%). The average pre-oviposition periods of females were 2.3 days and the average oviposition periods of females were 4.1 days. Each female laid an average of 84.2 eggs over a period of 4.1 days, with an average egg hatching rate of 73.4%. The mating rate of male and female decreased with the increasing dayage of males, and the male mating rate of 4-day-old was only 35%, which was significantly lower than that of 1-3 day-old males (P＜0.05). The increase of male mating frequency did not significantly affect the female egg production and egg hatchability, indicating that the male mating frequency did not affect the reproductive ability of the females. With the increase of female day-age, mating rate decreased gradually, and the female mating rate of 4-day-age was 31.3%, which was significantly lower than 87.5% of 1- day- old females (P=0.012). Moreover, the female egg production and egg hatching rate decreased with the increase of female day-age, and the egg production and egg hatching rate of 1-day-old females were significantly higher than those of 2-4 day-old females (P＜0.01), indicating that delayed mating of females significantly reduced reproductive ability.【Conclusion】The male of C. sasakii could mate with multiple females during its lifetime, and the mating rate with females decreased with the increase of male day- age, and the mating time was relatively concentrated. The multiple mating of C. sasakii males had little effect on the reproductive ability, while delayed mating of females significantly reduced the reproductive ability. Based on the above results, the corresponding control strategy could be formulated according to the density of pest population in the field. When the density of pests is low in the field, the sex pheromone could be used to kill males to effectively reduce the population of pests. However, when the density of pests is high in the field, it would be necessary to combine with other measures to reduce the number of adults to a low range in a short time to achieve the ideal effect.