| Octodonta nipae (Maulik) is one of the most damaging pests of palm tree, which poses a great threat to palm plants industry, economic palm planting, city landscaping and ecological safety. Originating in Malaysia, O. nipae has invaded to several areas in south China and caused a great economic loss. Since first found in Fujian province in 2007, it has spread across the cities of Fuqing, Quanzhou, Xiamen and Zhangzhou. The host ranges of O. nipae include many economic and/or ornamental palm plants, and injures from O. nipae are mainly in the heart young leaves, which is difficult for detection and application of chemical control. In addition, O. nipae has a short generation period but long life time, with the bionomics of severe overlapping generations, high degree of aggregation and almost lifetime breeding, which advantage for multiple mating and polygynandry. Therefore, once invades into a new area, O. nipae is able to spread widely with rapid population growth and acclimatize the environment soon for colonization.So far, the studies of O. nipae have been focused on biological characteristics, suitable environment and host selection, life tables, parasitoids, immunity trade off, etc. This paper aims in investigating mating behavior and copulation rhythm of O. nipae, the efficiencies of multiple mating on reproduction development, fecundity and reproductive fitness of female, as well as survival fitness and genetic divergence of filial generation. The adaption and mechanism of multiple mating in O. nipae will be analyzed, in the hope of providing theoretical basis for reproduction adaptability. The principal results are as follows:1) Aims to determine the mating behavior and copulation rhythms of O. nipae, a video recording system was used to record the mating behavior and copulation events of O. nipae. The results showed that a full process of copulation in O. nipae mainly includes approach, contaction and antennation, mounting, aedeagus insertion, turning around, mating posture, genital interlocking, separation and leaving. Copulation behavior could be observed all day long and was affected by light, with a higher mating rate from 11:00 to 17:00 and a peak in 13:00. The mating frequency in average is 12.6±0.7 per day, and the frequencies of courtship, copulation and mating success in photophases are obviously higher than those in scotophases. The duration of copulation with behavior of genital interlocking is obviously longer than those directly end in mating posture, and the duration of genital interlocking in scotophases are obviously longer than those in photophases. The duration in 60.6% copulation is less than 10 min, however, the longest duration is beyond 200 min. It is supposed that the male prolong the duration in order to increase occupancy with female.2) Laboratory observations on the reproductive system progress of ovarian development and efficiency of multiple mating on the development of ovarian before sexual mature in female of O. nipae were carried out in this experiment. The internal reproductive system of adult female contains panoistic ovaries, lateral and median oviduct, spermatheca and genital chamber. Each ovary of two consists of five ovarioles. Based on the morphological characteristics of ovaries, the development of ovarian can be classified into five stages, which are named nooocyte stage, vitellus forming stage, egg visible stage, egg maturation stage and sustainable ovipositing stage. The shape of ovarian in nooocyte stage is the smallest. In vitellus forming stage, there is not obvious difference in length or area of ovariole in average, only the width enlarges as vitellus forming. Ovarian grow rapidly in egg visible stage, which is obviously larger than before. No obvious difference is found in the width of ovarioles between females mating zero time or once, while ovarioles in females mating four times are obviously great in length, width and area than that of zero and one time. Only the length of ovarioles in females mating within 10 min is obviously great than female not mate, while no obvious difference is found in ovarioles between females mating in 10-20 min and beyond 20 min. To the growth of ovarioles, the path coefficient in mating number is greater than copulation duration.3) The impact of increased mating rate on reproductive fitness of the invasive nipa palm hispid beetle O. nipae is investigated. A series of mating frequencies (i.e.1, 5,10,15,20 times) is selected from video frame playback, ranking from the minimum to maximum mating rate observed under laboratory conditions over a given time period. Fecundity parameters such as life time egg production, egg-hatching rate, effective oviposition period and longevity are investigated for the evaluation of reproductive efficiency. For female O. nipae, increased fecundity is correlated with the mating frequency. Females mating 15 times lay the largest number of eggs (138.8 ±6.9) and have a hatching rate of 47.43±4.08%. After mating 20 times, females suffer significant declines in oviposition (90.3±8.4 eggs) and egg-hatching rate (34.16+4.93%). Moreover, the population growth rate reaches a maximum in the females that mate 15 times. The results show that multiple matings in O. nipae have an intermediate optimal range within which female reproductive success is enhanced, providing empirical evidence for the existence of a trade-off between costs and benefits during copulation based on resource allocation.4) Based on the first internal transcribed spacer (ITS-1) and the mitochondrial cytochrome oxidase I (COI) gene, a diagnostic technique was designed to quickly identify O. nipae. And furthermore, it paves the way for the subsequent experiment about polygynandry of O. nipae populations in different body color. SSR primers were tested randomly for polymorphism, and 9 loci of them were polymorphic.Their polymorphic information content is between 0.062 and 0.582 which shows medium polymorphic. Among different treatment, the offspring of female which mate with four different male has obvious gene differentiation, with the lowest ASM (allele sharing matrix) value in 0.64±2.80. The ASM of female which mate once and men mate triple time with another male is lower than which only mate once, while higher than that mate with four different males. The paternity index in offspring of female which mate once and then mate triple time with another male was the highest, which is 97.0±1.5% and obviously higher than that mate in reverse order. While the paternity index in offspring of female which mate with four different male was the lowest, within 79.0±4.1%. The results showeed that filial generation acquired a higher genetic diversity through female parent’s multiple mating; male enhanced the probability for filial generation to inherit its own genetic gene, and enhanced its paternity through repeated mating with a same non-virgin female. |
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