Abstract:

【Objective】 It is of great significance to determine the developmental status of male moths trapped by sex pheromone for objective evaluation of the effect of mass trapping. This study aims to research the internal reproductive system and developmental age of Spodoptera litura, determine the development situation of male moths captured in the field and the nature of insect source, and to provide a theoretical basis for the application of sex pheromone trapping of S. litura.【Method】 In 2014 and 2015, after eclosion from the laboratory-reared pupae, 1-10 day-old male moths were dissected under the microscope. The criterion of the developmental age of male S. litura moths was determined by the long semi-axis of testis. Using this criterion, the day-old of male moths captured daily with sex pheromone trapping in the fields of Dongpo and Jintang counties of Sichuan Province from 2015 to 2017 was identified. The effect of trapping male moths on mating behaviors and patterns was then analyzed.【Result】 The internal reproductive system of male S. litura moths was composed of testis, vas deferens, seminal vesicle, ejaculatory duct and accessory gland. The structure of testis was stable, elastic and easily-measured. With the increase of age, the length of long semi-axis of testis gradually decreased. The mean value of long semi-axis of testis of 10-day-old males decreased by 44.71%, compared with that of 1-day-old male testis (1 103.54 μm). The relationship equation between the long semi-axis (y) and day-old (x) was y=-48.52x+1084 (R ²=0.9472, RMSE=36.8). There were significant differences in the length of long semi-axis of testis among the age groups of 1-5, 6-8 and 9-10 day-old. The criterion table displaying the relationship between the day-old of male moths and the length of long semi-axis of testis was built to identify the age of male moths captured by pheromone trapping in the field. Similar day-age structures of male moths were found in Jintang from 2015 to 2017 and in Dongpo in 2017, with lower percentages of older male moths. Specifically, the mean percentage of 1-day-old male moths captured by sex pheromone trapping in Jintang was 39.89%, and that of 2- and 3 day-old was 21.42% and 15.75%, respectively. In other words, 1-3 day-old male moths accounted for 72.22%-79.02% in total, and the percentage from 5- to 10-day-old male moths was below 10%. In Dongpo, the percentage of 1-, 2- and 3-day-old male moths was 39.93%, 20.79% and 19.54%, respectively, as a total of 80.26%, after 5-day-old of age, the percentage was relatively small. The mean percentage of male moths of each day-old decreased exponentially with age. The daily trapping dynamic showed the 3 generations of adults in the fields of Jintang and Dongpo from the end of April to the end of August. The male moths of the 1st and 2nd generations were mainly between ages of 1-3 day-old, and the ratio of younger moths (1-3 day-old) of Jintang to older moths (4-10 day-old) was 3.32 and 1.54, and that of younger moth to older moths in Dongpo was 3.34 and 1.58, respectively. With increased numbers of adults in Dongpo, the majority of 3rd generation was older moths, with the ratio of younger moths to older moths of 0.76, which was lower than that of Jintang (2.34).【Conclusion】 The size of the testis of male S. litura moth can reflect its day-age. Male moths captured through sex pheromone trapping are mainly composed of 1-3 day-old, which is beneficial to reduce mating rate in the current generation and the whole population in the next ones.

Key words: Spodoptera litura, male moth, internal reproductive system, day-old, sex pheromone trapping