Comparison of Trapping Effects of Different Traps and Monitoring the Occurrence Dynamics of Spodoptera litura in Soybean Fields of Dangtu, Anhui Province, China

In order to clarify the trapping efficiency of different types of sex pheromone traps on populations of Spodoptera litura in soybean fields, three kinds of conventional traps, called YL-VT, YL-HEMT and YL-NMT, and types of traps equipped with a automatic catch monitoring mechanism, called AIM and Lite-AIM, have been tested. These last two allow monitoring the diurnal and seasonal rhythms of the catches. From 5 August to 5 October 2020, each YL-VT trap caught an average of 84.4 heads of S. litura moths per day, which was significantly higher than the YL-HEMT (11.8 heads), YL-NMT (16.5 heads) and AIM (9.7 heads), which did not show significant differences between them. The half-life of pheromone attraction effect in YL-VT trap is about 17–20 days. Considering the number of trapping and the duration of pheromone attraction effect, YL-VT trap is the best. For efficient monitoring, the validity period is approximately 15 days. Among the causes that could explain its higher capture rate and efficiency, the YL-VT trap has the smallest and largest number of inlet devices, and in it, the lure core is located inside of the insect inlet device. Under different occurrence numbers of S. litura, the accuracy of the automatic count of Lite-AIM is 90% greater than in the AIM trap. The diurnal rhythms of S. litura observed by Lite-AIM show that S. litura have two active periods that are from 18:00 to 21:00 and from 23:00 to 4:00 at night and that the first active period may be affected by sunshine and temperature. The annual activity rhythm of S. litura monitored by AIM showed that the activity of S. litura was related to temperature, there were approximately 6 generations of S. litura in a year and that the activity peak was from August to September in Dangtu, China. AIM and Lite-AIM can be used for the annual monitoring of S. litura population in soybean fields because of their automatic counting function. AIM can simultaneously record a variety of meteorological data, Lite-AIM has higher accuracy and a lower cost, which can be selected according to different situations. In conventional traps, the trap YL-VT can be used for the population monitoring of S. litura in soybean fields and pest control in the field, especially in greenhouses and net rooms where organic soybeans are grown, due to its low cost and efficient trapping ability.