Millimetric Scanning Entomological Radar Observations And Trajectory Analysis Of Migratory Behavior Of Planthoppers

The planthoppers are one of the most serious pests of rice in China. Successive outbreaks of planthoppers with serious damage to rice production have been recorded in recent years in China. Monitoring and forecasting is the basis for effective prevention and control. In order to obtain better understanding of the flight behavior parameters and population dynamics of planthoppers, we observates the migration behavior of the planthoppers by using an 8.0 mm wavelength scanning entomological radar, a searchlight trap and a Jiaoduo light trap. The Hysplit₄ software was used to calculate particle trajectories for clearifying the source areas of migrant planthoppers.The brown planthoppers formed 3 insect density layers at the heights of 300 to 400 m, 500 to 700 m and 800 to 1100 m above the ground in autumn, 2009. These layers were well-defined and related to the maximum wind speeds. The aerial insect density increased soon after the sunset, and reached the maximum at about 20:00 h. Generally, the insect density decreased after the midnight, but sometimes the high density kept through 5:00 in the morning. The collective orientation of brown planthoppers was observed with the radar and the orientation direction was toward south or north with an angle to the downwind direction.Although the time of peaking migration and the density of migrants varied through years, the general displacement direction was almost constant. In May to June, the planthoppers in the northern Vietnam and southern Guangxi Municipality immigrated into Xing'an, Guangxi in southwestern winds. When the early season rice was mature, the planthoppers immigrated into the middle-eastern Hunan province in 12 hrs, and into the middle Anhui province and southwestern Henan province in 24 hrs. The migration during autumn was complicated, with the immigration and emigration occurred at the same time, and the middle-eastern Hunan province was the main source area. The planthoppers in the Xing'an Guangxi Municipality in autumn would immigrate into the middle Guangxi in 12 hrs, and into the southwest Guangxi and northern Vietnam in 24 hrs.The rainfall caused mass descent into the immigration areas. The vertical air currents had little effects on the migration, because the vertical air currents were relatively weak during the peak migration season.The sex ratio (female: male) varied significantly. It was greater in the searchlight trap than that in the Jiaduo light trap for brown planthoppers. The sex ratio in the middle-season rice and late-season rice was greater than or equal to 1. The females of white back planthoppers in the searchlight trap were more than the males, in contrast to lesser females in the Jiaduo light trap. The sex ratio is greater than 1 in the tillering to jointing stage of middle-season rice and late waxen maturity stage of late-season rice.