Effect of alfalfa habitat change on dispersal behavior of Harmonia axyridis Pallas and Hippodamia variegata Goeze (Coleoptera: Coccinellidae)

Abstract

• The population of lady beetles was higher in the continuous habitat. • Habitat fragmentation affected the changes of habitat spatial pattern. • Habitat loss and fragmentation negatively impacted natural enemies searching. An alfalfa grassland landscape was divided into 36 plots during 2014 season in Yuanzhou District of Guyuan city in Ningxia Hui Autonomous Region of P.R. China. In these three times repeated experiments, treatment of habitat fragmentation was divided into two grades: continuity (H = 0.0) and fragmentation (H = 1.0), and their habitat loss rate was divided into 6 grades: 90, 80, 70, 50, 20 and 0%. Considering habitat loss 0% of the plot as the reference, as a result of sweeping net and visual methods, results showed that the flight distance of the Harmonia axyridis was much higher than that of the Hippodamia variegata both in fragmentation and continuous habitats. In the alfalfa landscape, H. axyridis moved more by flying, while H. variegata moved more by crawling. There was a threshold effect that affected the movement behavior of lady beetles between 70 and 100% of the habitat loss. The population of the two species of lady beetles in the continuous habitat was higher than that in the habitat fragmentation and was more obvious in 70 and 50% plots of the habitat loss. The dispersal rate of the two species of lady beetles inside plots was higher than outside of the experimental plots, which reflected the low diffusivity of the ladybeetle. Habitat fragmentation affected the dispersal, migration and construction of two species of lady beetles on different spatial scales by disturbing the spread of natural enemies and searching for prey.