What are the effects of aromatic plants and meteorological factors on Pseudococcus comstocki and its predators in pear orchards?

The interactions of major pests with their natural enemies in the environment of intercropped orchards have recently received much attention. In this study, eight aromatic plant species, namely Mentha canadensis L. (Lamiaceae), Tagetes patula L. (Asteraceae), Ocimum basilicum L. (Lamiaceae), Satureja hortensis L. (Lamiaceae), Agerarum houstonianum Mill (Asteraceae), Ocimum x citriodorum Vis. (Lamiaceae), Nepeta cataria L. (Lamiaceae) and Centaurea cyanus L. (Asteraceae), were used to evaluate the effects of intercropping with aromatic plants on Comstock mealybugs (Pseudococcus comstocki Kuwana) and their natural predators. The effects of meteorological factors on Comstock mealybug were also investigated. Compared with natural grass or clean tillage plots, intercropping with aromatic plants significantly reduced the abundance of Comstock mealybugs and increased that of their predators, thereby increasing the ratio of natural enemies to pests. In the intercropped plots, the individual number Comstock mealybugs was reduced by 22.71-76.76 %; the peak period for Comstock mealybugs was delayed by 10-20 days, and the peak period for their predators was advanced by 0-60 days. The presence of Comstock mealybugs was significantly positively correlated with precipitation in all plots and significantly negatively correlated with sunshine duration. In conclusion, intercropping with aromatic plants significantly reduced the individual number of Comstock mealybugs, especially intercropping with A. houstonianum. Furthermore, this effect was enhanced during the summer months with high precipitation levels and long periods of sunshine.