Seasonal occurrence of Aphis glycines and physiological responses of soybean plants to its feeding

The soybean aphid Aphis glycines Matsumura (Hemiptera: Aphididae) is an important pest of soybean in China. To monitor and manage this pest effectively it is necessary to understand its population dynamics and demographics, as well as the physiological responses of soybean plants to its feeding. In this study, using field surveying and suction-trap monitoring, we investigated the population dynamics of the soybean aphid in Xiuyan County, Liaoning Province in northeastern China during 2009-2012. The results indicated that the population dynamics of the soybean aphid followed a unimodal curve distribution, with the insect generally colonizing soybean fields from the middle of June to early July and the population reaching a peak between early July and early August. On the whole, soybean aphids occurred in suction-traps at least 2 weeks earlier than they were found in field surveys. A total of 72 alates were collected by suction-trapping over the 4 years, with the earliest alate captures occurring 011 28 May in 2009, 2011, 2012 and 4 June in 2010. The life table parameters clearly showed that this aphid had a short doubling time (4.73 +/- 0.21 days), and 7.36 +/- 0.98 nymphs were produced by a soybean aphid adult during its lifetime (13.57 +/- 0.30 days). Finally, biochemical assays indicated that the amount of malondialdehyde and the activities of four defense-related enzymes in soybean leaves significantly changed between 0 day and 7 days of aphid infestation. Polyphenol oxidase (PPO) and catalase (CAT) activities increased more dramatically after 1 day of aphid feeding. In addition, significantly higher levels of superoxide dismutase and CAT were found after aphid feeding for 7 days, whereas there was no significant change in the activities of peroxidase and PPO. Consequently, this study will be beneficial in determining the seasonal occurrence of the soybean aphid and selecting insect-resistant soybean varieties, and thus in developing a theoretical framework for appropriate management strategies.