Temporal dynamics and optimal partition of aphids in an alfalfa field

Aphids are one kind of serious insect pest in alfalfa fields. In order to clarify the spatial distribution pattern and population dynamics of alfalfa aphids in Qingdao, and provide a basis for integrated management, aphid population dynamics were analyzed in a Qingdao alfalfa field in 2013. We studied spatial distribution pattern and optimal partition using aggregation index method and optimal partition method, respectively. The results showed that the aphid population had two annual peak occurrences: late May and late October. The population demonstrated aggregate distribution when at a higher density, and the aggregation intensity decreased with an increase in population density. The population dynamics could be divided into seven periods using the optimal partition method: initial stage (before April 6); developing stage (April 14 to May 11); quick-increase stage (May 18-25); decline stage (June 1-8); secondary initial stage (June 8 to September 15); secondary developing stage (September 22 to October 2); and secondary quick-increase stage (October 7-27). We discussed the characteristics and impact factors of each stage. Alfalfa aphids in Qingdao demonstrated aggregate distribution and the population experienced two peaks. The suitable control stages are early May and early October.