Key factors affecting populations of Schizotetranychus nanjingensis, Aponychus corpuzae and Aculus bambusae in Fujian bamboo forests during different seasons: an analysis using methods of grey sequence

Abstract

The key factors affecting the population dynamics of mite pests on the moso bamboo (Phyllostaychs pubescens) in Fujian, China during different seasons were examined over a two-year cycle of bamboo growth from August 1996 to August 1998 using the methods of the grey sequence. The relative importance of temperature, relative humidity, rainfall and predation by predatory mites varied among species of mite pests, between years, among different seasons in the same year and among different stages of the same species. Schizotetranychus nanjingensis Ma & Yuan. In spring, when temperature increased, old bamboo leaves fell to the ground and new leaves appeared. The population of Typhlodromus bambusae Ehara decreased with many fallen leaves. During this stage, temperature was the most important factor influen- cing mite population growth in a big harvest year (the year of the two year cycle when bamboo changes leaves), but in a small harvest year when there was no change of leaves, many predatory mites were present on the old leaves and predation was the key factor influencing the population development of this species. In Summer, the raining season brought high relative humidity in the pro-period and the Typhoon often attacked the bamboo forests in the post- period. High temperature and high relative humidity appeared alternately. Re- lative humidity was most important to the population development of this spe- cies in a big harvest year, but in a small harvest year, predation was the key fac- tor (except in 1996 when rainfall was the key factor). In Autumn, temperature decreased slowly from early to late season. Temperature was the key factor for mite population development in a big harvest year, but in a small harvest the key factor was either rainfall or relative humidity. In Winter, temperature and predation were more important than other factors to the population deve-lop- ment of this species in a big harvest year, but relative humidity was the key fac- tor in a small harvest year. Aponychus corpuzae Rimando. In Spring, many individuals of this species dropped to the ground with fallen leaves; some of these mites moved onto the leaves again along the culm of the bamboo. The relative humidity was an important factor in a big harvest year, but in a small harvest year, predation was the key factor influencing its population dynamics. In Summer, predation was the key factor in a big harvest year, but in a small harvest year, temperature was the most important factor to its population development. In Autumn, relative humidity was the key factor influencing its population in a big harvest year, but in small harvest year, rainfall was the most important factor. In Winter preda- tion was the key factor in a big harvest year, but rainfall was the most impor- tant factor in a small harvest year. Aculus bambusae Kuang. In Spring, the relative humidity was the key fac- tor influencing its population in a big harvest year, but in a small harvest year, predation was the key factor. In Summer, predation was the key factor influ- encing its population in both big and small harvest years. In Autumn, relative humidity was the key factor influencing its population development in a small harvest year of 1996 and big harvest year of 1997, but predation was the key factor in the small harvest year of 1998. In Winter, rainfall was the key factor influencing its population in a small harvest year, but predation was the key factor in a big harvest year.