Abstract: To understand the seed production dynamics of Pinus thunbergii population in Yantai coastal protection forest, the relationships between the diameter at breast height (DBH) and cone/seed characters of the population were studied, with the DBH as the measurement of age and size. According to the DBH size and its distribution proportion, the population was divided into 5 diameter classes (35〖KG-*2〗-〖KG-*7〗65, 65〖KG-*2〗-〖KG-*7〗95, 95〖KG-*2〗-〖KG-*7〗125, 125〖KG-*2〗-〖KG-*7〗155, and 155〖KG-*2〗-〖KG-*7〗19 cm), with 5, 8, 11, 14, and 17 cm as the measurement of each diameter class, respectively. Multiple comparison and regression analysis were conducted for the cone/seed character of each diameter class. The results showed that DBH had significant influence on the fecundity of P. thunbergii. With increasing DBH, the fecundity increased first, but began to decrease when the DBH reached 17 cm. The seed size and 100-seed mass had a decreasing trend when the DBH increased, whereas the seed wing size was in adverse. This phenomenon might be a tradeoff in P. thunbergii seed production, i.e., to decrease seed size and mass to increase seed dispersal ability. For all DBH classes, the number of fertile scales was the most effective prediction variable of seed number and seed mass per cone, but could not better predict the other characters of cone, such as cone length, cone width, cone dry mass, and total number of scales, illustrating that the seed production of P. thunbergii was controlled by many factors.

Key words: Azadirachtin, Spodoptera litura, Bioactivity, Anti-feeding effect