Effect Of Nitrogen Application On The Community Of Ground-dwelling Spiders And The Predation Of Nilaparvata Lugens By Pardosa Pseudoannulata In Paddy Fields

In this paper, the effects of nitrogen application on the community of ground-dwelling spiders, the populations of wolf spider Pardosa pseudoannulata (B?Senberg et Strand) and brown planthopper Nilaparvata lugens (St?l) (BPH) were studied in rice paddy in Wuyishan, Fujian, China in 2009. N. lugens species-specific primers were designed, and the relationships between detectability of BPHs and the fators (digestion time, temperature, prey number and predator sex) were also studied. Then, a good pair of primers was used to study the effects of nitrogen application on the predation of P. pseudoannulata on N. lugens in rice paddy fields.1. Effects of nitrogen application on the community of ground-dwelling spiders in rice paddiesDuring the investigations, a total of 2,715 individuals of ground-dwelling spiders (belonging to 8 families, 15 genuses and 19 species) were collected by using pitfall traps sampling in rice paddy. Lycosidae was the most abundant family in which P. pseudoannulata was the dominant species. In the milk stage, the abundance of ground-dwelling spider community significantly decreased with nitrogen increasing. But, the abundance in other stages, as well as species richness, Shannon-Wiener index and eveness of the community showed no responses to the nitrogen application.2. Designing of N. lugens specific primersAfter testing 68 common species of arthropod in paddyfields for cross-amplification, only Lug-F1a/ Lug-R1 showed the specific and efficiency while detecting P. pseudoannulata with BPHs in its gut. Relationship between the fators (digestion time, temperature, prey number and predator sex) and the detectability of BPHs in spiders'guts by using Lug-F1a/ Lug-R1 was assessed. The results showed that the digestion time, temperature and meal size influenced the proportion of positive outcome but not predator sex. The detectability was significantly and negatively correlated with digestion time or temperature respectively, but positively with meal size. 3. Effects of nitrogen application on relationships between N. lugens and P. pseudoannulataPopulation growth of BPHs in the study fields was observed at all stages, and the max number of individuals recored at milk stage. For P. pseudoannulata, its population increased from tillering to heading stage, after that decreased. By using N. lugens specific primers, statistics of detection of predation by P. pseudoannulata collected in the study plots showed an increased predatory ratio as time went by, and the maximum percentage of positive amplification was 28.29% on samples collected at heading stage. In the milk stage, the relationship between predation and nitrogen application can be described by cubic function. As nitrogen increased, the rate of predation decreased from 0 to 50 kg?N?ha-1, increased from 50 to 230 kg?N ?ha-1, then decreased from 230 to 300 kg?N?ha-1. Nitrogen-induced increase of number of individuals of BPHs was significantly correlated with nitrogen-induced decrease of number of individuals of ground-dwelling spiders, especially P. pseudoannulata.