Effects of Urea Application on the Reproduction of Pardosa Pseudoannulata : Field and Laboratory Studies

As an important chemical fertilizer, urea can greatly increase crop yields, but also has negative effects on natural enemies of pests in agricultural field, such as spiders. Here we reported that urea application reduced the reproductive performance in Pardosa pseudoannulata, a dominant spider enemy in rice fields against a range of insect pests, from both field and laboratory aspects. In field test, urea application significantly reduced the egg production of females or subfemales collected in urea-treated fields around the rice field, regardless of whether there was maize on the urea-treated fields. Due to the complex factors contributing to the reproduction change in fields, we set up the laboratory test to evaluate urea application on P. pseudoannulata reproduction. The subadult spiderlings were reared in the test tube inserted in the soil mixed with urea to avoid the direct contact with urea, and the spiderlings were colleted at 14 d and 28 d following incubation. The collected spiderlings were cultured to female and male adults who then were paired to observe the reproduction parameters. Similar to field test, the laboratory treated spiders had lower reproduction ability than the control, including mating rate, egg production and hatchability. The transcriptomic sequencings were performed in samples collected at 28 d, which showed that urea application caused a number of differentially expressed transcripts. Some unigenes related to basic enzymes were down-regulated and several unigenes related to stress resistance were up-regulated. RNAi against a metalloproteinase gene caused the significant decreases in egg production, and RNAi against a carboxylesterase gene significantly reduced both the egg production and hatchability. Taken together, the present study found that urea application reduced P. pseudoannulata reproduction ability and down-regulation of some basic enzyme genes might provide partial explanation for the effects, which would be useful for the protection of P. pseudoannulate in fields