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 it also has negative effects on beneficial arthropods in the agricultural field, such as spiders. Here, we reported that urea application reduced the reproductive performance in Pardosa pseudoannulata, a dominant species of spider in rice fields, which preys on a range of insect pests, based on both field and laboratory studies. In a field test, urea application significantly reduced the egg production of adult and subadult females collected from the urea-treated fields. A laboratory test was set up to further evaluate the impact of urea application on P. pseudoannulata reproduction. In consistent with field test results, the spiders treated by urea for 14 d and 28 d had lower reproduction ability than their control counterparts, with regard to the mating rate, egg production, and egg hatchability. The transcriptomic sequencing of individuals treated by urea for 28 d showed that urea application caused a number of differentially expressed transcripts with several downregulated unigenes related to basic enzymes and several upregulated unigenes involved in stress resistance. The knockdown of a metalloproteinase gene caused a significant decrease in egg production, and the silencing of a carboxylesterase gene significantly reduced both the egg production and egg hatchability. Taken together, the present study found that urea application reduced P. pseudoannulata reproduction ability and the negative impact partially resulted from the downregulation of certain basic enzyme genes. The study provided a fresh view of fertilizers on beneficial arthropods with great potential in the protection of P. pseudoannulata in fields.