Abstract:

The functional response and searching behavior to the brown planthopper (BPH), Nilaparvata lugens by its predator, the wolf spider Pardosa pseudoannulata treated with the fittest low-dose concentration of 3 chemical pesticides were studied in the laboratory. The results showed that the predating number of the predator to the prey was significantly higher under the fittest low-dose pesticides (volume ratio of pesticide to water is 2∶5 000 for methamidophos, 12∶5 000 dimehypo, and 1∶20 d-allethrin, respectively) than those without treatment of pesticide or treated by high-dose pesticides. Although all predating functional responses were in accordance with the HollingⅡ model, the functional response of the spiders treated by low-dose chemical pesticides was obviously stronger than those without treatment of pesticide or treated by high-dose pesticides. The time spent in handling and/or killing a brown planthopper (T_h) by the spiders treated by the fittest low-dose pesticides were 0.45, 0.32 and 0.35 times, respectively, less than that by the spiders without treatment of pesticide. The time consumed by the spiders treated under the high-dose pesticides (volume ratio of pesticide to water is 8∶5 000 for methamidophos, 28∶5 000 dimehypo, and 6∶20 d-allethrin, respectively) were 9.70, 13.60 and 13.62 times, respectively, as much as that by the spiders treated under the fittest low-dose pesticides. The searching pattern of the spiders to BPH over rice plant was non-random. The searching efficiency decreased with the increase of prey density under the same chemical pesticide concentration. In the same BPH density, the searching efficiency of the predator varied more under different concentrations of pesticide. Under the influence of the fittest low-dose pesticides, the searching efficiency of the predator was the highest, and the total staying time and searching distance of the spiders were 1.56, 1.49, 1.48 times and 1.36, 1.42, 1.39 times as much as those under no pesticides, respectively. The results further proved that application of lowdose chemical pesticides might enhance spiders' efficiency of controlling pests and their relative activities to insect pests.

Key words: Pardosa pseudoannulata, Nilaparvata lugens, low-dose pesticide, functional responses, searching behavior