Enhancing spider families and spider webs in Indian rice fields for conservation biological control, considering local and landscape management

Spiders are omnipresent, occurring in almost all terrestrial habitats. They are generalist predators and important for conservation biocontrol in agricultural fields, helping to reduce pesticide applications. In this study, we examined how spider families and spider web types in rice fields are related to local and landscape management. Samples were taken in differently managed rice fields adjoining either homegarden polycultures or banana monocultures. Furthermore, landscape structure, prey abundance, herb richness and cover were taken into account. The results showed that prey availability explained most of the variation in spiders and their web’s abundance, indicating that spiders in the rice fields can potentially contribute to pest control. Adjacent habitat had no effect on the spider populations, but maintaining fallow fields in the surrounding landscape seems to be a useful measure to promote Erigoninae in rice fields. There was no evidence that local management practices such as fertiliser and pesticide use had an impact on spider families, which appeared to be due to the low level of these inputs. Spider web sampling can complement spider sampling as it detects spiders hidden at the base of the rice tillers, which are likely to be missed by sweep netting. Additionally, tetragnathid webs are easy to observe and thus can be used as an indication for farmers not to spray pesticides as spiders are potentially controlling the pest species. Interviews with farmers made clear that many farmers in the study area showed their interest in management methods that promote biological pest control.