Organic fertility management in cotton Gossypium hirsutum L. fosters arthropod biodiversity and complements pest suppression

Research on economic, ecological and relative benefits from organic and conventional farming systems has gained significant importance. Organic farming increases species diversity, enhances biological control services, and thus complements sustainable pest management. However, published literature is scarce on cotton crops grown organically with respect to the abundance and diversity of biological control agents and their effects on herbivore populations, typically from developing nations. To address the question, the non-transgenic cotton variety CIM-573 was cultivated under two fertility management systems, that is, organic and conventional in 2019 and 2021, and subsequently, differences in the abundance and diversity of arthropod communities were carried out. We applied cattle manure in organic fields 1 month before planting; however, synthetic fertilizers were used in conventional fields. We sampled arthropods weekly after 7 weeks of sowing from the middle rows of treatments for both types of fields. We recorded 10 herbivores as well as eight natural enemy species. Herbivores were more abundant in conventional cotton. However, natural enemies were higher in organic cotton fields. Principal component analysis of herbivores assemblages depicted that Shannon diversity and abundance were positively correlated in the conventional cotton while Menhinick richness and Simpson dominance index were higher in organic cotton. Likewise, natural enemies' abundance, Shannon diversity, Menhinick richness and Simpson dominance were typically more concentrated in organic cultivated cotton. Regression analysis confirmed that the abundance and diversity of natural enemies played a significant role in lowering herbivores populations. Seed cotton yield was significantly higher in conventional cotton and the yield difference between organic and conventional cotton was 27.98%. Our study clearly demonstrates that organic cotton provides more functional and complementary niches to natural enemies and plays a crucial role in pest suppression. Implications of our results for future pest management with respect to ecosystem services in organically grown cotton crops are also discussed.