Diversity and abundance of natural enemies in organic versus conventional cotton ecosystems

Abstract:

The hypothesis tested here is straightforward: if you stop spraying insecticides, do natural enemies return in numbers large enough to keep pests in check? This research compared the diversity, abundance, and seasonal dynamics of predatory and parasitoid arthropods in paired organic and conventional cotton fields at the Central Highlands Agricultural College, Buon Ma Thuot, Dak Lak, Vietnam, during the 2022 growing season. Weekly visual counts on 30 plants per field and pitfall traps were used to survey natural enemy communities from March through October. Organic fields harboured 97% more natural enemies per 10 plants (mean 22.3 vs 11.3) and 44% higher species richness (Shannon index H' = 2.84 vs 1.97) than conventional fields. Spiders were the dominant predator group in organic fields (31.2% of total), followed by coccinellids (23.1%) and parasitoid wasps (18.4%). The organic pest suppression index was 73.8% versus 61.2% in conventional fields, despite zero insecticide use. Aphid and bollworm populations were statistically similar between systems by mid-season, suggesting that natural enemy activity compensated for the absence of chemical control.