We concluded that populations of arthropod natural enemies (Encarsia formosa, O. indiosus, Coccinellids, C. carnea, Spiders and Formicids) recorded from organically managed fields were comparable with conventional fields. Moreover, generalist predator of Chrysopidae were observed only organic crop. The abundance of arthropods predator and their diversity has been reported to be influenced by different farming practices in cotton field. In two year study populations of predatory species Dolichopodidae, spiders, adults and immature of Orius spp., Geocoris spp., predatory Coccinellidae, and Nabidae, larvae of Corydalidae and Hemerobiidae were reported more in cotton field under organic farming practices than conventional field (Jackson, 2006).
Organic farming enhances the biological control services of ecosystem by provision of refuges to immature and breeding sites to adults of natural enemies (Lu et al., 2015; Muneret et al., 2018a; Swezey et al., 2007) consequently enhancing their densities. Our results suggests organic farming support higher abundance of natural enemies in both years, which is consistent with previous studies (Attwood et al., 2008; Bengtsson et al., 2005; Garratt et al., 2011; Hole et al., 2005). There were 17–56% more arthropods predators (Carabid beetle, Chrysopidae, Coccinellidae, Syrphidae and spiders) in organic field of wheat (Purtauf et al., 2005), vegetables (Aldebron et al., 2020), cotton (Lu et al., 2015) and 62% more population of ground-dwelling spiders in wheat field under organic farming practices as compared to conventional fields (Schmidt et al., 2005). The higher abundance of natural enemies in organic farming system might be due to absence of synthetic chemicals.
Populations of pests are reduced due to species richness (Mabin et al., 2020) and or their dominance (Crowder et al., 2010) of the biological control agents in the agricultural landscapes. Our results proved that organic farming cotton supported higher diversity (Shannon – weaver diversity) of natural enemies in both the years. Although species richness was lower in the year 2021 in organically managed cotton, but their dominance was also greater. Lower species richness might be due to the negative interaction of dominant natural antagonists with rear or less abundant natural enemies (Muneret et al., 2019). The limited number of natural enemy species with higher dominance also keeps prey species population at lower levels. Therefore, both cases will improve pest management, ultimately reducing the burden of pest management inputs. These results are inconsistent with previous studies on other ecological function documented that, only limited and more abundant pollinators take part in pollination in agroecosystems (Kleijn et al., 2015).
Organic fields supported more population of ladybird beetle and carabids beetle in wheat (Griffiths et al., 2008; Landis et al., 2000; Puech et al., 2014). Organic nutrients and plant residues increase the microbial activity in soil which provides the energy by decomposition for a new food web. Most of the collembolan, dipteran, mites and nematodes feed on these microorganism known as fungivores and these are fed up by different natural predators like spiders and carabid (Laakso & Setälä, 1999; Xu et al., 2011). Plant nourishment has ability to change the chemistry of volatiles. Crops grown in organic farming system produced such volatile compounds that attract natural enemies (McCormick et al., 2012; Naguib et al., 2012; Rossetto et al., 2013; Shrivastava et al., 2010) thus increase the bottom-up effect those may indirectly drive the top-down effect due to enhancement of natural enemies, consequently increasing the biological control of herbivores (Lu et al., 2015). Our study suggests that organic agricultural practices may induce the bottom-up effect that could indirectly drive the top-down effect with an increase in the population of predators which may enhance the biological control of insect pests (Walker & Jones, 2001).
Further research is needed to develop sensible pest management keeping the role of natural enemies in organic cotton production systems. One of the best options is the incorporation of the plant extracts derived from local plants, these have been proved effective in managing aphids on wheat and several lepidopterans species and aphids on crucifers (Razaq & Shah, 2022; Shah et al., 2017; Shah et al., 2019). Historically cotton is notorious for development of resistance to pests across the globe (Razaq et al., 2019). Resource poor farmers face economic difficulties to pay for costly chemicals and cannot manage insect pests mostly due to resistant populations. Biorational insecticides based upon extracts from local plants have also been proved favorable with respect to economic returns as compared to synthetic chemicals besides other several advantages (Amoabeng et al., 2014). Therefore, further research is required to determine role of biorationals insecticides so that subsistence growers of cotton for may get economic benefits.