Molecular Soil Biology 2024, Vol.15, No.3, 140-150 http://bioscipublisher.com/index.php/msb 141 The purpose of this study is to evaluate the impact of soil insecticides on WCR and maize yield. This study will synthesize current research findings on the effectiveness of various soil insecticides, the development of resistance in WCR populations, and the implications for maize yield. By providing a comprehensive overview of the existing literature, aims to inform future research and management practices to enhance the sustainability and efficacy of WCR control strategies. 2 Biology and Ecology of Western Corn Rootworm 2.1 Life cycle and behavior of WCR The Western Corn Rootworm (WCR), Diabrotica virgifera virgifera, is a significant pest of maize in North America and Europe. The life cycle of WCR includes egg, larval, pupal, and adult stages. Eggs are laid in the soil during late summer and hatch in the following spring. The larvae then feed on maize roots, causing substantial damage to the plant's root system, which can lead to reduced water and nutrient uptake, increased susceptibility to lodging, and ultimately, decreased maize yield (Devos et al., 2013). The adult beetles emerge in mid-summer, feed on maize silks and leaves, and mate to lay eggs, thus completing the cycle (Gassmann et al., 2011). 2.2 Feeding habits and impact on maize plants WCR larvae primarily feed on maize roots, which weakens the root system and diminishes the plant's ability to absorb water and nutrients. This root damage can also create entry points for fungal and bacterial pathogens, further compromising plant health and stability (Pingault et al., 2022). Severe root pruning by WCR larvae has been shown to decrease shoot dry weight and grain yields significantly (Gyeraj et al., 2021). Additionally, adult WCR beetles feed on maize silks, which can interfere with pollination and reduce kernel set, leading to further yield losses. The feeding behavior of WCR larvae and adults thus poses a dual threat to maize crops, affecting both root integrity and reproductive success (Jaffuel et al., 2019). 2.3 Ecological adaptations and resistance development WCR has demonstrated a remarkable ability to adapt to various management strategies, including crop rotation, soil insecticides, and genetically modified Bt-maize. The pest's adaptability is partly due to its non-recessive inheritance of resistance traits, minimal fitness costs associated with resistance, and limited adult dispersal, which facilitates localized resistance development (Darlington et al., 2022). Field-evolved resistance to Bt-maize has been documented, with WCR populations showing resistance to multiple Bt toxins, including Cry3Bb1 and Cry34/35Ab1 (Gassmann, 2021). This resistance evolution is exacerbated by continuous maize cultivation and insufficient planting of refuges, highlighting the need for integrated pest management strategies that combine multiple tactics to delay resistance development and ensure sustainable WCR management (Blandino et al., 2017). 3 Types of Soil Insecticides Used Against WCR 3.1 Classification of soil insecticides Soil insecticides used against the Western Corn Rootworm (WCR) can be broadly classified into several chemical classes, including organophosphates, pyrethroids, and neonicotinoids. Organophosphates, such as terbufos and isofenphos, have been traditionally used due to their effectiveness in controlling WCR larvae by inhibiting acetylcholinesterase, an essential enzyme for nerve function (Modic et al., 2020). Pyrethroids, including bifenthrin, tefluthrin, and cyfluthrin, act on the nervous system of insects by modifying the gating kinetics of sodium channels, leading to paralysis and death (Souza et al., 2019). Neonicotinoids, such as clothianidin and thiacloprid, target nicotinic acetylcholine receptors in the insect nervous system, causing overstimulation and eventual death (Alford and Krupke, 2018). 3.2 Mode of action of different insecticides The mode of action of these insecticides varies significantly. Organophosphates work by inhibiting acetylcholinesterase, leading to the accumulation of acetylcholine and continuous nerve impulse transmission, which results in paralysis and death of the insect9. Pyrethroids affect the nervous system by delaying the closure of sodium channels, causing prolonged depolarization of the nerve membrane, which also leads to paralysis and death (Alford and Krupke, 2018). Neonicotinoids bind to nicotinic acetylcholine receptors, causing continuous
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