Field Crop 2024, Vol.7, No.3, 182-190 http://cropscipublisher.com/index.php/fc 184 3 Soil Insecticides Overview Soil insecticides play a crucial role in managing the western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte, a significant pest of maize. These insecticides are applied to the soil to target the larval stages of WCR, which feed on maize roots, causing substantial yield losses and plant instability. The use of soil insecticides is part of an integrated pest management (IPM) strategy aimed at reducing WCR populations and mitigating damage to maize crops. 3.1 Types of soil insecticides Several classes of soil insecticides are used to control WCR, including pyrethroids, neonicotinoids, and organophosphates. Pyrethroids, such as tefluthrin and bifenthrin, are commonly used due to their effectiveness in reducing larval density and protecting maize roots (Souza et al., 2019; Ferracini et al., 2021). Neonicotinoids, like clothianidin, are systemic insecticides that are often applied as seed treatments, providing protection as the plant grows (Ferracini et al., 2021). Organophosphates, such as tebupirimphos, are another class of insecticides used in soil applications to manage WCR populations (Souza et al., 2019). 3.2 Modes of action The modes of action of soil insecticides vary depending on their chemical class. Pyrethroids, such as tefluthrin and bifenthrin, act on the nervous system of insects by disrupting sodium channels, leading to paralysis and death (Souza et al., 2019). Neonicotinoids, like clothianidin, target the nicotinic acetylcholine receptors in the insect nervous system, causing overstimulation and eventual death (Ferracini et al., 2021). Organophosphates, such as tebupirimphos, inhibit acetylcholinesterase, an enzyme essential for nerve function, resulting in the accumulation of acetylcholine and subsequent insect death (Souza et al., 2019). 3.3 Application methods Soil insecticides can be applied using various methods, including in-furrow applications, seed treatments, and broadcast applications. In-furrow applications involve placing the insecticide directly into the planting furrow, providing immediate protection to the emerging seedlings (Ferracini et al., 2021). Seed treatments involve coating the seeds with insecticides before planting, offering systemic protection as the plant grows (Ferracini et al., 2021). Broadcast applications involve spreading the insecticide over the soil surface, which can then be incorporated into the soil through irrigation or rainfall (Souza et al., 2019). The choice of application method depends on factors such as the level of WCR infestation, soil type, and environmental conditions. In conclusion, soil insecticides are a vital component of WCR management in maize production. Understanding the types, modes of action, and application methods of these insecticides can help optimize their use and improve maize yield outcomes. 4 Efficacy of Soil Insecticides on Western Corn Rootworm 4.1 Control success rates The efficacy of soil insecticides in controlling Western Corn Rootworm (WCR) varies significantly based on the resistance levels of the WCR populations. Field trials conducted in Nebraska demonstrated that soil insecticides such as tefluthrin, bifenthrin, and a combination of cyfluthrin and tebupirimphos effectively protected maize roots from pyrethroid-susceptible WCR populations. However, their efficacy was significantly reduced in areas with pyrethroid-resistant WCR populations (Souza et al., 2019). Similarly, a three-year field experiment in Slovenia showed that tefluthrin and entomopathogenic nematodes (Heterorhabditis bacteriophora) significantly decreased the number of emerging WCR beetles, indicating effective control of WCR larvae (Figure 2) (Modic et al., 2020). 4.2 Factors influencing efficacy Several factors influence the efficacy of soil insecticides against WCR. Resistance levels in WCR populations are a critical factor, as demonstrated by the reduced efficacy of bifenthrin and tefluthrin in pyrethroid-resistant populations (Souza et al., 2019). Additionally, environmental conditions such as soil type and pest density also play a role. For instance, the efficacy of treatments was consistent across different soil types and pest densities in Slovenia, suggesting that soil conditions did not significantly impact the effectiveness of the insecticides and
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