Molecular Soil Biology 2024, Vol.15, No.3, 140-150 http://bioscipublisher.com/index.php/msb 142 stimulation of the nerves, which results in paralysis and death (Clair et al., 2020). These differences in modes of action are crucial for integrated pest management strategies, as they allow for the rotation of insecticides to manage resistance development in WCR populations (Figure 1) (Meinke et al., 2021). Figure 1 (A) Adult Diabrotica virgifera virgifera LeConte; (B) example of severe root injury from Diabrotica virgifera virgifera LeConte (Dvv) larval feeding that can occur when Dvv larval density is high (right) versus uninjured root (left) (Adopted from Meinke et al., 2021) Meinke et al. (2021) found that the presence of Diabrotica virgifera virgifera LeConte, commonly known as the Western corn rootworm, poses a significant threat to corn crops due to its larval feeding behavior. The larvae of this species cause severe root injury, leading to reduced nutrient and water uptake in affected plants, which can ultimately result in stunted growth and lower crop yields. The study highlights that high larval density exacerbates the damage, making early detection and management crucial to preventing extensive agricultural losses. These findings underscore the importance of integrated pest management strategies to control Diabrotica virgifera virgifera populations and mitigate their impact on corn production. 3.3 Application methods and timing The application methods and timing of soil insecticides are critical for their effectiveness in controlling WCR. Soil insecticides can be applied as granular formulations at planting time, which ensures that the insecticide is present in the root zone when WCR larvae hatch and begin feeding (Sutter et al., 1989). Seed treatments with systemic insecticides, such as neonicotinoids, provide protection by allowing the insecticide to be taken up by the plant and distributed throughout its tissues, including the roots (Ferracini et al., 2021). In-furrow applications at planting time are also common, ensuring that the insecticide is placed directly in the root zone (Blandino et al., 2017). The timing of application is crucial; for instance, applying insecticides at sowing has been shown to significantly reduce WCR larval density and increase grain yield. Additionally, the use of entomopathogenic nematodes and fungi in combination with chemical insecticides has been explored to enhance control and reduce the impact on non-target organisms (Rauch et al., 2017). 4 Efficacy of Soil Insecticides on WCR Control 4.1 Evaluation of various soil insecticides in controlling WCR populations The application of soil insecticides has been shown to significantly reduce the population of Western Corn Rootworm (WCR) larvae, which are known to cause substantial damage to maize crops by feeding on the roots. In a study conducted over four years in Northern Italy, the use of soil insecticides at different planting times resulted in a 43% reduction in WCR larval density and a 65% decrease in root injury, leading to an 8% increase in grain yield (Blandino et al., 2017). Similarly, field trials in Nebraska, USA, demonstrated that soil insecticides effectively protected maize roots from WCR damage in areas with pyrethroid-susceptible populations, although their efficacy was reduced in regions with pyrethroid-resistant WCR populations (Souza et al., 2019). Another study in Central Europe compared the effectiveness of soil-applied granular insecticides, seed treatments, and entomopathogenic nematodes, finding that all treatments significantly decreased the number of emerging WCR beetles and increased maize plant weights (Modic et al., 2020).
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