Molecular Entomology 2024, Vol.15, No.2, 69-77 http://emtoscipublisher.com/index.php/me 71 2.5 Other notable herbivorous insects In addition to the major pests discussed above, several minor herbivorous insects can also affect barley cultivation. These include various species of thrips, leafhoppers, and caterpillars, which can cause damage to leaves, stems, and grains. While these pests are generally less impactful than aphids, cereal leaf beetles, and wireworms, they can still contribute to overall yield losses, particularly when present in high numbers or in combination with other stress factors. Integrated pest management strategies that include monitoring, biological control, and targeted insecticide applications are essential to manage these minor pests effectively. 3 Impact of Herbivorous Insects on Barley Yields 3.1 Direct damage: feeding and tunneling Herbivorous insects cause significant direct damage to barley crops through feeding and tunneling activities. For instance, the Oulema spp. beetles, which include Oulema melanopus and Oulema cyanella, are known to induce volatile organic compounds (VOCs) in barley as a defensive response to their herbivory. This indicates substantial feeding damage that triggers the plant's defense mechanisms (Piesik et al., 2011). Additionally, aphid species such as Rhopalosiphum padi and Rhopalosiphum maidis have been documented to cause a 25.5% reduction in barley yield due to their feeding activities. The direct consumption of plant tissues by these insects not only reduces the photosynthetic capacity of the plants but also weakens their overall structure, leading to decreased growth and productivity (Meijden, 2015). 3.2 Indirect effects: disease transmission and secondary infections Beyond direct feeding damage, herbivorous insects also play a crucial role in the transmission of plant diseases, which can further exacerbate yield losses. For example, the barley yellow dwarf virus (BYDV), transmitted by aphids such as Rhopalosiphum padi and Sitobion miscanthi, has been shown to cause a 39% reduction in barley yield, which is more severe than the damage caused by direct feeding (Kauppi et al., 2021). Furthermore, the presence of herbivorous insects can create entry points for secondary infections by pathogens. The mechanical injury caused by insects can facilitate the invasion of fungal pathogens like Fusariumspp., leading to additional stress and damage to the barley plants. This combination of direct and indirect effects significantly impacts the overall health and yield of barley crops. 3.3 Economic implications for barley production The economic implications of herbivorous insect damage on barley production are substantial. Yield reductions due to insect herbivory translate directly into financial losses for farmers (Figure 1). For instance, the economic loss attributed to aphid feeding on barley is estimated at $19 per hectare, while the loss due to BYDV transmission is approximately $21 per hectare (Sánchez‐Bayo, 2021). In boreal growing conditions, the yield reduction caused by insect pests in spring barley can range between 418 and 745 kg per hectare, highlighting the significant economic burden on barley producers (Bui et al., 2018). These losses underscore the importance of effective pest management strategies to mitigate the impact of herbivorous insects on barley yields and ensure the economic viability of barley cultivation. 4 Control Methods for Herbivorous Insects in Barley 4.1 Chemical control Chemical control of herbivorous insects in barley primarily involves the use of insecticides. Organophosphates, such as chlorpyrifos and methidathion, are commonly applied to control pests like false wireworms and earth mites. These insecticides are often used prophylactically or reactively at higher concentrations to ensure effective pest control (Hill et al., 2017). However, the efficacy of these insecticides can vary, and their application needs to be carefully managed to avoid non-target effects and resistance development. The use of broad-spectrum insecticides poses significant risks, including the disruption of natural enemy communities and the potential for secondary pest outbreaks. For instance, the application of organophosphates has been shown to reduce the number of predatory beetles, which in turn can lead to an increase in slug populations, causing significant yield loss in subsequent crops like canola (Thompson et al., 2022). Additionally, the overuse of chemical insecticides can lead to the development of resistance in pest populations, necessitating the exploration of alternative control methods.
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