Increased nitrogen fertilization inhibits the biocontrol activity promoted by the intercropping partner plant

A review of the impact of maize-legume intercrops on the diversity and abundance of entomophagous and phytophagous insects

In many parts of the world, chemical pesticides are the primary method of pest control in maize (Zea mays L.) crops. Concerns about the negative consequences of chemical pesticide use on people's health and the environment, as well as the emergence of insecticide resistance, have accelerated attempts to discover alternatives that are effective, low-risk, and cost-effective. Maize-legume intercropping systems are known to have multiple benefits to agroecosystem functioning, including pest regulation. This review focuses on the influence of maize-legume intercropping systems on insect diversity and abundance as a mechanism for insect pest regulation in maize crops. First, this review combines knowledge of maize-legume intercrops, with a particular emphasis on the mechanism by which this practice attracts beneficial insects (e.g., predators, parasitoids) to reduce pest damage in intercropping systems. In addition, the pairings of specific legume species with the greatest potential to attract more beneficial insects and therefore reduce maize pests are also discussed. Finally, future research needs are also recommended. Findings are reviewed in the context of looking for long-term management strategies that can increase the adoption of integrated pest management programs in maize-based production systems.

Population dynamics of herbivorous insects in polluted landscapes

Environmental pollution is one cause of insect decline in the Anthropocene, but the underlying mechanisms remain obscure due to a paucity of pollution-impact studies on insects that address density-dependent processes. Long data series (19-26 years) are available only for a few species monitored around two industrial polluters in north-western Russia. A particularly exciting current finding is that industrial pollution determines the relative strength of rapid (stabilising) and delayed (destabilising) density dependence operating on a herbivore population. Most studies address acute effects of traditional pollutants (e.g. sulphur dioxide and trace elements) and nitrogen deposition on agricultural pests, whereas the effects of realistic concentrations of ozone, particulate matter and emerging pollutants on insects feeding on noncultivated plants are unknown. The accumulated evidence remains insufficient to predict the effects of pollutants of global concern on the population dynamics of herbivorous insects.

Detrimental Impact of λ-Cyhalothrin on the Biocontrol Efficacy of Eocanthecona furcellata by Affecting Global Transcriptome and Predatory Behavior

Whether and how insecticide exposure will affect the biological control efficacy of predatory arthropods is critical in insecticide toxicology research but largely unexplored. In the current study, reduced biocontrol efficacy was observed in a predatory stink bug─Eocanthecona furcellata─after insecticide application in the field. Thus, we constructed a comparative transcriptome analysis and identified a total of 4364 upregulated and 1043 down regulated differentially expressed genes following the sublethal exposure of λ-cyhalothrin. The reduced juvenile hormone (JH) titer and increased trehalose content were observed. The predation capacity and theoretical maximum predation of predators were decreased by 31.08 and 48.90% in response to λ-cyhalothrin, respectively. Furthermore, JH supplementation after λ-cyhalothrin treatment could significantly stimulate trehalase and detoxification enzyme activities, as well as restore the predatory ability of E. furcellata. Our results help to understand the toxicological mechanism of predatory stink bug species in responding to insecticides, benefit predators' ecological services, and optimize the insecticide selection.

Moderately decreasing fertilizer in fields does not reduce populations of cereal aphids but maximizes fitness of parasitoids

Examination of the tradeoff between the extent of decreasing nitrogen input and pest suppression is crucial for maintaining the balance between essential yield and an efficient, sustainable pest control strategy. In this study, an experiment with four manipulated nitrogen fertilizer levels (70, 140, 210, and 280 kg N ha⁻¹ = conventional level) was conducted to explore the effects of decreasing nitrogen on cereal aphids (Sitobion avenae and Rhopalosiphum padi) (Hemiptera: Aphididae), Aphidiinae parasitoids (Hymenoptera: Braconidae: Aphidiinae), and body sizes of parasitoids. The results indicated that nitrogen application, in the range of 70–280 kg N ha⁻¹, has the potential to impact the populations of cereal aphids and their parasitoids. However, both differences between densities of cereal aphids and their parasitoids in moderate (140–210 kg N ha⁻¹) and those in high nitrogen input (280 kg N ha⁻¹) were not significant, and the parasitism rate was also unaffected. A higher parasitism rate reduced population growth of the cereal aphid (S. avenae). Additionally, a moderate decrease of nitrogen fertilizer from 280 to 140–210 kg N ha⁻¹ maximized the body sizes of Aphidiinae parasitoids, indicating that a moderate decrease of nitrogen fertilizer could facilitate biocontrol of cereal aphid by parasitoids in the near future. We conclude that a moderate decrease in nitrogen application, from 280 to 140–210 kg N ha⁻¹, does not quantitatively impact the densities of cereal aphids or the parasitism rate but can qualitatively maximize the fitness of the parasitoids.