Environmental consequences of deltamethrin residues in cattle feces in an African agricultural landscape

The Fall Armyworm and Larger Grain Borer Pest Invasions in Africa: Drivers, Impacts and Implications for Food Systems

Invasive alien species (IAS) are a major biosecurity threat affecting globalisation and the international trade of agricultural products and natural ecosystems. In recent decades, for example, field crop and postharvest grain insect pests have independently accounted for a significant decline in food quantity and quality. Nevertheless, how their interaction and cumulative effects along the ever-evolving field production to postharvest continuum contribute towards food insecurity remain scant in the literature. To address this within the context of Africa, we focus on the fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), and the larger grain borer, Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae), two of the most important field and postharvest IAS, respectively, that have invaded Africa. Both insect pests have shown high invasion success, managing to establish themselves in >50% of the African continent within a decade post-introduction. The successive and summative nature of field and postharvest damage by invasive insect pests on the same crop along its value chain results in exacerbated food losses. This systematic review assesses the drivers, impacts and management of the fall armyworm and larger grain borer and their effects on food systems in Africa. Interrogating these issues is important in early warning systems, holistic management of IAS, maintenance of integral food systems in Africa and the development of effective management strategies.

Comparative toxicity of two neonicotinoid insecticides at environmentally relevant concentrations to telecoprid dung beetles

Dung beetles (Coleoptera: Scarabaeinae) frequently traverse agricultural matrices in search of ephemeral dung resources and spend extended periods of time burrowing in soil. Neonicotinoids are among the most heavily applied and widely detected insecticides used in conventional agriculture with formulated products designed for row crop and livestock pest suppression. Here, we determined the comparative toxicity of two neonicotinoids (imidacloprid and thiamethoxam) on dung beetles, Canthon spp., under two exposure profiles: direct topical application (acute) and sustained contact with treated-soil (chronic). Imidacloprid was significantly more toxic than thiamethoxam under each exposure scenario. Topical application LD50 values (95% CI) for imidacloprid and thiamethoxam were 19.1 (14.5-25.3) and 378.9 (200.3-716.5) ng/beetle, respectively. After the 10-day soil exposure, the measured percent mortality in the 3 and 9 µg/kg nominal imidacloprid treatments was 35 ± 7% and 39 ± 6%, respectively. Observed mortality in the 9 µg/kg imidacloprid treatment was significantly greater than the control (p = 0.04); however, the 3 µg/kg imidacloprid dose response may be biologically relevant (p = 0.07). Thiamethoxam treatments had similar mortality as the controls (p > 0.8). Environmentally relevant concentrations of imidacloprid measured in airborne particulate matter and non-target soils pose a potential risk to coprophagous scarabs.

Dung beetle community composition affects dung turnover in subtropical US grasslands

An important service in many ecosystems is the turnover and degradation of dung deposited by cattle. Dung beetles are the primary group of insects responsible for dung turnover, and factors affecting their abundance and distribution thus impact dung degradation. Lands lost to grazing due to dung buildup and pasture contamination total millions of acres per year in US pastures.We evaluated the structural differences in dung beetle assemblages in natural grasslands versus a managed agroecosystem in subtropical southeastern Florida (USA). We measured the direct effect of dung longevity when dung beetle fauna normally inhabiting dung pats were excluded.Our results indicate dung beetle abundance, functional diversity, and species richness have a substantial impact on the rate of dung turnover in subtropical pastoral lands with ~70% of dung removed from the soil surface after three months. Functional diversity and evenness did not have a significant positive effect on dung removal in managed, versus natural grasslands demonstrating a strong relationship between dung beetle assemblage composition and delivery of a key ecological process, dung degradation.We suggest the importance of trees, which provide a thermal refuge for beetles, should be dispersed within matrixes of open pasture areas and within proximity to adjacent closed-canopy hammocks to facilitate the exchange of dung beetles between habitats and therefore maintain the provisioning of dung degradation services by dung beetle assemblages.

Dung beetle community assemblages in a southern African landscape: niche overlap between domestic and wild herbivore dung

Dung beetles provide important ecosystem functions in semiarid environments, improving the physiochemical characteristics of the soil through tunnelling and burying nutrient-rich dung. In sub-Saharan Africa, diverse indigenous mammal communities support highly abundant dung beetle populations in savannah ecosystems. However, the conversion of landscapes to livestock agriculture may result in changes in the abundance and diversity of wild mammal species. This is likely to have significant impacts on dung beetle communities, particularly because domestic livestock dung may be contaminated with toxic residues of veterinary parasiticides. The environmental impact is likely to be affected by the degree of niche overlap between the beetle communities that colonize cattle dung and those that colonize the dung of wild mammals. We compared dung beetle communities between a pristine national park habitat dominated by large wild herbivores, and a pastoral farming community dominated by domestic livestock. Diurnal dung beetles were attracted to cattle dung in greater abundance and diversity compared to elephant, zebra or giraffe dung. Nocturnal/crepuscular dung beetles were attracted to non-ruminant dung (elephant and zebra) in higher abundance compared to ruminant dung (cattle and giraffe). Although there were no clear trophic specializations, three diurnal species showed an association with cattle dung, whereas eight nocturnal/crepuscular species showed an association with non-ruminant (elephant and zebra) dung. Diurnal species may be at greater risk from the toxic effects of residues of veterinary parasiticides in domestic livestock dung. Although many species showed trophic associations with wild herbivore dung, these beetles can utilize a wide range of dung and will readily colonize cattle dung in the absence of other options. As more land is converted to livestock agriculture, the contamination of dung with toxic residues from veterinary parasiticides could therefore negatively impact the majority of dung beetle species.

Toxicological effects of deltamethrin on quail cerebrum: Weakened antioxidant defense and enhanced apoptosis

Deltamethrin is the most common type II synthetic pyrethroid insecticide, and has posed widespread residues to environment. However, whether deltamethrin has potential toxic effects on quail cerebrum remains greatly obscure. Accordingly, we investigated the impact of chronic exposure to deltamethrin on oxidative stress and apoptosis in quail cerebrum. Quails upon 12-week exposure of deltamethrin (0, 15, 30, or 45 mg/kg body weight intragastric administration) were used as a cerebrum injury model. The results showed that deltamethrin treatment led to cerebral injury dose-dependently through the weakened antioxidant defense by downregulating nuclear factor erythroid-2-related factor 2 (Nrf2) and its downstream proteins levels and mRNA expression. Furthermore, deltamethrin treatment induced apoptosis in cerebrum by decreasing B-cell lymphoma gene 2 (Bcl-2) level, as well as increasing Jun N-terminal kinase3, caspase-3, and Bcl-2-associated X protein levels. Simultaneously, toll-like receptor 4 (TLR4) downstream inflammation-related genes or proteins were significantly up-regulated by deltamethrin dose-dependently. Altogether, our study demonstrated that chronic exposure to deltamethrin induces inflammation and apoptosis in quail cerebrums by promoting oxidative stress linked to inhibition of the Nrf2/TLR4 signaling pathway. These results provide a novel knowledge on the chronic toxic effect of deltamethrin, and establish a theoretical foundation for the evaluation of pesticide-induced health risk.

Exposure to environmentally relevant concentrations of deltamethrin renders the Chinese rare minnow (Gobiocypris rarus) vulnerable to Pseudomonas fluorescens infection

In this study, to assess the immunotoxicity of deltamethrin on fish, adult Chinese rare minnows (Gobiocypris rarus) were exposed to 0.1, 0.3, and 1 μg/L deltamethrin for 28 d. Many immunological parameters and histopathological alterations were determined. The results showed that lymphocyte number was markedly decreased at 0.3 and 1 μg/L treatments, whereas the neutrophil number was strongly increased at 1 μg/L treatments (p < 0.05). Furthermore, lysozyme (LYS), immunoglobulin M (IgM), and complement component 3 (C3) levels at 0.3 and 1 μg/L treatments were markedly reduced, whereas alkaline phosphatase (ALP) activity were marked increased at 1 μg/L treatments (p < 0.05). The transcripts of almost all TLR (Toll-like receptor) signaling pathway-related genes were up-regulated. Histological lesions in the livers, intestines, and gills were observed at all treatments. Then, all remaining fish from controls and deltamethrin-exposed groups were injected with Pseudomonas fluorescens (P. fluorescens) for 48 h. At 24 and 48 h post-injection with P. fluorescens (hpi), the lymphocyte numbers were strongly reduced at 0.3 and 1 μg/L deltamethrin-exposed groups, whereas LYS and C3 levels were strongly reduced at 0.3 and 1 μg/L deltamethrin-exposed groups (p < 0.05). Obvious reduces in IgM levels were also detected at 0.3 and 1 μg/L deltamethrin-exposed groups at 48 hpi (p < 0.05). The transcripts of almost all TLR signaling pathway-related genes were significantly down-regulated, whereas the levels of related microRNAs (miRNAs) were markedly increased at all deltamethrin-exposed groups at 24 and 48 hpi. Moreover, the bacterial load in the liver and the mortality of fish were significantly increased at 1 μg/L deltamethrin-exposed groups at 24 and 48 hpi (p < 0.05). Furthermore, obvious histological damage in the livers, intestines, and gills were observed at all deltamethrin-exposed fish at 48 hpi. Overall, our results demonstrated that environmentally relevant concentration deltamethrin suppressed immunity and rendered the fish vulnerable to P. fluorescens infection, subsequently inducing mortality.

The synthetic pyrethroid deltamethrin impairs zebrafish (Danio rerio) swim bladder development

Deltamethrin (DM) is a widely used insecticide and reveals neural, cardiovascular and reproductive toxicity to various aquatic organisms. It has been known that DM negatively affects motion of zebrafish (Danio rerio). However, little is known in relation to the impacts of DM on development of swim bladder, which is a key organ for motion. In the present study, zebrafish embryos were exposed to 20 and 40 µg/L DM. The changes of swim bladder morphology were observed and transcription levels of key genes were compared between DM treatments and the control. The results showed that DM treatments significantly blocked the formation of progenitor and tissue layers in swim bladder of zebrafish embryos, leading to failed inflation of swim bladder. Compared with the control, the key genes (pbx1, foxA3, mnx1, has2, anxa5b, hprt1l and elovl1a) responsible for swim bladder development also showed decreased levels in response to DM treatments, suggesting that DM might specifically affect swim bladder development. Moreover, transcription levels of genes in the Wnt (wnt5b, tcf3a, wnt1, wnt9b, fzd1, fzd3 and fzd5) and Hedgehog (ihhb, ptc1 and ptc2) signaling pathways all decreased significantly in response to DM treatments, compared with the control. Considering the importance of Wnt and Hedgehog pathways in development of swim bladder, these results suggested that DM might affect swim bladder development through inhibiting the Wnt and Hedgehog pathways. Overall, the present study reported that swim bladder might be a potential target organ of DM toxicity in zebrafish, which contributed more information to the evaluation of DM's environmental risks.

Adverse effects of routine bovine health treatments containing triclabendazole and synthetic pyrethroids on the abundance of dipteran larvae in bovine faeces

Macrocyclic lactone treatments for livestock can have detrimental effects on the arthropod populations in livestock faeces. For the last twenty years, avoidance of these products has been a standard recommendation on livestock farms that are managed for wildlife by the Royal Society for Protection of Birds (RSPB). However, the continued decline in the populations of birds (in particular the red-billed chough Pyrrhocorax pyrrhocorax) that are dependent on dung invertebrates on islands in the Inner Hebrides of Scotland prompted us to investigate the effects of livestock treatments that are commonly used on these islands. We conducted a replicated field plot study over two years to quantify the effects of livestock treatments containing copper, deltamethrin and triclabendazole on invertebrate density in pooled, artificial faecal pats on the island of Islay. We found that the density of arthropod larvae was significantly reduced by the triclabendazole and deltamethrin treatments in both years and by as much as 86% when the treatments were combined. Copper-containing boluses did not consistently affect abundance of arthropod larvae. These results suggest that veterinary treatment of livestock might contribute to a reduction in the food supply of chough.

Cardiovascular toxicity and anxiety-like behavior induced by deltamethrin in zebrafish (Danio rerio) larvae

Deltamethrin is widely used because of its low toxicity and high efficiency. Although its potential toxicity has been reported, its effects on cardiovascular system and motor behavior and its underlying mechanisms have remained unclear. In this study, the effects of deltamethrin on the development, cardiovascular system and motor behavior of zebrafish larvae and their possible mechanisms were evaluated using the transgenic zebrafish Tg (kdrl:mCherry) and Tg(myl7:GFP). At 72 hpf, the body length of larvae shortened, the head and eye area decreased, and the hatching rate increased. Acridine orange staining showed that treated zebrafish larvae produced different degrees of apoptosis in the head, body, heart and tail regions. Quantitative fluorescence intensity showed a dose-dependent increase in apoptosis signal, indicating that deltamethrin could induce apoptosis. Confocal images and fluorescence intensity quantification of red fluorescent protein-labeled vascular endothelial cell and green fluorescent protein-labeled transgenic zebrafish more clearly reflected the dose-dependent cardiac and vascular morphology and the damage caused by deltamethrin. Deltamethrin significantly induced vascular endothelial growth factor flk1 and fli-1, cardiac development-related gene myl7 decreased in a dose-dependent manner. In addition, deltamethrin increased the thigmotaxis of zebrafish larvae, causing anxiety-like behavior. Our study showed that deltamethrin could cause developmental toxicity, apoptosis, cardiovascular system damage and anxiety-like behavior, which provided a reference for the use of deltamethrin in agricultural production.