Acetylcholinesterase and heat shock protein 70 response in larval brain tissue of Lymantria dispar L. (Lepidoptera, Limantriidae) upon chronic exposure to benzo(a)pyrene

Edible insects: Understanding benzo(a)pyrene toxicokinetics in yellow mealworms for safe and sustainable consumption

The global interest in edible insects as sustainable protein sources raises concerns about the bioaccumulation of contaminants, including polycyclic aromatic hydrocarbons (PAHs), to problematic levels. Understanding the accumulation dynamics of PAHs in edible insects is highly relevant due to the widespread sources and toxicological profiles; however, the bioaccumulative potential of PAHs in edible insects is unexplored. This study examined the uptake and elimination dynamics of benzo(a)pyrene (B(a)P), a representative and carcinogenic PAH, in yellow mealworm larvae (YMW, Tenebrio molitor). Larvae were exposed to feeding substrate with varying B(a)P concentrations (0.03, 0.3, and 3 mg kg-1), and uptake (21 days in B(a)P-contaminated substrate) and elimination (21 days in B(a)P-free substrate) kinetics were subsequently assessed. The results showed that YMW can eliminate B(a)P, revealing dose-dependent B(a)P bioaccumulation in these insects. Larvae fed on a substrate with 0.03 mg kg-1 accumulated B(a)P over 21 days, presenting values of 0.049 (Standard deviation - 0.011) mg kg-1 and a kinetic-based (BAFkinetic) of 1.93 g substrate g organism-1, exceeding the EU regulatory limits for food. However, with a B(a)P half-life (DT50) of 4.19 days in the larvae, an EU legislation safety criterion was met after a 13-day depuration period in clean substrate. Larvae exposed to substrates with 0.3 and 3 mg kg-1 showed B(a)P accumulation, with BAFkinetic values of 3.27 and 2.09 g substrate g organism-1, respectively, not meeting the current legal standards for food consumption at the end of the exposure to B(a)P. Although the B(a)P half-life values after 35 days were 4.30 and 10.22 days (DT50s), the larvae retained B(a)P levels exceeding permitted food safety limits. These findings highlight a significant oversight in regulating PAHs in animal feed and the need for comprehensive safety evaluations of PAH hazards in edible insects for improved PAH feeding guidelines.

The effects of temperature stress and population origin on the thermal sensitivity of Lymantria dispar L. (Lepidoptera: Erebidae) larvae

Increased environmental temperature is one of the most frequent stresses effecting metabolic rate in herbivorous insect species. Our goal was to compare the influence of increased environmental temperature and induced thermotolerance on the activity of midgut phosphatases and brain tissue hsp70 concentration in 5th instar Lymantria dispar larvae originating from an unpolluted and polluted forest. Induced thermotolerance (larval pre-treatment at high, sub-lethal temperature) increases the species ability to overcome the negative effects of thermal stress, therefore we monitored the effect of this regime in larvae originating from both forests. Thermal regimes in this experiment predominantly influenced the alkaline phosphatases activity and it was affected by temperature, population origin, and their combined effect. Total acid phosphatases activity was changed only by the joint effect of temperature and population origin. Brain hsp70 concentration was under a significant individual and joint effect of temperature and population. In both populations, brain tissue hsp70 concentration and alkaline phosphatases activity should be taken under consideration as a battery with biomarker potential for thermal stress in L. dispar larvae as a bioindicator species.

Sensitivity of midgut physiological parameters of Lymantria dispar L. larvae to benzo[a]pyrene in populations with different multigeneration contact to environmental pollutants

Accumulation of organic pollutants in the environment calls for sensing physiological parameters adequate to indicate the presence of contaminants and their effects on ecosystems. Evidence points to the importance of insect adaptations in their habitats for the assessment of sensitive biomarkers so we examined the influence of origin and multigenerational adaptations of the Lymantria dispar larvae to chronic benzo[a]pyrene (B[a]P) treatment under laboratory conditions. The main aim was to compare reactions of larvae from unpolluted and polluted forests using alkaline phosphatase (ALP), acid phosphatase (ACP), and carboxylesterase (CE) specific activities in the midgut, including electrophoretic isoform patterns; midgut expression levels of Hsp70, larval development time (DT), and midgut mass (MM), after chronic exposure to 5 and 50 ng of B[a]P/g dry food weight. The biomarker potential of these parameters regarding larval pre-exposure history to pollution was estimated by principal component analysis (PCA). B[a]P treatment resulted in inhibition of ALP activity, a rise of CE activity, and reduction of MM in larvae from the unpolluted forest, while the population from the polluted forest showed significant elevation of Hsp70 expression in the midgut, prolonged DT, and reduction of MM. PCA confirmed variations in responses of the selected parameters regarding population origin. The obtained results provide insight into insect population variability concerning physiological responses to pollutants. It is indicative that all investigated physiological parameters of L. dispar larvae showed origin-dependent responses to long-term presence of B[a]P, which may be of great importance in ecotoxicological research.

Heat Shock Protein 70 Family in Response to Multiple Abiotic Stresses in the Silkworm

Simple Summary

Heat shock protein 70 family is widely distributed in all the organisms, which plays important roles in protein folding and preventing protein denaturation. Heat or cold stress response has been studied in some insects, but there is a lack of systematic investigation on the response of the same species to multiple stressors. Here, we performed genome-wide identification of heat shock protein 70 family in the silkworm, Bombyx mori. Using the silkworm as a model, the transcription profiles of all the genes against heat, cold, and pesticides were studied. Our findings would provide insights into the functional diversification of heat shock proteins 70 in insects.

Abstract

The 70 kDa heat shock proteins play important roles in protecting organisms against environmental stresses, which are divided into stress-inducible forms (HSP70s) and heat shock cognates (HSC70s). In this study, heat shock protein 70 family was identified in the whole genome of the silkworm. Based on the known nomenclature and phylogenetic analysis, four HSP70s and five HSC70s were classified. Relatively, heat shock cognates were more conservative and were constitutively expressed in various tissues of the silkworm larvae. Under thermal (37 °C and 42 °C) and cold (2 °C) stresses, the expressions of HSP70–1, HSP70–2, and HSP70–3 were up-regulated, and the highest induction reached 4147.3, 607.1, and 1987.3 times, respectively. Interestingly, HSC70–1, HSC70–4, and HSC70–5 also showed slight induced expressions in the fat body and/or midgut under thermal stresses. In addition, the expression of HSP70–1 was induced by dichlorvos and phoxim insecticides, while most HSC70 genes were inhibited. The results suggested that stress-inducible forms play more important roles in adaptation to various stresses than HSC70s.

Relative gene expression, micronuclei formation, and ultrastructure alterations induced by heavy metal contamination in Pimelia latreillei (Coleoptera: Tenebrionidae) in an urban-industrial area of Alexandria, Egypt

The present research aims to evaluate the impact of industrial processes and anthropogenic activities on the beetle Pimelia latreillei inhabiting the polluted site at Zawya Abd El- Qader, Alexandria, Egypt. Beetles were collected from the vicinity of five factories. The genotoxic effects of environmental exposures to industrial heavy metals were monitored using a broad range of assays, including energy-dispersive X ray microanalysis and X-ray diffraction (SEM and EDX)), qRT-PCR gene expression assay, micronuclei formation, and transmission electron microscope (TEM). Energy dispersive X-ray microanalysis for the soil and testicular tissues of beetles collected from the polluted site revealed a higher percentage of heavy metals than the beetles collected from the reference site (Sidi Kirier, Alexandria, Egypt). To analyze/monitor genotoxicity in P. latreillei sampled from the polluted site, the transcription levels of levels of heat shock proteins (Hsps) and accessory gland seminal fluid protein (AcPC01) in testicular tissues were recorded. The incidence of micronuclei (MN) formation in the testicular cells was also observed. Quantitative RT-PCR (RT-qPCR) analysis was carried out to detect the changes in the gene expression of the aforementioned proteins. Genes encoding heat shock proteins (Hsp60, Hsp70, and Hsp90) were significantly overexpressed (> 2-fold) in specimens sampled from the polluted site; however, AcPC01 gene expression was under-expressed (<1.5-folds). The incidence of MN was significantly increased in specimens sampled from the polluted site. Ultrastructure anomalies (nuclear and cytoplasmic disruption) were also observed in the testicular cells of the beetles sampled from the polluted site compared to those sampled from the unpolluted site. Our results, therefore, advocate a need for adequate measures to reduce increasing environmental pollution in the urban-industrial areas.

Nickel oxide nanoparticles induce genotoxicity and cellular alterations in the ground beetle Blaps polycresta (Coleoptera: Tenebrionidae)

Nickel nanoparticles (Ni-NPs) have advantageous applications in the industry; however, little is known of their adverse effects on biological tissues. In the present study, the ground beetle Blaps polycresta was employed as a sensitive indicator for nickel oxide nanoparticles (NiO-NPs) toxicity. Adult male beetles were injected with six dose levels of NiO-NPs (0.01, 0.02, 0.03, 0.04, 0.05, and 0.06 mg/g body weight). Mortality was reported daily over 30 days under laboratory conditions to establish an LD₅₀. Nickel was detected in the testicular tissues of the beetles using X-ray analysis and transmission electronic microscopy. Beetles treated with the sublethal dose of 0.02 mg/g were selected to observe molecular, cellular, and subcellular changes. Gene transcripts of HSP70, HSP90, and MT1 were found to be increased >2.5-, 1.5-, and 2-fold, respectively, in the treated group compared with the controls. Decreased gene expression of AcPC01, AcPC02, and AcPC04 (≤1.5-, ≤2-, and < 2.5-fold, respectively, vs. controls) also were reported in the treated group. Under light microscopy, various structural changes were observed in the testicular tissues of the treated beetles. Ultrastructure observations using scanning and transmission electron microscopy showed severe damage to the subcellular organelles as well as deformities of the heads and flagella of the spermatozoa. Therefore, the present study postulated the impact of NiO-NPs in an ecological model.

Parameters of oxidative stress, cholinesterase activity, Cd bioaccumulation in the brain and midgut of Lymantria dispar (Lepidoptera: Lymantriidae) caterpillars from unpolluted and polluted forests

Cadmium (Cd) can display a variety of different effects on living organisms. The objectives of the present study were to investigate Cd bioaccumulation and differences in parameters of oxidative stress (activities of the enzymes: superoxide dismutase, catalase, glutathione reductase, ascorbate peroxidase, glutathione S-transferase, and amounts of non-enzymatic free sulfhydryl groups and total glutathione) and cholinesterase activity in larval brain and midgut tissues of the polyphagous forest insect Lymantria dispar collected from unpolluted and polluted oak forests. Fourth instar L. dispar caterpillars from the unpolluted forest had higher body mass but accumulated more Cd in comparison to caterpillars from the polluted forest. In both populations the midgut was more sensitive than the brain to the prooxidative effects of Cd. Enzyme activities and amounts of non-enzymatic parameters tended to be greater in midgut tissues than in the brain, except for cholinesterase activity. Parameters of oxidative stress had higher values in caterpillar tissues from the polluted than from the unpolluted oak forest. The observed differences between the two natural populations point to the importance of knowing the history of population exposure to environmental pollution when monitoring forest ecosystems.