Chlorantraniliprole degenerates microvilli goblet cells of the Anticarsia gemmatalis (Lepidoptera: Noctuidae) midgut

The promoting effects of pyriproxyfen on autophagy and apoptosis in silk glands of non-target insect silkworm, Bombyx mori

Pyriproxyfen is a juvenile hormone analogue. The physiological effects of its low-concentration drift during the process of controlling agricultural and forestry pests on non-target organisms in the ecological environment are unpredictable, especially the effects on organs that play a key role in biological function are worthy of attention. The silk gland is an important organ for silk-secreting insects. Herein, we studied the effects of trace pyriproxyfen on autophagy and apoptosis of the silk gland in the lepidopteran model insect, Bombyx mori (silkworm). After treating fifth instar silkworm larvae with pyriproxyfen for 24 h, we found significant shrinkage, vacuolization, and fragmentation in the posterior silk gland (PSG). In addition, the results of autophagy-related genes of ATG8 and TUNEL assay also demonstrated that autophagy and apoptosis in the PSG of the silkworm was induced by pyriproxyfen. RNA-Seq results showed that pyriproxyfen treatment resulted in the activation of juvenile hormone signaling pathway genes and inhibition of 20-hydroxyecdysone (20E) signaling pathway genes. Among the 1808 significantly differentially expressed genes, 796 were upregulated and 1012 were downregulated. Among them, 30 genes were identified for autophagy-related signaling pathways, such as NOD-like receptor signaling pathway and mTOR signaling pathway, and 30 genes were identified for apoptosis-related signaling pathways, such as P53 signaling pathway and TNF signaling pathway. Further qRT-PCR and in vitro gland culture studies showed that the autophagy-related genes Atg5, Atg6, Atg12, Atg16 and the apoptosis-related genes Aif, Dronc, Dredd, and Caspase1 were responsive to the treatment of pyriproxyfen, with transcription levels up-regulated from 24 to 72 h. In addition, ATG5, ATG6, and Dronc genes had a more direct response to pyriproxyfen treatment. These results suggested that pyriproxyfen treatment could disrupt the hormone regulation in silkworms, promoting autophagy and apoptosis in the PSG. This study provides more evidence for the research on the damage of juvenile hormone analogues to non-target organisms or organs in the environment, and provides reference information for the scientific and rational use of juvenile hormone pesticides.

Imidacloprid-induced pathophysiological damage in the midgut of Locusta migratoria (Orthoptera: Acrididae) in the field

Neonicotinoids are modern insecticides widely used in agriculture worldwide. Their impact on target (nervous system) and non-target (midgut) tissues has been well studied in beneficial insects including honeybees under controlled conditions. However, their detailed effects on pest insects on the field are missing to date. Here, we have studied the effects of the neonicotinoid imidacloprid on the midgut of the pest insect Locusta migratoria caught in the field. We found that in the midgut of imidacloprid-exposed locusts the activity of enzymes involved in reactive oxygen metabolism was perturbed. By contrast, the activity of P450 enzymes that have been shown to be activated in a detoxification response and that were also reported to produce reactive oxygen species was elevated. Probably as a consequence, markers of oxidative stress including protein carbonylation and lipid peroxidation accumulated in midgut samples of these locusts. Histological analyses revealed that their midgut epithelium is disorganized and that the brush border of the epithelial cells is markedly reduced. Indeed, microvilli are significantly shorter, misshapen and possibly non-functional in imidacloprid-treated locusts. We hypothesize that imidacloprid induces oxidative stress in the locust midgut, thereby changing the shape of midgut epithelial cells and probably in turn compromising their physiological function. Presumably, these effects reduce the survival rate of imidacloprid-treated locusts and the damage they cause in the field.

Deltamethrin-Mediated Effects on Locomotion, Respiration, Feeding, and Histological Changes in the Midgut of Spodoptera frugiperda Caterpillars

Simple Summary

Spodoptera frugiperda is controlled mainly with chemical insecticides. Toxicity, survival, respiration, mobility, anti-feeding effect, and histology of the midgut of S. frugiperda caterpillars exposed to deltamethrin were evaluated. Deltamethrin was toxic to third-instar caterpillars, decreasing survival. The insecticide reduces the respiratory rate and food consumption, and causes repellency. Exposure to deltamethrin causes histological alterations in the midgut, damaging the digestive cells and peritrophic matrix. Deltamethrin is toxic to S. frugiperda caterpillars, causing mortality, alteration of locomotor behavior, reduced respiration and feeding, and irreversible damage to the midgut epithelium.

Abstract

Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) is the main pest of maize crops, and effective methods for pest management are needed. The insecticidal efficacy of deltamethrin was evaluated against S. frugiperda for toxicity, survival, locomotion, anti-feeding, and histological changes in the midgut. Concentration–mortality bioassays confirmed that deltamethrin (LC₅₀ = 3.58 mg mL⁻¹) is toxic to S. frugiperda caterpillars. The survival rate was 99.7% in caterpillars not exposed to deltamethrin, decreasing to 50.3% in caterpillars exposed to LC₅₀, and 0.1% in caterpillars treated with LC₉₀. Spodoptera frugiperda demonstrated reduced mobility on deltamethrin-treated surfaces. Deltamethrin promoted a low respiration rate of S. frugiperda for up to 3 h after insecticide exposure, displaying immobilization and inhibiting food consumption. Deltamethrin induces histological alterations (e.g., disorganization of the striated border, cytoplasm vacuolization, and cell fragmentation) in the midgut, damaging the digestive cells and peritrophic matrix, affecting digestion and nutrient absorption.