Exposure to spinosad induces histopathological and cytotoxic effects on the salivary complex of the non-target predator Podisus nigrispinus

Sublethal exposure to thiamethoxam and pyraclostrobin affects the midgut and Malpighian tubules of the stingless bee Frieseomelitta varia (Hymenoptera: Apidae: Meliponini)

The stingless bee Frieseomelitta varia Lepeletier 1836 (Hymenoptera: Apidae) is an essential pollinator in natural and agricultural ecosystems in the Neotropical region. However, these bees may be exposed to pesticides during foraging, which can affect both individuals and their colonies. One example comes from the use of pyraclostrobin (a fungicide) and thiamethoxam (an insecticide) for pest control in pepper crops, which F. varia visits. This study aimed to evaluate the isolated and combined sublethal effects of thiamethoxam (TMX) (0.000543 ng a.i./µL) and pyraclostrobin (PYR) (1.5 ng i.a./µL) on the morphology of the midgut and Malpighian tubules of F. varia workers. Results showed that both pesticides, regardless of the exposure time (through feeding during 48 h or 96 h), disturbed the morphology of the analyzed organs. Specifically, F. varia exposed orally to sublethal concentrations of thiamethoxam and pyraclostrobin, either alone or in combination, exhibited a higher rate of damage to the midgut (e.g., vacuolization, apocrine secretion, and cellular elimination) compared to the bees in the control groups, both after 48 h and 96 h of exposure. In Malpighian tubules, vacuolation is the only damage present. As the observed morphological alterations likely compromise the excretion and absorption functions, exposure to pyraclostrobin and thiamethoxam may lead to disturbances at both the individual and colony levels. These results highlight the urgent need for a future reassessment of the safety of fungicides and insecticides regarding their potential effects on bee populations.

Exploring the effects of the acaricide cyflumetofen on the vital organs of the honey bee Apis mellifera (Hymenoptera: Apidae) workers

Bees are important for maintaining ecosystems, pollinating crops and producing marketable products. In recent years, a decline in bee populations has been reported, with multifactorial causes, including the intensification of pesticide use in agriculture. Among pesticides, cyflumetofen is an insecticide and acaricide used in apple, coffee and citrus crops, whose main pollinator is the honey bee Apis mellifera. Therefore, this bee is a potential target of cyflumetofen during foraging. This study evaluated the histopathological and cytological damage in the midgut, hypopharyngeal glands and fat body of A. mellifera workers exposed to LC50 of cyflumetofen. The midgut epithelium of exposed bees presented cytoplasmic vacuolization, release of vesicles and cell fragments, which indicate autophagy, increased production of digestive enzymes and cell death, respectively. The cytological analysis of the midgut revealed the dilation of the basal labyrinth and the presence of spherocrystals in the digestive cells. The hypopharyngeal glands produced greater amounts of secretion in treated bees, whereas no changes were observed in the fat body. The results indicate that acute exposure to cyflumetofen negatively affect A. mellifera, causing damage to the midgut and changes in the hypopharyngeal glands, which may compromise the survival and foraging of this pollinator.

First report on evaluation of commercial eugenol and piperine against Aedes aegypti L (Diptera: Culicidae) larvae: Mortality, detoxifying enzyme, and histopathological changes in the midgut

Dengue fever is a worldwide public health problem, and efforts to eradicate it have focused on controlling the dengue vector, Aedes aegypti. This study aims to assess the toxicity and effect of commercial eugenol and piperine on Ae. aegypti larvae through enzyme detoxification and histopathological changes in the midgut. Laboratory-reared Ae. aegypti larvae were treated with various concentrations of commercial eugenol and piperine and observed after 24, 48, and 72 h. Biochemical methods were used to assess detoxification enzyme activity for acetylcholinesterase, glutathione S-transferase, and oxidase, and changes in the midgut were examined using routine histological examination. In terms of larvicidal activity, piperine exceeded eugenol. Piperine and eugenol had LC50 and LC90 values of 3.057 and 5.543 μM, respectively, and 6.421 and 44.722 μM at 24 h. Piperine and eugenol reduced oxidase activity significantly (p < 0.05), but increased acetylcholinesterase and glutathione S-transferase activity significantly (p < 0.05). After being exposed to piperine and eugenol, the food bolus and peritrophic membrane ruptured, the epithelial layer was interrupted and irregular, the epithelial cells shrank and formed irregularly, and the microvilli became irregular in shape. Commercial piperine and eugenol behave as potential larvicides, with processes involving altered detoxifying enzymes, specifically decreased oxidase function and increased GST activity, as well as midgut histological abnormalities.

Indoxacarb effects on non-target predator, Podisus distinctus (Hemiptera: Pentatomidae)

Forestry pest management includes biological and chemical methods of pest control. Using insecticides and natural enemies can be compatible in forest pest management programs. The compatibility of the predatory stink bug Podisus distinctus with the insecticide indoxacarb, used in forestry, needs to be evaluated in Brazil. This study investigated the mortality, survival, respiration, preference, prey consumption, and locomotor activity of P. distinctus adults exposed to indoxacarb. In concentration-mortality bioassays, the lethality of indoxacarb (LC₅₀ = 2.62 g L^-1 and LC₉₀ = 6.11 g L^-1) was confirmed in P. distinctus adults. The survival rate was 100% in predator insects not exposed to indoxacarb, declining to 40.7% in predator insects exposed to 2.62 g L^-1 and 0.1% in predators treated with 6.11 g L^-1. Indoxacarb reduced the respiration of P. distinctus from 18.45 to 14.41 µL CO₂ h^-1 at 2.62 g L^-1 for up to 3 h after insecticide exposure, inhibiting food consumption and displaying hyperexcitation. The harmful effects of indoxacarb to the natural enemy suggest that it should be better assessed for use with P. distinctus for pest management in forestry.

Side-effects of pesticides on non-target insects in agriculture: a mini-review

Climate change mediated by anthropogenic activity induces significant alterations on pest abundance and behavior and a potential increase in the use of agrochemicals for crop protection. Pesticides have been a tool in the control of pests, diseases, and weeds of agricultural systems. However, little attention has been given to their toxic effects on beneficial insect communities that contribute to the maintenance and sustainability of agroecosystems. In addition to pesticide-induced direct mortality, their sublethal effects on arthropod physiology and behavior must be considered for a complete analysis of their impact. This review describes the sublethal effects of pesticides on agriculturally beneficial insects and provides new information about the impacts on the behavior and physiology of these insects. The different types of sublethal effects of pesticides used in agriculture on pollinators, predators, parasitoids, and coprophagous insects were detailed.

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.

Imidacloprid-mediated alterations on the salivary glands of the Neotropical brown stink bug, Euschistus heros

The management of the Neotropical brown stinkbug Euschistus heros (Hemiptera: Pentatomidae) in soybean fields has been heavily dependent on the application of neonicotinoid insecticides. Neonicotinoids act primarily by impairing the function of the nicotinic acetylcholine receptors of the nervous system. These compounds also target specific organs (e.g., salivary glands), which may potentiate their insecticidal efficacy. Here, we evaluated whether the exposure to the neonicotinoid imidacloprid would cause cytomorphological changes in the salivary glands of E. heros. First, we determined the lethal concentrations (LCs) of imidacloprid through contact and ingestion. Subsequently, the cytomorphology of the salivary glands were evaluated in insect groups that survived exposure to the LC₅ (3.75 mg a.i./L), LC₅₀ (112.5 mg a.i./L), or LC₇₅ (375.0 mg a.i./L, equivalent to the recommended field rate) doses. Imidacloprid induced apoptosis and necrosis in the salivary gland cells according to the insecticide concentration and salivary gland region. All concentrations increased apoptosis and injured cells (e.g., vacuolization, chromatin condensation, swelling of organelles, and plasma membrane rupture) in the principal and accessory salivary glands. Individuals that survived exposure to the highest concentrations (i.e., LC₅ and LC₅₀) were more affected, and exhibited several necrotic cells on their main principal salivary glands. Collectively, our results indicate that imidacloprid exerts toxic effects on the non-target organs, such as the salivary glands, which increases the efficacy of this compound in the management of stink bug infestations.

Spiromesifen induces histopathological and cytotoxic changes in the midgut of the honeybee Apis mellifera (Hymenoptera: Apidae)

The honeybee Apis mellifera is an important pollinator that, similarly to other bees, undergoes colony losses due to several problems, including the use of pesticides in the agriculture. In addition to direct mortality, pesticides cause side-effects in some non-target organs, such as the midgut, which is the main organ for digestion and absorption. Spiromesifen is a pesticide used to control mites and whiteflies, which can be ingested by bees feeding on contaminated floral resources. This study evaluated the histopathological and cytological effects of the ingestion of spiromesifen on the midgut of A. mellifera workers. The bees were exposed per os to the field recommended dose of spiromesifen, and the midgut was analyzed after 24h and 48h of exposure to the pesticide. The midgut has a single layer of digestive cells, with spherical nucleus, nests of regenerative cells and layers of peritrophic matrix in the lumen. Bees treated with spiromesifen presented histological and cytological changes in the midgut, including disorganization of the epithelial architecture, release of cell fragments to the lumen, accumulation of mitochondria in the apical cytoplasm, alteration of the basal labyrinth, changes in the rough endoplasmic reticulum and cell degeneration. The occurrence of damage in the digestive cells of the A. mellifera midgut indicates that spiromesifen does not cause mortality in honeybees, but its side-effects can damage the midgut, which may affect the longevity and behavior of this pollinator.

Exposure of Rhipicephalus sanguineus sensu lato Latreille, 1806 (Acari: Ixodidae) to hexane extract of Acmella oleracea (Jambu): semi-engorged and engorged ticks

The present study analyzed the efficacy of hexane extract of Acmella oleracea against Rhipicephalus sanguineus sensu lato. After exposure of R. sanguineus s. l. female ticks to 14 different concentrations of the hexane extract of A. oleracea, the LC₅₀ was established as 18.135 mg/mL (limits: 16.251-22.675). The effects of the extract were more significant in the ovary of the semi-engorged females, that presented damages in most oocytes. Since such changes would not be repaired, the oocytes could not advance to further stages of development (I-V), thereby causing the inhibition of ovary development, interruption of vitellogenesis, oocyte death and, consequently, infertility. The semi-engorged females also presented extensive damages in the midgut cells, which would prevent (totally or partially) these cells from functioning properly (blood intake and release of nutrients), impairing the ectoparasite nutrition and the viability of the individual. Thus, the hexane extract of A. oleracea can be considered as a promising alternative to chemical control of pests of medical and veterinary importance, due to its efficient acaricidal activity and lesser environmental impact, when used against female ticks in the middle feeding stage.

Respiration, predatory behavior and prey consumption by Podisus nigrispinus (Heteroptera: Pentatomidae) nymphs exposed to some insecticides

Podisus nigrispinus Dallas (Heteroptera: Pentatomidae) preys on insect pests in eucalyptus plantations where it can be exposed to insecticides used in pest control. The effect of insecticides on non-target natural enemies requires further study. The objective of the present study was to evaluate the side-effects of Bacillus thuringiensis (Bt), permethrin, tebufenozide and thiamethoxam on third instar nymphs of the predator P. nigrispinus in the laboratory. The toxicity of insecticides for this insect was determined by estimating their lethal concentrations. Podisus nigrispinus behavior after exposure to insecticides was analyzed using a video tracking system and the respiratory rate with a respirometer. Prey/nymph consumption was assessed after 24 h of starvation. The preference of P. nigrispinus nymphs, for prey treated or not with the insecticides, was evaluated in free choice tests. The insecticides Bt [LC₅₀ = 1.10(0.83-1.46) mg mL^-1], permethrin [LC₅₀ = 0.25(0.17-0.34) mg mL^-1], tebufenozide [LC₅₀ = 5.71(4.17-7.57) mg mL^-1] and thiamethoxam [LC₅₀ = 0.04(0.02-0.06) mg mL^-1] are toxic to P. nigrispinus nymphs. Bt and the insecticides tebufenozide, permethrin and thiamethoxam reduced the respiratory rate of P. nigrispinus. The insecticides permethrin, tebufenozide and thiamethoxam affect the locomotion of this insect's nymphs. Prey treated with Bt, permethrin and thiamethoxam are less preferred by P. nigrispinus. The survival of the nymphs of this predator was 93.3%, 66.7%, 56.6%, 0% and 0% in the control, tebufenozide, Bt, permethrin and thiamethoxam treatments, respectively. In addition, the reduction of prey consumption, treated with neurotoxic insecticides, reduces the predatory potential of this natural enemy. Bt and tefubenozide present low toxicity for P. nigrispinus, but the neurotoxic products have low compatibility with this natural enemy and, therefore, are not recommended, with this predator in the management of forest insect pests.

Histopathological and cytotoxic changes induced by spinosad on midgut cells of the non-target predator Podisus nigrispinus Dallas (Heteroptera: Pentatomidae)

Broad-spectrum insecticides used in pest control are a risk for non-target insects. Their compatibility to the insecticide spinosad, used in agriculture and forestry as a biological control tool, needs to be evaluated. Podisus nigrispinus Dallas (Heteroptera: Pentatomidae) is a predatory bug used in the pest management of agricultural and forest systems where spinosad is also frequently applied. The aim of this study was to evaluate the toxicity, histopathology and cytotoxicity in midgut cells of P. nigrispinus exposed to spinosad. The toxicity test was performed to determine the lethal concentrations of spinosad after exposure by ingestion. The histopathology and cytotoxicity caused by spinosad were analyzed in the three midgut regions (anterior, middle and posterior) of P. nigrispinus during different exposure periods. Spinosad, at low concentrations, was toxic to P. nigrispinus [LC₅₀ = 3.15 (3.02-3.26) μg.L^-1]. Cell degeneration features such as cytoplasm vacuolization, chromatin condensation and release of cell fragments to the midgut lumen were observed in this organ. Cell death via apoptosis was found in the three midgut regions of this predator after exposure to the insecticide. Spinosad is toxic to P. nigrispinus, and causes histological and cytological damage followed by cell death in the midgut, suggesting a dangerous effect on a beneficial non-target insect.

Semi-quantitative analysis of morphological changes in bee tissues: A toxicological approach

During foraging, bees are exposed to sublethal doses of insecticides, which can cause morphological changes to various organs, such as the midgut, Malpighian tubules, and mushroon body. Thus, the purpose of this study was to establish a scoring system to evaluate these alterations based on the damage caused and its reversibility. Therefore, a grade 1 score indicates a minimal and easily reversible lesion, increased apocrine secretion, increased cell elimination into the lumen, and a larger quantity of spherocrystals; grade 2 was assigned to moderate and typically reversible injuries, such as changes in the brush border, vacuolation/loss of cytoplasmic material, presence/height of the brush border, and cell swelling; and grade 3 was assigned to serious and irreversible, loss of cell nests of regenerative cells, pyknosis, and loss of contact between Kenyon cells. In addition, frequency values were assigned since the alterations can occur at different frequencies according to the insecticide and the bees exposed; the frequency ranges from 0 to 6, with 0 representing the absence of an alteration and 6 representing a high-frequency occurrence. Based on the analyses, we conclude that each change causes morphological damage, which may or may not be irreversible and could affect the health of the colony.

Properties, toxicity and current applications of the biolarvicide spinosad

Characterized as a highly valuable bioactive natural product, spinosad is a pesticide with a complex chemical structure, composed of spinosyn A and D, molecules synthesized by the actinomycete Saccharopolyspora spinosa. The larvicidal activity of spinosad was postulated to be a promising approach to combat crop pests and control species responsible to transmit mosquito-borne illness, including Aedes aegypti. Although initially deemed as relatively safe for non-target organisms and highly effective against insects and crop pests, recent studies focused on the toxicity profile detected the occurrence of side effects in different living species. Thus, the present review was undertaken to describe the properties and characteristics of spinosad. In addition to indicating potential adverse effects on living organisms, alternative uses of the biopesticide as a mixture with different compounds are provided.