Sickly Sweet: Insecticidal Polyols Induce Lethal Regurgitation in Dipteran Pests

Polyols induce acute oxidative stress and mortality in Indian malaria vector Anopheles stephensi (Diptera: Culicidae): potential for use as sugar-cum-toxin source in toxic sugar baits

BACKGROUND

Development of insecticide resistance in the major malaria vectors has necessitated the development of novel vector control tools. One such strategy involves the use of toxic sugar baits that targets the sugar-feeding behaviour of mosquito vectors. In this study, we investigated the potential of polyols, as a toxic food (sugar) source in toxic sugar baits against the malaria vector Anopheles stephensi Liston. We examined the acute toxicity of six polyols, namely, erythritol, glycerol, mannitol, propylene glycol (PG), sorbitol, and xylitol on adult female An. stephensi mosquitoes at two different concentrations - 2% and 10%. We also studied changes in fecundity, egg hatchability and mid-gut peroxide levels induced by polyol exposure.

RESULTS

Among the six polyol compounds tested, PG was most toxic and lethal followed by glycerol and erythritol (P < 0.001) compared to the control (sucrose). PG induced acute mortality at different tested concentrations. In the erythritol- and glycerol-fed groups, a dose-dependent effect on mortality was observed. Glycerol evidently reduced fecundity and egg-hatchability in gonotrophic cycles G1 and G2. Sucrose was the preferred food source (48%), followed by erythritol (18%), PG (10%) and glycerol (8%). Ingestion of polyols increased peroxide levels in mosquito guts, which persisted for extended durations ultimately resulting in rapid mortality (P < 0.05).

CONCLUSION

The present study highlights the usefulness of sugar polyols for the development of toxic sugar baits with minimal yet effective ingredients. Further research could be focused on field experiments and on the exploration of synergistic effects of different polyols for optimization of field applications. © 2024 Society of Chemical Industry.

Diuresis and α-glucosidase inhibition by erythritol in Aedes aegypti (Diptera: Culicidae) and viability for efficacy against mosquitoes

BACKGROUND

Sugar alcohols, such as erythritol, are low-impact candidates for attractive toxic sugar baits (ATSB) to kill mosquitoes. To determine whether erythritol has a viable future in ATSB formulations, a suite of assays was conducted to diagnose toxicity mechanisms and starvation effects on mortality in Aedes aegypti (L.) as a model system.

METHODS

We measured general carbohydrate load, glucosidase levels, and free glucose in intoxicated adult mosquitoes to observe whether sugar digestion was impaired. We assayed the effects of sugar combinations with erythritol on larvae and adults. To measure erythritol effects when mosquitoes were not resource-deprived, additional assays manipulated the prior starvation status.

RESULTS

Up to 50,000 ppm of erythritol in water had no effect on larvae within 72 h, but an ammonia spike indicated diuresis in larvae as early as 4 h (F8,44 = 22.50, P < 0.0001) after sucrose/erythritol combinations were added. Adult consumption of erythritol was diuretic regardless of the sugar pairing, while sucrose and erythritol together generated above 80% mortality (F2,273 = 33.30, P < 0.0001) alongside triple the normal excretion (F5,78 = 26.80, P < 0.0004). Glucose and fructose paired individually with erythritol had less mortality, but still double the fecal excretion. When ingesting erythritol-laced meals, less sugar was detected in mosquitoes as compared to after sucrose meals (χ2 = 12.54, df = 1, P = 0.0004).

CONCLUSIONS

Data showed that erythritol is a linear competitive inhibitor of α-glucosidase, marking it as a novel class of insecticide in the current research climate. However, the efficacy on larvae was null and not persistent in adult mosquitoes when compared across various starvation levels. Despite significant diuresis, the combined effects from erythritol are not acute enough for vector control programs considering ATSB against mosquitoes.

A series of methods incorporating deep learning and computer vision techniques in the study of fruit fly (Diptera: Tephritidae) regurgitation

In this study, we explored the potential of fruit fly regurgitation as a window to understand complex behaviors, such as predation and defense mechanisms, with implications for species-specific control measures that can enhance fruit quality and yield. We leverage deep learning and computer vision technologies to propose three distinct methodologies that advance the recognition, extraction, and trajectory tracking of fruit fly regurgitation. These methods show promise for broader applications in insect behavioral studies. Our evaluations indicate that the I3D model achieved a Top-1 Accuracy of 96.3% in regurgitation recognition, which is a notable improvement over the C3D and X3D models. The segmentation of the regurgitated substance via a combined U-Net and CBAM framework attains an MIOU of 90.96%, outperforming standard network models. Furthermore, we utilized threshold segmentation and OpenCV for precise quantification of the regurgitation liquid, while the integration of the Yolov5 and DeepSort algorithms provided 99.8% accuracy in fruit fly detection and tracking. The success of these methods suggests their efficacy in fruit fly regurgitation research and their potential as a comprehensive tool for interdisciplinary insect behavior analysis, leading to more efficient and non-destructive insect control strategies in agricultural settings.

Re-evaluation of erythritol (E 968) as a food additive

This opinion addresses the re-evaluation of erythritol (E 968) as food additive and an application for its exemption from the laxative warning label requirement as established under Regulation (EU) No 1169/2011. Erythritol is a polyol obtained by fermentation with Moniliella pollinis BC or Moniliella megachiliensis KW3-6, followed by purifications and drying. Erythritol is readily and dose-dependently absorbed in humans and can be metabolised to erythronate to a small extent. Erythritol is then excreted unchanged in the urine. It does not raise concerns regarding genotoxicity. The dataset evaluated consisted of human interventional studies. The Panel considered that erythritol has the potential to cause diarrhoea in humans, which was considered adverse because its potential association with electrolyte and water imbalance. The lower bound of the range of no observed adverse effect levels (NOAELs) for diarrhoea of 0.5 g/kg body weight (bw) was identified as reference point. The Panel considered appropriate to set a numerical acceptable daily intake (ADI) at the level of the reference point. An ADI of 0.5 g/kg bw per day was considered by the Panel to be protective for the immediate laxative effect as well as potential chronic effects, secondary to diarrhoea. The highest mean and 95th percentile chronic exposure was in children (742 mg/kg bw per day) and adolescents (1532 mg/kg bw per day). Acute exposure was maximally 3531 mg/kg bw per meal for children at the 99th percentile. Overall, the Panel considered both dietary exposure assessments an overestimation. The Panel concluded that the exposure estimates for both acute and chronic dietary exposure to erythritol (E 968) were above the ADI, indicating that individuals with high intake may be at risk of experiencing adverse effects after single and repeated exposure. Concerning the new application, the Panel concluded that the available data do not support the proposal for exemption.

Effect of non-essential amino acids (proline and glutamic acid) and sugar polyol (sorbitol) on brood of honey bees

Dietary nutrients provide fuel for the growth and development of insects as well as chemicals for their tissue construction. Apis mellifera L., an important pollinator, collects nectar and pollens from different plants to get their nutritional needs. Honey bees use protein for growth and development and carbohydrates as energy sources. Pollens predominantly contain proline and glutamic acid (non-essential amino acids). This is the first study to evaluate the role of proline, glutamic acid and sorbitol on bee broods. The composition of the diet can optimize the in vitro rearing process. Therefore, we elaborated on the possible impact of these amino acids and sugar alcohol on bee broods. This study aimed to achieve this objective by rearing honey bee larvae under different concentrations of proline, glutamic acid, and sorbitol (1, 4 and 8%), which were supplemented into the standard larval diet. The supplementation of proline helped the quick development of larvae and pupae of honey bees, whereas developmental time only decreased in pupae in the case of glutamic acid. The duration of the total bee brood development was the shortest (20.1 and 20.6 days) on Pro8 and Glu4, respectively. Proline only increased larvae survival (93.8%), whereas glutamic acid did not increase the survival of any brood stage. Pupal and adult weights were also increased with proline and glutamic acid-supplemented diets. Sorbitol did not change the developmental period of the honey bee brood but increased larval survival (93.7%) only at the lowest concentration (Sor1). The small concentration of sorbitol can be used to increase the survival of the honey bee brood. However, a higher concentration (Sor8) of sorbitol reduced the body weight of both pupae and adults. This study predicted that rearing bee brood could be one of the factors for the selectivity of pollen with higher proline and glutamic acid during the foraging of bees.

Effects of diluted Concord grape juice laced with sodium chloride and selected boron-containing compounds on attraction, consumption, crop muscle contractions, and mortality of adult Drosophila suzukii Matsumura (Diptera: Drosophilidae)

BACKGROUND

In recent years, there has been interest in low-cost, reduced-risk materials that could be used for attract-and-kill of the invasive pest, spotted-wing Drosophila, Drosophila suzukii. This pest causes heavy economic damage to soft-skinned fruits in many countries. In this study, we evaluated physiological and behavioral effects of adding either borax, boric acid, or sodium chloride to diluted Concord grape juice (DGJ), a material that is attractive to adult D. suzukii.

RESULTS

Results showed that the addition of borax, sodium chloride and boric acid did not significantly affect the response of adult D. suzukii, relative to DGJ alone. Increases in concentrations (to 5% and 10%) of borax, sodium chloride and boric acid were correlated with decreased ingestion of materials. Mortality of males and females was almost 100% with lower concentrations (1% and 5%) of borax and boric acid within 72 h. The higher concentrations of sodium chloride (5% and 10%) resulted in 100% mortality of both sexes within 72 h. There was no significant effect of chemicals on the number of crop contractions of flies when fed for 4 h.

CONCLUSIONS

This study suggests that some substances such as boric acid and borax may act as toxicants without influencing the behavioral response of D. suzukii. © 2021 Society of Chemical Industry.

Erythritol, an Artificial Sweetener, Is Acaricidal Against Pest Mites and Minimally Harmful to a Predatory Mite

Erythritol, an artificial sweetener, has shown promise as an organic, human-safe insecticide. Recently, erythritol applications were shown to be successful at controlling pear psylla (Cacopsylla pyricola (Förster)) (Hempitera: Psyllidae), the most important pest of pear in the Pacific Northwest, USA. Twospotted spider mite (Tetranychus urticae Koch) (Trombidiformes: Tetranychidae) and pear rust mite (Epitrimerus pyri (Nalepa)) (Trombidiformes: Eriophyidae) can also be highly damaging pear pests. Their common natural enemy, Galendromus occidentalis (Nesbitt) (Mesostigmata: Phytoseiidae), can provide biological control if selective pesticides are used for managing other pests. Through a series of bioassays, we sought to determine whether erythritol could also be used for controlling either species of pest mite. We also examined whether erythritol had acute or sublethal impacts on G. occidentalis, through a variety of exposure methods. Effects examined included mortality, fecundity, prey consumption, and locomotion. We determined that a high concentration of erythritol (30%) had efficacy against both pest mite species and caused arresting behavior in twospotted spider mite. Erythritol caused little acute mortality in G. occidentalis, but did reduce fecundity and prey consumption through some exposure methods. Through motion-capture software, we determined that this is primarily due to reduced movement, likely caused by difficulty walking on residues and excessive grooming behavior. Because the predatory mite non-target effects were less acute than those for the two pest mites, we concluded that erythritol could likely be integrated into pear IPM with little or no disruption of mite biological control.

Synthetic and Natural Insecticides: Gas, Liquid, Gel and Solid Formulations for Stored-Product and Food-Industry Pest Control

The selective application of insecticides is one of the cornerstones of integrated pest management (IPM) and management strategies for pest resistance to insecticides. The present work provides a comprehensive overview of the traditional and new methods for the application of gas, liquid, gel, and solid physical insecticide formulations to control stored-product and food industry urban pests from the taxa Acarina, Blattodea, Coleoptera, Diptera, Hymenoptera, Lepidoptera, Psocoptera, and Zygentoma. Various definitions and concepts historically and currently used for various pesticide application formulations and methods are also described. This review demonstrates that new technological advances have sparked renewed research interest in the optimization of conventional methods such as insecticide aerosols, sprays, fumigants, and inert gases. Insect growth regulators/disruptors (IGRs/IGDs) are increasingly employed in baits, aerosols, residual treatments, and as spray-residual protectants for long-term stored-grain protection. Insecticide-impregnated hypoxic multilayer bags have been proven to be one of the most promising low-cost and safe methods for hermetic grain storage in developing countries. Insecticide-impregnated netting and food baits were originally developed for the control of urban/medical pests and have been recognized as an innovative technology for the protection of stored commodities. New biodegradable acaricide gel coatings and nets have been suggested for the protection of ham meat. Tablets and satchels represent a new approach for the application of botanicals. Many emerging technologies can be found in the form of impregnated protective packaging (insect growth regulators/disruptors (IGRs/IGDs), natural repellents), pheromone-based attracticides, electrostatic dust or sprays, nanoparticles, edible artificial sweeteners, hydrogels, inert baits with synthetic attractants, biodegradable encapsulations of active ingredients, and cyanogenic protective grain coatings. Smart pest control technologies based on RNA-based gene silencing compounds incorporated into food baits stand at the forefront of current strategic research. Inert gases and dust (diatomaceous earth) are positive examples of alternatives to synthetic pesticide products, for which methods of application and their integration with other methods have been proposed and implemented in practice. Although many promising laboratory studies have been conducted on the biological activity of natural botanical insecticides, published studies demonstrating their effective industrial field usage in grain stores and food production facilities are scarce. This review shows that the current problems associated with the application of some natural botanical insecticides (e.g., sorption, stability, field efficacy, and smell) to some extent echo problems that were frequently encountered and addressed almost 100 years ago during the transition from ancient to modern classical chemical pest control methods.

The Impact of Artificial Sweeteners on Insects

Artificial sweeteners are sweet-tasting additives found in consumable products as substitutes for naturally occurring sugars. They are derived from plant extracts or manufactured by chemical synthesis. Ingestion of sweeteners by insects can lead to significant physiological effects, such as mortality, decreased fecundity, and behavioral change. Due to their low toxicity toward humans and the issues associated with conventional insecticide usage, artificial sweeteners have recently gained attention for their potential use as biorational insecticides. Here, we review their impact on insects and potential as novel insecticides.

Potential for Use of Erythritol as a Socially Transferrable Ingested Insecticide for Ants (Hymenoptera: Formicidae)

Ants are significant structural and agricultural pests, generating a need for human-safe and effective insecticides for ant control. Erythritol, a sugar alcohol used in many commercial food products, reduces survival in diverse insect taxa including fruit flies, termites, and mosquitos. Erythritol also decreases longevity in red imported fire ants; however, its effects on other ant species and its ability to be transferred to naïve colony members at toxic doses have not been explored. Here, we show that erythritol decreases survival in Tetramorium immigrans Santschi (Hymenoptera: Formicidae) in a concentration-dependent manner. Access to ad-libitum water reduced the toxic effects of erythritol, but worker mortality was still increased over controls with ad-lib water. Foraging T. immigrans workers transferred erythritol at lethal levels to nest mates that had not directly ingested erythritol. Similar patterns of mortality following erythritol ingestion were observed in Formica glacialis Wheeler (Hymenoptera: Formicidae), Camponotus subarbatus Emery (Hymenoptera: Formicidae), and Camponotus chromaiodes Bolton (Hymenoptera: Formicidae). These findings suggest that erythritol may be a highly effective insecticide for several genera of ants. Erythritol's potential effectiveness in social insect control is augmented by its spread at lethal levels through ant colonies via social transfer (trophallaxis) between workers.

Erythritol Ingestion Causes Concentration-Dependent Mortality in Eastern Subterranean Termites (Blattodea: Rhinotermitidae)

Damage from termite infestations is economically significant and control can be costly when requiring the widespread use of conventional insecticides. Erythritol, a polyalcohol sweetener that is safe for human consumption, causes increased mortality when ingested by some insects, indicating potential as a safe alternative insecticide. Here, we investigated the applicability of erythritol as a novel toxicant method of termite control. Eastern subterranean termites, Reticulitermes flavipes Kollar (Blattodea: Rhinotermitidae), were fed paper foods treated with increasing concentrations of erythritol and were assessed for mortality and bait consumption. Termite survival to 8 d (the duration of the experiment) significantly decreased as erythritol treatment concentration increased, indicating that the lethal effects of erythritol were concentration-dependent. Termites consumed erythritol-treated paper at all concentrations and did not display avoidance in choice assays, suggesting that erythritol may be practical for use as an ingestible bait. These results provide a basis for further development of erythritol as a safe alternative method of termite control.

Larval mannitol diets increase mortality, prolong development and decrease adult body sizes in fruit flies (Drosophila melanogaster)

The ability of polyols to disrupt holometabolous insect development has not been studied and identifying compounds in food that affect insect development can further our understanding of the pathways that connect growth rate, developmental timing and body size in insects. High-sugar diets prolong development and generate smaller adult body sizes in Drosophila melanogaster We tested for concentration-dependent effects on development when D. melanogaster larvae are fed mannitol, a polyalcohol sweetener. We also tested for amelioration of developmental effects if introduction to mannitol media is delayed past the third instar, as expected if there is a developmental sensitive-period for mannitol effects. Both male and female larvae had prolonged development and smaller adult body sizes when fed increasing concentrations of mannitol. Mannitol-induced increases in mortality were concentration dependent in 0 M to 0.8 M treatments with mortality effects beginning as early as 48 h post-hatching. Larval survival, pupariation and eclosion times were unaffected in 0.4 M mannitol treatments when larvae were first introduced to mannitol 72 h post-hatching (the beginning of the third instar); 72 h delay of 0.8 M mannitol introduction reduced the adverse mannitol effects. The developmental effects of a larval mannitol diet closely resemble those of high-sugar larval diets.This article has an associated First Person interview with the first author of the paper.

Fly foregut and transmission of microbes

Two areas of research that have greatly increased in attention are: dipterans as vectors and the microbes they are capable of vectoring. Because it is the front-end of the fly that first encounters these microbes, this review focuses on the legs, mouthparts, and foregut, which includes the crop as major structures involved in dipteran vectoring ability. The legs and mouthparts are generally involved in mechanical transmission of microbes. However, the crop is involved in more than just mechanical transmission, for it is within the lumen of the crop that microbes are taken up with the meal of the fly, stored, and it is within the lumen that horizontal transmission of bacterial resistance has been demonstrated. In addition to storage of microbes, the crop is also involved in depositing the microbes via a process known as regurgitation. Various aspects of crop regulation are discussed and specific examples of crop involvement with microorganisms are discussed. The importance of biofilm and biofilm formation are presented, as well as, some physical parameters of the crop that might either facilitate or inhibit biofilm formation. Finally, there is a brief discussion of dipteran model systems for studying crop microbe interactions.