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Insecticidal peptides as sustainable tools for future agriculture.

The increasing global human population and the intensification of agriculture present unprecedented challenges for pest control. The escalating resistance of pests to conventional synthetic insecticides, coupled with ecological and health concerns, underscores the urgent need for innovative and sustainable management approaches. Insecticidal peptides, due to their structural diversity, molecular specificity, and biodegradability, are emerging as promising candidates for the development of next-generation bioinsecticides. This strategic roadmap synthesizes recent advances in peptide architectures, ranging from pore-forming scaffolds to designs targeting enzyme inhibition and mimicking neuroendocrine actions, with a focus on the molecular mechanisms underpinning their selectivity and efficacy. By integrating structure-function insights with translational frameworks, we identify critical knowledge gaps and propose a pathway toward biotechnological tools, including bioinspired synthesis, artificial intelligence (AI)-guided peptide engineering, and nanodelivery systems for controlled release. Our analysis positions peptide-based insecticides at the forefront of sustainable agriculture, with the potential to minimize off-target effects, reduce environmental impact, and enhance crop resilience in the face of global change.

Agricultural biotechnology↗

Peptides of arachnid venoms with insecticidal activity targeting sodium channels.

Arachnids have a venom apparatus and secrete a complex chemical mixture of low molecular mass organic molecules, enzymes and polypeptide neurotoxins designed to paralyze or kill their prey. Most of these toxins are specific for membrane voltage-gated sodium channels, although some may also target calcium or potassium channels and other membrane receptors. Scorpions and spiders have provided the greatest number of the neurotoxins studied so far, for which, a good number of primary and 3D structures have been obtained. Structural features, comprising a folding that determines a similar spatial distribution of charged and hydrophobic side chains of specific amino acids, are strikingly common among the toxins from spider and scorpion venoms. Such similarities are, in turn, the key feature to target and bind these proteins to ionic channels. The search for new insecticidal compounds, as well as the study of their modes of action, constitutes a current approach to rationally design novel insecticides. This goal tends to be more relevant if the resistance to the conventional chemical products is considered. A promising alternative seems to be the biotechnological approach using toxin-expressing recombinant baculovirus. Spider and scorpion toxins having insecticidal activity are reviewed here considering their structures, toxicities and action mechanisms in sodium channels of excitable membranes.

Animals↗

Analysis of nicotinoid insecticides residues in honey by solid matrix partition clean-up and liquid chromatography-electrospray mass spectrometry.

An analytical method for the routine simultaneous determination of four nicotinoid insecticides (acetamiprid, imidacloprid, thiacloprid and thiamethoxam) in commercial multifloral honey was developed. Fortified honey samples, dissolved in water, were cleaned up through Extrelut NT20 column and, finally, insecticides were eluted with dichloromethane. The eluate was evaporated, the residue redissolved in methanol and then analyzed by LC-ESI(+)-MS. Average recoveries of the four analytes were in the range of 76% and 99% at both spiking levels 0.1 and 1.0 mg kg(-1). Relative standard deviations (RSDs) were less than 10% for all of the recovery tests. The detection limits (LODs) of the method ranged from 0.01 to 0.1 mg kg(-1) for the different insecticides studied. The developed method is linear over the range assayed, 0.5-5.0 microg mL(-1), with linear correlation coefficients higher than 0.9993.

Honey↗

Cryptic endotoxic nature of Bacillus thuringiensis Cry1Ab insecticidal crystal protein.

Cry1Ab is one of the most studied insecticidal proteins produced by Bacillus thuringiensis during sporulation. Structurally, this protoxin has been divided in two domains: the N-terminal toxin core and the C-terminal portion. Although many studies have addressed the biochemical characteristics of the active toxin that corresponds to the N-terminal portion, there are just few reports studying the importance of the C-terminal part of the protoxin. Herein, we show that Cry1Ab protoxin has a unique natural cryptic endotoxic property that is evident when their halves are expressed individually. This toxic effect of the separate protoxin domains was found against its original host B. thuringiensis, as well as to two other bacteria, Escherichia coli and Agrobacterium tumefaciens. Interestingly, either the fusion of the C-terminal portion with the insecticidal domain-III or the whole N-terminal region reduced or neutralized such a toxic effect, while a non-Cry1A peptide such as maltose binding protein did not neutralize the toxic effect. Furthermore, the C-terminal domain, in addition to being essential for crystal formation and solubility, plays a crucial role in neutralizing the toxicity caused by a separate expression of the insecticidal domain much like a dot/anti-dot system.

Agrobacterium tumefaciens↗

The insecticidal potential of scorpion beta-toxins.

Voltage-gated sodium channels are a major target for toxins and insecticides due to their central role in excitability, but due to the conservation of these channels in Animalia most insecticides do not distinguish between those of insects and mammals, thereby imposing risks to humans and livestock. Evidently, as long as modern agriculture depends heavily on the use of insecticides there is a great need for new substances capable of differentiating between sodium channel subtypes. Such substances exist in venomous animals, but ways for their exploitation have not yet been developed due to problems associated with manufacturing, degradation, and delivery to the target channels. Engineering of plants for expression of anti-insect toxins or use of natural vectors that express toxins near their target site (e.g. baculoviruses) are still problematic and raise public concern. In this problematic reality a rational approach might be to learn from nature how to design highly selective anti-insect compounds preferably in the form of peptidomimetics. This is a complex task that requires the elucidation of the face of interaction between insect-selective toxins and their sodium channel receptor sites. This review delineates current progress in: (i) elucidation of the bioactive surfaces of scorpion beta-toxins, especially the excitatory and depressant groups, which show high preference for insects and bind insect sodium channels with high affinity; (ii) studies of the mode of interaction of scorpion beta-toxins with receptor site-4 on voltage-gated sodium channels; and (iii) clarification of channel elements that constitute receptor site-4. This information may be useful in future attempts to mimic the bioactive surface of the toxins for the design of anti-insect selective peptidomimetics.

Agriculture↗

Multiresidue analysis of insecticides in soil by gas chromatography with electron-capture detection and confirmation by gas chromatography-mass spectrometry.

A rapid multiresidue method has been developed for the analysis of nine insecticides (organochlorines, pyrethroids and organophosphorus) in soil. The method is based on the sonication extraction of residues from a certain amount of soil placed in a small column, using ethyl acetate. The effect of the residence time of insecticides in soil, the material of the columns used (glass or plastic columns) and the soil moisture content on the recovery of these compounds was also studied. Residues were determined by gas chromatography with electron-capture detection. The average recovery through the method obtained for these compounds varied from 90 to 108% with a relative standard deviation between 1 and 11%. The results of this study pointed out that the recoveries of insecticide residues obtained with plastic or glass columns at different soil moisture content were similar and that the residence of these compounds in soil during several days did not affect their recovery from soil. Confirmation of residue identity was performed by gas chromatography coupled with mass spectrometry.

Chromatography, Gas↗

Statistical analysis of decay of organophosphorus and pyrethroid insecticides and carbaryl on paddy rice, maize, sunflowers and field peas.

A model is developed to describe the decay of seven insecticides on stored paddy rice, maize, sunflowers and peas, and is shown to be more precise than each of six literature models on pesticide decay. It relates residues (R), as a ratio of applied concentration (R(0)), to time after insecticide application (t), modifying the usual first-order kinetics equation lnR=lnR(0)-kt by assuming that the rate constant k has a mixture of values according to a gamma distribution with mean K. The resulting equation is lnR=lnR(0)-Kcln(1+t/c), where c is a constant determined empirically. For large c, this model reduces to the first-order model with K=k. The parameter K is further modelled as linear in temperature for maize and rice. The rate of loss of protectants was found not to be seriously affected by co-application with other insecticides, and this is a useful finding for future studies on rates of loss of grain protectants. The apparent rate of loss was also not seriously affected by the method of analysis, whether by gas chromatography or high-performance liquid chromatography, and this finding supports previous validation of the methods.

Journal Article↗

Occurrence of organochlorine insecticides, PCBs and PCB congeners in waters and sediments of the Ebro River (Spain)

Organochlorine insecticides and poychlorinated biphenyls (PCBs) were measured in water and sediment samples taken from thirteen sites along the Ebro River (Spain), the most agricultural and industrial basin in the North of the Iberian Peninsula. Concentrations of 10 insecticides, PCBs and 13 PCB congeners were determined: grouping all chemicals by structural affinity, these can be arranged in descending order as follow: PCBs > total DDT > total cyclodiene insecticides > total HCH. Higher levels of organochlorine pollutants were detected in sediments from the middle and lower parts of the stream where are located the main important inputs in Ebro River.

Journal Article↗

Metabolic activation of three arylamines and two organophosphorus insecticides by coriander (Coriandrum sativum) a common edible vegetable.

Organophosphorus insecticides and arylamines, widely distributed in the environment, can be activated into mutagens by plants. Plant activation of three aromatic amines, 4-nitro-o-phenylenediamine (NOP), m-phenylenediamine (m-PDA) and 2-aminofluorene (2AF), and two organophosphorus insecticides, dimethoate and methyl parathion has been the focus of this study. The plant cell/microbe coincubation assay was used employing coriander (Coriandrum sativum) suspended cell cultures as the activating system. Interestingly, this vegetable is included in the Mexican diet and ingested generally uncooked and could have epidemiological consequences. As a genetic end point, the Salmonella typhimurium tester strain TA98 was used. Protein contents, as well as peroxidase activity and peroxidase activity inhibited by diethyldithiocarbamate (DEDTC) of coriander cultures were determined after the coculture. Coriander cells highly activated three aromatic amines, NOP, m-PDA and 2-AF to mutagenic products detected in Salmonella. On the other hand, insecticides were only lightly activated, probably because peroxidase activity of coriander cells was inhibited, corroborated by DEDTC peroxidase inhibition. In all the assays, NOP was the more potent mutagenic compound. The results demonstrated that coriander cells were metabolically competent and suitable for a plant cell microbe coincubation assay, developed to analyze the promutagen activation by plant systems and can be used as a indicator of potential genetic effects.

Biotransformation↗

Partition of the organochlorine insecticide lindane into the human sperm surface induces membrane depolarization and Ca2+ influx.

The effects of the insecticide lindane (the gamma-isomer of 1,2,3,4,5,6-hexachlorocyclohexane) on membrane potential, cytosolic free Ca2+ concentration ([Ca2+]i) and surface biophysical properties were studied in human spermatozoa. The insecticide induces rapid, transient and reproducible membrane depolarization and opening of voltage-dependent Ca2+ channels leading to an increase in [Ca2+]i. In contrast with the effect in somatic cells, lindane did not affect gamma-aminobutyric acid receptor-linked Cl- currents. Ca2+ and K+ currents were found to drive lindane-induced membrane depolarization and repolarization respectively, whereas Na+ and Cl- fluxes appear not to have a role in the phenomenon. The insecticide was still able to produce membrane depolarization both in the combined absence of extracellular Ca2+ and Na+ and in high-K+ buffer, suggesting that lindane alters the membrane dipole potential. In agreement with this, Laurodan and Prodan fluorescence spectroscopy revealed that lindane partition into the sperm plasma membrane lowers water molecular dynamics in the uppermost region of the membrane external leaflet, probably as the result of reordering of water dipoles. We propose that the first effect of lindane partitioning into the sperm plasma membrane is a change in the membrane dipole potential, which results in the activation of membrane-located Ca2+-influx pathways.

2-Naphthylamine↗

Isolation, synthesis and pharmacological characterization of delta-palutoxins IT, novel insecticidal toxins from the spider Paracoelotes luctuosus (Amaurobiidae).

Four novel insecticidal toxins were isolated from the venom of the spider Paracoelotes luctuosus (Araneae: Amaurobiidae) and named delta-palutoxins IT1 to IT4. The four toxins are homologous 36-37 amino acid peptides reticulated by four disulfide bridges and three have amidated C-terminal residues. The delta-palutoxins are highly homologous with the previously described mu-agatoxins and curtatoxins (77-97%). The four peptides demonstrated significant toxicity against larvae of the crop pest Spodoptera litura (Lepidoptera: Noctuidae) in a microinjection bioassay, with LD50 values in the 9-50 microg per g of insect range. This level of toxicity is equivalent to that of several of the most active scorpion toxins used in the development of recombinant baculoviruses, and the delta-palutoxins appear to be insect specific. Electrophysiological experiments demonstrated that delta-palutoxin IT1, the most active toxin acts by affecting insect sodium channel inactivation, resulting in the appearance of a late-maintained sodium current, in a similar fashion to insecticidal scorpion alpha and alpha-like toxins and is thus likely to bind to channel receptor site 3. However, delta-palutoxin IT1 was distinguished by its lack of effect on peak sodium conductance, on the early phase of sodium current inactivation and the absence of a shift in the activation voltage of the sodium channels. delta-Palutoxins are thus proposed as new insecticidal toxins related to the alpha and alpha-like scorpion toxins. They will be useful both in the development of recombinant baculoviruses in agrochemical applications and also as molecular probes for the investigation of molecular mechanisms of insect selectivity and structure and function of sodium channels.

Agatoxins↗

A survey of Anopheles gambiae (species A) and An. arabiensis (species B) of the An. gambiae Giles complex in the Kisumu area of Kenya following insecticidal spraying with OMS-43 (Fenitrothion).

After village huts in the Kisumu area of Kenya had been sprayed with a nominal 2 g/m2 of OMS-43 (fenitrothion) as part of an insecticidal evaluation programme 964 adults of the Anopheles gambiae complex collected from huts were identified cytogenetically as either An. gambiae (species A) or An. arabiensis (species B). Similarly, cytogenetic methods were used to identify 349 adults collected from granaries and artificial pit-shelters. In addition, 2203 larvae of the gambiae complex collected from different types of habitats were specifically identified cytogenetically. As in a previous survey made prior to insecticidal spraying, adults of An. arabiensis predominated in outdoor collections while An. gambiae was highly endophilic. However, it appeared that spraying with fenitrothion had resulted in an increase in both the degree of exophily in An. arabiensis and also its relative numbers in respect to An. gambiae, although the overall pooulation of both species was greatly reduced by spraying. Insecticidal spraying may have diverted both species from feeding on man to cattle. Except for one village, where larvae of An. arabiensis were commoner than expected in cattle hoof-prints, there was little difference between the selection of different types of larval habitats by the two sibling species. Chromosomal inversions were more common in adults of An. arabiensis than in An. gambiae.

Animals↗

In vivo methylation of guanine by the organophosphorus insecticide tetrachlorvinphos.

The in vivo methylating capability of the organophosphorus insecticide tetrachlorvinphos, assayed by the formation of 7-methyl-guanine in mouse liver, was investigated. Following intraperitoneal injection of male mice with different doses of the 14C-insecticide, labelled at the OCH3 groups, the total and specific radioactivity of nucleic acids and protein were determined. The 14C-labelling in the isolated macromolecules reached its maximum 24 hours following administration of the insecticide. Analysis of the acid hydrolysate of DNA and of RNA on Dowex-50 WX-12 revealed the presence of (7-14C) methylguanine. At maximum 14C-labelling, the amount of radioactive 7-MeGu, calculated as fraction of total dose, was around 9 X 10(-5) and 39 X 10(-5) for DNA and RNA, respectively.

Animals↗

Bioaccumulation of endosulfan (Thiodan insecticide) in the tissues of Louisiana crayfish, Procambarus clarkii.

The bioaccumulation potential of endosulfan was determined by constantly exposing male and female adult crayfish, Procambarus clarkii to 100 ppb Thiodan insecticide for 8 wks. The crayfish were removed at 2 wk intervals and the uptake by tissues (whole-body) was determined by electron capture gas-chromatography. The same number of pre-exposed crayfish (100 ppb Thiodan) were transferred to endosulfan-free water after 8 wks, and insecticide loss (depuration) was similarly quantitated. The maximum amount of insecticide and its metabolites detected after 8 wks were 197 ppb endosulfan II, 18 ppb endosulfan I and 3 ppb endosulfan sulfate. During the first 4 wks of depuration, endosulfan loss from cryfish tissues occurred rapidly, and only 3 ppb endosulfan I remained. No endosulfan II and sulfate were detected beyond 4 wks. The residues in male vs female were not significant statistically. Bioaccumulation factor (BF) for endosulfan II for crayfish tissues was 1.97, which is considerably lower than for other aquatic invertebrates (26 for scallop, Chlamys opercularis and 600 for mussel, Mytilus edulis. The presence of endosulfan sulfate in the tissues cannot be considered as 'detoxification' which is as toxic as the parent compound.

Animals↗

The persistence of insecticidal chemicals in soils treated with granular formulations of disulfoton and their uptake by potato plants.

Potatoes were grown from cut seed in Plainfield sand treated in-furrow with disulfoton (Di-Syston 15G, 3.36 kg AI/ha) in 1983 and from whole seed in similarly treated loam in 1991. Soils were contained in 2 m2 field plots. Soil, seed potato and foliage were analyzed for the insecticide and its sulfoxide and sulfone metabolites during the 8-12 wk following planting. Disulfoton disappeared at different rates from the two soils (ksand = 0.024 day-1, kloam = 0.056 day-1) with partial conversion to the sulfoxide and sulfone in both. Larger quantities of the three insecticidal components were absorbed by the seed potato in the cut-seed/sand combination. The relative amounts of these components in the seed potato also differed between treatments with disulfoton being the largest component of the cut-seed/sand and smallest in the whole-seed/loam. Disulfoton sulfoxide and sulfone were the major insecticidal components of the foliage and concentrations in the initial foliage (each ca. 10 ppm) were similar for both treatments. Sulfoxide concentrations in the foliage decreased more rapidly than the sulfone and the decrease in concentration of each of the components was similar for the two treatments.

Disulfoton↗

Insecticidal compounds against Drosophila melanogaster from Cornus officinalis Sieb. et Zucc.

Dimethyl malate (1) and 5-hydroxymethyl furfural (2) were isolated as insecticidal compounds by bioassay-guided fractionation from MeOH extract of the fruits of Cornus officinalis Sieb. et Zucc. Insecticidal activity against larvae of D. melanogaster was demonstrated: 1 and 2 gave the LC50 value of 6.15 and 11.8 micromol/mL of diet concentration, respectively. Acute toxicity against adults of D. melanogaster, 1 and 2 had the insecticidal activity, with the LD50 value of 21.5 and 34.0 microg/adult.

Animals↗

Evaluation of human exposure to the persistent insecticides DDT and HCH in Ahmedabad, India.

Concentrations of two organochlorine insecticides, DDT and HCH, in 21 human adipose tissue samples (from cadavers) and 20 venous blood samples collected in Ahmedabad, India were determined. None of the cases had any history of occupational exposure to organochlorine insecticides. Residue concentrations of DDT and HCH in these samples indicated considerable exposure of the general population to these chemicals. Samples from males had comparatively higher concentrations of these insecticide residues than females. The mean residue concentrations of total DDT and HCH in the blood serum of males was 213.83 and 70.051 ppb, respectively, whereas females had DDT and HCH concentrations of 177.38 and 65.44 ppb, respectively. Total DDT and HCH in adipose tissue was 3.967 and 4.054 ppm in males, and 3.538 and 3.144 ppm in females, respectively. Residue concentrations reported here are lower than those reported earlier.

Adipose Tissue↗

Effects of methoxyfenozide, indoxacarb, and other insecticides on the beneficial egg parasitoid Trichogramma nr. brassicae (Hymenoptera: Trichogrammatidae) under laboratory and field conditions.

Trichogramma nr. brassicae is a common egg parasitoid of Helicoverpa species in Australian processing tomatoes, but its effectiveness can be severely curtailed by insecticide applications. To identify insecticides that are potentially compatible with this species, the effects of seven insecticides, including newly introduced compounds and a surfactant, were screened in laboratory and glasshouse assays for their toxicity to the wasps. Assays involved direct applications on adults, residual effects on adults, and applications on life stages still inside the host. Methoxyfenozide and indoxacarb were not toxic to Trichogramma in any assay when applied at field rates. Naled and chlorfenapyr caused 100% mortality when directly applied to adults, and 95% mortality when adults were exposed to residues of these chemicals within 24 h of application. The effects of naled residues were short lived (<48 h). Naled and chlorfenapyr were also toxic when applied to Trichogramma developing inside host eggs, reducing emergence of adults by >25%. Imidacloprid, emamectin, and tau-fluvalinate were toxic in some experiments; they caused >97% mortality in adults 1 h after direct application and in residue assays they caused 23-64% mortality during the first 24 h. In field trials, methoxyfenozide had no harmful effects on emergence from sprayed parasitized eggs, whereas indoxacarb had a small impact (<8%) on emergence. Methoxyfenozide and indoxacarb are potentially suitable for inclusion in integrated pest management strategies for management of Helicoverpa because they do not influence adult survival or development of immature stages, whereas other chemicals need to be treated cautiously.

Animals↗