Selective Insecticides Research Articles

Integrated Pest Management Programs for Pear Psylla, Cacopsylla pyricola (Förster) (Hemiptera: Psyllidae), Using Kaolin Clay and Reflective Plastic Mulch.

Pear psylla, Cacopsylla pyricola (Förster) (Hemiptera: Psyllidae), is the most economically important pest of pears grown in Washington State. Standard conventional management programs involve season-long broad-spectrum insecticide sprays. Although the industry uses some tools that are not disruptive to biological control, such as kaolin clay and selective insecticides, they are additions to broad-spectrum insecticides instead of replacements. Conventional sprays suppress pear psylla through the spring and early summer; however, disruption of biological control leads to pear psylla outbreaks near harvest. In 2018 and 2019, we tested two season-long programs that used only selective approaches. The programs began with either kaolin clay or reflective plastic mulch and were followed by identical spray programs using only selective insecticides. Programs were compared with an industry standard conventional program that used numerous broad-spectrum insecticides throughout the season, and a check program with no insecticides for pear psylla. Experiments were conducted using replicated 40-tree plots in a research orchard near Wenatchee, WA with high pear psylla pressure. In both years, selective programs had similar pear psylla densities to the industry standard program and all had lower pear psylla densities and fruit injury than the check. Both selective programs had lower fruit injury than the industry standard in the first year, and similar injury to the industry standard in the second year. Our results suggest kaolin clay and reflective mulch can effectively suppress pear psylla populations and injury in the early season and support season-long selective management programs without the use of broad-spectrum insecticides.

Insect kinin mimics act as potential control agents for aphids: Structural modifications of Trp4.

Insect kinins are endogenous, biologically active peptides with various physiological functions. The use of insect kinins in plant protection is being evaluated by many groups. Some kinins have been chosen as lead compounds for pest control. We previously reported an insect kinin mimic IV-3 that had insecticidal activity. And by introducing a strong electron withdrawing group (-CF3 ) on the benzene ring (Phe2 ), we discovered a compound, L7 , with better activity than lead IV-3. In this work, taking L7 as the lead compound, we designed and synthesized 13 compounds to evaluate the influence of position 4 (Trp4 ) of insect kinin on insecticidal activity, by replacing the H atom on tryptophan with -CH3 and -Cl or substituting the indole ring of tryptophan with the benzene, naphthalene, pyridine, imidazole, cyclohexane, and alkyl carboxamides. The aphid bioassay results showed that the compounds M1 , M3 , and M5 were more active than the positive control, pymetrozine. Especially, replacing the side chain by an indole ring with 4-Cl substitution (M1 , LC50 = 0.0029 mmol/L) increased the aphicidal activity. The structure-activity relationships (SARs) indicated that the side chain benzene ring at this position may be important to the aphicidal activity. In addition, the toxicity prediction by Toxtree, and the toxicity experiments on Apis mellifera suggested that M1 was no toxicity risk on a non-target organism. It could be used as a selective and bee-friendly insecticide to control aphids.

Regional selection of insecticides and fungal biopesticides to control aphids and thrips and improve the forage quality of alfalfa crops

The efficacies of biological and conventional chemical insecticides against two major insect pests of alfalfa (aphids and thrips) were compared in three sites across China’s alfalfa belt. In addition, the persistence of the residues of chemical insecticides in alfalfa and their influence on the quality of alfalfa hay were examined. Efficacy varied among the different biological and chemical insecticides. The chemical insecticides were significantly more effective than biopesticides in a short time-frame. The efficacy period of biopesticides was significantly longer than that of chemical insecticides, and the corrected mortality rate of aphids in all regions was above 50% at 14 days after application. The analysis of pesticide residues showed that the residual doses of all the pesticides were within the allowed ranges after the safe period. The acid detergent fiber and neutral detergent fiber contents in alfalfa hay were higher and the protein content was lower in chemical insecticide treatments than in biopesticide treatments in Hebei. The relative feeding value of alfalfa hay treated with Metarhizium anisopliae IPP330189 was the highest among the treatments. Compared with chemical insecticides, the yield of alfalfa hay was higher in the biopesticides treatments. Biopesticides show a stronger control effect on insect populations and also a better improvement in the quality of alfalfa hay than chemical insecticides. This study provides a basis for exploring and developing a comprehensive control regime for alfalfa insect pests in the different alfalfa-growing regions in China, and for reducing chemical insecticide usage and improving forage quality.

Appraising the role of anti-thermal activity of beta-cyclodextrin on selective insecticides against Thrips tabaci (Thysanoptera: Thripidae)

Abstract Evaluation studies investigated the leverage effects of beta-cyclodextrin (β-CD) on the long-termed toxicity of cypermethrin 25% EC, sulfoxaflor 24% SC, acetamiprid 20% SL and chlorfenapyr 24% SC against adults of Thrips tabaci laboratory strain (Thysanoptera: Thripidae) (Lindeman, 1889) from 8 up to 40 °C. Laboratory studies showed no toxicity for β-CD alone at all tested concentrations. Concentrations of β-CD at 1.25 and 2.50 gm L−1 had potent leverage effects on the LC50s of cypermethrin within 30–35 °C and sulfuxoflor at 40 °C. β-CD at 0.5 gm L−1 had no leverage effect on tested insecticides. All the tested concentrations of β-CD decreased the toxicity of acetamiprid. Semi-field trials (≥28 °C) along 12 days declared that β-CD (equivalent to 1.25 gm L−1) increased the overall mean mortality percentages of 0.5 FRs of cypermethrin (73.08%) and sulfoxaflor (54.74%) compared to their 0.5 FRs alone of 63.70 and 44.30%, respectively in season 2020. While in season 2021, only cypermethrin at 0.5 FR + β-CD (74.45%) surpassed its 0.5FR (61.83%). Lethal times (LT50) values in semi-field trials showed a prolonged residual toxicity periods for the 0.5 FRs of cypermethrin + β-CD (8.58 days) and sulfoxaflor + β-CD (4.80 days) compared to their 0.5 FRs of 6.65 and 3.24 days, respectively in season, 2020. Furthermore, LT50 values of the 0.5 FRs of cypermethrin + β-CD (9.02 days) and sulfoxaflor + β-CD (7.34 days) exceeded their 0.5 FRs of 6.24 and 4.07 days, respectively in 2021. Thus β-CD could realize leverage efficacy and longer-termed toxicity for cypermethrin and sulfoxaflor in high temperatures.

Electrical impedance’s effects of flying insects on selectivity of electrical insecticides

The history of controlling destructive insects in the twentieth century makes it clear that the difficulties we encounter today in dealing with these types of insects come from our almost total reliance on one single controlling method, namely the use of chemical insecticides. These toxic and suspected carcinogenic products pose a serious threat to agriculture and the environment. However, the possibility of directing researchers in developing a new way considered as more efficient, more selective and less toxic has proved to be possible. The principle of this approach is based on an attractive effect and an electric effect. Nevertheless, the development of a bio and selective electrical system requires taking into account certain parameters involved in the attraction of insects and electrical discharge such as the electrical impedance. The results showed that the threshold at which the insect is disturbed depends on its conductivity.

Recent progress in the structural study of ion channels as insecticide targets

Ion channels, many expressed in insect neural and muscular systems, have drawn huge attention as primary targets of insecticides. With the recent technical breakthroughs in structural biology, especially in cryo-electron microscopy (cryo-EM), many new high-resolution structures of ion channel targets, apo or in complex with insecticides, have been solved, shedding light on the molecular mechanism of action of the insecticides and resistance mutations. These structures also provide accurate templates for structure-based insecticide screening and rational design. This review summarizes the recent progress in the structural studies of 5 ion channel families: the ryanodine receptor (RyR), the nicotinic acetylcholine receptor (nAChR), the voltage-gated sodium channel (VGSC), the transient receptor potential (TRP) channel, and the ligand-gated chloride channel (LGCC). We address the selectivity of the channel-targeting insecticides by examining the conservation of key coordinating residues revealed by the structures. The possible resistance mechanisms are proposed based on the locations of the identified resistance mutations on the 3D structures of the target channels and their impacts on the binding of insecticides. Finally, we discuss how to develop "green" insecticides with a novel mode of action based on these high-resolution structures to overcome the resistance.

Toxicity and biochemical impact of methoxyfenozide/spinetoram mixture on susceptible and methoxyfenozide-selected strains of Spodoptera littoralis (Lepidoptera: Noctuidae)

Methoxyfenozide (M) is one of the selective insecticides used in integrated pest management (IPM) programs for lepidopteran pests. However, recent studies reported a development of M-resistance, which prompted us to look for alternatives. Here, we investigate the potency of a mixture of M with spinetoram (Sp) on M-resistant insects. In the laboratory, a selection pressure with M has carried out on Spodoptera littoralis (Lepidoptera: Noctuidae) strains. A dipping technique was used to evaluate the toxicity of a sublethal concentration of M and Sp. on S. littoralis larvae, and the same concentrations were used to assess the toxic impact of their combination on susceptible (SUS) and M-selected (MS) strains. The toxicity of M/Sp mixtures was computed using a combination index equation, and a potentiation effect was observed in the two tested strains. Synergism tests revealed that piperonyl butoxide had considerable synergistic effects on M toxicity in the MS strain. The results revealed that the M/Sp mixture's negative effect on both monooxygenases and esterases is most likely the cause of its potentiation effect on the SUS and MS strains. It was concluded that M/Sp mixtures are effective against M-resistant S. littoralis strains, so these can be used in IPM programs.

Combining Cultural Tactics and Insecticides for the Management of the Sweetpotato Whitefly, Bemisia tabaci MEAM1, and Viruses in Yellow Squash

The sweetpotato whitefly, Bemisia tabaci MEAM1 Gennadius (Hemiptera: Aleyrodidae), and the complex of viruses it transmits are major limiting factors to squash production in the southeastern United States. At this time, insecticides are extensively relied upon for the management of whiteflies and, indirectly, whitefly-transmitted viruses. The development of a multi-faceted, integrated pest management (IPM) program is needed to increase the sustainability and profitability of squash production. Experiments in 2018 and 2019 evaluated the effects of insect exclusion netting (IEN) in combination with selected pesticides on whitefly population dynamics and virus incidence in greenhouse-grown squash seedlings. Field experiments from 2018 to 2021 evaluated the effects of mulch type (UV-reflective mulch, live mulch, and white plastic mulch), row covers, and insecticides on whitefly population dynamics, silver leaf disorder (SSL) intensity, virus symptom severity, and marketable yield. IEN significantly reduced whiteflies and virus incidence on squash seedlings in the greenhouse study. In the field mulch study, lower whitefly abundance and SSL intensity, as well as reduced virus symptom severity, were observed in plots with reflective mulch compared with white plastic or live mulch. In the insecticide/row cover study, whitefly abundance, SSL intensity, and virus symptom severity were lowest in the row cover and cyantraniliprole- and flupyradifurone-treated plots. Field plots with row covers and those with UV-reflective mulch consistently produced the greatest marketable yields. These findings demonstrate that growers can reduce whitefly and virus pressure and preserve yields in squash production in the southeastern United States by combining cultural and chemical tactics, including row covers, UV-reflective mulch, and select insecticides.

Impact of insecticide programs on pests, the predatory mite Phytoseiulus persimilis, and staked tomato profitability.

Various insecticides are available to manage diverse pest complexes in commercial vegetable production, but knowledge gaps exist regarding their overall performance in pest suppression, profitability, and compatibility with biological control. We conducted trials in staked tomatoes in western North Carolina in 2017-2018 to compare how different insecticide programs managed key pests and their interactions with Phytoseiulus persimilis Athias-Henriot, a predator of the twospotted spider mite (TSSM, Tetranychus urticae Koch). Treatments compared no insecticides to broad-spectrum ('hard') foliar applications, selective ('soft') foliar applications, and to chemigation of selective systemic insecticides. Treatment efficacy was based on pest control, net profitability, and Environmental Impact Quotient (EIQ) ratings comparing environmental and human health risks. All programs similarly suppressed aphids, while flower thrips and flea beetle populations were low and unaffected by program. Only the 'hard' foliar program suppressed TSSM (including P. persimilis), which quickly rebounded. This program inhibited biological control, and eventual TSSM suppression was likely caused by P. persimilis immigrating from nearby plots. All programs were generally equivalent in reducing fruit damage. Net profits were similar among insecticide programs, which were significantly greater than in untreated plots. Yield and profit trends were similar both years, but impacted by record flooding in 2018. Safer and more selective chemigation and 'soft' foliar programs were as effective and economical as the 'hard' foliar program, while also conserving biological control. These results support existing research demonstrating that improved insecticide use can be integrated with biological control for more profitable and environmentally sustainable vegetable production. © 2022 Society of Chemical Industry.

Efficacy of Insecticides Against American Serpentine Leaf Miner Liriomyza trifolii (Burgess) in Water Melon

A field experiment was conducted to evaluate the efficacy of certain selective insecticides against the serpentine leaf miner Liriomyza trifolii (Burgess) in water melon Citrullus lanatus (Thunb.) Matsum and Nakai. The hybrid F1 (Melody) was sown in protray and 13 days old seedlings were transplanted in the main field. Significant less live mines (1.48/leaf) was observed with chlorantraniliprole 18.5%SC @0.6 ml/l. This was followed by flubendiamide 39.35%SC @0.6 ml/l (2.09/leaf) and indoxacarb 14.5%SC @0.65ml/l (3.05/leaf). Leaf damage/plot was 2.72, 3.48 and 4.03%, with chlorantraniliprole, flubendiamideand indoxacarb, respectively. Significantly maximum yield of fruits (25.5 t/ha) was obtained withchlorantraniliprole given as three sprays at 15 days interval. Thus, chlorantraniliprole 18.5%SC @0.6ml/l can be recommended against L. trifolii in water melon.

Methodology to Test Control Agents and Insecticides Against the Coffee Berry Borer Hypothenemus hampei.

Prior to recommending insecticides to treat the coffee berry borer (CBB) Hypothenemus hampei, it is valuable to know the mortality and repellency of these insecticides against adult insects or their impact on reproductive output. However, currently available methods assess adult mortality only, limiting the selection of novel insecticides with a different mode of action. In this work, different experimental methods were examined to identify the diverse effects on the CBB under laboratory conditions. For this, green coffee fruits (GFs) were collected and disinfected by immersion in sodium hypochlorite solution followed by UV light irradiation. In parallel, CBB adults from a colony were disinfected by immersion in sodium hypochlorite solution. To assess fruit protection (preinfestation), the fruits were placed in plastic boxes, and the insecticides were applied. Then, the CBB adults were released at a rate of two CBBs per GF. The GFs were left under controlled conditions to evaluate CBB infestation and survival after 1, 7, 15, and 21 days. To evaluate insecticide efficacy after CBB infestation (postinfestation), CBB adults were released to the GFs in a 2:1 ratio for 3 h at 21 °C. Infested fruits showing CBB adults with their abdomens partially exposed were selected and placed in 96-well racks, and the CBBs boring into the fruits were treated directly. After 20 days, the fruits were dissected, and the CBB biological stages inside each fruit were recorded. The GFs served as substrates that mimic natural conditions to evaluate toxic, chemical, and biological insecticides against the CBB.

A near-chromosome level genome assembly of the European hoverfly, Sphaerophoria rueppellii (Diptera: Syrphidae), provides comparative insights into insecticide resistance-related gene family evolution

BackgroundSphaerophoria rueppellii, a European species of hoverfly, is a highly effective beneficial predator of hemipteran crop pests including aphids, thrips and coleopteran/lepidopteran larvae in integrated pest management (IPM) programmes. It is also a key pollinator of a wide variety of important agricultural crops. No genomic information is currently available for S. rueppellii. Without genomic information for such beneficial predator species, we are unable to perform comparative analyses of insecticide target-sites and genes encoding metabolic enzymes potentially responsible for insecticide resistance, between crop pests and their predators. These metabolic mechanisms include several gene families - cytochrome P450 monooxygenases (P450s), ATP binding cassette transporters (ABCs), glutathione-S-transferases (GSTs), UDP-glycosyltransferases (UGTs) and carboxyl/choline esterases (CCEs).Methods and findingsIn this study, a high-quality near-chromosome level de novo genome assembly (as well as a mitochondrial genome assembly) for S. rueppellii has been generated using a hybrid approach with PacBio long-read and Illumina short-read data, followed by super scaffolding using Hi-C data. The final assembly achieved a scaffold N50 of 87Mb, a total genome size of 537.6Mb and a level of completeness of 96% using a set of 1,658 core insect genes present as full-length genes. The assembly was annotated with 14,249 protein-coding genes. Comparative analysis revealed gene expansions of CYP6Zx P450s, epsilon-class GSTs, dietary CCEs and multiple UGT families (UGT37/302/308/430/431). Conversely, ABCs, delta-class GSTs and non-CYP6Zx P450s showed limited expansion. Differences were seen in the distributions of resistance-associated gene families across subfamilies between S. rueppellii and some hemipteran crop pests. Additionally, S. rueppellii had larger numbers of detoxification genes than other pollinator species.Conclusion and significanceThis assembly is the first published genome for a predatory member of the Syrphidae family and will serve as a useful resource for further research into selectivity and potential tolerance of insecticides by beneficial predators. Furthermore, the expansion of some gene families often linked to insecticide resistance and selectivity may be an indicator of the capacity of this predator to detoxify IPM selective insecticides. These findings could be exploited by targeted insecticide screens and functional studies to increase effectiveness of IPM strategies, which aim to increase crop yields by sustainably and effectively controlling pests without impacting beneficial predator populations.

Toxicity of selective insecticides against sap sucking insect pests of cotton (Gossypium hirsutum)

Toxicity of selective insecticides against sap sucking insect pests of cotton (Gossypium hirsutum)

Toxicity of selective insecticides against sap sucking insect pests of cotton (Gossypium hirsutum)

Toxicity of selective insecticides against sap sucking insect pests of cotton (Gossypium hirsutum)

Detection of insecticide susceptibility and target-site mutations in field populations of Spodoptera frugiperda (Lepidoptera: Noctuidae)

Fall armyworm, Spodoptera frugiperda (J. E. Smith), is an economically important pest throughout the world. At present, the control of S. frugiperda in China largely relies on the application of chemical insecticides. In this study, the susceptibility of nine field populations of S. frugiperda to eight recommended insecticides was evaluated by using the diet-overlay method. The results indicated that spinetoram, lufenuron, and emamectin benzoate exhibited high acute toxicity to S. frugiperda, whereas chlorantraniliprole, indoxacarb, tetrachlorantraniliprole, chlorfenapyr, and lambda-cyhalothrin exhibited relatively low toxicity. Two site mutations (A201S and F290V) of the Ace-1 gene were identified from the field populations, the R allele frequencies of A201S and F290V ranged from 5.0% to 29.6% and 21.2% to 67.3%, respectively. In addition, the resistant homozygote F290V was detected in the field, with the highest genotype frequency of 40.0% in the JZ population. However, no site mutation in VGSC was detected in any tested field population of S. frugiperda. These results provide valuable information for the selection of insecticides and are helpful for insecticide resistance management of S. frugiperda.

Review of Integrated Pest Management of Alfalfa Hay Crop: A Successful Example at TADCO

Alfalfa hay crop was grown at TADCO, mainly for dairy farms companies in Saudi Arabia on contract basis. This crop and due to the application of broad-spectrum contact insecticides lead to aphids’ outbreak during spring and autumn and worms’ outbreak during the summer month of each year leading to loss of hay quality and yield quantity. An Integrated Pest Management program was applied at TADCO in the period 2000 to 2010, and it succeeded to regulate the aphids and worms’ insects’ numbers on the alfalfa crop which resulted in a smaller number of sprays per season and lowered the cost of pest control over the years. This success was due to using selective insecticides which has little impact on the predators and parasites insects and allowed the company to produce high quality hay desired by the dairy farm companies and reduced the cost of production. Alfalfa was an ideal crop for applying integrated pest management program (IPM) as it is a perennial crop grown at each pivot for an average of two years, and this allowed the beneficial insects to stay on it and survive between the seasons feeding on insect pests. Keywords: IPM; Predators; Parasites; Alfalfa Hay; Selective Insecticides

Insecticide resistance in Australian Spodoptera frugiperda (J.E. Smith) and development of testing procedures for resistance surveillance.

Spodoptera frugiperda (J.E. Smith) is a highly invasive noctuid pest first reported in northern Australia during early 2020. To document current status of resistance in S. frugiperda in Australia, insecticide toxicity was tested in field populations collected during the first year of establishment, between March 2020 and March 2021. Dose-response was measured by larval bioassay in 11 populations of S. frugiperda and a susceptible laboratory strain of Helicoverpa armigera. Emamectin benzoate was the most efficacious insecticide (LC50 0.023μg/ml) followed by chlorantraniliprole (LC50 0.055μg/ml), spinetoram (LC50 0.098μg/ml), spinosad (LC50 0.526μg/ml), and methoxyfenozide (1.413μg/ml). Indoxacarb was the least toxic selective insecticide on S. frugiperda (LC50 3.789μg/ml). Emamectin benzoate, chlorantraniliprole and methoxyfenozide were 2- to 7-fold less toxic on S. frugiperda compared with H. armigera while spinosyns were equally toxic on both species. Indoxacarb was 28-fold less toxic on S. frugiperda compared with H. armigera. There was decreased sensitivity to Group 1 insecticides and synthetic pyrethroids in S. frugiperda compared with H. armigera: toxicity was reduced up to 11-fold for methomyl, 56 to 199-fold for cyhalothrin, and 44 to 132-fold for alpha cypermethrin. Synergism bioassays with metabolic inhibitors suggest involvement of mixed function oxidase in pyrethroid resistance. Recommended diagnostic doses for emamectin benzoate, chlorantraniliprole, spinetoram, spinosad, methoxyfenozide and indoxacarb are 0.19, 1.0, 0.75, 6, 12 and 48μg/μl, respectively.

Multiple factors mediate insecticide toxicity to a key predator for cotton insect pest management.

Mortality of agricultural pests caused by arthropod predators is a valuable ecosystem service for crop production. The earwig, Euborellia annulipes (Lucas), attacks different pest species in various crop ecosystems, including larvae and pupae of the boll weevil, Anthonomus grandis grandis (Boh.). In this study, multiple factors were assessed to measure the selectivity of insecticides used against sap-sucking and chewing cotton pests for two E. annulipes populations. Nymphs and adults of E. annulipes were exposed to the insecticides in two ways: ingestion of contaminated prey, and contact with dried residues on either inert surfaces or treated plants bearing prey. Pymetrozine, chlorantraniliprole, and spinetoram had little effect on the predator regardless the tested earwig population, life stage with developmental time and survival, or the route of exposure (ingestion and residual). Cyantraniliprole dried-residue impeded nymph to complete development and only 27% of adults survived until 20 days after exposure. Pyriproxyfen was harmless through acute toxicity to nymphs and adult earwigs (70-100% survival 72 h after exposure), but prevented normal development of nymphs to adults causing chronic toxicity. Chlorfenapyr, indoxacarb, lambda-cyhalothrin, chlorpyrifos, dimethoate, and malathion were harmful to the predator regardless life stage or method of exposure. The negative impact of thiamethoxam, lambda-cyhalothrin and indoxacarb was diminished when exposure occurred on plants with predator allowed to shelter in the soil. The results indicate that insecticide selectivity outcome varies by the insecticide, predator life stage and the predator's behavior. Therefore, testing different predator life stages via several routes of exposure, without denying the insect the opportunity to engage in its normal behavior can provide better estimates of insecticide selectivity.

Lethal, sublethal and transgenerational effects of insecticides labeled for cotton on immature Trichogramma pretiosum

The parasitoid Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae) is often released to manage lepidopteran pests in cotton crops. However, growers rely on multiple insecticide applications to manage cotton pests. A harmonious integration of control tactics is required for proper pest management, and the use of selective insecticides (i.e., those promoting effective pest control while causing little impact on natural enemies) fits within this scope. This study aimed to assess the lethal, sublethal and transgenerational effects of insecticides from varying chemical groups on T. pretiosum. The insecticides were sprayed on parasitized host [Ephestia kuehniella (Zeller), Lepidoptera: Pyralidae] eggs with developing T. pretiosum stages (egg-larva, prepupa, and pupa), and biological traits were assessed following adult emergence. Overall, pupae were more susceptible to insecticides. We found thiodicarb and chlorfenapyr to reduce F0 adult emergence in rates comparable to the positive control (methomyl). Adult F0 deformation was the highest on flupyradifurone-treated organisms, and both the F0 parasitism rate and female survival were reduced by the insecticides (except for teflubenzuron). The sex ratio (proportion female) was affected by thiodicarb and flupyradifurone. Transgenerational effects occurred on adult emergence, which was reduced on the offspring (F1) of thiodicarb, chlorfenapyr, and flupyradifurone treated T. pretiosum. In addition, thiodicarb decreased the F1 sex ratio (≤ 0.33) compared to the other compounds (sex ratio ≥ 0.45). These results indicate that teflubenzuron is the safest insecticide; the other insecticides are non-selective to T. pretiosum. Field and semifield studies are required to confirm the harmfulness of chlorfenapyr, flupyradifurone and thiodicarb toward T. pretiosum.

Metabarcoding of canopy arthropods reveals negative impacts of forestry insecticides on community structure across multiple taxa

Abstract Insecticides used to combat outbreaks of forest defoliators can adversely affect non‐target arthropods. Forestry insecticides typically suppress Lepidoptera larvae which are the cornerstone of the canopy community of deciduous oak forests. The abrupt removal of this dominant component of the food web could have far‐reaching implications for forest ecosystems, yet it is rarely investigated in practice owing to several methodological shortcomings. The taxonomic impediment and the biased nature of arthropod sampling techniques particularly impede the assessment of insecticide impacts on diverse communities. To tackle this issue, we propose an experimental approach combining sampling by pyrethrum knockdown and species determination via DNA metabarcoding, using community subsampling to derive estimates of species abundances. We applied this protocol to investigate the short‐term effects of the insecticides diflubenzuron (DFB) and Bacillus thuringiensis var. kurstaki (BTK) on canopy‐dwelling arthropod communities in German oak woodlands. Our approach allowed us to detect most of the diversity and integrate species abundances in our analyses. By classifying arthropod species into assemblages based on their expected sensitivity rather than coarse taxonomic groupings, we could unveil substantial effects of DFB across multiple taxa 5 weeks after application. Although strong effects on single species appear related to direct toxicity, substantial impacts of DFB on parasitoids and xylophagous beetles suggest that anti‐defoliator treatments can have previously unsuspected indirect effects on some components of forest arthropod communities. The impacts of BTK on community structure were consistent with that of DFB though much weaker. Synthesis and applications. Comparing diversity patterns in the arthropod communities of sprayed and unsprayed oak canopies, our results show that selective insecticides can alter species diversity in presumably non‐sensitive taxa. Even though the ecological significance of these impacts has yet to be assessed in an operational setting, their existence calls for increased regulatory scrutiny on indirect effects. As community approaches become more attainable with the rapid development of DNA metabarcoding, we suggest the inclusion of community‐level end points as regulatory requirements for the approval of forest‐use insecticides.