Susceptibility of Four Species of Aphids in Wheat to Seven Insecticides and Its Relationship to Detoxifying Enzymes

Towards Sustainable Pest Management: Toxicity, Biochemical Effects, and Molecular Docking Analysis of Ocimum basilicum (Lamiaceae) Essential Oil on Agrotis ipsilon and Spodoptera littoralis (Lepidoptera: Noctuidae)

Over the last decade, essential oils (EOs) have become potential ingredients for insecticide formulations due to their widespread availability and perceived safety. Therefore, this study aimed to evaluate the toxicity and biochemical efficacy of basil (Ocimum basilicum) (Lamiaceae) against two destructive pests Noctuidae, Agrotis ipsilon (Hufnagel) and Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae). In addition, a molecular docking study was performed to gain insight into the binding pattern between glutathione S-transferase (GST) and linalool, the main component of EO. GC-MS analysis of O. basilicum EO revealed that linalool is the most abundant compound (29.34%). However, the toxicity tests showed no significant difference between the values of LC50 of O. basilicum EO to A. ipsilon and S. littoralis. On the other hand, the sublethal experiments indicated that treating the second instar larvae with LC15 or LC50 values of O. basilicum EO significantly prolonged the larval duration in both insects, compared to the control. Regarding the biochemical effect of O. basilicum EO, the treatments significantly impacted the activity of detoxification enzymes. A notable elevation in glutathione S-transferase (GST) activity was recorded in A. ipsilon larvae compared with a reduction in S. littoralis larvae. The molecular docking analysis revealed that linalool bonded with the amino acid serine (SER 9) of GST, indicating its binding affinity with the enzyme. The obtained results could offer valuable insights into the mode of action of O. basilicum and can encourage the adoption of sustainable pest control practices that incorporate essential oils.

Discovery of insecticide resistance in field-collected populations of the aphid pest, Acyrthosiphon kondoi Shinji

BACKGROUND

The bluegreen aphid (Acyrthosiphon kondoi) is a worldwide pest of alfalfa, pulses, and other legume crops. An overreliance on insecticides to control A. kondoi has potentially placed populations under selection pressure favouring resistant phenotypes, but to date, there have been no documented cases of insecticide resistance. Recently, Australian growers began reporting that conventional insecticides were failing to adequately control A. kondoi populations, prompting this laboratory-based investigation into whether these populations have evolved resistance.

RESULTS

We discovered four A. kondoi populations with moderate resistance (10-40-fold) to three different insecticide groups: organophosphates, carbamates and pyrethroids. However, A. kondoi populations showed no resistance to the butenolide, flupyradifurone. We were unable to identify general metabolic mechanisms using synergist assays (cytochromes P450, glutathione S-transferases, or esterases), indicating that further detailed molecular investigations to characterise the putative resistance mechanism are needed.

CONCLUSION

Insecticide-resistant A. kondoi present an emerging challenge to Australian agriculture. Growers require new tools and updated strategies, including access to newer chemistries, to alleviate their reliance on the few insecticides currently registered against A. kondoi. The implications of insecticide resistant A. kondoi for future management, the potential mechanisms of resistance, and future research priorities are discussed. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Anopheles funestus Populations across Africa Are Broadly Susceptible to Neonicotinoids but with Signals of Possible Cross-Resistance from the GSTe2 Gene

Evaluating the susceptibility of malaria vectors to the new WHO-recommended products is a key step before large-scale deployment. We mapped the susceptibility profile of Anopheles funestus to neonicotinoids across Africa and established the diagnostic doses of acetamiprid and imidacloprid with acetone + MERO as solvent. Indoor resting An. funestus were collected in 2021 in Cameroon, Malawi, Ghana and Uganda. Susceptibility to clothianidin, imidacloprid and acetamiprid was evaluated using CDC bottle assays and offsprings of the field-caught adults. The L119F-GSTe2 marker was genotyped to assess the potential cross-resistance between clothianidin and this DDT/pyrethroid-resistant marker. Mosquitoes were susceptible to the three neonicotinoids diluted in acetone + MERO, whereas low mortality was noticed with ethanol or acetone alone. The doses of 6 µg/mL and 4 µg/mL were established as diagnostic concentrations of imidacloprid and acetamiprid, respectively, with acetone + MERO. Pre-exposure to synergists significantly restored the susceptibility to clothianidin. A positive correlation was observed between L119F-GSTe2 mutation and clothianidin resistance with the homozygote resistant mosquitoes being more able to survive than heterozygote or susceptible. This study revealed that An. funestus populations across Africa are susceptible to neonicotinoids, and as such, this insecticide class could be effectively implemented to control this species using IRS. However, potential cross-resistance conferred by GSTe2 calls for regular resistance monitoring in the field.

Effects of imidacloprid-induced hormesis on the development and reproduction of the rose-grain aphid Metopolophium dirhodum (Hemiptera: Aphididae)

Field populations of insect pests are affected by sub-lethal doses of insecticides, leading to hormesis. Imidacloprid is a neonicotinoid insecticide widely used to control various sucking insect pests, including aphids. In this study, the effects of sub-lethal concentrations of imidacloprid on the life table traits of the rose-grain aphid Metopolophium dirhodum (Walker) were evaluated on parental and first filial generations. The results showed that sub-lethal concentrations of imidacloprid significantly reduced the fecundity, adult longevity, and reproductive period of M. dirhodum in parental generation (F₀). However, the imidacloprid-induced hormetic effects on development and reproduction were detected in the F₁ generation. These hormetic effects were indicated by significantly higher adult longevity, fecundity, survival rate, intrinsic and finite rates of increase, and net reproductive rate of first filial generation (F₁) of M. dirhodum. Our finding indicated that the application of sub-lethal concentrations of imidacloprid inhibited parental generation (F₀), but it significantly stimulated the population growth of filial generation (F₁) in the M. dirhodum. The results support the inclusion of insecticides in integrated pest management programs for managing wheat aphids.

Insecticidal properties of Ocimum basilicum and Mentha piperita essential oils against South American Tomato moth, Phthorimaea absoluta (Meyrick) (Lepidoptera: Gelichiidae)

Phthorimaea absoluta (Meyrick) is one of the most destructive pests of tomato, causing 100% yield loss in the absence of control measures. The important method of managing the pest is by using synthetic insecticides. However, intermittent and indiscriminate uses of certain insecticides have negative effect on the environment. Use of herbal insecticides such as secondary metabolites and essential oils is a key for sustainable long term crop protection. Investigation on the insecticidal properties of Ocimum basilicum, Mentha piperita essential oils (EOs) and their constituents was carried out against P. absoluta. The M. piperita EO showed highest mortality (100%) of P. absoluta with LC₅₀ 1.78 μl/ml due to alloaromadendrene (27.99%), levomenthol (18.31%) and santolina triene (9.78%). The O. basilicum EO also had significant mortality (90%) effect with LC₅₀ 3.58 μl/ml due to humulene (32.31%), alpha farnesense (27.22%), estragole (19.24%) and 4-cerene (10.61%). Among binary compounds, levomenthol showed highest mortality (100%) having LC₅₀ 13.18 μl/ml followed by alpha-pinene (100%) with LC₅₀ 16.10 μl/ml, 4-cerene (95%) with LC₅₀ 38.20 μl/ml and alpha-phellandrene (90%) having LC₅₀ 46.83 μl/ml. The observed toxicity in all compounds was due to significant changes in the activity of esterases, glutathione S-transferase and acetylcholine esterases over the time. The present study suggests that O. basilium and M. piperita EOs would provide an additional approach for the management of P. absoluta over synthetic insecticides.

Efficacy of Imidacloprid Seed Treatments against Four Wheat Aphids under Laboratory and Field Conditions

Imidacloprid seed treatments are effective at reducing the cohorts of many insect pests on crops such as cotton, corn, and cereals. The effects of imidacloprid seed treatments depend on the aphid species. In China, there are four wheat aphid species-Sitobion avenae (Fabricius), Rhopalosiphum padi (Linnaeus), Schizaphis graminum (Rondani), and Metopolophium dirhodum (Walker)-and for a given region, these four aphid species differ in dominance with changes in cultivation practices and climate. Therefore, it is necessary to evaluate the effects of imidacloprid seed treatments on the four different aphid species. In experiments in the laboratory, imidacloprid seed treatments significantly reduced the survival rates of S. avenae, R. padi, and S. graminum to 57.33 ± 2.86%, 12.67 ± 1.92%, and 20.66 ± 2.33%, respectively, but for M. dirhodum, there was no significant difference between the control (96.33 ± 1.08%) and the treatment (97.00 ± 0.98%). The fecundities of the four aphid species were much reduced, especially for R. padi when feeding on treated wheat plants. For the field survey, only three aphid species were considered because the density of S. graminum was too low to be analyzed. The effects of imidacloprid seed treatment on the three aphid species in the field were consistent with the laboratory results. Imidacloprid seed treatment reduced the population sizes of S. avenae and R. padi at rates of 70.30 ± 3.15% and 87.62 ± 2.28%, respectively, for the whole wheat season in the field. For M. dirhodum, imidacloprid seed treatments were less effective, and the densities of M. dirhodum increased on four sample days. From this study, we confirmed that the effect of imidacloprid seed treatment varied with the composition of aphid species, being especially less effective for M. dirhodum.

Exploring the effect of Jasmonic Acid for Aphids control for improving the yield of Triticum aestivum varieties

Many biotic and abiotic factors influence the production of wheat (Triticum aestivum L.). Among biological agents, aphids are destructive pests effecting wheat yield drastically. This study was designed to evaluate the impact of foliar Jasmonic acid spray on aphid population as well as on plant growth during aphid infestation in two wheat varieties i.e., Borlaug-2015 and Zincol-2015. Plants are cultivated in pots and treated with jasmonic acid at concentrations of 0.1 and 1 mM (JA). The results revealed that length of shoot and roots decreased after aphid stress and was improved (21-24%) by JA spray. Photosynthetic pigments increased after applying the jasmonic acid spray compared to control plants. Jasmonic acid spray helped the plants to recover from aphid stress by enhanced production of antioxidant enzymes CAT (Catalase) (65-71%), SOD (Superoxide dismutase) (71-74%) and POD (Peroxidase) (61-65%). Consequent to improved defence system, plants treated with JA had fewer aphids as compared to control (60-73% reduction), 24 h after spray. The higher concentration of JA (1 mM) proved more effective as compared to 0.1 mM jasmonic acid. Moreover, Zincol-2015 appeared tolerant as compared to Borlaug-2015 against aphid infestation. The application of jasmonic acid as an exogenous foliar application showed an overall positive impact on the physiological and biochemical attributes of both varieties. It helps the plants to enhance resistance against the biotic stress and can be adopted as future alternative for aphid management. However, detailed studies regarding understanding of underlying molecular mechanisms are needed to optimize the mode for field application.

The sweet wormwood essential oil and its two major constituents are promising for a safe control measure against fall webworm

The fall webworm, Hyphantria cunea (Drury), is a harmful polyphagous global defoliator. The major chemical components of Artemisia annua essential oil (EO) was found to contain (±)-camphor (16.42%), 1,8-cineole (6.22%), α-pinene (6%), caryophyllene (5.19%), and α-selinene (5.17%). The highest toxicity was recorded for EO of A. annua (LD₅₀ = 305.05 μg/larva), followed by (±)-camphor (LD₅₀ = 465.03 μg/larva) and 1,8-cineole (LD₅₀ = 573.49 μg/larva). The binary mixtures of compounds expressed a weaker activity compared to individuals. The (±)-camphor was found to be antagonistic to 1,8-cineole. The biochemical compounds of treated larvae were also determined. The activity level of alanin and aspartate aminotransferase decreased sharply while acid and alkaline phosphatase increased. Activity of lactate dehydrogenase was significantly higher than the control group at 24 h, but decreased significantly after 48 h in all treatments. The activity of esterases were decreased in the treated larvae. The glutathione S-transferase significantly increased in all time intervals. Overall the current results suggest that the sweet wormwood (A. annua) EO and its components could be a safe and environmentally friendly approach in possible control of fall webworm (H. cunea).

Insecticidal Activity of Lemongrass Essential Oil as an Eco-Friendly Agent against the Black Cutworm Agrotis ipsilon (Lepidoptera: Noctuidae)

Simple Summary

The insect pest, black cutworm, Agrotis ipsilon (Lepidoptera: Noctuidae), attacks the seedling stage of many field crops in several countries around the world. To control this insect pest, in this study, lemongrass (Cymbopogon citratus) essential oil observed potential insecticidal activity against the second-instar larvae of A. ipsilon.

Abstract

Background: The destructive insect pest Agrotis ipsilon (Hufnagel) (Lepidoptera: Noctuidae) is a polyphagous species targeting many economically important plants. The extensive and arbitrary use of insecticides has resulted in the build-up of insecticide resistance and pesticide residues accumulating in food. Therefore, it is becoming evident that alternative pest management tools are needed to reduce risks to humans, the environment, and non-target organisms, and at the same time, they should be used in field application at the lowest cost. Methods: In view of this objective, the present study demonstrates the toxicity of lemongrass (Cymbopogon citratus (DC.) Stapf) essential oil (EO), against the black cutworm A. ipsilon under controlled laboratory conditions in terms of measuring the activity of peroxidase and detoxification enzymes. The chemical components of the EO were analyzed using GC–MS. Results: The results show that after 96 h post treatment, the LC₁₅ and LC₅₀ values were 427.67 and 2623.06 mg/L, respectively, of C. citratus EO on second-instar larvae of A. ipsilon. A slight significance in elongation of the larval duration with LC₁₅ and LC₅₀ value was found with control. By GC–MS analysis, the main compounds identified in the EO were α-citral and β-citral with percentages of 35.91%, and 35%, respectively. The oxidative stress indicates a significant increase in CAT and lipid peroxidase enzyme activity after 96 h post treatment at the LC₁₅ and LC₅₀. Conversely, the detoxification enzyme activity shows an inhibition of CarE and GST enzymes of larvae exposed to LC₁₅ and LC₅₀ values in response to C. citratus EO. Conclusions: The present data show that lemongrass EO has insecticidal activity against the black cutworm, A. ipsilon.