Selective Insecticides Research Articles

A scaffold-level genome assembly of a minute pirate bug, Orius laevigatus (Hemiptera: Anthocoridae), and a comparative analysis of insecticide resistance-related gene families with hemipteran crop pests

BackgroundOrius laevigatus, a minute pirate bug, is a highly effective beneficial predator of crop pests including aphids, spider mites and thrips in integrated pest management (IPM) programmes. No genomic information is currently available for O. laevigatus, as is the case for the majority of beneficial predators which feed on crop pests. In contrast, genomic information for crop pests is far more readily available. The lack of publicly available genomes for beneficial predators to date has limited our ability to perform comparative analyses of genes encoding potential insecticide resistance mechanisms between crop pests and their predators. These mechanisms include several gene/protein families including cytochrome P450s (P450s), ATP binding cassette transporters (ABCs), glutathione S-transferases (GSTs), UDP-glucosyltransferases (UGTs) and carboxyl/cholinesterases (CCEs).Methods and findingsIn this study, a high-quality scaffold level de novo genome assembly for O. laevigatus has been generated using a hybrid approach with PacBio long-read and Illumina short-read data. The final assembly achieved a scaffold N50 of 125,649 bp and a total genome size of 150.98 Mb. The genome assembly achieved a level of completeness of 93.6% using a set of 1658 core insect genes present as full-length genes. Genome annotation identified 15,102 protein-coding genes - 87% of which were assigned a putative function.Comparative analyses revealed gene expansions of sigma class GSTs and CYP3 P450s. Conversely the UGT gene family showed limited expansion. Differences were seen in the distributions of resistance-associated gene families at the subfamily level between O. laevigatus and some of its targeted crop pests. A target site mutation in ryanodine receptors (I4790M, PxRyR) which has strong links to diamide resistance in crop pests and had previously only been identified in lepidopteran species was found to also be present in hemipteran species, including O. laevigatus.Conclusion and significanceThis assembly is the first published genome for the Anthocoridae family and will serve as a useful resource for further research into target-site selectivity issues and potential resistance mechanisms in beneficial predators. Furthermore, the expansion of gene families often linked to insecticide resistance may be an indicator of the capacity of this predator to detoxify selective insecticides. These findings could be exploited by targeted pesticide screens and functional studies to increase effectiveness of IPM strategies, which aim to increase crop yields by sustainably, environmentally-friendly and effectively control pests without impacting beneficial predator populations.

In silico identification of potential phytochemical inhibitors targeting farnesyl diphosphate synthase of cotton bollworm (Helicoverpa armigera)

Helicoverpa armigera (Ha), a polyphagous pest, causes significant damage to several crop plants, including cotton. The control of this cosmopolitan pest is largely challenging due to the development of resistance to existing management practices. The Juvenile Hormone (JH) plays a pivotal role in the life cycle of insects by regulating their morphogenetic and gonadotropic development. Hence, enzymes involved in JH biosynthesis are an attractive target for the development of selective insecticides. Farnesyl diphosphate synthase (FPPS), a member protein of (E)-prenyl-transferases, is one of the most crucial enzymes in the biosynthetic pathway of JHs. It catalyzes the condensation of isopentenyl diphosphate (IPP) with dimethylallyl diphosphate (DMAPP), forming farnesyl diphosphate (FPP), a precursor of JH. The study was designed to identify an effective small inhibitory molecule that could inhibit the activity of Helicoverpa armigera – FPPS (HaFPPS) for an effective pest control intervention. Therefore, a 3D model of FPPS protein was generated using homology modeling. The FooDB database library of small molecules was selected for virtual screening, following which binding affinities were evaluated using docking studies. Three top-scored molecules were analyzed for various pharmacophore properties. Further, molecular dynamics (MD) simulation analysis showed that the identified molecules (mitraphylline-ZINC1607834, chlorogenic acid-ZINC2138728 and llagate-ZINC3872446) had a reasonably acceptable binding affinity for HaFPPS and resulted in the formation of a stable HaFPPS-inhibitor(s) complex. The identified phytochemical molecules may be used as potent inhibitors of HaFPPS thus, paving the way for further developing environment-friendly insect growth regulator(s). Communicated by Ramaswamy H. Sarma

Determination of hormoligosis of organophosphate insecticides against Phenacoccus solenopsis.

Cotton mealybug is a highly invasive pest of agricultural crops worldwide. Major agriculturists most rely on the use of insecticides for the control of pesticides. So, the indiscriminate use of insecticides leads to resistance development in recent years. For this purpose, an experiment was conducted using different concentrations of the three insecticides (profenfos chlorpyrifos and triazophos) to check the hormoligosis effects against cotton mealybug (CMB) in laboratory conditions. Investigation of variations for % mortality of adults of CMB after three days revealed that all treatments had statistically significant (P ˂ 0.05). The highest mortality was observed at the highest concentrations of profenofos 2.4% (38.55%). After 7 days, all the treatments were significant with difference in means (P ˂ 0.05). The highest mortality was recorded at the highest dilution of pesticide profenofos 2.4% (77.11%). The values of fecundity and longevity exposed a valid difference among treatments (P ˂ 0.05). Maximum fecundity was observed at the concentration 2.4% (181.41%) and longevity showed (38.46%). The highest mortality was observed at a concentration of triazophos 4% (27.98%). For chlorpyriphos the highest mortality was examined at concentration 4% (24.79%). The fecundity showed a statistically significant difference for different concentrations of triazophos and chlorpyriphos (P ˂ 0.05). The results of the recent study provide valuable information regarding the selection of insecticides and hormoligosis effects. The study can be helpful in the implications of integrated pest management of P. solenopsis.

Exposure to Temperature and Insecticides Modulates the Expression of Small Noncoding RNA-Associated Transcripts in the Colorado Potato Beetle, Leptinotarsa decemlineata (Coleoptera: Chrysomelidae).

The Colorado potato beetle (Leptinotarsa decemlineata (Say)) is an insect that can adapt to various challenges, including temperature fluctuations or select insecticide treatments. This pest is also an ongoing threat to the potato industry. Small noncoding RNAs such as miRNAs, which can control posttranscriptionally the expression of various genes, and piRNAs, which can notably impact mRNA turnover, are modulated in insects under different conditions. Unfortunately, information regarding the expression status of key players involved in their synthesis and function is for the most part lacking. The current study thus aims at assessing the levels of such targets in L. decemlineata exposed to hot and cold temperatures as well as treated to the insecticides chlorantraniliprole, clothianidin, imidacloprid, and spinosad. Transcript expression levels of Ago1, Ago2, Ago3, Dcr2a, Dcr2b, Expo-5, Siwi-1, and Siwi-2, components of pathways associated with small noncoding RNA production or function, were measured by qRT-PCR and revealed modulation of select transcripts in response to temperature challenges and to select insecticides. RNAi-mediated reduction of Ago2 transcript levels in L. decemlineata injected with Ago2-targeting dsRNA and exposed to cold and warm temperatures was also conducted. Changes in survival rates were observed for the latter condition in dsRNA- versus saline-injected insects. These results showcase the differential expression of select targets involved in small noncoding RNA homeostasis and provide leads for the subsequent assessment of their involvement during stress response in L. decemlineata using RNAi-based approaches.

Effects of Selective Hemipteran-Targeting Insecticides and One Broad-Spectrum Insecticide on Squash Bug, 2018

Effects of Selective Hemipteran-Targeting Insecticides and One Broad-Spectrum Insecticide on Squash Bug, 2018

Ryanodine Receptor as Insecticide Target.

The ryanodine receptor (RyR) is one of the primary targets of commercial insecticides. The diamide insecticide family, including flubendiamide, chlorantraniliprole, cyantraniliprole, etc., targets insect RyRs and can be used to control a wide range of destructive agricultural pests. The diamide insecticides are highly selective against lepidopteran and coleopteran pests with relatively low toxicity for non-target species, such as mammals, fishes, and beneficial insects. However, recently mutations identified on insect RyRs have emerged and caused resistance in several major agricultural pests throughout different continents. This review paper summarizes the recent findings on the structure and function of insect RyRs as insecticide targets. Specifically, we examine the structures of RyRs from target and non-target species, which reveals the molecular basis for insecticide action and selectivity. We also examine the structural and functional changes of RyR caused by the resistance mutations. Finally, we examine the progress in RyR structure-based insecticide design and discuss how this might help the development of a new generation of green insecticides.

Efficacy of Select Insecticides to Control Pyrethroid Resistant Alfalfa Weevils, 2021

Efficacy of Select Insecticides to Control Pyrethroid Resistant Alfalfa Weevils, 2021

Insecticide resistance to insect growth regulators, avermectins, spinosyns and diamides in Culex quinquefasciatus in Saudi Arabia

BackgroundCulex quinquefasciatus is not only a biting nuisance but also an important vector of fatal diseases. In Saudi Arabia, management measures to control this mosquito and thereby prevent associated disease transmission have focused on insecticides. Nevertheless, information on the resistance status of C. quinquefasciatus is insufficient, especially concerning insecticides containing novel classes of insecticides.MethodsWe evaluated six insecticides belonging to four classes of insecticides (insect growth regulators [3], avermectins [1], diamides [1] and spinosyns [1]) for toxicity and resistance in eight C. quinquefasciatus populations (from Ishbiliya, Al-Masfa, Al-Masanie, Al-Washlah, Al-Nakhil, Irqah, Al-Suwaidi and Al-Ghanemiya) following World Health Organisation protocols.ResultsResistance status ranging from susceptibility/low resistance to high resistance, in comparison with the susceptible strain, was detected for cyromazine in the eight C. quinquefasciatus populations: Ishbiliya (resistance ratio [RR] = 3.33), Al-Masfa (RR = 4.33), Al-Masanie (RR = 3.67), Al-Washlah (RR = 2.33), Al-Nakhil (RR = 5.33), Irqah (RR = 7.00), Al-Suwaidi (RR = 21.33) and Al-Ghanemiya (RR = 16.00). All C. quinquefasciatus populations exhibited a high level of resistance to diflubenzuron (RR = 13.33–43.33), with the exception of Al-Nakhil which exhibited moderate resistance (RR = 10.00). Susceptibility/low resistance to high resistance was observed for triflumuron in the eight C. quinquefasciatus populations: Ishbiliya (RR = 0.50), Al-Ghanemiya (RR = 3.00), Al-Suwaidi (RR = 10.00), Al-Masfa (RR = 5.00), Al-Masanie (RR = 10.00), Al-Nakhil (RR = 5.00), Irqah (RR = 5.00) and Al-Washlah (RR = 15.00). Susceptibility/low resistance was assessed for abamectin, chlorantraniliprole and spinosad in all C. quinquefasciatus populations, with RR ranges of 0.25–3.50, 0.17–2.19, and 0.02–0.50, respectively. However, the population collected from Irqah showed high resistance to chlorantraniliprole (RR = 11.93).ConclusionsThe detection of widespread resistance to insect growth regulators in C. quinquefasciatus highlights an urgent need to establish integrated vector management strategies. Our results may facilitate the selection of potent insecticides for integrated vector management programmes for C. quinquefasciatus.Graphical

Contemporary Resistance Status of Anopheles Stephensi against Insecticides in District Dungarpur, Rajasthan, India

Pyrethroids are powerful insecticides used in the vector control program with impregnated mesh, and residual indoor sprays. However, resistance to insecticide reduces the effectiveness. The present susceptibility study carried out against theAnopheles Stephensi to monitor the sensitivity conditions of An. Stephensi vector, which raises the need to understand the state of vector resistance in the Dungarpur region of Rajasthan, India in order to better report vector-based interventions. The sensitivity study was carried out by the WHO standard method using recommended diagnostic doses of DDT, alpha-cypermethrin, permethrin, and deltamethrin. An. Stephensi showed resistance to DDT from the entire study while sensitive to alpha-cypermethrin, permethrin, and deltamethrin. The study looks at the selection and circulation of the appropriate insecticide’s molecule for a vector control program as insecticide need constant monitoring to develop effective vector control strategies such as improving insecticide by applying integrated biological and ecological methods.

EVALUATION OF DIFFERENT INSECTICIDES AGAINST VIRACHOLA ISOCRATES INFESTATION IN POMEGRANATE ORCHARDS OF GILGIT-BALTISTAN, PAKISTAN

Pomegranate (Punica granatum) is a native tree of Iran and cultivated throughout the world including Himalayan regions of Pakistan and India. Pomegranate fruit is also considered as a medicinal fruit. It can act as antioxidant, anti-tumoral or anti-hepatotoxic agents, and improve cardiovascular health. Pomegranate fruit is cultivated in Gollapor vellay, Diamer, Gilgit and Ghizer areas of Gilgit-Baltistan, Pakistan. Pomegranate fruit borer (Virachola isocrates) is the main insect pest infesting the fruit orchards in this region. Present study was designed to evaluate the infestation level of pomegranate fruit borer against different commercial insecticides available to local formers. Two commercially available insecticides chloropyrifos and cypermethrine along with neem seed oil were used against the pomegranate fruit borer. Results of the study showed that cypermthrin was recorded with maximum efficacy against V. isocrates followed by chloropyrifos. All the treatments were significantly different from each other. Neem oil was also evaluated as effective treatment to reduce infestation in pomegranate orchards. This study will be helpful in control program of pomegranate fruit borer for this region and will also be very helpful to local pomegranate growers for selection of effective insecticide for the management of pomegranate fruit borer.

Effect of three pest-control management systems on abundance, species richness, and selected traits of spiders (Araneae) assemblage in apple orchard

There are various modern pest-control management systems used in the current apple production, such as integrated pest management (IPM) or organic systems. All aims to support occurrence of natural enemies that should help to reduce populations of pests. Here we investigated the effect of fungicide-treated and fungicide-free (resistant tree varieties) treatment combined with biological, IPM, and conventional systems on spiders, as the major group of natural enemies occurring on foliage of apple trees. The biological treatment was based on the use of biopesticides; IPM system was based on the use of selective insecticides, conventional included the use of broad-spectrum insecticides. Abandoned plot served as a control. The study was done for three consecutive years. Spiders were sampled from canopies by beating at weekly intervals during season. We found that fungicide-treated plots had lower abundance of spiders for two years but not species richness than fungicide-free plots. Among the three pest-control management systems, IPM and conventional supported greater spider abundance but not species richness than the biological treatment. Comparison of spider abundance before and after insecticide applications revealed that only very few pesticides, particularly the broad-spectrum ones, reduced spider numbers. In addition, we focused on the comparison of three traits (body size, maturity, fecundity) among treatments. Of six species, only Philodromus cespitum showed a smaller body size on biological than the other treatments. There were three species in which adults occurred earlier on conventional treatment than on the other treatments. Neither clutch size of Phylloneta impressa nor egg size was different among treatments. The small though significant differences in abundance, richness, and selected traits, found among IPM, conventional, and biological treatments and the control show that these pest-control management systems had similar effect on spiders. Use of IPM system combined with scab resistant apple varieties is recommended.

Future of Insecticide Seed Treatment

Seed treatment as a method of local application of pesticides in precise agriculture reduces the amount of pesticides used per unit area and is considered to be the safest, cheapest and most ecologically acceptable method of protecting seeds and young plants from pests in the early stages of their development. With the introduction of insecticides from the neonicotinoid group in the mid-1990s, the frequency of seed treatment increased. Due to suspected negative effects on pollinators, most of these insecticides are banned in the European Union. The ban has therefore led to a reduction in the number of active substances approved for seed treatment and to an increased re-use of active substances from the group of pyrethroids as well as other organophosphorus insecticides, which pose potentially very serious risks, perhaps even greater than those of the banned neonicotinoids. The objective of this review is to analyze the advantages and disadvantages of seed treatment and the potential role of insecticide seed treatment in reducing the negative impact of pesticides on the environment. The main disadvantage of this method is that it has been widely accepted and has become a prophylactic protective measure applied to almost all fields. This is contrary to the principles of integrated pest management and leads to an increased input of insecticides into the environment, by treating a larger number of hectares with a lower amount of active ingredient, and a negative impact on beneficial entomofauna. In addition, studies show that due to the prophylactic approach, the economic and technical justification of this method is often questionable. Extremely important for a quality implementation are the correct processing and implementation of the treatment procedure as well as the selection of appropriate insecticides, which have proven to be problematic in the case of neonicotinoids. The ban on neonicotinoids and the withdrawal of seed treatments in oilseed rape and sugar beet has led to increased problems with a range of pests affecting these crops at an early stage of growth. The results of the present studies indicate good efficacy of active ingredients belonging to the group of anthranilic diamides, cyantraniliprole and chlorantraniliprole in the treatment of maize, soybean, sugar beet and rice seeds on pests of the above-ground part of the plant, but not on wireworms. Good efficacy in controlling wireworms in maize is shown by an insecticide in the naturalites group, spinosad, but it is currently used to treat seeds of vegetable crops, mainly onions, to control onion flies and flies on other vegetable crops. Seed treatment as a method only fits in with the principles of integrated pest management when treated seeds are sown on land where there is a positive prognosis for pest infestation.

Management of Cabbage Aphid (Brevicoryne brassicae L. (Homoptera: Aphididae)) on Ethiopian Mustard (Brassica carinata Braun) using Entomopathogenic Fungi and Selected Insecticides

Cabbage aphid (Brevicoryne brassicae L.) is an important sucking insect pest of cabbage and other vegetables. It can be controlled using continuous chemical insecticides that cause human health and environmental problems. The present study was, therefore, designed to evaluate antagonistic activities of indigenous entomopathogenic fungi together with selective insecticides within the context of integrated pest management (ipm). To this effect, four strains of entomopathogenic fungi from Beauveria bassiana and Metarhizium anisopliae were tested for their antagonistic activities against the cabbage aphid. The result showed that microbial inoculums of 1×107 and 1×108 conidia mL-1 showed high mortality (66.7-100%) of aphids after 6 days of incubation under laboratory condition. Among them, bei1 (B. bassiana) isolate was the most virulent strain on adult aphids and nymphs showing 67 to 100% and 39-72% mortality after 4th-5th days of treatments. The data also indicated that the fungal isolates were compatible to the three insecticides with 70% - 91% conidial germination by M. anisopliae and 68%-98% conidial germination by B. bassiana after 24 hours of treatment of which Karate was the most compatible insecticide to the isolates. The single treatment with the entomopathogens gave a substantial percentage mortality of insect pests after 11 days compared to (80-100%) mortality obtained from a combined treatment with half recommended dose of Karate in seven days, which was similar to the treatment with full dose of the insecticide control. The treatments were slightly more effective on adults than they were on aphid larvae. It is interesting to note that the combination of bei1 + Ka induced 100% mortality of adult aphids after seven days of incubation compared to the 11 day incubation required to kill the nymphs. Given that the full dose of karate killed the adult aphids in five days, the 100% mortality of the half dose of karate with bei1 within seven days was a good indication that the ipm could reduce pollution problem. Thus, B. bassiana and M. anisopliae with Karate could be further tested in the field to realize their potential as bioinsecticides for integrated pest management to control mustard aphids.

Seasonal diversity of entomofauna, their impact and management practices in tomato fields in Meru district, Tanzania

Tomato is a highly cultivated vegetable in Tanzania. The intensive tomato cultivation and production in Tanzania has resulted in high pests and diseases build-up. A survey to identify and quantify entomofauna diversity in different seasons and pest management practices in Meru District was conducted. In addition, a laboratory experiment was done to assess the effectiveness of commonly used pesticides SnowBecco (Thiamethoxam)and Belt (Flubendiamide) against two dominating insect pests, white flies (Bemisia tabaci (Gennadius, 1889)) and leaf miner (Tuta absoluta (Meyrick, 1917)), respectively. The results obtained revealed that, tomato fields in Meru District had significantly higher entomofauna build up during dry season than the rainy season (U0.05 (df, 24)= 45, p = 0.0441). More than 70% of all collected entomofauna were dominated by the whiteflies (Bemisia tabaci) and tomato leaf miners (Tuta absoluta) belonging to orders Hemiptera and Lepidoptera, respectively. It was also observed that, the common pesticides management practices were the use of pesticidal cocktail, broad spectrum insecticides, use of botanical pesticides, frequent application of pesticide and insecticides over dosage. Moreover, yield reduction due to whiteflies and tomato leaf miners infestation were observed in terms of reduced fruits number per plant (38 and 18.4%), fruit size (22.4 and 14.2%), and fruits weight per plant by 43.6 and 26.2%, for Bemisia tabaci and Tuta absoluta, respectively. The study showed that the recommended doses in both tested insecticides caused significant pest mortality (F0.05 (df, 19) = 4.367, p = 0.0199) and (F0.05(df, 19) = 4.761, p = 0.0147) for B. tabaci and T. absoluta, respectively, within a specified period of time. The results suggest that high insect pest infestations could be caused by factors other than development of insecticidal tolerance including inappropriate identification of insect pests due to lack of training, and inappropriate selection and application of insecticides. Consequently, frequent application of broad spectra insecticides not only increases production expenses but also disrupts agroecosystem by killing beneficial entomofauna and disrupting soil organisms that are susceptible to insecticide toxicity.

Field and Laboratory Testing of Feeding Stimulants to Enhance Insecticide Efficacy Against Spotted-Wing Drosophila, Drosophila suzukii (Matsumura).

The invasive spotted-wing drosophila, Drosophila suzukii (Matsumura), is a key insect pest of berries globally, causing lost revenues and increased production costs associated with applications of insecticides. The insecticides utilized are commonly broad-spectrum pyrethroids, organophosphates, or carbamates in conventionally managed fields and spinosad in organically managed fields. Adoption of more selective insecticides has been limited due to their lower residual activity, and the requirement that some must be ingested to be effective. We investigated the use of feeding stimulants for D. suzukii as a method to improve longevity and efficacy in a range of insecticides. In laboratory bioassays, sugar increased the efficacy of all chemical classes tested; however, the inclusion of yeast only showed a benefit with malathion. Feeding stimulants had a limited effect in some cases under field conditions. Similarly, infestation in field plots and a semifield bioassay showed no significant decreases in infestation with the inclusion of feeding stimulants for the insecticides tested in these trials. We discuss the implications of these findings for managing D. suzukii in fruit crops to help ensure the harvest of marketable fruit.

Pyrethrin-resembling pyrethroids are metabolized more readily than heavily modified ones by CYP9As from Helicoverpa armigera

The cotton bollworm, Helicoverpa armigera, is a polyphagous pest threatening many economically important crops worldwide. Until recently, synthetic pyrethroids remain in wide use for controlling pest insects including the cotton bollworm. Understanding the metabolic mechanism of pyrethroids in a given pest can provide significant implication for a smart choice of insecticides, and such information is useful for the development of novel selective and safe insecticides. In this study, we used complexes of recombinant H. armigera cytochrome P450 CYP9A and NADPH-dependent cytochrome P450 reductase to investigate the capacity of three CYP9A paralogs in the transformation of seven structurally different pyrethroids by metabolism assays. The results showed that the three paralogous CYP9As were able to metabolize multiple pyrethroids. Interestingly, all the three CYP9As transformed pyrethrin-resembling pyrethroids (e.g. bioallethrin) more efficiently than the heavily modified ones (e.g. bifenthrin). These findings suggest that herbivorous insects can cope with synthetic insecticides using their physiological systems that initially evolved to survive exposure to the defensive chemicals in their host plants, adding support to the pre-adaptation hypothesis.

Survival, development and reproduction of Harmonia axyridis (Pallas, 1773) (Coleoptera: Coccinellidae) under effects of insecticides used in tomato plants.

Agriculture depends on the correct use of different methods for pest control, however the cultivation methods adopted for Solanaceae demands numerous pesticide applications. These products can be either harmful or selective to beneficial organisms, such as Coccinellidae predators. The aim of this study was to assess the physiological selectivity of insecticides, registered for tomato pest control, on Harmonia axyridis (Pallas, 1773) (Coleoptera: Coccinellidae). The maximum recommended field dosage of the insecticides spinetoram, spiromesifen, methoxyfenozide, metaflumizone, tebufenozide and methomyl was used. They were sprayed on eggs, third instar larvae, pupae and adults of H. axyridis using Potter´s tower; control treatment consisted of water. Methoxyfenozide didn't reduce any biological feature of the predator. Spiromesifen only reduced survival over time when sprayed on third instar larvae. Spinetoram shortened larval period and reduced survival of adults. When sprayed on larvae, metaflumizone reduced larval survival. Tebufenozide reduced egg viability, pupal period and larval survival over time. It is concluded that methoxyfenozide, spiromesifen and spinetoram are the least toxic to H. axyridis, and their usage should be prioritized in integrated pest management (IPM) programs; both tebufenozide and metaflumizone are harmful to some important biological features of the predator. Methomyl is highly toxic in controlled conditions, so its toxicity to H. axyridis should be confirmed in field and greenhouse tests, we also suggest further studies with the other compounds in different concentration and route of exposure.

Relative Yield Loss From Stem Borers (Lepidoptera: Crambidae) and Rice Water Weevil (Coleoptera: Curculionidae) in Rice.

The rice water weevil, Lissorhoptrus oryzophilus Kuschel, is the most important economic pest of rice in the United States with the ability to substantially reduce rice yields. Stem borers, including the Mexican rice borer, Eoreuma loftini (Dyar), are emerging as more consistent pests in Louisiana and Texas, but the relationship between blanked panicles (whiteheads) caused by stem borer feeding and yield loss is not well understood. A series of field trials was conducted in Louisiana from 2019 to 2020 to determine the relative yield loss by manipulating infestations of both pests with selective insecticides. Results indicate losses from L. oryzophilus infestations are greater than those for E. loftini in early planted rice. In contrast, relative yield losses were approximately equal in later planted rice in 2019, in which E. loftini infestations were high. Additive impacts of the root-feeding L. oryzophilus and the stem-feeding E. loftini were not observed in our study. Linear regression revealed that each increase of one whitehead per square meter is associated with a 1.7% loss in yield. Results from ratoon rice suggest that protection from L. oryzophilus in the main crop also improves yield in the second crop. Collectively, results demonstrate the continued need for effective L. oryzophilus management programs to prevent economic losses. Conversely, findings suggest that benefits of E. loftini control may be minimal in many instances. Control of E. loftini is most likely to be economical under conditions where high populations are anticipated such as in late-planted fields or regions that previously had high infestations.

Insecticide Resistance Monitoring of the Diamondback Moth (Lepidoptera: Plutellidae) Populations in China.

The diamondback moth, Plutella xylostella L., is a worldwide crop pest that is difficult to control because of its ability to develop resistance to many insecticides. To provide a reference for resistance management of P. xylostella in China, the present study used a leaf-dip bioassay to monitor the resistance of P. xylostella to nine insecticides in eight regions of China. The results showed that P. xylostella had developed a high level of resistance to beta-cypermethrin (resistance ratio [RR] > 112), and moderate (RR < 40) to high levels of resistance to indoxacarb, abamectin, and chlorfluazuron. For chlorantraniliprole, RRs > 100 were found in Midu (Yunnan Province) and Jinghai (Tianjin). In most regions, the resistance to spinetoram and chlorfenapyr and Bacillus thuringiensis (Bt) was low. No resistance was detected to diafenthiuron. Overall, P. xylostella resistance to insecticides was higher in Midu than in other regions. The data in this study should help guide the selection of insecticides for management of P. xylostella in China.

Monitoring and assessment of resistance to insecticides in the lacewing Chrysoperla carnea (Stephens).

Chrysoperla carnea (Stephens) is a key predator of several soft-bodied arthropods across various cropping ecosystems. Biological control is a prime strategy to reduce the harmful effects of pesticides on environment especially plants and arthropods. Collection of lacewings (Field Populations) was made during 2014 and repeated in 2016 from five different districts composed mainly by row and vegetable crops under conventional cropping system. For these populations, resistance level to four insecticides representing different mode of action was measured using topical treatment of 1st-instar larvae with prepared dilutions of commercial formulation. The highest resistance levels were found for chlorfenapyr (100.86- to 423.78-fold) and indoxacarb (131.28- to 255.05-fold) in populations from all districts, while buprofezin and nitenpyram resistance was low to high and moderate to high, respectively. The levels of resistance to nitenpyram increased from 2014 to 2016 for populations of 3 out of 4 surveyed areas, while the susceptibility to buprofezin remained unchanged. Decrease in resistance levels for chlorfenapyr and indoxacarb in 2years was marginal. These results suggest that field populations of C. carnea maintained resistance to buprofezin, chlorfenapyr, indoxacarb, and nitenpyram. Current outcomes support the fact that this bio-control agent could be a main nominee for mass release under judicious application of selective insecticides.