Concentration-mortality Response Research Articles

Imidacloprid-induced mortality, histopathology and biochemical impairments in the larvae of oriental latrine fly (Chrysomya megacephala).

The concentration-mortality response of third instar larvae of Chrysomya megacephala (Diptera: Calliphoridae) to a synthetic insecticide, imidacloprid, and its impact on histopathological, histochemical, and biochemical parameters were determined in laboratory assays. Larvae displayed a concentration and time-dependent mortality response for the insecticide. Histopathological studies exhibited quite noticeable modifications in the epithelial cells, peritrophic membrane, basement membrane and muscular layer of the larval midgut. The ultrastructural analysis demonstrated alterations in nuclei, lipid spheres, microvilli, mitochondria, rough endoplasmic reticulum and lysosomes. In addition, histochemical tests on the midgut were performed, which revealed a strong reaction for proteins and carbohydrates in the control group and a weak reaction in the group exposed to imidacloprid in a dose and time-dependent manner. Imidacloprid also caused a significant reduction in the total midgut content of carbohydrates, proteins, lipids and cholesterol. Larvae treated with imidacloprid also showed a reduction in the activities of acid and alkaline phosphatases at all concentrations compared to untreated larvae.

Flubendiamide Resistance and Its Mode of Inheritance in Tomato Pinworm Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae).

Tomato pinworm, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) is the major pest of tomato crops in Pakistan. Insecticides are commonly used for the management of this insect-pest. To develop a better insecticide resistance management strategy and evaluate the risk of resistance evolution, a field collected population of the tomato pinworm was selected with flubendiamide in the laboratory. We investigated the genetics of flubendiamide resistance and concentration-mortality response to other insecticides by selecting a field strain of tomato pinworm with commercial flubendiamide formulation. Tuta absoluta was reciprocally crossed with resistant strain (Fluben-R) and was selected up to 13 generations, while F1 progeny was back-crossed with resistant parent (Fluben-R). The results of LC50 and Resistance Ratio (RR) demonstrated a higher resistance developed in field and laboratory-selected strains (G2 and G13, respectively). Field-collected and laboratory-selected (Fluben-R) strains demonstrated higher intensity of concentration-mortality response against chlorantraniliprole, thiamethoxam, permethrin, abamectin and tebufenozide compared to susceptible ones. Based on the overlapping of 95% FL, it demonstrated significant differences, revealing that it was not sex linked (autosomal) with no maternal effects. The backcross analysis of the F1´ resistant parent resulting in significant differences at all concentrations suggests that resistance is controlled by more than one factor; the null hypothesis was rejected and inheritance was under polygenic control. Resistance progression from 38 to 550 folds demonstrated that T. absoluta can develop a higher level of resistance to flubendiamide. Concentration-mortality response experiments demonstrated that the LC50 of some tested insecticides was higher for field-collected and laboratory-selected strains, suggesting that resistance mechanisms should be studied at a molecular level for better understanding. These results could be helpful to design resistance management strategies against the tomato pinworm.

Potential of Turkish Beauveria bassiana isolates for the management of the polyphagous planthopper, Orosanga japonica Melichar 1898 (Hemiptera: Ricaniidae)

BackgroundEntomopathogenic fungi are a potential biological control agent for many pests. In this study, 14 native Beauveria bassiana isolates were molecularly identified and assessed for their virulence and mortality against adults of the polyphagous planthopper Orosanga japonica, Melichar (Hemiptera: Ricaniidae) a polyphagous sap-feeding insect, under laboratory conditions.ResultsIsolates obtained from naturally infected adults O. japonica were molecularly identified as B. bassiana by sequencing the internal transcribed spacer and 26S large subunit of ribosomal DNA. In the bioassay, the radial growth and sporulation of isolates significantly differed (P < 0.05). Concentration–time bioassays demonstrated that all isolates had a lethal effect on adult O. japonica at the concentration of 1 × 108 conidia ml–1. The lethal times LT50 and LT90 values for each B. bassiana isolate, which indicate the time required to kill O. japonica, ranged between 2.44–3.19 and 3.78–5.01 days, respectively, at 20 °C, while their values were 1.74–2.76 and 2.76–4.10 days, respectively, at 25 °C depending on the native isolates. The concentration–mortality response showed a statistically significant difference between some isolates B. bassiana tested against adult O. japonica individuals (P < 0.05). With an LC50 value of 2.29 × 106 conidia ml–1, the lowest effective EPF isolate for O. japonica was KA-78-14. The isolates caused 100% adult mortality in O. japonica within five days, while the mortality in the control group was less than 10%.ConclusionsThese findings suggest that some B. bassiana isolates were more virulent on O. japonica and may play an important role in the biocontrol of O. japonica in Turkey.

Susceptibility of a Mexican Field-Collected Wild Population of Diaphorina citri (Hemiptera: Liviidae) to Selected Insecticides

Abstract The Asian citrus psyllid, Diaphorina citri (Kuwayama) (Hemiptera: Liviidae), is a severe pest of citrus orchards worldwide. Its control is based mainly on the use of conventional insecticides, and resistance to many of those compounds is widespread. Phenotypic bioassays to detect resistance compare the response of a field-collected population with a laboratory-reared population that is susceptible to insecticides. This comparison usually does not involve a susceptible field-collected counterpart since its existence is currently rare. We found an isolated field population of D. citri living on a wild host, orange jasmine (Murraya paniculata [L.] Jack). Considering its lifetime fly capacity, gene flow with any insecticide-treated population was nonexistent or negligible. Thus, we determined the response in fourth-instar nymphs and unsexed 2- to 5-d-old adults in bioassays of commercial formulations of the commonly used insecticides chlorpyrifos, malathion, imidacloprid, and spinosad. In the bioassays, insects were placed on leaf discs previously immersed for 10 s in the respective insecticide concentrations. For adults, the lowest concentration–mortality response was with chlorpyrifos (lethal concentration 50 [LC50] of 0.72 mg L-1 and lethal concentration 95 [LC95] of 1.02 mg L-1). The highest toxicity response was with malathion (LC95 of 0.05 mg L-1). The highest toxicity response with fourth-instar nymphs was observed with spinosad (LC50 of 0.007, LC95 of 0.021 mg L-1). The estimated LC50 and LC95 values for chlorpyrifos, malathion, and spinosad were lower than those documented worldwide for these insecticides in susceptible populations of D. citri.

Evaluation of Metarhizium rileyi Farlow (Samson) impregnated with azadirachtin and indoxacarb against Helicoverpa armigera (Hubner)

BackgroundEntomopathogenic fungi are the most versatile having a wide host range, capable of infecting insects at different developmental stages. In the present study, Metarhizium rileyi, at the concentrations of 102, 103, 104, 105, 106, 107 and 108 conidia/ml and sub-lethal concentrations of azadirachtin (1.02 and 1.53 ppm) and indoxacarb (0.72 ppm) were evaluated against the 1st, 2nd, 3rd, 4th and 5th larval instars of Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae) under laboratory conditions.ResultsM. rileyi applied at 106 conidia/ml caused a maximum mortality of 83.33 and 80.00% of 1st and 2nd larval instars of H. armigera, respectively. The maximum mortality of 3rd, 4th and 5th larval instars of H. armigera with 108 conidia/ml of M. rileyi was 83.33, 76.67 and 53.33%, respectively. When M. rileyi blended with azadirachtin at 1.02 ppm, the highest mortality rate of 86.21% at 106 conidia/ml against 2nd instar larvae was resulted. Similarly, M. rileyi applied at 108 conidia /ml mixed with azadirachtin (1.53 ppm) showed 89.66% mortality of 3rd instar larvae. The 2nd instar larvae treated with M. rileyi at 106 conidia/ml, mixed with indoxacarb (0.72 ppm), the corrected mortality rate was 82.14%. Concentration mortality response of 3rd instar larvae to M. rileyi blended with indoxacarb (0.72 ppm) was 85.71% at 108 conidia/ml. The median lethal concentration (LC50) values were 5.51 × 103, 1.86 × 104, 2.81 × 105 and 5.55 × 105 conidia/ml for 1st, 2nd, 3rd and 4th larval instars, respectively, after 7 days of treatment. M. rileyi when mixed with sub-lethal concentrations of azadirachtin (1.02 ppm) and indoxacarb (0.72 ppm) resulted LC50 values of 1.09 × 104 conidia/ml and 1.37 × 104 conidia/ml against 2nd instar larvae, respectively, after 24 hours. Similarly, M. rileyi mixed with sub-lethal concentrations of azadirachtin (1.53 ppm) and indoxacarb (0.72 ppm) resulted LC50 values of 3.12 × 108 and 3.06 × 105 conidia/ml against 3rd instar larvae, respectively, after 24 hours. The study revealed that the susceptibility of larvae decreased in case of large larval instars.ConclusionsM. rileyi can be utilized as one of the component of Integrated Pest Management Program for the eco-friendly management of H. armigera. As the application of M. rileyi @ 107 conidia/ml alone or in combination with azadirachtin (1.02 and 1.53 ppm) or indoxacarb (0.72 ppm) resulted to the highest mortality.

Lethal and sublethal effects of synthetic and bio-insecticides on Trichogramma brassicae parasitizing Tuta absoluta.

The tomato leaf miner (TLM), Tuta absoluta (Meyrick), is an invasive tomato pest found worldwide. Sustainable control strategies aimed at increasing biological control approaches and decreasing chemical inputs are required, due to the tendency to develop insecticide resistance. In this study, the lethal and sublethal effects of four chemical insecticides (abamectin, indoxacarb, chlorantraniliprole, and spinosad) and the sublethal effects of the entomopathogenic fungus Metarhizium anisopliae (Metschnikoff) on a widespread TLM egg parasitoid, Trichogramma brassicae Bezdenko, were estimated. Concentration mortality response bioassays enabled the estimation of lethal concentrations of the tested insecticides for the parasitoids, with chlorantraniliprole having the lowest LC50 and indoxacarb the highest. The LC25 and LC50 of the tested insecticides on the TLM were sprayed on eggs and then offered at three time intervals to the parasitoids. The fertility and other life table parameters of the individuals emerging from the treated eggs were estimated. All of the chemical insecticides, but not the fungus, had harmful effects on T. brassicae. The insecticide applications caused a 3.84–5.17 times reduction in the net reproductive rate (R0) compared with the control. No parameters were affected by spraying the fungus in the 0h treatment, but effects were recorded at 24 and/or 48h, except for the gross reproduction rate (GRR). The value of the intrinsic rate of increase (rm) also decreased to 0.528–0.617 after the insecticide treatments. The doubling time (DT) increased in all treatments compared to the control. Nevertheless, the generation time (T) was only very slightly affected. In addition, in the combination experiments, M. anisopliae showed a remarkable synergism with T. brassicae in controlling TLM eggs. These results indicate that low levels of lethal effects on key biological control agents should be considered in the choice of insecticides to be included in sustainable TLM control packages.

Monitoring and mechanisms of insecticide resistance in Spodoptera exigua (Lepidoptera: Noctuidae), with special reference to diamides

The beet armyworm, Spodoptera exigua, is a major lepidopteran pest of global importance in cultivation of numerous crops including cotton, maize, soybean, onion, cabbage, and ornamentals. It has evolved resistance to different insecticides. However, the current status of insecticide resistance in S. exigua has not been well examined in China. In this study, concentration-mortality responses of S. exigua to seven insecticides, including chlorantraniliprole, tetraniliprole, methoxyfenozide, indoxacarb, chlorfenapyr, emamectin benzoate and beta-cypermethrin were evaluated. The results showed that most of the tested populations had developed moderate to high resistance to chlorantraniliprole, with resistance ratios ranging from 6.3 to 2477.3-fold. Our results also showed that chlorantraniliprole have cross-resistance with tetraniliprole in S. exigua. The AY19 population collected from Anyang in Henan Province in 2019 exhibited a high resistance level to beta-cypermethrin (RR = 277.5). Methoxyfenozide and chlorfenapyr were highly effective against all of the tested populations with resistance ratios (RR) ranging from 0.1 to 2.2-fold. One of the tested populations showed moderate resistance to indoxacarb and emamectin benzoate. We detected the known ryanodine receptor target site resistance mutation, I4743M, in the field populations of S. exigua with different levels of diamide resistance.

Concentration–Mortality Response of Mexican Populations Fall Armyworm (Lepidoptera: Noctuidae) to Commercial Formulations of Bacillus Thuringiensis

Abstract The fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), is the most economically important pest of maize (Zea mays L.) grown in Mexico. In order to identify biologically based management tactics for this pest, we determined the concentration–mortality response of 16 S. frugiperda populations collected in Mexico to two commercial formulations of Bacillus thuringiensis Berliner (Bt) (XenTari® [Bt subsp. aizawai] and DiPel® [Bt subsp. kurstaki]; Valent de México SA De CV, Jalisco, México). Laboratory bioassays established median lethal concentrations (LC50s) for each Bt formulation × population combination. We also determined mean larval weight 7 d after exposure and the number of larvae that reached the third instar of development. The populations were susceptible to both Bt formulations but they were, overall, more susceptible to Bt subsp. aizawai (XenTari) than to Bt subsp. kurstaki (DiPel). These results can serve as a reference to detect changes in S. frugiperda response to these Bt commercial products over time.

RNA Interference-Based Silencing of the Chitin Synthase 1 Gene for Reproductive and Developmental Disruptions in Panonychus citri.

Simple SummaryThe Chitin Synthase 1 gene, when suppressed with RNAi, imparts differences in the structural development, physiology, and synthesis of epidermal chitin, which ultimately leads to the mortality of the target pest. The results presented here will help to illuminate the molecular mechanism and function of the PcCHS1 gene, which regulates the egg-laying potential in adult citrus red mites. Using the leaf dip method, we found that dsRNA was potent and effective, and significantly reduced the egg-laying potential and hatching of citrus red mite eggs. These results show the potential utility of the PcCHS1 gene in the development of novel RNA interference strategies for controlling the citrus red mite.Chitin synthase 1 (CHS1) is an essential gene regulating chitin during different developmental stages of arthropods. In the current study, we explored for the first time the role of CHS1 gene regulation in the citrus red mite, Panonychus citri (McGregor) (Acari: Tetranychidae), by silencing its expression using (RNA interference) RNAi-based strategies. The results reveal that P. citri tested in different developmental stages, including larvae, protonymphs, deutonymphs, and adults fed on sweet orange leaves dipped in various concentrations (200, 400, 600, and 800 ng/μL) of dsRNA-PcCHS1, resulted in a continuous reduction in their gene expression, and the extent of transcript knockdown was positively correlated with the concentration of dsRNA. Concentration–mortality response assays revealed a mortality of more than 50% among all the studied developmental stages, except for adulthood. Furthermore, the target gene dsRNA-PcCHS1 treatment of larvae, protonymphs, deutonymphs, and females at a treatment rate of 800 ng/mL of dsRNA significantly decreased the egg-laying rates by 48.50%, 43.79%, 54%, and 39%, respectively, and the hatching rates were also considerably reduced by 64.70%, 70%, 64%, and 52.90%, respectively. Moreover, using the leaf dip method, we found that the RNA interference effectively reduced the PcCHS1 transcript levels by 42.50% and 42.06% in the eggs and adults, respectively. The results of this study demonstrate that the RNAi of PcCHS1 can dramatically reduce the survival and fecundity of P. citri, but the dsRNA concentrations and developmental stages can significantly influence the RNAi effects. These findings indicate the potential utility of the PcCHS1 gene in causing developmental irregularities, which could aid in the development of effective and novel RNAi-based strategies for controlling P. citri.

Potential Synergy between Spores of Metarhizium anisopliae and Plant Secondary Metabolite, 1-Chlorooctadecane for Effective Natural Acaricide Development.

Date palm dust mites are important pests severely infesting valuable nutritious fruits (dates) of date palm. In search of an alternative to acaricides, joint action of Metarhizium anisopliae EBCL 02049 spores and 1-Chlorooctadecane was evaluated as a potential candidate for the management of Oligonychus afrasiaticus through natural products. In this regard, in vitro tests were performed to evaluate the interaction of M. anisopliae spores with multiple doses of 1-Chlorooctadecane (0.8, 1.6, 2.4, 3.2, and 4.0 mg/mL). Compatibility bioassay results evidenced from vegetative growth (77.7–84.40 mm), sporulation (5.50–7.30 × 106 spores/mL), and germination (96.70–98.20%), revealed that all the tested doses are compatible (biological index > 82) with the spores of M. anisopliae. The impact of combined treatment of spores with 1-Chlorooctadecane in different proportions (Scheme I, II, III, and IV) compared to their sole application against O. afrasiaticus was evaluated by concentration–mortality response bioassays. Results showed that all the combined treatments revealed high mortality compared to the sole application, which showed relatively slow mortality response over time. Toxicity recorded from Scheme IV combinations (80% 1-Chlorooctadecane: 20% Spores), exhibited strong synergistic interaction (joint toxicity = 713). Furthermore, potent interactions have overcome the host antioxidant defense at the final stage of infection by tremendously reducing catalase, and superoxide dismutase activities. These experiments demonstrated fungal–toxin joint synergistic interaction as a promising date palm dust mite management option.

The Time-Concentration-Mortality Responses of Western Flower Thrips, Frankliniella occidentalis, to the Synergistic Interaction of Entomopathogenic Fungus Metarhizium flavoviride, Insecticides, and Diatomaceous Earth.

Western flower thrips (WFT), Frankliniella occidentalis (Pergande), is a highly invasive pest which is harmful to many cash crops globally and resistant to various insecticides. Entomopathogenic fungi (EPF), as biological control agents, have demonstrated a good control effect on WFT. The aim of this study was to evaluate the synergistic and pathogenicity efficacy of the fungal strain Metarhizium flavoviride WSWL51721 when distributed with diatomaceous earth (DE) and the active ingredient imidacloprid using four bioassay methods against adult and second instar larvae of WFT. The data of the four bioassays have been fitted to the time–concentration–mortality (TCM) model. The corrected mortality ranges of WFT adults were 75–100%, 82.69–100%, 78.85–100%, and 92.31–100%, and the corrected mortality ranges of WFT second instar larvae were 72.22–100%, 85.19–100%, 77.77–100%, and 100% in the four bioassays at concentrations of 1.2 × 106 to 1.2 × 108 conidia/mL, respectively. At 1.2 × 108 conidia/mL, assays 2 (M. flavoviride with DE), 3 (M. flavoviride with imidacloprid), and 4 (M. flavoviride with DE and imidacloprid) had the shortest median lethal time (LT50), compared with that of assay 1 (M. flavoviride alone) for adults at 2.26 d, 2.06 d, and 1.53 d, and second instar larvae at 2.45 d, 1.70 d, and 1.41 d, respectively. The median lethal concentration (LC50) in the four bioassays decreased within 3–10 days of inoculation. On the third day, it was found that the lowest median lethal concentrations in assays 2, 3, and 4 were 1.58 × 107, 1.13 × 107, and 3.39 × 106 conidia/mL, respectively, which were significantly different from that in assay 1 for the adults. For the second instar larvae, assays 2, 3, and 4 also had the lowest lethal concentrations and were significantly different from those of assay 1. There were significant differences in sporulation between adults and second instar larvae under the four bioassays. Our results indicate that assays 2 (M. flavoviride with DE), 3 (M. flavoviride with imidacloprid), and 4 (M. flavoviride with DE and imidacloprid) demonstrate synergistic effects on the control of both adult and second instar larvae of WFT under laboratory conditions.

Inheritance and fitness costs of sulfoxaflor resistance in Nilaparvata lugens (Stål).

Sulfoxaflor has been considered as a new tool for Nilaparvata lugens control in the field. In this study, a laboratory-selected resistant strain and a susceptible strain were used to evaluate the inheritance and fitness costs of sulfoxaflor resistance in N. lugens. The resistant strain (SFX-SEL) showed 123.63-fold resistance compared with the susceptible strain (SS). Progenies of reciprocal crosses (F1 RS and F1 SR) showed similar concentration-mortality responses (LC50 ) to sulfoxaflor and also exhibited a similar degree of dominance; -0.16 for F1 RS and -0.26 for F1 SR. Significant differences between the observed and expected mortalities of F2 individuals suggested that sulfoxaflor resistance is associated with multiple genes. The resistant strain had a relative fitness of 0.75 with substantially decreased female adult period, oviposition days, total fecundity, egg hatchability and female adult survival rate, and prolonged pre-adult period and total pre-oviposition period. Sulfoxaflor resistance in N. lugens was inherited as autosomal, incompletely recessive and multigene. The development of resistance may have a significant fitness cost for the resistant population. Current research provides valuable information for researchers to establish management strategies to delay the development of sulfoxaflor resistance and control N. lugens sustainably in the field. © 2019 Society of Chemical Industry.

Quantification of dose-mortality responses in adult Diptera: Validation using Ceratitis capitata and Drosophila suzukii responses to spinosad.

Quantitative laboratory bioassay methods are required to evaluate the toxicity of novel insecticidal compounds for pest control and to determine the presence of resistance traits. We used a radioactive tracer based on 32P-ATP to estimate the volume of a droplet ingested by two dipteran pests: Ceratitis capitata (Tephritidae) and Drosophila suzukii (Drosophilidae). Using blue food dye it was possible to distinguish between individuals that ingested the solution from those that did not. The average volume ingested by C. capitata adults was 1.968 μl. Females ingested a ~20% greater volume of solution than males. Adults of D. suzukii ingested an average of 0.879 μl and females ingested ~30% greater volume than males. The droplet feeding method was validated using the naturally-derived insecticide spinosad as the active ingredient (a.i.). For C. capitata, the concentration-mortality response did not differ between the sexes or among three different batches of insects. Lethal dose values were calculated based on mean ingested volumes. For C. capitata LD50 values were 1.462 and 1.502 ng a.i./insect for males and females, respectively, equivalent to 0.274 and 0.271 ng a.i./mg for males and females, respectively, when sex-specific variation in body weight was considered. Using the same process for D. suzukii, the LD50 value was estimated at 2.927 ng a.i./insect, or 1.994 ng a.i./mg based on a mean body weight of 1.67 mg for both sexes together. We conclude that this technique could be readily employed for determination of the resistance status and dose-mortality responses of insecticidal compounds in many species of pestiferous Diptera.

Mortality, Biological, and Biochemical Response ofMusca domestica(Diptera: Muscidae) to Selected Insecticides1

Abstract The concentration–mortality response of Musca domestica L. (Diptera: Muscidae) to nine insecticides, and the impacts of these insecticides on selected biological and biochemical parameters of the insect, were determined in laboratory assays. Adults displayed a concentration-dependent response for each insecticide. Median lethal concentration (LC50) values in baits were: acetamiprid (0.39 μg/ml), bifenthrin (0.22 μg/ml), chlorpyriphos (0.21 μg/ml), deltamethrin (0.41 μg/ml), emamectin benzoate (0.001 μg/ml), fipronil (0.002 μg/ml), imidacloprid (0.27 μg/ml), profenophos (0.63 μg/ml), and lufenuron (0.001 μg/ml). Based on 95% confidence intervals, fipronil proved to be the most lethal of the insecticides tested. LC10, LC30, and LC50 values of each of the insecticides were used to assess impacts on M. domestica longevity, fecundity, percentage eclosion, larval duration, percentage pupation, pupal weight, pupal duration, adult emergence, and sex ratio. In general, development parameters, with the ex...

Geographical variation in susceptibility of tea red spider mite, Oligonychus coffeae (Nietner) (Acari: Tetranychidae) to commonly used acaricides in tea plantations of Assam, north east India

ABSTRACTThe tea red spider mite, Oligonychus coffeae, is one of the most destructive pests of tea in the world which is mainly managed by chemical acaricides. In the present study, concentration-mortality responses of O. coffeae from eight tea geographical populations along with a laboratory susceptible strain against five acaricides, viz., ethion, dicofol, propargite, fenazaquin and fenpropathrin were assayed based on standard leaf-dipped method. Although observed levels of susceptibility varied between populations and acaricides, population from Cachar region registered a high LC50 value to most of the acaricides evaluated. Almost all of the tested field populations had developed high to very high level of resistance to ethion and dicofol, with resistance ratios ranging from 13.58 to 134.27-fold. Fenazaquin and propargite were very effective against O. coffeae in all tested populations, while fenpropathrin showed minor variation in their susceptibility. Significant positive correlation was only observed between the LC50 values of ethion and dicofol (r = 0.95, P = 0.005) suggesting the potential for cross-resistance. These results indicated that control failure was associated with resistance to ethion and dicofol therefore reinforcing the need of resistance management program and offered useful information about alternative acaricides to control O. coffeae.

Postharvest fumigation of California table grapes with ozone to control Western black widow spider (Araneae: Theridiidae)

Ozone fumigations were evaluated for postharvest control of Western black widow spider (BWS), Latrodectus hesperus (Chamberlin and Ivie), in fresh table grapes destined for export from California USA. Mature adult female black widow spiders were contained in separate gas-permeable cages within a flow-through vacuum chamber and exposed for 1h at 3±1°C (x¯±s) and 67.5kPa to gaseous ozone at eight steady-state concentrations (i.e, [O3]ss) over the range 0.71±0.04–16.91±0.28gm−3 (x¯±s) (i.e., 500±25–12,000±200ppmv (μLL−1)) with or without supplementation of atmospheric carbon dioxide levels, respectively 129.3 or ca. 0.8gm−3 [CO2]ss (i.e., 100,000 or ca. 600ppmv). Regression models of the concentration-mortality response predict 98% mortality of adult female BWS populations following ozone fumigation for 1h at 3±1°C when headspace [O3]ss is maintained at ∼14gm−3 (i.e., 10,000ppmv) with ambient atmospheric CO2 levels ([CO2]ss=0.8gm−3). Providing evidence to support the use of these treatment parameters for control of BWS in packed table grapes, 0 survivors were observed from 268 total specimens treated in a series of confirmatory fumigations conducted for 1h at 3±1°C and 67.5kPa with headspace [O3]ss and [CO2]ss maintained ≥14 and ca. 0.8gm−3, respectively.

Behavioral and hormetic effects of the butenolide insecticide, flupyradifurone, on Asian citrus psyllid, Diaphorina citri

Huanglongbing (HLB) or citrus greening is an economically important disease of citrus associated with the bacterium ‘Candidatus Liberibacter asiaticus’. The pathogen is transmitted by the Asian citrus psyllid, Diaphorina citri Kuwayama. Currently, insecticide management of D. citri and removal of infected trees are the only means of decreasing HLB infections. Therefore, with continuous use of insecticides, resistance is one of the most important problems facing citrus production. Flupyradifurone is a new generation butenolide insecticide that has been shown to deter insect feeding and reduce pathogen transmission. We determined the concentration-mortality response of D. citri to flupyradifurone. We also quantified sublethal effects of flupyradifurone on D. citri feeding, settling, flight behaviors, as well as, fecundity of females. We found that after 24 and 48 h of exposure, the LC50 was 0.39 ng/μl (0.16–0.82) in a bottle bioassay and 10.43 ng/μl (2.07–55.87) in a leaf dip bioassay, respectively. D. citri that fed on citrus leaves treated with 0.001, 0.02, 0.39, 8.25 and 130.13 ng/μl solution of flupyradifurone excreted significantly less honeydew (8–83%) compared with a negative control; feeding inhibition occurred in a concentration dependent manner suggesting an antifeedant effect of flupyradifurone. There was no effect of flupyradifurone on D. citri settling behavior at 24 and 48 h after leaf treatment. However, there were significantly fewer adults on treated leaves at 72 h after treatment compared to untreated leaves. D. citri exposed to sublethal concentrations of flupyradifurone initiated flight at greater frequency than negative controls. D. citri exposed to sublethal concentrations (LC10 and LC25) of flupyradifurone laid more eggs than those treated with the negative control. Exposure to lethal and sublethal concentrations of flupyradifurone induced hormesis in D. citri with respect to fecundity. Our data indicate that flupyradifurone may be a useful tool for managing D. citri; however, unexpected sublethal effects must be considered when integrating this chemistry into management programs.

Pathogenicity of selected entomopathogenic fungal isolates against the oak lace bug, Corythucha arcuata Say. (Hemiptera: Tingidae), under controlled conditions

Corythucha arcuata (Say) (Hemiptera: Tingidae) is a pest of oaks that is highly distributed in several regions of the world, including North America, the Balkan Peninsula, Europe, and Turkey. In the present study, ten entomopathogenic fungi belonging to four different genera (Metarhizium (×4), Beauveria (×4), Isaria (×1), and Myriodontium (×1)) were tested against nymphs and adults of C. arcuata under laboratory conditions. Based on the initial screening studies, it was shown that all isolates were able to infect both nymph and adult individuals of the pest after application of 1 × 10 7 mL -1 conidial concentration. Among the tested isolates, Beauveria bassiana KTU-24 caused the highest mortality against both nymphs and adults within 14 days, with 80% and 90% mortality, respectively. This isolate also produced the highest mycosis values on both nymphs and adults, with 77% and 83% mycosis, respectively. Therefore, this isolate (B. bassiana KTU-24) was selected for concentration-mortality response tests for further characterization. The concentration- mortality response tests showed that the conidial concentrations of 1 × 10 8 and 1 × 10 9 mL -1 of B. bassiana KTU-24 produced 100% mortality against nymphs and the conidial concentration of 1 × 10 9 mL -1 of this isolate caused 100% mortality against adults. Based on probit analysis, the LC 50 values of the isolate B. bassiana KTU-24 were calculated as 1.17 × 10 7 and 6.44 × 10 6 conidia mL -1 against nymphs and adults, respectively. This study indicates that B. bassiana KTU-24 has a significant potential for further investigation as biological control agent against C. arcuata.

Estimation of future PM2.5- and ozone-related mortality over the continental United States in a changing climate: An application of high-resolution dynamical downscaling technique

This paper evaluates the PM2.5- and ozone-related mortality at present (2000s) and in the future (2050s) over the continental United States by using the Environmental Benefits Mapping and Analysis Program (BenMAP-CE). Atmospheric chemical fields are simulated by WRF/CMAQ (horizontal resolution: 12 × 12km), applying the dynamical downscaling technique from global climate-chemistry model under the Representative Concentration Pathways scenario (RCP 8.5). Future air quality results predict that the annual mean PM2.5 concentration in continental U.S. decreases nationwide, especially in the Eastern U.S. and west coast. However, the ozone concentration is projected to decrease in the Eastern U.S. but increase in the Western U.S. Future mortality is evaluated under two scenarios (1) holding future population and baseline incidence rate at the present level and (2) using the projected baseline incidence rate and population in 2050. For PM2.5, the entire continental U.S. presents a decreasing trend of PM2.5-related mortality by the 2050s in Scenario (1), primarily resulting from the emissions reduction. While in Scenario (2), almost half of the continental states show a rising tendency of PM2.5-related mortality, due to the dominant influence of population growth. In particular, the highest PM2.5-related deaths and the biggest discrepancy between present and future PM2.5-related deaths both occur in California in 2050s. For the ozone-related premature mortality, the simulation shows nation-wide rising tendency in 2050s under both scenarios, mainly due to the increase of ozone concentration and population in the future. Furthermore, the uncertainty analysis shows that the confidence interval of all causes mortality is much larger than that for specific causes, probably due to the accumulated uncertainty of generating datasets and sample size. The confidence interval of ozone-related all cause premature mortality is narrower than the PM2.5-related all cause mortality, due to its smaller standard deviation of the concentration-mortality response factor.Implications: The health impact of PM2.5 is more linearly proportional to the emission reductions than ozone. The reduction of anthropogenic PM2.5 precursor emissions is likely to lead to the decrease of PM2.5 concentrations and PM2.5 related mortality. However, the future ozone concentrations could increase due to increase of the greenhouse gas emissions of methane. Thus, to reduce the impact of ozone related mortality, anthropogenic emissions including criteria pollutant and greenhouse gas (i.e. methane) need to be controlled.

Monitoring Field Populations ofPlutella xylostella(Lepidoptera: Plutellidae) for Resistance to Eight Insecticides in China

The diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), is the main destructive insect pest of brassicaceous vegetables around the world. It has developed resistance to various classes of insecticides. However, the current status of insecticide resistance in P. xylostella has not been examined in China. In this study, concentration-mortality responses of P. xylostella to 8 insecticides, including abamectin, chlorantraniliprole, spinosad, beta-cypermethrin, chlorfenapyr, diafenthiuron, chlorfluazuron and the bio-pesticide Bacillus thuringiensis kurstaki (Btk) were evaluated. The results showed that almost all of the tested populations had developed high to very high resistance to abamectin and beta-cypermethrin, with resistance ratios ranging from 62.9 to 1494.7-fold. Chlorantraniliprole was very effective against P. xylostella in most tested populations except those from Taihe and Wuxi. Approximately 61% of tested populations displayed moderate resistance to spinosad, while other field populations showed minor changes (3-fold) in their susceptibility to this insecticide. Obvious variation (93-fold) of susceptibility to chlorfenapyr existed in field populations of which 32% displayed low level resistance, and 36% exhibited moderate resistance. Only one field population (Wuxi) showed very high resistance to chlorfenapyr (RR = 260.1). Diafenthiuron and chlorfluazuron were highly effective against all of the tested populations with resistance ratios (RR) ranging from 0.4 to 8.7 — fold. Decreased susceptibility ranging to moderate resistance to Btk was observed (RR = 3.8 – 35.3). Significant correlations were detected between the values of logLC50 of chlorantraniliprole and 4 insecticides (abamectin, spinosad, beta-cypermethrin and chlorfenapyr). The results of this study provided valuable information for choosing alternative insecticides and for integrated resistance management of P. xylostella.