Lethal Exposure Time Research Articles

Comparison on mortality, pupation, and emergence of Plodia interpunctella (hübner) treated by 2, 4, 6, and 8% carbon dioxide mixed with 2 and 4% oxygen at three temperatures

Low concentration CO2 (e.g., 2–8%) mixed with 2–4% O2 balanced by N2 is more economically feasible than applying 99.99% N2 alone. Mortality, pupation, and emergence of the fifth instar larvae of Plodia interpunctella (Lepidoptera: Pyralidae) were tested in 2 or 4% O2 mixed with 2, 4, 6, or 8% CO2 balanced by N2 at 28, 23, and 18 °C. Mortality of eggs, second instar larvae, and pupae was tested in the mixture of 2% O2, 4% CO2, and 94% N2 at the three temperatures. When fifth instar larvae were exposed in 2% O2 mixed with 0, 2, 4, 6, and 8% CO2 or increasing temperature, the LT50, LT99 value, and time reaching 100% mortality was decreased significantly. Exposing in 4% O2 mixed with 0, 2, 4, 6, and 8% CO2, the pupation and emergence of the surviving fifth instar larvae were also decreased significantly, and reduced more in higher temperatures. This study found 2, 4, 6, and 8% CO2 had additive effect to low O2 on insect mortality, pupation, and emergence at any tested temperature, and higher CO2 concentration or temperature resulted in a higher additive percentage. The fifth instar was the most tolerant stage to the gas mixtures followed by second instar larvae, pupae, and egg; and increasing temperature would sufficiently decrease the lethal exposure time.

Effect of a low oxygen and high carbon dioxide modified atmosphere on the mortality of different life stages of Carpophilus hemipterus

• Modified atmosphere (2.1% O 2 with 90% CO 2 ) was evaluated in terms of efficacy at 20 °C. • Different life stages of Carpophilus hemipterus were exposed to MA for 48–120 h. • LT 95 values are 221 h, 82 h and 65 h for egg, larva and adult, respectively. • Based on LT 95 values, tolerance order was found as eggs > larvae > adults. Carpophilus hemipterus is an important cosmopolitan pest species that causes high economic losses in fruits before and after harvest. In this study, 0–2 d old eggs, 12 d old mature larvae and 1 week old adults of C. hemipterus were exposed to a modified atmosphere with low oxygen and high carbon dioxide content (2.1% O 2 + 90% CO 2 + 7.9% N 2 ) for 48–120 h at 20 °C and 75 ± 5% relative humidity. Time-mortality responses were subjected to probit analysis, and the difference between lethal exposure times (LTs) for the different life stages were compared using a lethal dose ratio test. LT 95 values were recorded as 221.83 h, 82.79 h and 65.31 h for egg, larval and adult stages, respectively. The statistical difference between LT 95 values was significant and egg stage was found to be more tolerant than the other two life stages. In addition, the larvae were found to be more tolerant than adults. According to the results of this study, a long time was needed to control the eggs of C. hemipterus .

Mortality and physiological impacts of the tea saponin against Ephestia kuehniella Zeller (Lepidoptera: Pyralidae)

The toxicity of a tea saponin (TS) was investigated on mortality, digestive system, detoxifying and antioxidant enzymes of Ephestia kuehniella Zeller. The larvae were fed on a diet containing different concentrations of TS (5, 10, 20, 40, and 80 mg/mL) to determine the lethal dose and the lethal exposure time. The LC50 of TS was calculated as 28 mg/mL while the LT5 value was found to be 4.14 days following the bioassay experiment. The activities of all enzymes except for lipase decreased in the TS-fed larvae, while the activities of general esterase and glutathione S-transferases as the detoxification enzymes significantly increased contradictory. Moreover, the larvae fed on TS demonstrated the higher activities of antioxidant enzymes including superoxide dismutase, peroxidase, and catalase in addition to the content of malondialdehyde. These findings indicated the significant toxic effects of TS on inhibition of digestive activities and induction of antioxidant enzymes which developed our knowledge on physiological disruptions due to TS treatment.

Evaluation of Hydrogen Peroxide Fumigation and Heat Treatment for Standard Emergency Arthropod Inactivation in BSL-3 Insectaries.

Climate change and global movements of people and goods have accelerated the spread of invasive species, including insects that vector infectious diseases, which threaten the health of more than half of the world’s population. Increasing research efforts to control these diseases include the study of vector – pathogen interactions, involving the handling of pathogen-infected vector insects under biosafety level (BSL) 2 and 3 conditions. Like microbiology BSL-3 laboratories, BSL-3 insectaries are usually subjected to fixed-term or emergency room decontamination using recognized methods such as hydrogen peroxide (H2O2) or formaldehyde fumigation. While these procedures have been standardized and approved for the inactivation of diverse pathogens on surfaces, to date, there are no current standards for effective room-wide inactivation of insects in BSL-3 facilities in case of an emergency such as the accidental release of a large number of infected vectors. As H2O2 is often used for standard room decontamination in BSL-3 facilities, we evaluated H2O2 fumigation as a potential standard method for the safe, room-wide deactivation of insects in BSL-3 insectaries in comparison to heat treatment. To account for physiological diversity in vector insect species, six species from three different orders were tested. For the H2O2 fumigation we observed a strong but also varying resilience across all species. Lethal exposure time for the tested dipterans ranged from nine to more than 24 h. Furthermore, the coleopteran, Tribolium castaneum, did not respond to continuous H2O2 exposure for 48 h under standard room decontamination conditions. In contrast, temperatures of 50°C effectively killed all the tested species within 2 to 10 min. The response to lower temperatures (40–48°C) again showed a strong variation between species. In summary, results suggest that H2O2 fumigation, especially in cases where a gas generator is part of the laboratory equipment, may be used for the inactivation of selected species but is not suitable as a general emergency insect inactivation method under normal room decontamination conditions. In contrast, heat treatment at 48 to 50°C has the potential to be developed as an approved standard procedure for the effective inactivation of insects in BSL-3 facilities.

Mortality of Different Stages of Plodia interpunctella (Lepidoptera: Pyralidae) at Three Temperatures in Controlled Atmosphere of High Nitrogen.

The lethal exposure time to controlled atmospheres of high nitrogen at stored grain temperatures is an important information for control of stored-product insects. The mortality of 1-d-old egg, 1-wk-old (first or second instar) larva, 3-wk-old (fourth or fifth instar) larva, and 1-d-old pupa of Plodia interpunctella (Hübner) was determined at 18 ± 1, 23 ± 1, and 28 ± 1°C in 98% N2 mixed with air. At 18°C, the lethal exposure times to achieve 100% mortality were 12.7 ± 0.7, 16.3 ± 0.3, 19.7 ± 0.7, and 14.7 ± 0.7 d for 1-d-old egg, 1-wk-old larva, 3-wk-old larva, and 1-d-old pupa, respectively. Temperature had significant effect on the lethal exposure time, and increase of the temperature significantly decreased the lethal exposure time. The order of the insect stages from the highest to lowest for LT50 values was follows: 3-wk-old larva > 1-wk-old larva > 1-d-old pupa ≥ 1-d-old egg. The minimum lethal exposure times required to kill all stages of P. interpunctella were about 20, 16, and 12 d at 18, 23, and 28°C, respectively.

Cold Tolerance and Supercooling Capacity of the Redbanded Stink Bug (Hemiptera: Pentatomidae).

The redbanded stink bug Piezodorus guildinii (Westwood) (Hemiptera: Pentatomidae) is an invasive stink bug species in the United States. First documented as a soybean pest in Louisiana in the year 2000, this species continues to spread in the Mid-South region of the United States. We designed laboratory and field studies to investigate supercooling points, lethal exposure time (LT), critical thermal minimum (CTmin), and winter mortality of this species. The mean supercooling points (SCP) ± SE of adult field collected P. guildinii ranged from -8.3 ± 0.2°C (highest) in March to -11.0 ± 0.2°C (lowest) in January. Significant differences in SCP occurred over the months and between sexes with significant interactions between month and sex. The CTmin was significantly different between adults and nymphs (third, fourth, and fifth instars combined). LT50 and LT90 were evaluated at subzero temperatures of 0°C, -2°C, and -5°C. There were significant differences in LT50 and LT90 among the temperature treatments. Winter survival significantly differed between the two study years and decreased with progression of winter months.

Toxicity of Aqueous Alkaline Solutions to New Zealand Mudsnails, Asian Clams, and Quagga Mussels

Abstract We modeled the toxicity response of three important aquatic nuisance species to alkaline solutions of pH 12 to explore the potential use of chemical treatments for decontaminating infested water distribution systems, tanks, and other facilities in confined freshwater environments. Groups of quagga mussels Dreissena bugensis, New Zealand mudsnails Potamopyrgus antipodarum, and Asian clams Corbicula fluminea were tested in temperatures from 19 to 22°C in aqueous solutions adjusted to pH 12 with NaOH. The predicted 99% lethal exposure time (LT99) for adult-sized quagga mussels and New Zealand mudsnails respectively was 31.3 and 35.1 h. Longer exposures were needed to kill adult-sized Asian clams (LT99 = 208.9 h). Because of the worldwide use of NaOH as an alkaline reagent in a variety of industrial and pesticide applications, and its ease of neutralization with CO2, elevating the pH of freshwater solutions with NaOH may be a practicable management tool to remove nuisance species in biofouled canals, pipes, hatchery tanks, and other confined structures.

Laboratory Activity to Promote Student Understanding of UV Mutagenesis and DNA Repair.

Changes in DNA molecules are common, due to the effects of UV light and other external and internal mutagens. Cells have a variety of repair mechanisms which serve to maintain the accuracy of the genetic code. This activity includes a low-cost, safe and technically feasible experiment, which allows students to observe the effects of UV mutagenesis and DNA photorepair in the halophilc archaeon, Haloferax volcanii. An optional extension links this activity to topics of immediate concern to students – how exposure to UVC light contributes to skin cancer risk and the protective effects of sunscreen. Students design and carry out an experiment to test whether SPF 15 sunscreen increases the lethal exposure time for H. volcanii by a factor of 15. Throughout the activity, discussion questions engage students in actively thinking about the biological phenomena and experimental procedures and analysis. This activity is designed for students in college or university genetics, microbiology, or introductory biology courses as well as in high school honors biology courses. Teachers report that this activity was valuable in helping students understand mutagenesis and photorepair and in developing student skills in designing and analyzing experiments.

Efficacy of indoxacarb and chlorfenapyr against Subterranean termite Heterotermes indicola (Wasmann) (Isoptera: Rhinotermitidae) in the laboratory

Efficacy, feeding deterrence and transfer of indoxacarb and chlorfenapyr by the subterranean termite, Heterotermes indicola (Wasmann), were evaluated in laboratory tests at Nuclear Institute for Food and Agriculture (NIFA), Peshawar, Pakistan during 2013-2014. Chemical concentrations tested ranged from 1 to 100 ppm (wt/wt) of indoxacarb and 1 to 7 ppm (wt/wt) of chlorfenapyr. Observations revealed that indoxacarb caused rapid mortality at doses > 50 ppm. At 10 ppm, mortality was relatively slower and ELT50 and ELT90 (effective lethal exposure times for 50 and 90% mortality) were recorded as 6.7 and 25.3 d, respectively. At concentrations below 10 ppm, it took longer for indoxacarb to cause 100% mortality. In comparison, chlorfenapyr caused rapid mortality at all tested concentrations except the lowest concentration of 1 ppm, and 100% mortality occurred at 9 d, ELT50 and ELT90 calculated as 2.7 and 8.6 d, respectively. Various concentrations of both termiticides ranging from 1 to 100 ppm (wt/wt) were evaluated in feeding deterrence and transfer studies. The results showed that indoxacarb did not deter feeding of H. indicola at any concentration, and only consumption of filter paper treated with 100 ppm indoxacarb resulted in 100% mortality. Chlorfenapyr did not deter feeding at concentrations below 100 ppm. Mortality remained low regardless of concentration and did not exceed 60% in the feeding deterrence tests. In transfer studies, indoxacarb was successfully transferred from donors to recipients at concentrations of 70 and 100 ppm. Chlorfenapyr transfer generally caused low recipient mortality and transfer from donors to recipients was only evident at 1 ppm where recipient mortality exceeded 80%

Assessing Insecticide Susceptibility of LaboratoryLutzomyia longipalpisandPhlebotomus papatasiSand Flies (Diptera: Psychodidae: Phlebotominae)

Chemical insecticides are effective for controlling Lutzomyia and Phlebotomus sand fly (Diptera: Psychodidae) vectors of Leishmania parasites. However, repeated use of certain insecticides has led to tolerance and resistance. The objective of this study was to determine lethal concentrations (LCs) and lethal exposure times (LTs) to assess levels of susceptibility of laboratory Lutzomyia longipalpis (Lutz and Nieva) and Phlebotomus papatasi (Scopoli) to 10 insecticides using a modified version of the World Health Organization (WHO) exposure kit assay and Centers for Disease Control and Prevention (CDC) bottle bioassay. Sand flies were exposed to insecticides coated on the interior of 0.5-gallon and 1,000-ml glass bottles. Following exposure, the flies were allowed to recover for 24 h, after which mortality was recorded. From dose-response survival curves for L. longipalpis and P. papatasi generated with the QCal software, LCs causing 50, 90, and 95% mortality were determined for each insecticide. The LCs and LTs from this study will be useful as baseline reference points for future studies using the CDC bottle bioassays to assess insecticide susceptibility of sand fly populations in the field. There is a need for a larger repository of sand fly insecticide susceptibility data from the CDC bottle bioassays, including a range of LCs and LTs for more sand fly species with more insecticides. Such a repository would be a valuable tool for vector management.

A comparison of Reduced Life Expectancy (RLE) model with Haber's Rule to describe effects of exposure time on toxicity

The Reduced Life Expectancy (RLE) Model (LC50 = [ln(NLE) – ln(LT50)]/d) has been proposed as an alternative to Haber's Rule. The model is based on a linear relationship between LC50 (Lethal Exposure Concentration) and lnLT50 (Lethal Exposure Time) and uses NLE (Normal Life Expectancy) as a limiting point as well as a long term data point (where d is a constant). The purposes of this paper were to compare the RLE Model with Haber's Rule with available toxicity data and to evaluate the strengths and weaknesses of each approach. When LT50 is relatively short and LC50 is high, Haber's Rule is consistent with the RLE model. But the difference between the two was evident in the situation when LT50 is relatively long and LC50 is low where the RLE model is a marked departure from Haber's Rule. The RLE Model can be used to appropriately evaluate long term effects of exposure.

Invaders in hot water: a simple decontamination method to prevent the accidental spread of aquatic invasive non-native species.

Watersports equipment can act as a vector for the introduction and spread of invasive non native species (INNS) in freshwater environments. To support advice given to recreational water users under the UK Government’s Check Clean Dry biosecurity campaign and ensure its effectiveness at killing a range of aquatic INNS, we conducted a survival experiment on seven INNS which pose a high risk to UK freshwaters. The efficacy of exposure to hot water (45 °C, 15 min) was tested as a method by which waters users could ‘clean’ their equipment and was compared to drying and a control group (no treatment). Hot water had caused 99 % mortality across all species 1 h after treatment and was more effective than drying at all time points (1 h: χ2 = 117.24, p < 0.001; 1 day χ2 = 95.68, p < 0.001; 8 days χ2 = 12.16, p < 0.001 and 16 days χ2 = 7.58, p < 0.001). Drying caused significantly higher mortality than the control (no action) from day 4 (χ2 = 8.49, p < 0.01) onwards. In the absence of hot water or drying, 6/7 of these species survived for 16 days, highlighting the importance of good biosecurity practice to reduce the risk of accidental spread. In an additional experiment the minimum lethal temperature and exposure time in hot water to cause 100 % mortality in American signal crayfish (Pacifastacus leniusculus), was determined to be 5 min at 40 °C. Hot water provides a simple, rapid and effective method to clean equipment. We recommend that it is advocated in future biosecurity awareness campaigns.Electronic supplementary materialThe online version of this article (doi:10.1007/s10530-015-0875-6) contains supplementary material, which is available to authorized users.

Effect of High Temperature and Exposure Time on Erysiphe necator Growth and Reproduction: Revisions to the UC Davis Powdery Mildew Risk Index.

Epidemics of powdery mildew, the most important disease of grapevines in California, are driven by moderate temperatures (21 to 30°C). High temperatures can delay or stop the growth and sporulation of Erysiphe necator. Using controlled conditions, we investigated the response of the pathogen's colony growth, conidiospore production, and germination to eight temperatures (30 to 44°C) at 12 exposure times (0.25 to 24 h). The pathogen survived, grew, and reproduced at higher temperatures than previously reported; exposure time was as important as temperature in defining lethal and sublethal effects. Lethal effects started at 36 to 38°C. Lethal exposure times decreased with increasing temperature. Based on this new information on the pathogen's biology, we tested revisions to the high-temperature threshold of the UC Davis Powdery Mildew Risk Index in field settings. No differences in the total number of fungicide applications resulted from the use of either the original or the revised models. However, use of the 38°C for 2 h threshold consistently showed equal (leaves) or better (fruit) disease control compared with the original model, as well as equal disease control compared with a calendar schedule, but with five fewer applications over the 2 years of the study.

Evaluation of Biocontrol Potential of Metarhizium anisopliae Strains Against Larvae and Adults of Aedes eegypti (l.)

In the present study, we exposed larvae and adult females of Aedes aegypti (L.) to fungal suspensions of three virulent strains of Metarhizium anisopliae (Metsch.), viz., M34412, M34311 and M81123. The strains resulted in 7 to 37% survival as a result of fungal infection over the 8 d test period in case of adults and 2 to 90% survival for larvae. Mean survival period varied between 3 and 4 d for treated adults, whilst control survival exceeded 28 d. Values of LC 50 varied from 5.92×10 3 conidia/ml for M34412, 3.49×10 4 conidia/ml for M34311 and 5.12×10 5 conidia/ml for M81123. Based on virulence and stability, the most promising strain, M. anisopliae M34412 was used for lethal exposure time determination. An exposure time of only 4 h was necessary to cause 50% mortality. Supplementation with M. verrucaria chitinase enzyme increased the larval mortality at lower conidial concentrations.

Eugenol as an anesthetic for juvenile common snook

The objective of this work was to evaluate the efficacy of eugenol as an anesthetic for juvenile common snook, and to determine the minimum effective concentration for use in handling procedures. In the first trial, juvenile common snook were subjected to immersion baths at 25, 50, 75, 100, 125, and 150 mg L-1 eugenol concentrations, after which induction and recovery times were evaluated. In the second experiment, the lethal exposure time (LT50) at 75 mg L-1 was estimated. Minimum effective eugenol concentration was 50 mg L-1, andthe stage of deep anesthesia and recovery were, respectively, reached at 126.3 and 208.8 s. At 75 mg L-1, LT50 was 1,314 s, and induction time and recovery were also satisfactory; however, fish cannot tolerate over 229 s exposure.

RESPONSES OF DEVELOPING CHICKEN EMBRYOS TO ACUTE CHANGES IN AMBIENT TEMPERATURE: NONINVASIVE STUDY OF HEART RATE

ABSTRACT Responses of embryonic heart rate to acute changes in ambient temperature were determined in order to elucidate tolerance limits of developing chicken embryos to decreased and increased ambient temperature. The heart rate was measured noninvasively by ballistocardiography, or invasively by electrocardiography, which gave similar results to noninvasive determination. Tolerance to lower temperature was estimated by measuring (1) time of cardiac arrest in 10-day-old embryos exposed to 28, 18, and 8 °C environments and (2) lethal exposure time at 8 °C during development. The embryos survived 8 °C exposure without heartbeat for prolonged periods. The younger the embryo, the longer its tolerance to cardiac arrest at 8 °C. Tolerance to increased temperature was estimated first by determining the lethal ambient temperature for 5 h exposure. Then, the lethal internal egg temperature at 48 °C was determined. The embryos could withstand the increased temperature until their internal egg temperature reached ...

Bioactivity of Jatropha curcas L. to insect pests of stored products

The objective of this research was to assess insecticidal activity of seeds and derivatives of Jatropha curcas to insect pests of stored grains. Lethal exposure times were estimated for 50 and 95% (LT50 and LT95) of the adults of Sitophilus zeamais and Rhyzorpertha dominica to seeds of four genotypes of J. curcas: Gonçalo, Paraguaçu, Filomena and Bento. Toxicity of powders and aqueous extracts from seeds and pericarps of J. curcas were tested on S. zeamais, R. dominica, Tribolium castaneum and Oryzaephilus surimanensis. A uniform toxic response was observed among the four genotypes for S. zeamais and R. dominica. The powders and aqueous extracts from seeds and pericarps were lethal to S. zeamais, R. dominica, T. castaneum and O. surimanensis. However, insect mortality was higher in the treatments from seeds, compared to the treatments from pericarps.

Toxicidade da combinação de dióxido de carbono e fosfina sob diferentes temperaturas para Tribolium castaneum

O objetivo deste trabalho foi avaliar o efeito da temperatura sobre a toxicidade da combinação de dióxido de carbono e fosfina, para os estágios de desenvolvimento de Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae). A toxicidade da combinação de 5% de dióxido de carbono e 1 g m-3 de fosfina para os estágios de ovo, larvas de 5, 10 e 15 dias, pupa e adulto de T. castaneum, foi estudada nas temperaturas de 25, 30, 35, 40 e 45 °C, por meio de estimativas dos tempos de exposição letais para 50 e 95% dos insetos (TL50 e TL95). Curvas tempo-resposta foram estabelecidas mediante bioensaios com períodos crescentes de exposição à combinação do dióxido de carbono com a fosfina. Observou-se que os TL50 e TL95 reduziram com a elevação da temperatura em todos os estágios de T. castaneum avaliados. O estágio de larva de cinco dias foi a mais susceptível à combinação de dióxido de carbono e fosfina. De acordo com os resultados, a combinação do dióxido de carbono com a fosfina é alternativa potencial para diminuir a quantidade de fosfina aplicada em produtos armazenados, por apresentar alta toxicidade para todos os estágios de T. castaneum sob diferentes temperaturas.

Susceptibility of adult Aedes aegypti (Diptera: Culicidae) to infection by Metarhizium anisopliae and Beauveria bassiana: prospects for Dengue vector control

Dengue fever vectored by the mosquito Aedes aegypti is one of the most rapidly spreading insect-borne diseases, stimulating the search for alternatives to current control methods. Screening assays using a range of Metarhizium anisopliae and Beauveria bassiana isolates were performed against adult female Ae. aegypti. Four virulent isolates were selected for detailed study. Adult female mosquitoes were exposed to supports previously inoculated with fungal suspensions. Fungal isolates were suspended in Tween 80+8% vegetable oil. The isolates caused between 70 and 89% mortality as a result of fungal infection over the 7-day test period. Mean survival times varied between 3 and 5 days for treated insects, whilst control survival exceeded 40 days. The most promising isolate, M. anisopliae LPP133, based not only on virulence but facility for mass production, was used for lethal exposure time determinations. An exposure time of only 3.5 h was necessary to cause 50% mortality. Large cage trails were also carried out and mean survival time of insects exposed to fungus impregnated black cloths was significantly reduced. These results show that entomopathogenic fungi could be promising biological control agents for use against adult Ae. aegypti, by inoculating fungi onto surfaces on which the mosquitoes tend to rest. The subsequent mortality caused by the fungi could potentially reduce the populations of this insect thus reducing the incidence of Dengue.

Mortality of Tribolium confusum J. du Val (Coleoptera: Tenebrionidae) in controlled atmospheres at different oxygen percentages

Since the 1990s an ecologically friendly alternative to insecticide treatments for controlling stored-product insect pests has been available: the methods of modified and controlled atmospheres, which involve reducing the quantity of oxygen (O 2) in the air in order to kill insects by anoxia. This study examines the effect of treatments with controlled atmospheres, considering the time necessary to obtain total mortality of insects at percentages of O 2 higher than those normally used in controlled atmospheres and estimating the possible positive influence of a temperature increase in order to compensate for the effects of the reduced anoxia. Adult populations of Tribolium confusum J. du Val were treated at various O 2 percentages (1, 3, 5, 6, 7, 8 and 10%) and temperatures (23, 26, 29, 32, 35, 37 and 40 °C). The relative humidity was very low (<18%) in all the treatments considered. Lethal exposure times varied from less than one day to a week (longer times were not considered). A multiple regression procedure was applied to the experimental data, considering the time necessary to obtain total mortality as the dependent variable. The analysis provided a good fit to the experimental data and indicated a positive correlation with the percentage of O 2 and an inverse one with temperature.