Prediction of the toxic effects of (agro) chemical mixtures on organisms using simple time-based models.

The lethal effect of a chemical acting alone can be predicted using the simple hyperbolic model, which relies on the chemicals' median lethal time (LT50). However, this model cannot be used to predict mixture toxicity, considering that toxicity in natural ecosystems often results from exposure to mixtures rather than single chemicals. The lethal time addition method was developed to calculate the LT50 of a pesticide mixture from the LT50 of its components. It enables the hyperbolic model to estimate the lethal effects of a mix of pesticides at various exposure times. The hyperbolic model, complemented by the lethal-time addition model, predicted the percentage mortality of Clarias gariepinus and Oreochromis niloticus exposed to binary and quaternary mixtures of atrazine, mancozeb, chlorpyrifos, and lambda-cyhalothrin and estimated the 96 hr LC50 of the pesticide mixture.

You are what you eat: fungal metabolites and host plant affect the susceptibility of diamondback moth to entomopathogenic fungi.

Background: Beauveria are entomopathogenic fungi of a broad range of arthropod pests. Many strains of Beauveria have been developed and marketed as biopesticides. Beauveria species are well-suited as the active ingredient within biopesticides because of their ease of mass production, ability to kill a wide range of pest species, consistency in different conditions, and safety with respect to human health. However, the efficacy of these biopesticides can be variable under field conditions. Two under-researched areas, which may limit the deployment of Beauveria-based biopesticides, are the type and amount of insecticidal compounds produced by these fungi and the influence of diet on the susceptibility of specific insect pests to these entomopathogens. Methods: To understand and remedy this weakness, we investigated the effect of insect diet and Beauveria-derived toxins on the susceptibility of diamondback moth larvae to Beauveria infection. Two New Zealand-derived fungal isolates, B. pseudobassiana I12 Damo and B. bassiana CTL20, previously identified with high virulence towards diamondback moth larvae, were selected for this study. Larvae of diamondback moth were fed on four different plant diets, based on different types of Brassicaceae, namely broccoli, cabbage, cauliflower, and radish, before their susceptibility to the two isolates of Beauveria was assessed. A second experiment assessed secondary metabolites produced from three genetically diverse isolates of Beauveria for their virulence towards diamondback moth larvae. Results: Diamondback moth larvae fed on broccoli were more susceptible to infection by B. pseudobassiana while larvae fed on radish were more susceptible to infection by B. bassiana. Furthermore, the supernatant from an isolate of B. pseudobassiana resulted in 55% and 65% mortality for half and full-strength culture filtrates, respectively, while the filtrates from two other Beauveria isolates, including a B. bassiana isolate, killed less than 50% of larvae. This study demonstrated different levels of susceptibility of the insects raised on different plant diets and the potential use of metabolites produced by Beauveria isolates in addition to their conidia.

Does Bacillus thuringiensis Affect the Stress and Immune Responses of Rhynchophorus ferrugineus Larvae, Females, and Males in the Same Way?

Bacillus thuringiensis (Bt) is considered a potentially useful entomopathogen against red palm weevil (RPW) Rhynchophorus ferrugineus. We compared the effects of Bt on mature larvae, females, and males. The pathogenicity of Bt was evaluated, estimating: Median Lethal Dose (LD50), Median Lethal Time (LT50), Total Hemocyte Count (THC), and Differential Hemocyte Counts (DHC), and the expression of the stress protein Heat Shock Protein 70 (Hsp 70) in hemocytes and the brain. Mortality exhibited a positive trend with the dosage and duration of exposure to Bt. Larvae were more susceptible than adults, and the LD50 of females was almost double the value of that of the larvae. LT50 value was higher for females than for males and larvae. Treatment with sub-lethal doses of Bt induced a decrease in THC in larvae, females, and males. In treated larvae, plasmatocytes decreased, while oenocytes and spherulocytes increased. In treated females, all types of hemocytes decreased, while in males the number of plasmatocytes decreased and granulocytes increased. We also registered the stress response directly on hemocytes showing that, already at 3 h after eating Bt, the expression of the stress protein Hsp 70 was modulated. This effect was also observed in brain tissue at 6 h after treatment. The results confirm that Bt treatment induces a pathogenic state in larvae and adults of both sexes, with effects after only a few hours from ingestion; however, the effects are different in magnitude and in type of target.

Biological Control of Diamondback Moth-Increased Efficacy with Mixtures of Beauveria Fungi.

Diamondback moth (DBM) is an important horticultural pest worldwide as the larvae of these moths feed on the leaves of cruciferous vegetables. As DBM has developed resistance to more than 100 classes of synthetic insecticides, new biological control options are urgently required. Beauveria species are entomopathogenic fungi recognized as the most important fungal genus for controlling a wide range of agricultural, forestry, and veterinary arthropod pests. Previous research, aimed at developing new Beauveria-based biopesticides for DBM, has focused on screening single isolates of Beauveria bassiana. However, these fungal isolates have individual requirements, which may limit their effectiveness in some environments. This current study separately assessed 14 Beauveria isolates, from a range of habitats and aligned to four different species (Beauveria bassiana, B. caledonica, B. malawiensis, and B. pseudobassiana), to determine the most effective isolate for the control of DBM. Further assays then assessed whether selected combinations of these fungal isolates could increase the overall efficacy against DBM. Six Beauveria isolates (three B. bassiana and three B. pseudobassiana) achieved high DBM mortality at a low application rate with the first documented report of B. pseudobassiana able to kill 100% of DBM larvae. Further research determined that applications of low-virulent Beauveria isolates improved the control of DBM compared to mixtures containing high-virulent isolates. This novel approach increased the DBM pest mortality and shortened the time to kill.

Tolerance of northern Gulf of Mexico eastern oysters to chronic warming at extreme salinities.

The eastern oyster, Crassostrea virginica, provides critical ecosystem services and supports valuable fishery and aquaculture industries in northern Gulf of Mexico (nGoM) subtropical estuaries where it is grown subtidally. Its upper critical thermal limit is not well defined, especially when combined with extreme salinities. The cumulative mortalities of the progenies of wild C. virginica from four nGoM estuaries differing in mean annual salinity, acclimated to low (4.0), moderate (20.0), and high (36.0) salinities at 28.9 °C (84 °F) and exposed to increasing target temperatures of 33.3 °C (92 °F), 35.6 °C (96 °F) or 37.8 °C (100 °F), were measured over a three-week period. Oysters of all stocks were the most sensitive to increasing temperatures at low salinity, dying quicker (i.e., lower median lethal time, LT50) than at the moderate and high salinities and resulting in high cumulative mortalities at all target temperatures. Oysters of all stocks at moderate salinity died the slowest with high cumulative mortalities only at the two highest temperatures. The F1 oysters from the more southern and hypersaline Upper Laguna Madre estuary were generally more tolerant to prolonged higher temperatures (higher LT50) than stocks originating from lower salinity estuaries, most notably at the highest salinity. Using the measured temperatures oysters were exposed to, 3-day median lethal Celsius degrees (LD50) were estimated for each stock at each salinity. The lowest 3-day LD50 (35.1-36.0 °C) for all stocks was calculated at a salinity of 4.0, while the highest 3-day LD50 (40.1-44.0 °C) was calculated at a salinity of 20.0.

Manifold passages in an assorted infection in a host could improve virulence of Helicoverpa armigera Nucleopolyhedrovirus (HaNPV).

Helicoverpa armigera Hübner (Lepidoptera: Noctuidae) is serious pests of cotton and several other crops. Helicoverpa armigera Nucleopolyhedrovirus (HaNPV) can be important alternative to synthetic insecticides for the management of H. armigera. However, the efficacy of HaNPV can vary in horizontal and vertical transmission. In the current study, we evaluated the efficacy of HaNPV of a virulent strain (vertically transmitted up to six generations) and wild strains (used after isolation from the field infected larvae). Both strains were applied to the 2nd instar larvae of H. armigera @ 1 × 109 polyhedral inclusion bodies (PIB)/ml. There were six replications of each strain (strains). The results indicated higher mortalities in larvae exposed to virulent strains (68.33 ±â€¯6.07%) as compared to wild strain (45 ±â€¯2.24%). Virulent strains killed the larvae quite faster than wild strain. The lethal time (LT50) to kill 50% of the larvae by virulent strain was 7.15 days and for wild strain it was 19.47 days. The results showed that multiple passage of HaNPV through several generations enhances its efficacy to kill H. armigera larvae faster. The results of this study will be helpful to manage H. armigera and other related lepidopoterous pests.

Effects of thermal stress on mortality and HSP90 expression levels in the noble scallops Chlamys nobilis with different total carotenoid content.

The noble scallop Chlamys nobilis is an economically important marine bivalve cultivated in the southern sea of China since the 1980s. Unfortunately, mass mortality of this scallop species often occurs in summer. The present study was conducted to investigate whether the expression of heat shock protein 90 (HSP90) and level of carotenoids could enhance high-temperature stress resistance in scallop. First, the HSP90 homolog of C. nobilis (designated CnHSP90) was identified and cloned. The complete cDNA sequence of CnHSP90 was 2631 bp, including a 2181-bp open reading frame (ORF) encoding a 726 amino acid polypeptide with five HSP90 family signatures, and sharing high homology with members of the HSP90 family. CnHSP90 was ubiquitously expressed in all examined tissues including the intestine, kidney, adductor, mantle, gill, and gonad, with the highest in the gonad. Golden and brown scallops, which contain significantly different total carotenoid content (TCC), were subjected to acute thermal challenge, and the LTE50 (semi-lethal temperature at 36 h heat shock) and LTI50 (semi-lethal time after heat shock) as well as the correlation between CnHSP90 gene expression and TCC were determined. The LTE50 of golden scallop (32.14 °C) was higher than that of brown scallops (31.19 °C), with longer LTI50 at all tested temperatures, indicating that golden scallops were more resistant to thermal stress than brown scallops. Similarly, the mRNA expression levels of CnHSP90 in gill of golden scallops were significantly higher (P < 0.05) than that of brown scallops at 6, 12, 24, and 36 h, with a strong positive correlation between CnHSP90 expression level and TCC. This suggests that both carotenoids and HSP90 levels could improve thermal resistance in the noble scallops.

Residual Toxicity of Insecticides to Neoseiulus fallacis (Acari: Phytoseiidae) in Apples.

Neoseiulus fallacis (Garman) is a predatory mite that is common in apple orchards and distributed throughout North America. However, N. fallacis may be susceptible to pesticides used for the management of crop pests. This study aimed to evaluate the temporal effects of commonly used insecticides on N. fallacis survival. Neoseiulus fallacis adults were exposed to field-aged residues, and mortality and lethal time were measured over 96 h of exposure. Carbaryl caused high mortality to N. fallacis and the shortest lethal time values (LT50), followed by spinetoram, with moderate lethal time values. Esfenvalerate, acetamiprid, chlorantraniliprole, and novaluron showed little to no lethality to N. fallacis following exposure to dry field-aged residues. The results of this study provide important field-relevant knowledge that is often void from laboratory-based studies, which can aid integrated pest management (IPM) decision-makers in apple production systems.

Thermal Death Kinetics of Cryptolestes pusillus (Schonherr), Rhyzopertha dominica (Fabricius), and Tribolium confusum (Jacquelin du Val) Using a Heating Block System.

Thermal treatment has been extensively used to control pests in stored grains for a long time. The objective of this study was to analyze thermal death kinetics of adult flat grain beetle, Cryptolestes pusillus (Schonherr), lesser grain borer, Rhyzopertha dominica (Fabricius), and confused flour beetle, Tribolium confusum (Jacquelin du Val), using a heating block system (HBS), at temperatures of 46, 48, 50, and 52 °C for C. pusillus and T. confusum, and 48, 50, 52, and 54 °C for R. dominica with a heating rate of 5 °C/min. Thermal death curves of those three insects followed a 0th-order reaction model. Complete mortality of C. pusillus, R. dominica, and T. confusum were observed after exposure to 1.4, 5.0, and 0.9 min at 52, 54 and 52 °C, respectively. The thermal death activation energy for controlling C. pusillus, R. dominica, and T. confusum was 689.91, 380.88, and 617.08 kJ/mol with z values of 2.88, 5.18, and 3.22 °C, respectively. The cumulative lethal time model can also be used to predict mortality of these three insects during a practical heating process. The information provided by this study on storage pests may be useful for developing effective thermal treatment protocols.

Development of Baits for Population Management of Subterranean Termites.

The objective of bait application envisioned by early researchers was to eliminate the source of infestation, the colony, but because of the lack of adequate evaluation tools, results of field trials with mirex baits in the 1960s were mostly inconclusive. On-the-ground monitoring stations and mark-recapture protocol developed in the 1970s marked the turning point in the field studies of termite baits. Results of field studies with metabolic inhibitors and chitin synthesis inhibitors (CSIs) in the 1990s indicated that a bait toxicant has to be slow-acting and nonrepellent, and its lethal time has to be dose independent. A recent discovery that termites return to the central nest to molt and CSI-poisoned termites die near the royal pair further explains the success of CSI baits in eliminating colonies. Owing to the availability of durable baits that require less-frequent site inspection, more termite control professionals have adopted baiting systems in recent years.

Life-history changes in the cold tolerance of the two-spot spider mite Tetranychus urticae: applications in pest control and establishment risk assessment.

Lethal time50 (LTime50) and lethal temp (LTemp50) are commonly used laboratory indices of arthropod cold tolerance, with the former often being employed to predict winter survival in the field. In the present study, we compare the cold tolerance of different life-history stages (nondiapausing and diapausing females, as well as males and juveniles) of a major agricultural pest: the two-spot spider mite Tetranychus urticae Koch (Acarina: Tetranychidae). Diapausing females from European populations of this species are shown to be freeze avoiding, supercooling to -23.6 ± 0.37  °C and with an LTemp50 of -23.2 °C. However, nondiapausing females [supercooling point (SCP) -19.1 ± 0.49 °C, LTemp50 -14.32 °C], males (SCP -21.27 ± 0.52  °C, LTemp50 -16 °C) and juveniles (SCP -25.34 ± 0.29 °C, LTemp50 -18.3 °C) are subclassified as strongly chill tolerant juveniles. LTime50 is 148.3 days for non-acclimated diapausing females, whereas nondiapausing females, males and juveniles reach 50% mortality by 21.7 days. When individuals are acclimated at 10 °C for a period of 7 days, no effect is found. Cold tolerance is suggested to be a major contributor to the successful spread of T. urticae across temperate countries, although it is dependent on a diapause trait, suggesting a potential target for control. Winter field trial data from diapausing females indicate that LTime50 is a reliable indicator of winter survival even within diapause, supporting the use of these indices as a valuable component within environmental niche models for the prediction of future pest invasions.

HPLC Analysis to Determine the Half-life and Bioavailability of the Termiticides Bifenthrin and Fipronil in Soil.

The aim of this study was to test the bioavailability and degradation in soil of the termiticides bifenthrin and fipronil, which are used to treat subterranean termites (Heterotermes indicola, Wasmann). Soil collected from different areas of Lahore was categorized as sandy clay loam (SCL) or sandy loam (SL). Laboratory bioassays were conducted to determine the bioavailability ratio of bifenthrin and fipronil in each type of soil after different periods of time. LT50 values were determined posttreatment at different time intervals. Regarding soil type, both termiticides were more effective in SL soil, compared with SCL soil posttreatment. There were significant differences in termite mortality in treated compared with untreated control samples (P < 0.005). To test the degradation rate of soil termiticides, both qualitative and quantitative analyses were carried out by HPLC, and the effect of time on termiticide recovery rate determined. Calculated half-life values for bifenthrin (maximum, 1,002 and 1,262 d in SCL soil and SL soil, respectively) indicated that it persisted in both soil types at all concentrations. The maximum calculated half-life values of fipronil were 270 and 555 d in SCL and SL soil, respectively. At lower concentrations and over longer periods of time, fipronil completely degraded in SL soil, while a negligible amount was detected in SCL soil. Termiticide concentration decreased over time, as did the termiticide recovery rate. Overall, bifenthrin was more persistent than fipronil under all treatment conditions tested.

Effects of abamectin and deltamethrin to the foragers honeybee workers of Apis mellifera jemenatica (Hymenoptera: Apidae) under laboratory conditions.

This study aimed at evaluating the toxicity of some insecticides (abamectin and deltamethrin) on the lethal time (LT50) and midgut of foragers honeybee workers of Apis mellifera jemenatica were studied under laboratory conditions. The bees were provided with water, food, natural protein and sugar solution with insecticide (concentration: 2.50 ppm deltamethrin and 0.1 ppm abamectin). The control group was not treated with any kind of insecticides. The mortality was assessed at 1, 2, 4, 6, 12, 24, 48, and 72 hour (h) after insecticides treatment and period to calculate the value of lethal time (LT50). But the samples the histology study of midgut collected after 24 h were conducted by Scanning Electron Microscope. The results showed the effects of insecticides on the current results show that abamectin has an adverse effect on honeybees, there is a clear impact on the lethal time (LT50) was the abamectin faster in the death of honeybee workers compared to deltamethrin. Where have reached to abamectin (LT50 = 21.026) h, deltamethrin (LT50 = 72.011) h. However, abamectin also effects on cytotoxic midgut cells that may cause digestive disorders in the midgut, epithelial tissue is formed during morphological alterations when digestive cells die. The extends into the internal cavity, and at the top, there is epithelial cell striated border that has many holes and curves, abamectin seems to have crushed the layers of muscle. Through the current results can say abamectin most toxicity on honeybees colony health and vitality, especially foragers honeybee workers.

Studying DDT Susceptibility at Discriminating Time Intervals Focusing on Maximum Limit of Exposure Time Survived by DDT Resistant Phlebotomus argentipes (Diptera: Psychodidae): an Investigative Report.

Extensive application of routine insecticide i.e., dichlorodiphenyltrichloroethane (DDT) to control Phlebotomus argentipes (Diptera: Psychodidae), the proven vector of visceral leishmaniasis in India, had evoked the problem of resistance/tolerance against DDT, eventually nullifying the DDT dependent strategies to control this vector. Because tolerating an hour-long exposure to DDT is not challenging enough for the resistant P. argentipes, estimating susceptibility by exposing sand flies to insecticide for just an hour becomes a trivial and futile task.Therefore, this bioassay study was carried out to investigate the maximum limit of exposure time to which DDT resistant P. argentipes can endure the effect of DDT for their survival. The mortality rate of laboratory-reared DDT resistant strain P. argentipes exposed to DDT was studied at discriminating time intervals of 60 min and it was concluded that highly resistant sand flies could withstand up to 420 min of exposure to this insecticide. Additionally, the lethal time for female P. argentipes was observed to be higher than for males suggesting that they are highly resistant to DDT's toxicity. Our results support the monitoring of tolerance limit with respect to time and hence points towards an urgent need to change the World Health Organization's protocol for susceptibility identification in resistant P. argentipes.

Time-to-response toxicity analysis as a method for drug susceptibility assessment in salmon lice.

The salmon louse Lepeophtheirus salmonis (Krøyer, 1837) is an ectoparasite causing infections of wild and farmed Atlantic salmon (Salmo salar L.) in the Northern hemisphere. While L. salmonis control at commercial mariculture sites increasingly employs non-medicinal approaches, such as cage designs reducing infection rates and biological control through cleaner fish, anti-parasitic drugs are still a requirement for effective fish health care. With only a limited range of salmon delousing agents available, all of which have been in use for more than a decade, drug resistance formation has been reported for different products. Successful resistance management requires reliable susceptibility assessment, which is usually achieved through L. salmonis bioassays. These tests involve the exposure of parasites to different drug concentrations and require significant numbers of suitable L. salmonis stages. The present study reports an alternative bioassay that is based on time-to-response toxicity analyses and can be carried out with limited parasite numbers. The assay determines the median effective time (ET50), i.e., the time required until impaired swimming and/or attachment behaviour becomes apparent in 50% of parasites, by conducting repeated examinations of test animals starting at the time point where exposure to a set drug concentration commences. This experimental approach further allows the estimation of the apparent drug susceptibility of individual L. salmonis by determining their time to response, which may prove useful in experiments designed to elucidate associations between genetic factors and the drug susceptibility phenotype of parasites. Three laboratory strains of L. salmonis differing in susceptibility to emamectin benzoate were characterised using standard 24 h bioassays and time-to-response toxicity assays. While both the median effective concentration (EC50) and the ET50 showed variability between experimental repeats, both types of bioassay consistently discriminated susceptible and drug-resistant L. salmonis laboratory strains. STATEMENT OF RELEVANCE: Infections by sea lice cause significant costs to the global salmon farming industry, which have been estimated to exceed €300 million per year worldwide. Control of sea lice still relies to a significant extent on chemical delousing; however, chemical control is threatened by resistance formation. Resistance can be combated by rotation between different drugs and strategic implementation of non-medicinal strategies. However, resistance management requires reliable and feasible methods of susceptibility assessment. The present study is a technical note introducing a novel approach to susceptibility assessments in sea lice. The method can be applied in susceptibility assessments on farms, where it offers the advantage of a reduced requirement of parasites for testing. In addition, the novel method allows deriving the times of parasite require to show a response after drug treatment has started, thus providing a variable characterizing the drug susceptibility phenotype of individual parasites. Accordingly, the bioassay approach presented here will be useful for studies aiming at unravelling the genetic determinants of drug resistance.

Acaricidal activity of methanol extract of Acmella oleracea L. (Asteraceae) and spilanthol on Rhipicephalus microplus (Acari: Ixodidae) and Dermacentor nitens (Acari: Ixodidae).

We evaluated the acaricidal activity of Acmella oleracea methanol extract and spilanthol on Rhipicephalus microplus and Dermacentor nitens. The extract was made through maceration with methanol. From this extract, a dichloromethane fraction with 99% spilanthol was obtained and tested on R. microplus larvae and engorged females and D. nitens larvae. For evaluation against larvae, the modified larval packet test was used, and both the methanol extract and dichloromethane fraction were tested at concentrations of 0.2-50mg/mL. The modified larval packet test was also used in the lethal time (LT) test, with the methanol extract at a concentration of 12.5mg/mL and the percentage mortality was assessed after 15, 30, 45, 60, 75, 90, 120min and 24h. The 50% lethal time calculation (LT50) was performed in this test. The engorged female test was performed with R. microplus only, at concentrations of 25-200mg/mL for methanol extract and 2.5-20.0mg/mL for spilanthol. The methanol extract caused 100% mortality of the R. microplus and D. nitens larvae at concentrations of 3.1 and 12.5mg/mL, respectively. Spilanthol resulted in 100% mortality of R. microplus larvae at concentration of 1.6mg/mL and of D. nitens at 12.5mg/mL. In the lethal time assay using the methanol extract, the mortality rate was 100% for R. microplus and D. nitens larvae after 120min and 24h, with LT50 values of 38 and 57min, respectively. In the test of females, the egg mass weight and the hatching percentage of the groups treated with concentrations equal to or higher than 50.0mg/mL of methanol extract were significantly reduced (p<0.05), while for spilanthol, the reduction of the egg mass weight and hatching percentage occurred from concentrations of 10.0mg/mL and 2.5mg/mL, respectively. Females treated with 200.0mg/mL of extract died before starting oviposition, resulting in 100% effectiveness, while the best efficacy for spilanthol was 92.9% at a concentration of 20.0mg/mL. Thus we conclude that the methanol extract of A. oleracea and spilanthol have acaricidal activity against R. microplus and D. nitens.

Supercooling capacity and cold hardiness of band-winged grasshopper eggs (Orthoptera: Acrididae).

The band-winged grasshopper, Oedaleus asiaticus Bei-Bienko, is one of the most dominant and economically important grasshopper species in the steppe grasslands and farming-pastoral ecotone in northern China. It is a univoltine species and overwinters as eggs in soil. The cold hardiness of its eggs was examined in the laboratory. Water content in soil significantly affected the supercooling points (SCPs), water content and fat content of prediapause eggs. With the increase of water content in soil, the SCP, and water content of prediapause eggs rose whereas the fat content declined. There was a significant relationship between the SCP and water content or fat content of prediapause eggs. The SCPs of prediapause and diapause eggs varied from -7.6 to -28.4°C and the SCPs of eggs 30 d after oviposition could be divided into two groups. The means of high SCP group (-11.0 to -11.9°C) were much higher than those of low SCP group (-21.8 to -21.9°C), and the majority belonged to the latter (90.48-93.33%). The SCPs of prediapause eggs and early-diapause eggs 30 d after oviposition were significantly higher than those of deep-diapause eggs 60 d after oviposition. The survival rates of diapause eggs were significantly different among different temperature treatments. The survival rate was higher than 88% at greater than -20°C and declined significantly to 57% at -25°C, and suddenly dropped to zero at -30°C. The lower lethal temperature (Ltemp50) for 12 h exposure was -25.3°C and the lower lethal time (Ltime50) at -20°C was 32.8 d. As the mean SCPs of diapause eggs were similar to their Ltemp50, the SCP of eggs can be considered as a good indicator of cold hardiness for O. asiaticus and that this grasshopper is a freeze-intolerant insect.

Temperature and Time Requirements for Controlling Bed Bugs (Cimex lectularius) under Commercial Heat Treatment Conditions.

Developing effective alternative approaches for disinfesting bed bugs from residential spaces requires a balance between obtaining complete insect mortality, while minimizing costs and energy consumption. One method of disinfestation is the application of lethal high temperatures directly to rooms and contents within a structure (termed whole-room heat treatments). However, temperature and time parameters for efficacy in whole-room heat treatments are unknown given the slower rate of temperature increase and the probable variability of end-point temperatures within a treated room. The objective of these experiments was to explore requirements to produce maximum mortality from heat exposure using conditions that are more characteristic of whole-room heat treatments. Bed bugs were exposed in an acute lethal temperature (LTemp) trial, or time trials at sub-acute lethal temperatures (LTime). The lethal temperature (LTemp99) for adults was 48.3 °C, while LTemp99 for eggs was 54.8 °C. Adult bed bugs exposed to 45 °C had a LTime99 of 94.8 min, while eggs survived 7 h at 45 °C and only 71.5 min at 48 °C. We discuss differences in exposure methodologies, potential reasons why bed bugs can withstand higher temperatures and future directions for research.

Survival and gill morphology of different life stages of Tilapia guineensis exposed to the drilling fluid XP-07 / Sobrevivência e morfologia branquial de Tilapia guineensis expostos ao líquido de perfuração XP-07 em diferentes estágios de vida

The toxicity of drilling fluid XP-07 on gills of three life stages (fry, fingerling and post fingerling) of Tilapia guineensis was evaluated in a 96h static bioassay. The mortality rates of the organisms were determined using the same concentrations of XP-07 in all the life stages. At the end of 96h, the gills were examined for histopathological changes. The 96h median lethal concentrations for fry (Fr), fingerlings (F) and post fingerlings (PF) were 5.03, 7.77 and 6.93 percent XP-07 respectively. The median lethal time values decreased as concentration and time of exposure increased. The histopathological studies carried out on gills of T. guineensis showed injuries, which increased progressively with the concentration of the fluid. The fry stage was the most susceptible to the drilling fluid. This states the need for care to be taken in handling drilling fluids in Niger delta, since this area serves as breeding and nursery ground for several fish species.

A toxicidade do líquido de perfuração XP-07, nas brânquias de Tilapia guineensis, foi avaliada por meio de um bioensaio estático de 96h em três estágios da vida do peixe (larva, alevino e juvenil). As taxas de mortalidade do organismo foram avaliadas nas mesmas concentrações de XP-07 para todos os estágios de vida do peixe. As brânquias foram avaliadas ao final de 96 horas, com o objetivo de observarem-se mudanças histopatológicas. A concentração média letal para 96h foi de 5,03; 7,77 e 6,93 por cento para larvas, alevinos e juvenis, respectivamente. O tempo médio letal diminuiu à medida que a concentração e o tempo de exposição aumentaram. Os estudos histopatológicos realizados nas brânquias de T. guineensis indicaram lesões que aumentaram progressivamente com a concentração do fluido. A fase larval é a mais suscetível ao fluido de perfuração. Concluiu-se que é necessário cuidado no manuseio de fluidos de perfuração no Delta do Niger, uma vez que esta é uma área de reprodução e berçário para várias espécies de peixes.