Dose-mortality Relationships Research Articles

CHOOSING THE OPTIMAL CONCENTRATION OF INOCULUM FOR EFFECTIVE REDUCTION OF THE NUMBER OF ASIAN LOCUST LARVAE

The article presents the results of experiments to determine the dose-mortality relationships for 10 selected strains of the fungus B. bassiana (mountain and steppe) on younger larvae of natural populations of Asian locusts. Working suspensions with four different titers of conidia (1x106, 5x106, 1x107, 5x107) were used. All tested strains related to Asian locust larvae showed high toxicity on the titers of working suspensions 1x107 and 5x107.According to the mortality rate and the rate of death of the organism, the host had the best effect even at all concentrations, showing the specificity of BSc1-15, BSc2-15, BTr1-16, BPit-16, BCa3(m)-09 among the strains. And the maximum biological activity was observed in the BSc1-15 strain on the 15th day, and the mortality rate of test insects in all variants was 100%. The lowest activity was shown by the strain BHy-09 in the range of 47.5-82.5%. The remaining strains showed moderate biological activity. At the same time, the mortality rate of Asian locust larvae in the control variant (without treatment) for 17 days was 17.5±4.78%. As a result of the experiments, we selected strains BSc1-15, BCa3(m)-09 from one of the mountainous and steppe regions, which have high toxicity (75-100%) to Asian locust larvae at relatively low concentrations (1x106 and 5x106 conidia/ml), because when using low titers (1x106 and 5x106), the effect of entomopathogenic fungal strains showed that they stretch over time. Based on the data of this experiment, it was concluded that the optimal titers of the working suspension of the fungus for controlling the number of larvae of Asian locusts are 1x107 and 5x107.

Azadirachtin effects on mating success, gametic abnormalities and progeny survival in Drosophila melanogaster (Diptera).

Azadirachtin is a prominent natural pesticide and represents an alternative to conventional insecticides. It has been successfully used against insect pests. However, its effects on reproduction require further analysis. Here we investigated lethal and sublethal effects of azadirachtin, on treated adults in a model insect, Drosophila melanogaster (Meigen). Dose-mortality relationships as well as several parameters of reproduction (mating, spermatogenesis, oogenesis and fertility) were examined. Neem-Azal, a commercial formulation of azadirachtin, applied topically on newly emerged adults, increased mortality with a positive dose-dependent relationship. The LD50 (0.63 μg) was determined 24 h after treatment using a non-linear regression. Adults surviving this dose had a mating success that was divided by 3 and a progeny production reduced by half when males were treated, and even more when females were treated. When combining probability of survival, of mating and reduced progeny, it appeared that LD50 induced a 98% reduction in reproductive rates. Reduced progeny was partially explained by the effect of adult treatment on gametes number and abnormalities. The number of cysts and the apical nuclei positions within the cysts decreased by 29.7% and 20%, respectively, in males. In females, the number of oocytes per ovary and the volume of basal oocytes also decreased by 16.1% and 32.4%, respectively. Azadirachtin causes significant toxic effects in both sexes and decreases the fecundity and fertility of D. melanogaster. Females are more sensitive to azadirachtin. © 2017 Society of Chemical Industry.

Dialysis dose scaled to body surface area and size-adjusted, sex-specific patient mortality.

When hemodialysis dose is scaled to body water (V), women typically receive a greater dose than men, but their survival is not better given a similar dose. This study sought to determine whether rescaling dose to body surface area (SA) might reveal different associations among dose, sex, and mortality. Single-pool Kt/V (spKt/V), equilibrated Kt/V, and standard Kt/V (stdKt/V) were computed using urea kinetic modeling on a prevalent cohort of 7229 patients undergoing thrice-weekly hemodialysis. Data were obtained from the Centers for Medicare & Medicaid Services 2008 ESRD Clinical Performance Measures Project. SA-normalized stdKt/V (SAN-stdKt/V) was calculated as stdKt/V × ratio of anthropometric volume to SA/17.5. Patients were grouped into sex-specific dose quintiles (reference: quintile 1 for men). Adjusted hazard ratios (HRs) for 1-year mortality were calculated using Cox regression. spKt/V was higher in women (1.7 ± 0.3) than in men (1.5 ± 0.2; P<0.001), but SAN-stdKt/V was lower (women: 2.3 ± 0.2; men: 2.5 ± 0.3; P<0.001). For both sexes, mortality decreased as spKt/V increased, until spKt/V was 1.6-1.7 (quintile 4 for men: HR, 0.62; quintile 3 for women: HR, 0.64); no benefit was observed with higher spKt/V. HR for mortality decreased further at higher SAN-stdKt/V in both sexes (quintile 5 for men: HR, 0.69; quintile 5 for women: HR, 0.60). SA-based dialysis dose results in dose-mortality relationships substantially different from those with volume-based dosing. SAN-stdKt/V analyses suggest women may be relatively underdosed when treated by V-based dosing. SAN-stdKt/V as a measure for dialysis dose may warrant further study.

Systemic effects of thiamethoxam and chlorantraniliprole seed treatments on adult Lissorhoptrus oryzophilus (Coleoptera: Curculionidae) in rice

Feeding assays using adult rice water weevils and foliage of plants treated as seeds with chlorantraniliprole and thiamethoxam at different rates were conducted to evaluate the systemic adulticidal and feeding effects. Dose-mortality relationships were determined for thiamethoxam seed treatments by combining leaf area lost due to feeding and insecticide residues analyzed by LC/MS/MS. Changes in adulticidal activity of thiamethoxam were also investigated by contrasting adult mortalities at the 5-6-leaf and tillering stages of rice. Adult weevil mortalities and leaf consumption rates on foliage were affected in thiamethoxam but not in chlorantraniliprole treatments when rice was at the 6-7-leaf stage. The LD(50) for weevils feeding on thiamethoxam-treated rice at the 2-3-leaf stage was 447 pg insecticide weevil(-1) (95% CL: 25-830 pg weevil(-1)) but was lower (142 pg weevil(-1); 95% CL: 102-180 pg weevil(-1)) in experiments with 3-4-leaf-stage plants. Mortalities on leaves from 5-6-leaf-stage plants were consistently higher than on leaves from tillering plants. Thiamethoxam residues measured by ELISA increased with seed treatment rate and differed between plant stages. The LD(50) values developed in this study are the first values for leaf-feeding insects on foliage of plants treated as seeds with thiamethoxam. The attrition of adulticidal activity of thiamethoxam in foliage of older plants may help to explain the reduced effectiveness of seed treatments against rice water larvae that is seen at later stages of rice growth in field studies. The differential activity of these two seed treatments on adults suggests that adult mortality contributes to the field efficacy of thiamethoxam but not to that of chlorantraniliprole.

Insecticide resistance of Triatoma infestans (Hemiptera, Reduviidae) vector of Chagas disease in Bolivia

To define the insecticide resistance status of Triatoma infestans to deltamethrin (pyrethroid), malathion (organophosphate) and bendiocarb (carbamate) in Bolivia. Fifty populations of T. infestans were sampled in Bolivian human dwellings. Quantal response data were obtained by topical applications of 0.2 μl of insecticide-acetone solutions on nymphs N1 of the F1 generations. For most populations, dose-mortality relationships and resistance ratios (RR) were analysed. Discriminating concentrations were established for each insecticide with a susceptible reference strain and used on the other field populations. A tarsal-contact diagnostic test using insecticide impregnated papers was designed to rapidly identify deltamethrin-resistant populations in the field. Discriminating concentrations for topical applications were 5, 70 and 120 ng active ingredient per insect for deltamethrin, bendiocarb and malathion, respectively. The diagnostic concentration for deltamethrin was 0.30% for the 1-h exposure by tarsal contact. All populations sampled in human dwellings exhibited significant levels of resistance to deltamethrin, from 6 to 491 and varied among regions. Resistant populations did not recover complete susceptibility to deltamethrin when the synergist piperonyl butoxide (PBO) was used. None of the sampled populations exhibited significant resistance to bendiocarb (all RR(50) < 1.8) or malathion (all RR(50) < 2.2). In Bolivia, most 'domestic' T. infestans populations are resistant to deltamethrin. Because insecticide vector control is the only selection pressure, resistance likely originates from it. Switching from pyrethroids to organophosphates or carbamates could be a short-term solution to control this vector, but other alternative integrated control strategies should also be considered in the long term.

Susceptibility of Sitophilus zeamais (Motsch.) (Coleoptera: Curculionidae) and Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae) to Entomopathogenic Fungi from Ethiopia

The efficacy of 13 isolates of entomopathogenic fungi belonging to Beauveria , Metarhizium or Paecilomyces spp. was assessed against Sitophilus zeamais (Coleoptera: Curculionidae) and Prostephanus truncatus (Coleoptera: Bostrichidae) using a total immersion bioassay technique in the laboratory. Fungi were applied at concentrations of 1 2 10 7 and 1 2 10 8 conidia mL -1 for P. truncatus and S. zeamais , respectively. All isolates tested were virulent to P. truncatus (98-100% mortality, and median survival time (MST) ranged from 2.85-4.05 days). Metarhizium anisopliae and B. bassiana were also virulent to S. zeamais (92-100% mortality, MST ranged from 3.58-6.28 days). The isolate of Paecilomyces sp. was found to be the least virulent against S. zeamais , causing only 26.32 - 4.29% mortality with MST of 10.38 - 0.29 days. P. truncatus proved more susceptible to the entomopathogenic fungi tested than S. zeamais . One M. anisopliae (PPRC-EE) and three B. bassiana isolates (PPRC-HH, PPRC-9609 and PPRC-9614) were selected for further study and dose-mortality relationships were assessed on S. zeamais . The tested concentrations ranged from 1 2 10 4 -1 2 10 7 conidia mL -1 . M. anisopliae (PPRC-EE) showed the lowest LC 50 (3.39 2 10 5 conidia mL -1 ) followed by B. bassiana PPRC-HH (2.04 2 10 6 conidia mL -1 ). PPRC-9609 and PPRC-9614 showed slight differences in LC 50 but not at LC 90 . The results revealed the higher potency of M. anisopliae as compared with the B. bassiana isolates tested. The study suggests that the use of entomopathogenic fungi may hold promise as an alternative method to control pests of stored-products in Ethiopia.

Preliminary studies on the use of Beauveria bassiana to control Sitophilus zeamais (Coleoptera: Curculionidae) in the laboratory

The virulence of ten isolates of Beauvena bassiana (Balsamo) Vuillemin to the maize weevil, Sitophilus zeamais Motsch., was tested in the laboratory. All isolates tested were capable of infecting S. zeamais but their virulence, determined by adult mortalities and median lethal time, varied. A total of five (I89-481, I90-520, I89-477, I90-533, and I94-907) highly virulent, three (I92-736, I93-906 and I92-761A) intermediate and two (I93-868 and I93-870) weakly virulent isolates were identified for S. zeamais. The growth and sporulation rates and persistency of water formulated conidia of the most virulent isolates were also studied. I90-520 was selected for further work and dose-mortality relationships and the infectivity of dry conidia against Sitophilus zeamais were determined. The lowest dose (10 4 conidia ml −1) caused about 88% mortality within eight days. To assess the infectivity of a dry formulation of the isolate, conidial doses of 0, 0.1, 0.5 and 1 g of B. bassiana per 25 g of popping maize seeds were compared with pirimiphos-methyl at 10 ppm. This demonstrated the potential of dry conidia of the isolate to infect and cause mycosis to S. zeamais. Adult mortality of S. zeamais and damage to maize seeds treated with different levels of dry conidia were not statistically significantly different from pirimiphos-methyl-treated maize after 14 days of storage period, but the chemical pesticide killed all target insects within 24 h, whereas mortality began at day 3 for the best B. bassiana treatment.

Comparative Pathogenesis of Autographa californica M Nuclear Polyhedrosis Virus in Larvae of Trichoplusia ni and Heliothis virescens

We compared early viral pathogenesis and dose mortality relationships for larvae of two highly susceptible hosts, Trichoplusia ni and Heliothis virescens, using a construct of AcMNPV containing the lacZ reporter gene. Larvae were inoculated either as newly molted fourth instars (40) or 15 hr after the molt (415). In 40-inoculated larvae, first lacZ expression was detected in the midgut epithelium of T. ni at 4 hr postinoculation (hpi) compared to 18 hpi in H. virescens, and systemic infections were initiated from tracheole cells servicing the midgut epithelia beginning at 12 and 20 hpi, respectively. The longer viral tenure within the midgut and the slower progression of systemic infections within H. virescens ultimately contributed to its longer time to death. For 40-inoculated H. virescens, proportions of lacZ-expressing larvae increased from 18 hpi until the onset of the molt to the fifth instar at 36 bpi; at this time point, the proportion of signaling insects equaled the final larval mortality. Viral infections within the midgut epithelium of H. virescens were lost during the molt to the fifth instar. Dose-mortality relationships suggested that the peritrophic membrane provided little protection from AcMNPV infections for either species.

Dose-Mortality Relationships for Eggs and Larvae of Bactrocera tryoni (Diptera: Tephritidae) Immersed in Hot Water

Heat dose-mortality relationships at 44, 45, 46, 47, and 48°C were determined for new (5% developed) and old (80% developed) eggs and first, second, and third instars of the Queensland fruit fly, Bactrocera tryoni (Froggatt). The most tolerant stages were mature eggs at the lower temperatures, and third instars at the higher temperatures. New eggs were the least tolerant stage at all temperatures. First and second instars were intermediate in their tolerance. Determination of heat disinfestation treatment efficacy should thus be directed against third instars or mature eggs (depending on the temperature). Predicted times to achieve probit 9 quarantine security at these temperatures for all stages are presented. This information may be used to determine heat disinfestation times with hot water and vapor heat for commodities subject to infestation by this insect.

Glossina morsitans morsitans: Mortalities caused in adults by experimental infection with entomopathogenic fungi

Various strains of the entomopathogenic fungi: Beauveria bassiana, Metarhizium anisopliae, Paecilomyces fumosoroseus and P. farinosus were found to be pathogenic for adult tsetse, Glossina morsitans morsitans but B. bassiana and M. anisopliae were the most pathogenic, often causing mortalities of up to 100%. Dose-mortality relationships were demonstrated for both B. bassiana and M. anisopliae and male tsetse were observed to be more susceptible to infection than females. Pure cultures of B. bassiana and M. anisopliae were isolated from haemolymph and fat body of tsetse previously exposed to fungal spores and hyphal fragments were often observed floating freely in the haemolymph. No increase in abortions was observed in female pregnant tsetse infected with B. bassiana and M. anisopliae and pupae produced by the infected females showed no increase in pupal mortality. Furthermore, when larvae were heavily dusted with spores of B. bassiana and M. anisopliae prior to pupation and incubation, no increase was observed in pupal mortality suggesting lack of fungal infection.

Dose-Mortality Relationships in RFM Mice Following 137 Cs g-Ray Irradiation

The effect of single-exposure /sup 137/Cs ..gamma..-ray irradiation on overall and tumor-specific mortality is examined using data from a large study of RFM mice conducted at the Oak Ridge National Laboratory. The use of a proportional-hazards regression technique leads to the exploration and quantification of mortality rates as a function of both radiation dose and animal age. Relative risks for most mortality types were found to be predominantly linear as a function of dose and were found to decrease markedly with increasing time since exposure. An exception occurs with ovarian cancer. Rates of mortality with ovarian cancer increase very sharply and nonlinearly for doses as low as 50 rad. Further, the increased ovarian cancer relative risks do not appear to decline as the animals age. In spite of rather different overall relative risks for male and female mice at particular doses the age-specific relative risks are rather similar, thereby giving a unified dose-response model for all natural causes of mortality. Implications of these analyses for low-dose extrapolation are mentioned.

Biological activities ofTrewia nudiflora extracts against certain economically important insect pests

An ethanol extract ofTrewia nudiflora (Euphorbiaceae) seed was tested as an agent for controlling several economically important insects. Results suggest that this plant extract acts as an antifeedant for the spotted cucumber beetle (Diabrotica undecimpunctata howardi Barber) and the European corn borer [Ostrinia nubilalis (Hübner)] but not for the other insects tested. Also indicated were morphogenic effects on the codlingmoth [Laspeyresia pomonella (L.)], disruption of the normal life cycle of the redbanded leafroller [Argyrotaenia velutinana (Walker)], and reduction in the progeny of the plum curculio [Conotrachelus nenuphar (Herbst)]. In addition, the extract was toxic to the striped cucumber beetle [Acalymma vittatum (F.)] and gave 100% control of the chicken body louse [Menacanthus stramineus (Nitzsch)] from 5 to 28 days. Fractionation of the extract was monitored by a bioassay usingO. nubilalis. This fractionation yielded six pure compounds, the most abundant of which was trewiasine. Its LD50 was 7.4 ppm when incorporated into the diet ofO. nubilalis. Dose-mortality relationships for the other compounds withO. nubilalis are presented.

Cross resistance to rabon in the house fly pressured with diazinon in the field and in the laboratory.

Dose-mortality relationships were established for 2 strains of Musca domestica L. exposed as larvae and as adults to Rabon® (2-chloro-1-(2,4,5-trichlorophenyl) vinyl dimethyl phosphate) and to diazinon. The W strain larvae, which had been pressured with diazinon in the field as both larvae and adults, had higher resistance to both diazinon and Rabon than did larvae of the L strain, which had been pressed as adults with diazinon in the laboratory. However, L strain adults were more resistant to diazinon than were W strain adults and were equally as resistant to Rabon.