Toxicity of Bacillus thuringiensis to laboratory populations of the olive fruit fly (Dacus oleae)
A survey of Bacillus thuringiensis recovered from the environments of olive groves in Greece was carried out. Of 80 soil samples, 24 were found to contain B. thuringiensis with parasporal crystal inclusions; these were tested for toxicity against the olive fruit fly (Dacus oleae). Mortality levels of larvae caused by the different isolates varied from 7 to 87%. Higher levels of mortality were observed if a mixture of relatively pure crystals and spores was used compared with the mortality resulting from either fraction alone. We were able to show that the toxicity of the most active isolate is likely to be specific for D. oleae.
Toxicity of Bacillus thuringiensis beta-exotoxin to three species of fruit flies (Diptera: Tephritidae).
The current study describes toxic effects of the Bacillus thuringiensis beta-exotoxin toward 3rd instars of 3 fruit fly species: Anastrepha ludens (Loew), A. obliqua (Macquart), and A. serpentina (Wiedemann). The beta-exotoxin was highly toxic to all 3 species tested, with LC50 values calculated as 0.641, 0.512, and 0.408 microgram/cm2 of filter paper used to expose the larvae, for A. ludens, A. obliqua, and A. serpentina, respectively. Exposure to beta-exotoxin was associated with an increase in the incidence of deformed pupae. The adult survivors from beta-exotoxin treatments showed no negative effects in terms of their longevity, fecundity, or egg eclosion (fertility). We conclude that the beta-exotoxin may have potential as a control agent for fruit fly pests.
Modelling of Mooney viscosity relaxation in natural rubber
Abstract Better assessment of natural rubber (NR) quality and processability, through the identification of new attributes, is still a major challenge. With this scope, 12 model samples of natural polyisoprene and two of synthetic polyisoprene were characterized in terms of Mooney torque relaxation, using the standardized ISO289 method (ML(1+4)100, explained later in the Section 1 ). The main purpose of this study was to identify a model that gave a better fit for the experimental decay of Mooney torque over time (ML(t)=f(t)) than the usual power law model used before (Y=at−b, [G.M. Bristow, A.G. Sears, The use of novel parameters in the assessment of natural rubber processability, NR Technol. 18 (1987); H.G. Burhin, W. Spreutels, J.M. Campbell, MV2000 Mooney viscometer: Mooney relaxation measurements on raw polymers and compounded rubber stocks, Kautsch. Gummi Kunstst. 43 (1990) 431]). The results showed that a generalized Maxwell model, and the Wu–Abbott empirical model ( Y = 1 − a Ln ( t ) − ( b t / ( c + t ) ) ) [T. Wu, J.A. Abbott, Firmness and force relaxation characteristics of tomatoes stored intact or as slices, Postharvest Biol. Technol. 24 (2002) 59–68], recently used for describing stress relaxation of tomato flesh, allowed a better description of the relaxation curve for the samples studied than the power law or stretched exponential traditionally used. Moreover, the total relaxation time (τm) given by the generalized Maxwell model showed good correlation with the total gel content of the samples studied.