Dudley E. Pinnock

The field persistence of Bacillus thuringiensis spores

Abstract A method for measuring viable spore counts on leaf surfaces is described and utilized to provide data for estimating the field persistence of four Bacillus thuringiensi formulations. The estimates of persistence are based on the assumption of constant average force of mortality acting on the spores over time and are expressed in terms of viable spore half-life. For one of the formulations, persistence is compared at two differing environmental settings.

The field persistence of Bacillus thuringiensis spores on Cercis occidentalis leaves

Abstract The field persistence of viable spores of four Bacillus thuringiensis formulations, Amdal ® , Biotrol ® BTB 183, Thuricide ® HP, and Thuricide ® 90TS, was measured and compared on leaves of Cercis occidentalis . For Amdal, Biotrol BTB 183, and Thuricide 90TS the field persistence was compared also at two locations, Auburn and Sacramento, California, which differed in altitude and climate. The comparisons of field persistence were based on a segmented linear model of the decay of average viable spore count on a logarithmic scale, because much of the field data strongly rejected the simple log linear model. No significant difference in field persistence of viable spores was found between the two locations. Significant differences were found in both magnitude and pattern of field persistence compared to previously reported measurements of Thuricide 90TS, where leaves of Quercus agrifolia were the substrate, and a log linear pattern of decay of viable spore count was found. The persistence half-life of Thuricide 90TS on Q. agrifolia leaves at Monterey, California, was 3.9 days, compared to a persistence half-life during the first 3 days of 0.63 day on leaves of C. occidentalis with the pooled Auburn/Sacramento data (two-sided P The persistence half-life for Thuricide HP during the first 3 days was 1.85 days, which was significantly different from the corresponding result of 0.58 day for Amdal and 0.63 day for Thuricide 90TS ( P

Physicochemical Characterization of a Small RNA Virus Associated with Baculovirus Infection in Trichoplusia ni

An RNA virus was isolated from Trichoplusia ni larvae infected with inoculum of the baculovirus of Autographa californica. Physicochemical characterization has revealed a 35-nm virus with a density in CsCl of 1.3 g/cm3 and a sedimentation coefficient of 200S. The virus consisted of 10--15% single-stranded RNA with an apparent molecular weight of 1.9 x 10(6) and coat protein with a subunit size of 67,000. The virus is similar to the Nudaurelia capensis beta virus and also possesses some interesting similarities to the mammalian caliciviruses. The proposed cryptogram of the virus is R/1:1.9/12:S/S:I/O.

Beauveria tenella as a control agent for mosquito larvae.

Abstract Beauveria tenella was found to be a naturally occurring pathogen in field populations of Aedes sierrensis larvae. Bioassays showed that B. tenella is also pathogenic for larvae of A. aegypti, A. dorsalis, A. hexodontus, Culex pipiens, C. tarsalis , and Culiseta incidens . Inoculation of 5 × 10 3 or 5 × 10 5 blastospores per milliliter into breeding sites of A. sierrensis produced marked reductions in the number of emerging adults.

Effect of tree species on the coverage and field persistence of Bacillus thuringiensis spores

Abstract The effect of leaves of Quercus agrifolia, Cercis occidentalis, Eucalyptus globulus, and Juglans regia on the initial deposit and subsequent rate of decay of viable spores of Bacillus thuringiensis was investigated. Significant differences in the size of the initial viable spore deposit were found between the various species, with E. globulus markedly lower than the others. The viable spore decay patterns of the various species were analyzed using a segmented linear model and significant differences in initial rates of decay were also measured. Thus it appears that the characteristics of the leaves of the treated plants may have an effect on the coverage and field persistence of viable B. thuringiensis spores. Some possible mechanisms for these effects are discussed.

Characterization of Nucleic Acids Associated with Arkansas Bee Virus

Arkansas bee virus (ABV) is a 30-nm isometric virus composed of one major species of polypeptide (mol. wt. 43 X 10(3] and one species of single-stranded RNA (mol. wt. 1.8 X 10(6]. The size of the genomic RNA and the lack of evidence for encapsidation or synthesis of a second smaller RNA species exclude further consideration of this virus for inclusion with the physicochemically similar viruses of the Nodaviridae. Several independent isolations of ABV were made from bees, and in each case it was associated in mixed infection with a picorna-like virus termed Berkeley bee picornavirus (BBPV). No evidence for replicative dependence, serological relationship, or genome relatedness by complementary DNA hybridization was obtained between ABV and BBPV.

The Ultrastructure of a complex basal lamina in the midgut of larvae of Oryctes rhinoceros L. (Coleoptera, Scarabaeidae)

SummaryThe midgut basal lamina of third instar Oryctes rhinoceros larvae was observed to consist of three structured layers. Each layer contained two structural elements regularly arranged with respect to one another. Type I elements appeared to be morphological variations of closed cylinders with increasing diameters in each layer. The layer of basal lamina closest the midgut epithelium had the smallest, most regular Type I elements. In that layer furthest from the midgut cells the Type I elements were the largest and irregular in shape. Type II elements were morphologically similar in all layers, appearing as dense rod-like elements with a triangular cross section in the plane of the lamina. These elements were interconnected by fine fibrils to form a basic repeating unit: One Type II element surrounded by three Type I elements. Perfect packing of the basic units within the layers of the basal lamina resulted in a pattern of each element type surrounded by three elements of the opposite type. However, variability in the packing of the basic repeating unit frequently occurred.Comparison of the basal lamina of 0. rhinoceros with those of other beetles and fleas previously described showed that this repeating unit occurs in almost all basal laminae containing similar structural units. The basal lamina of 0. rhinoceros, however, appears to be the most complex one yet described.

Methods for assessing field persistence of Bacillus thuringiensis spores.

Field persistence was investigated for three concentrations of a Bacillus thuringiensis formulation, Dipel, on leaves of Cercis occidentalis. The application levels were 0.0025%, 0.025%, and 0.25% wv. Logarithmically transformed viable spore counts were analyzed using a segmented linear model. No biologically significant differences were found in rates of viable spore decay for the three levels of application. Statistical methods used in the analysis are described in detail. A model for assessing total effective dose delivered by a B. thuringiensis application is proposed. Application of the total dose model indicates that for typical field application levels more than 90% of total dose is delivered to the insect population during the first day following application.

Development of a model for prediction of target insect mortality following field application of a Bacillus thuringiensis formulation

Abstract A model for predicting mortality of Schizura concinna larvae on Cercis occidentalis trees following application of Bacillus thuringiensis formulations is based on an estimation of the effective dose. This is calculated from the initial application level and field persistence characteristics of the pathogen and from the feeding rate of the target insects. Using the estimated effective dose and the time the pathogen was on the host plant, the probability of larval mortality is calculated by means of a multiple logistic dose-response model. Predicted mortalities for B. thuringiensis applications at concentrations 0.00025, 0.0025, 0.025, and 0.25%, w v , were 7.7, 23.3, 46.2, and 87.1%, respectively. Corresponding, observed mortalities adjusted for larval loss due to forces unrelated to the B. thuringiensis application were 6, 54, 66, and 100%.

Electron microscope observations on granulosis virus replication in the fruit tree leaf roller, Archips argyrospila: Infection of the midgut

Abstract An electron microscope study was made of a granulosis virus causing epizootics in three consecutive generations of the fruit free leaf roller, Archips argyrospila. Replication of the virus in midgut epithelial cells was observed in only one insect, and the cytopathology indicated that viral replication at this site was partially blocked or inhibited.