G. R. Sutter

Reciprocal infectivity of nuclear polyhedrosis viruses of the cabbage looper and alfalfa looper

The cross-infectivity of two distinct nuclear polyhedrosis viruses, one isolated from the cabbage looper, Trichoplusia ni, which has the virions embedded singly in the polyhedral matrix; and one isolated from the alfalfa looper, Autographa californica, in which the virions are embedded multiply, was investigated. The multiply embedded virus was at least four times more pathogenic than the singly embedded virus to the cabbage looper and was also highly infective to the alfalfa looper. In contrast, the singly embedded cabbage looper virus was less infective to both the original and the alternate hosts. Cross-infectivity of the viruses was confirmed with both light and electron microscopes.

Ecological factors affecting the pathogenicity of Bacillus thuringiensis var. thuringiensis to the European corn borer and fall armyworm

Ecological factors which might affect the pathogenicity of Bacillus thuringiensis when it is used to control field pouplations of the European corn borer, Ostrinia nubilalis, and the fall armyworm, Spodoptera frugiperda were tested in the laboratory. The bacterium caused only minor changes in the pH of the hemolymph and hindgut, but changes in the foregut and midgut were considerable. Gut contents of normal European corn borers, injected into the hemolymph of normal corn borers, caused death within 20 hours. A bacteriophage isolated from a corn borer and from a spore powder of B. thuringiensis reduced the rapidity with which the treated larvae died, but did not reduce the final mortality. Ultraviolet irradiation of a spore powder of B. thuringiensis for 72 hours eliminated its pathogenicity for both insect species. A temperature of 32°C was more conducive to rapid mortality of larvae treated with B. thuringiensis than were lower temperatures. A spore suspension of B. thuringiensis stored for 1–10 months was more pathogenic than a fresh preparation of the same spore powder.

The effect of Bacillus thuringiensis components on the development of the European corn borer

Abstract Spores, crystals, and exotoxin from Bacillus thuringiensis were fed to larvae of the European corn borer, Ostrinia nubilalis . Used separately, the spores and crystals retarded the growth rates of the host insect, but a combination of spores and crystals was necessary to cause mortality of treated larvae. The exotoxin produced by B. thuringiensis did not affect the European corn borer under the conditions of the test.

Influence of corn planting date on the life stage development and phenology of Diabrotica virgifera virgifera.

Under field conditions in eastern South Dakota, USA three different planting dates of corn and three times of egg infestation were used to imposed synchronous and asynchronous timing of corn growth and Diabrotica virgifera virgifera LeConte egg hatch and subsequent development. Median occurrence of each of the three larval stages and of the adult stage for each of the infestation‐planting treatments was determined by relating occurrence to thermal units and to days after infestation. No significant differences were found among the treatments for median occurrence of each life stage when the thermal unit approach was used. However, significant differences were found among treatments for median occurrence when the day after infestation approach was used. Consistent parameters are needed for prediction of the occurrence of life stages of this insect. Despite the various imposed conditions, this study indicates that the least variable method of predicting life stage occurrence and adult emergence of D. v. virgifera was the use of thermal unit accumulations (base 11 °C).

Characterization of entomopox virions of the army cutworm, Euxoa auxiliaris (Lepidoptera: Noctuidae)

Abstract Virions were released from virus-containing inclusions (VCI) of an entomopoxvirus of the army cutworm, Euxoa auxiliaris , with carbonate-thioglycolate solution. Knoblike projections present on the surface of the viral envelope were removed by digestion with trypsin. Trypsin-treated virions were homogeneous in both sucrose and CsCl gradients. The virions were similar to vertebrate poxviruses in morphology, contained 1.13 ± 0.3% DNA and had a buoyant density of 1.261 ± 0.003 gm/cm 3 in CsCl. The virion preparations were infective and possessed RNA polymerase activity. Of eight species of Lepidoptera tested, only the species from which the virus was originally isolated proved susceptible to infection.