James D. Harper

Effects of Bacillus thuringiensis Nuclear-Polyhedrosis Virus Mixtures on Trichoplusia ni Larvae

Effects of exposure to Bacillus thuringiensis and a nuclear-polyhedrosis virus (NPV) on larvae of the cabbage looper, Trichoplusia ni , were determined in laboratory experiments. Mortality curves Were established for each pathogen and served as the basis for the tests. Third-instar larvae averaging 15 mg body weight were inoculated by being on a diet containing desired concentrations of the pathogens. The ELD 50 for B. thuringiensis was 300 IU/ml of diet and for NPV, 2.27 × 10 3 polyhedral inclusion bodies/ml of diet. Mortality data from larvae exposed to both pathogens simultaneously at generally low dosages indicated that the effects of the pathogens in combination were additive. Results from experiments in which larvae were stressed by exposure to NPV for 24-96 hr prior to exposure to B. thuringiensis showed that increased mortality was an additive effect of the two pathogens. Pupae from larvae exposed to B. thuringiensis were significantly smaller than those from larvae exposed to NPV alone or to no pathogen.

Biochemical comparison of virion proteins from five nuclear polyhedrosis viruses infecting plusiine larvae (Lepidoptera: Noctuidae)

Abstract The virions of six isolates of five nuclear polyhedrosis viruses (NPV) infecting plusiine larvae (Lepidoptera: Noctuidae) were reproducibly separated by sucrose density gradient centrifugation and fractionation. Purity of the preparations was established by electron microscopy. Virion proteins were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE); each produced 12 distinct polypeptides ranging from 10,300 to 82,900 mw. Qualitative and quantitative differences were found between most of the polypeptide patterns. The singly embedded viron (SEV)-type isolates had two major components with mw in the range of 32,900–35,200; multiply embedded virion (MEV)-type isolates had a major component of ca. 12,500 mw. SEV isolates showed almost no within-group differences, while minor differences were found among the MEV banding patterns in both intensity and presence of certain bands. Capsids and envelopes from MEV had two to four polypeptides with mw between 10,800 and 26,900. The presence of more than one polypeptide and electron microscopy of sample composition suggested that the capsid and envelope are composed of several distinct proteins.

Food consumption by cabbage loopers infected with nuclear polyhedrosis virus

Abstract The effects of age, temperature, and dose on artificial medium consumption by healthy and nuclear polyhedrosis virus-infected cabbage looper larvae were measured using gravimetric methods. Instar in which lethal infection occurred was more closely related to subsequent food consumption than was larval age in days. Larval cabbage loopers, lethally infected in either the first or second instar, consumed 2% or less of their potential consumption. Larvae infected in the third instar consumed ca. 5% of their subsequent potential. In the fourth instar, this amount increased to ca. 10%. If infection occurred in the fifth instar, no significant amount of feeding was prevented. Increasing the virus dosage significantly decreased consumption and length of feeding period over the range of dosages tested. The relationship between consumption patterns of diseased and healthy insects remained constant over a 20–35°C temperature range.

Incidence of Entomophthora sp. and other natural control agents in populations of Pseudoplusia includens and Trichoplusia ni

Abstract A species of Entomophthora was observed as a mortality factor in populations of Pseudoplusia includens and Trichoplusia ni in cotton and soybean fields throughout Alabama. Resting spores appear identical to those of Tarichium gammae . The incidence of this fungus in host populations, as well as other disease agents and parasites, was determined from larval samples collected throughout the State. Entomophthora infected 8% of all loopers collected on cotton as compared to 35% on soybeans. T. ni nuclear polyhedrosis virus infected 41% of all loopers collected from cotton but no mortality attributable to virus was found in loopers collected on soybeans, which were predominantly P. includens . Studies in 1969 and 1970 on the incidence of Entomophthora sp. in a population of P. includens infesting soybeans in central Alabama have shown it to infect between 50 and 95% of all individuals present from early August through mid-September, the period of densest abundance of the caterpillars. Spicaria sp. was also present during August and September but did not contribute significantly to reduction in population levels until late in the season. Parasites accounted for less than 1% of all mortality in each year and predator populations were very small during the periods of observation.

Analysis of deoxyribonucleic acid from five nuclear polyhedrosis viruses infecting plusiine larvae (Lepidoptera: Noctuidae)

Deoxyribonucleic acid (DNA) from isolates of five nuclear polyhedrosis viruses (NPV) from lepidopterous hosts of the noctuid subfamily Plusiinae was analyzed by ion-exchange and paper chromatography. Viruses and production hosts were: Trichoplusia ni singly embedded virion type (SEV) from T. ni, Pseudoplusia includens SEV from P. includens, T. ni multiply embedded virion type (MEV) from T. ni, Autographa californica MEV from A. californica, A. californica MEV from T. ni, and Rachiplusia ou MEV from R. ou. Neither uracil nor 5-methyl cytosine was detected in the DNAs. Adenine:thymine (A:T) and guanine:cytosine (G:C) ratios were nearly constant for all the NPVs. AT:GC ratios for the SEVs were 1.60 and 1.57 and were clearly separable from those of the MEVs which ranged from 1.32 to 1.38. No differences in DNA composition within SEV or MEV groups were apparent.

Serological comparison of polyhedron protein and virions from four nuclear polyhedrosis viruses of plusiine larvae (Lepidoptera: Noctuidae)

Abstract Purified polyhedron proteins and purified, ultrasonicated virions of four nuclear polyhedrosis viruses (NPVs), separable into two morphologic groups of singly and multiply embedded virion types (SEVs and MEVs), were investigated by immunodiffusion and immunoelectrophoresis. The four viruses were Pseudoplusia includens SEV, Trichoplusia ni SEV, T. ni MEV, and Autographa californica MEV. In immunodiffusion, SEV polyhedron proteins formed two precipitin bands with antiserum to SEV polyhedron proteins, while MEV polyhedron proteins formed only one. All four proteins formed one precipitin band with antiserum to MEV polyhedron protein, with a spur between SEV and MEV proteins. In immunoelectrophoresis, mobilities of SEV proteins were significantly different from those of MEVs. Precipitin arc patterns were similar to those in immunodiffusion when electrophoresis was carried out at 4 C; at room temperature, a single arc of precipitation formed with all four proteins. SEV virions formed five possibly identical precipitin bands in immunodiffusion with antiserum to SEV virions. MEV virions formed three possibly identical precipitin bands when reacted with antiserum to MEV virions. Little or no cross-reactions were observed between SEV and MEV virions or between virions and polyhedron proteins. In immunoelectrophoresis, SEV virions formed three precipitin arcs in reactions with SEV antisera and none with MEV antisera; MEV virions formed two arcs with MEV antisera and none with SEV antisera. When antisera were subjected to electrophoresis, five arcs were formed by SEVs and three by MEVs in homologous systems, and none were formed in heterologous systems.