D. L. Hostetter

Natural and induced epizootics of Nomuraea rileyi in soybean caterpillars

Abstract A heavy application of Nomuraea rileyi conidia significantly altered the epizootic pattern normally associated with soybean caterpillars. The initial detection and peak incidence of infected caterpillars from treated plots was advanced at least 14 days compared with untreated plots. The peak therefore occurred prior to and during the stages of soybean growth that were most sensitive to defoliation by caterpillars (R-8, R-9). In untreated plots the peak incidence of infection occurred after the damage had been done. Low populations of susceptible caterpillars (less than 1/row-ft) that are infected with N. rileyi may produce sufficient conidia to regulate incipient pest populations. The half-life of conidia applied to soybean foliage was 2 days, and only 3% of the original conidia activity was present after 9 days.

Activity of the nuclear-polyhedrosis virus of the cabbage looper evaluated at programmed temperature regimens

Abstract Each larval instar of the cabbage looper, Trichoplusia ni, was treated in the laboratory with a peroral, standardized lethal dose of the nuclear polyhedrosis virus disease and maintained until death at one of three programmed regimens of temperature. The resulting experimental data were tested in the field and found to provide a reliable method of predicting the course of epizootics.

Efficacy of insect viruses propagated in vivo and in vitro

Laboratory bioassay and field trials demonstrated that the Autographa multiple-embedded (MEV) nucleopolyhedrosis virus (NPV) and Trichoplusia ME-NPV produced in cell culture was as effective as that produced in larvae. No difference in activity between the Autographa MEV, Trichoplusia MEV, and Trichoplusia SEV NPV was detected.

The recovery of virulent nuclear-polyhedrosis virus of the cabbage looper, Trichoplusia ni, from the feces of birds

English sparrows have been observed methodically searching cabbage plants for insects. Cabbage loopers, Trichoplusia ni, in the advanced stages of nuclear polyhedrosis, lose their natural defense mechanisms and become easy prey for birds. Examination of individual aqueous suspensions of bird feces collected from a cabbage field in St. Louis County, Missouri, in July 1968, revealed high numbers of polyhedra inclusion bodies in 9 of the 12 samples. Per os inoculation of third instar T. ni larvae proved that all 12 suspensions contained virulent polyhedra (i.e., virus) capable of producing the polyhedrosis.

Laboratory studies of the entomopathogenic fungus Nomuraea rileyi: Soil-borne contamination of soybean seedlings and dispersal of diseased larvae of Trichoplusia ni

Abstract Germinating soybean seedlings were contaminated by soil-borne conidia of the entomogenous fungus Nomuraea rileyi . Although N. rileyi was detected on the unifoliate and trifoliate leaflets, most of the inoculum was found on the cotyledons. Diseased larvae of Trichoplusia ni released on the first trifoliate leaves of soybean plants dispersed to all trifoliates and died. In this way, inoculum is produced that infects other larvae feeding on these leaves.