John D. Paschke

Pathology of an Entomophthora infection in the eastern subterranean termite Reticulitermes flavipes (Kollar)

Abstract In laboratory pathogenicity tests with the eastern subterranean termite, Reticulitermes flavipes (Kollar), Entomophthora coronata Kevorkian produced a mortality of 97 percent 84 hours after inoculation. Entomophthora virulenta Hall and Dunn was found to be nonpathogenic under similar conditions. In a virulence test against termites, two isolates of E. coronata showed no significant difference. Histological examination indicated that germ tube penetration of the integument resulted before death of the termite and apparently was not restricted to a particular site. In the digestive tract, germinating conidia of E. coronata were found penetrating the oesophageal wall but not the crop, midgut and hindgut. Invading hyphae first attacked the fat body and musculature and then rapidly destroyed the remaining tissue as early as 32 hours after inoculation.

Alkali-liberated granulosis virus of Trichoplusia ni: I. Density gradient purification of virus components and some of their in vitro chemical and physical properties

Abstract Trichoplusia ni capsules were purified by a combination of differential and ratezonal centrifugation on 50 to 80% sucrose gradients. The virus was released and purified from the inclusion body protein by exposure to weak alkali and subsequent centrifugation on 10 to 40% sucrose gradients. Virus preparations maintained in 0.01 m phosphate buffer (pH, 7.8) demonstrated 3 sedimenting forms on 10 to 40% sucrose gradients which were designated as A and B (with outer envelope) and Y (without outer envelope). The virus was unstable in 0.01 m phosphate buffer pH 7.8, and had a tendency to aggregate, and/or dissociate into the outer and inner membranes and a top fraction. The infection properties of each virus form and the top fraction were tested. Other buffers or additives did not change these phenomena. These virus forms and components were separated by a combination of sedimentations on 10 to 40% and 5 to 20% sucrose gradients and their ultrastructure confirmed by electron microscopy. Solutions containing virus forms A and B exhibited an E 260 E 280 of 1.26 and DNA and protein concentrations of 27.4 and 28.8 μg DNA/E260 and 105 and 109 μg protein/E260 for forms A and B, respectively. Preparations of the Y form contained 73.0 μg DNA/E260 and 258 μg protein/E260, but exhibited only 53% the ultraviolet extinction of virus forms A and B. Studies confirmed that the granulosis virus of Trichoplusia ni is ultrastructurally similar to other granuloses.

Midgut pH in different instars of three Aedes mosquito species and the relation between pH and susceptibility of larvae to a nuclear polyhedrosis virus.

Abstract Midgut pH values were determined for second, third, and fourth instar larvae of Aedes epactius, A. atropalpus, and A. scutellaris. Larvae were fed mixtures of pH indicators and kaolin clay and observed with a stereoscope to determine midgut pH. No significant difference was found in midgut pH values among the three species when the same instar was compared. However, significant differences were found in the length of the high (9.0 to 10.0) pH region when comparing the three instars for each species. Increasing age of treated A. epactius larvae caused a decrease in susceptibility to a nuclear polyhedrosis virus—from 56% infection for 12-hr-old larvae declining to 8% infection for 72-hr larvae. The increased length of the high pH region may relate to decreasing susceptibility of A. epactius to a nuclear polyhedrosis virus as the larvae age.

Crowding as the primary factor in the production of the agamic alate form of Therioaphis maculata (Homoptera: Aphididae)

Abstract The influence of various environmental factors on the production of the agamic alate form of the spotted alfalfa aphid, Therioaphis maculata (Buckton), has been investigated in the laboratory. Results indicate that crowding is the only factor inducing the development of winged forms, whereas parentage and nutritional state are secondary modifiers. The stimulus is entirely postnatal and is confined to the first instar. Time of inception and duration of crowding are both of importance and appear to reinforce one another in determining alate percentages. There is a specific length of time during which initiation of the stimulus is effective, since animals more than 18 hr of age are no longer receptive. If parents are prevented from depositing, so that larvae are held in utero beyond their normal birth hour, the duration of stimulus initiation time is correspondingly shortened. The crowding stimulus does not involve excretory products, pheromones, or induced changes in the host plants. It appears to require physical contact between live animals.

Density-gradient centrifugation of the virions liberated from Rachiplusia ou nuclear polyhedra

Abstract Rate zonal centrifugation of the virions liberated from Rachiplusia ou nuclear polyhedra results in the formation of numerous opalescent zones within the sucrose gradient. Evidence is presented which indicates that the various zones correspond to virions containing different numbers of nucleocapsids. That is, the virions are sedimenting according to the number of nucleocapsids within. This physical evidence, in conjunction with the morphology of the virions (ultrastructure), suggests that the R. ou nuclear polyhedrosis virus produces multiploid virions.

Biochemical and biophysical properties of two strains of mosquito iridescent virus.

Abstract Properties of “R” and “T” strains of mosquito iridescent virus (MIV) were investigated. Several differing biophysical properties of the two strains were observed due to size differences. The electrophoretic mobility curves of the two strains were somewhat different although the isoelectric points of pH 3.15 and pH 3.30 for RMIV and TMIV, respectively, were similar. The two strains appeared to be antigenically identical but the per cent protein, DNA, and lipid of the two were dissimilar. Other than size variation, no morphological differences between RMIV and TMIV could be detected.

Simultaneous infection with the nucleopolyhedrosis and granulosis viruses of Trichoplusia ni

Abstract Simultaneous infection with nucleopolyhedrosis and granulosis viruses produced an increased percentage mortality of the test insects as compared to that caused by either virus individually. Thermal inactivation of quantified doses of the virus provided various combinations of active and inactive inocula. It was determined that no synergism or interference occurred and that the increased mortality was due to an additive effect of the two infectious agents.

Bioassay of the nucleopolyhedrosis and granulosis viruses of Trichoplusia ni

Abstract Bioassays of nucleopolyhedrosis and granulosis viruses of Trichoplusia ni were conducted utilizing different viral preparations during a 3-year period. All data were analyzed using Berksons minimum logit chi-square ( χ 2 ) method for estimation of the mld . The method was facilitated by the development of a computer program for the IBM 7094-1401 system.

Histopathology of a nuclear polyhedrosis infection in Aedes epactius with observations in four additional mosquito species

Abstract Aedes epactius larvae were utilized to study the infection sequence of the nuclear polyhedrosis virus (NPV) from Aedes sollicitans. From 30 min to 6 hr postinoculation, polyhedra and many free virions were observed in the larval midgut lumen. Penetration of the midgut cells by virions was not observed. The first infected nuclei were observed 12 hr postinoculation. Nucleocapsids initially exhibited electron translucent cores which became electron dense before the nucleocapsids acquired an envelope. Envelope acquisition occurred through a process of de novo membrane morphogenesis. Occlusion of the singly embedded virions began by 18 hr postinoculation with the mature rough-surfaced polyhedra averaging approximately 1 by 2 μm. Unusually long nucleocapsids (approximately two or three times the length of other nucleocapsids) were only observed in late infection period nuclei. There was no evidence that long nucleocapsids represented an early developmental stage for nucleocapsids of standard length. Infection was restricted to midgut nuclei and gastric caecae cells. Infected early instar A. epactius larvae became moribund 36 to 40 hr postinoculation and infected midgut nuclei were observed to undergo lysis. The late stages of NPV infection were observed in larvae of A. annandalei, Wyeomyia smithii, Toxorhynchites brevipalpus, and Eretmapodites quinquevittatus. Virion development and occlusion in these species was basically identical to the sequence observed in A. epactius larvae.

Proteins of Two Strains of Mosquito Iridescent Virus

A comparison of the proteins of ‘R’ and ‘T’ strains of mosquito iridescent virus (M1V) was made using PAGE and amino acid analysis. The banding patterns of RMIV and TM1V were similar, each showing 9 proteins. None of the proteins reacted with Schiff’s reagent. When the proteins of RMIV and TMIV were S-carboxymethylated, PAGE showed only 4 proteins for both strains compared with the 9 bands detected in control preparations. Amino acid analyses and tryptic peptide analyses indicated that the proteins of the two strains were very similar.