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Physiopathology in the lawn armyworm, Spodoptera mauritia acronyctoides (Guenée) (Lepidoptera: Noctuidae) caused by a nuclear polyhedrosis virus and a Nosema

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Title:Physiopathology in the lawn armyworm, Spodoptera mauritia acronyctoides (Guenée) (Lepidoptera: Noctuidae) caused by a nuclear polyhedrosis virus and a Nosema
Authors:Takei, Gerald Hideo
Date Issued:1971
Abstract:Two infectious diseases found associated within the armyworm Spodoptera mauritia acronyctoides (Guenee) in Hawaii were investigated. One disease is caused by a nuclear polyhedrosis virus, NPV, and the other is caused by a microsporidian. The host, apparently was introduced from the Pacific in 1953. The two pathogens were found infecting the armyworm in the field later, and were both reported to be highly infectious. The virus has been described as Borrelinavirus sp. and the microsporidian, as Nosema sp. The axenically reared hosts were fed purified inocula of the pathogens and observed individually to record the effects. Synxenic combinations of only pathogen and host were maintained throughout the treatments by working within 8 dram vials in which the armyworms were reared and by including antimicrobial agents in the oligidic diet devised for the axenic rearing of the insect host. Under synxenic conditions the NPV was determined to be very infective to the armyworm. The LD50 for 4th instar larvae was 9.29 x 104 polyhedra per vial which contained diet medium for one larva averaging 6.33 ± 0.14 gms. With Nosema, infection of 4th instar armyworms by the microsporidian was not as high as previously reported. A concentration of 1.25 x 10 8 spores per vial was required before overt infection by the microsporidian could be observed. Nosema appears to require the effects of other microorganisms and stress factors in order for it to be highly infective to the armyworm. Simultaneous infections of the 4th instar armyworm by both the virus and the microsporidian could not be observed through applications of inocula for both pathogens. The hemocytes in S. mauritia were observed to change in quantity and form with larval growth and with metamorphosis. Most of the different types of blood cells described partially in each of many different insect species were believed to be observed in this one host species during its growth and development. An increase in content of each of the proteins separated in the hemolymph of armyworms was also observed to occur with age. Twenty basic protein bands were separated by the electrophoresis, at pH 8.4, of hemolymph from armyworms older than 15 days. The effects of stress factors on the host insect which included sub-lethal inoculations of NPV and Nosema, were apparent in the hemolymph from specimens subjected to these stresses. Some hemocytes appeared to fuse together prematurely and manifested functions which were usually found in older larvae. There appeared, generally, to be a precocity in the development of hemocytes. The precocious development was also apparent with certain blood proteins which were determined to be present in the hemolymph in greater quantities than expected for the age of larvae bled. For high sub-lethal NPV inoculations, the increases in these hemolymph proteins were believed to be due to early stages of infection by the virus and were detected by comparing treated armyworms reared on diet containing formaldehyde with similarly treated armyworms reared on diet not containing formaldehyde. Hemolymph from armyworms which were definitely infected by virus but were living, revealed a. general reduction in quantities of blood proteins. This was similar to the reduction in proteins in hemolymph from morbid and dead larvae which resulted from virus infections. The electrophoregrams for such hemolymph samples appeared to be like those for hemolymph from young larvae. Other disease symptoms were observed for the lawn armyworm. Some symptoms appeared to be associated with two different forms of polyhedra-like bodies. One, a square for~, was found in the accessory glands of adult females, and the other, an oblong form, was found throughout various host tissues but in low numbers. These bodies were also present in specimens from field populations. The bodies appeared to be produced or altered by the reaction of the host insect to stress factors. The survival of S. mauritia appeared to be better when reared on axenic diet containing formaldehyde at levels of about 0.01% by mass.
Thesis (Ph. D.)--University of Hawaii, 1971.
Bibliography: leaves [173]-179.
xi, 179 l illus., graphs, tables
Rights:All UHM dissertations and theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission from the copyright owner.
Appears in Collections: Ph.D. - Entomology

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