Six antibiotics were individually incorporated into holidic diets to feed female adults of the Brown Planthopper, Nilaparvata lugens. The results showed that 0.3% Polyoxin S and 0.1% chloramphenicol were best for reducing the number of yeast‐like symbiote (YLS). The presence of 0.1% cycloheximide in the diet resulted in a high nymphal mortality of N. lugens, and induced abnormal YLS or reduced its number. Ampicilline trihydrate, Blasticidin‐S and nystatin were not markedly effective in suppressing the YLS population.
The YLS could be destroyed by exposing the newly hatched nymphs to 35°C for 3 days (heat treatment), but its host insects might grow to the fifth instar; while some of them died due to failure in ecdysis. Electron micrographs showed that the symbiotes of the heat‐treated planthoppers were vacuous with a few residual bodies inside the cell. Death of the heat‐treated insects might be ascribed to partial loss of their symbiotes.
Zusammenfassung
Untersuchungen über einen intrazellulären befeähnlichen Symbionten der Braunen Heuschrecke, Nelaparvata lugens Stal. II. Zur Wirkung von Antibiotika und hohen Temperaturen auf die Symbionten und ihren Wirt
Sechs Antibiotika wurden einzeln der künstlichen Nahrung beigefügt, mit der N. lugens gefüttert wurde. Die Ergebnisse zeigen, daß 0,3% Polyoxin‐S sowie 0,1% Chloramphenicol die Zahl der Symbionten am stärksten reduzierten. Die Anwesenheit von 0,1% Cycloheximid in der Nahrung führte zu hoher Nymphensterblichkeit von N. lugens sowie zur Verminderung der Zahl an Symbionten bzw. zur Entstehung abnormaler Symbionten. Ampicillin‐Trihydrat, Blasticidin‐S und Nystatin hatten keine deutliche Wirkung auf die Symbiontenpopulation.
Die Symbionten konnten dadurch zerstört werden, daß man die frischgeschlüpften Nymphen 3 Tage lang hoher Temperatur (35° C) aussetzte. Ihre Wirtstiere wuchsen zum größten Teil ohne Symbionten bis zur L5, zum geringeren Teil starben sie wegen unterbleibender Häutung. Elektronenmikroskopische Untersuchungen zeigten, daß die Symbionten der mit Hitze behandelten Heuschrecken bis auf einige in der Zelle befindliche Restkörper leer waren. Der Tod der mit Hitze behandelten Heuschrecken kann dem partiellen Verlust an Symbionten zugeschrieben werden.
A nonpathogenic mild strain is essential for control of plant viruses by cross protection. Three amino acid changes, Arg(180)-->Ile(180) (GA mutation), Phe(205)-->Leu(205) (GB mutation), and Glu(396)-->Asn(396) (GC mutation), of the conserved motifs of the helper component-protease (HC-Pro) of a severe strain TW-TN3 of Zucchini yellow mosaic virus (ZYMV), a member of the genus Potyvirus, were generated from an infectious cDNA clone that carried a green fluorescent protein reporter. The infectivity of individual mutants containing single, double, or triple mutations was assayed on local and systemic hosts. On Chenopodium quinoa plants, the GB mutant induced necrotic lesions; the GA, GC, and GBC mutants induced chlorotic spots; and the GAB and GAC mutants induced local infection only visualized by fluorescence microscopy. On squash plants, the GA, GB, GC, and GBC mutants caused milder mosaic; the GAC mutant induced slight leaf mottling followed by recovering; and the GAB mutant did not induce conspicuous symptoms. Also, the GAC mutant, but not the GAB mutant, conferred complete cross protection against the parental virus carrying a mite allergen as a reporter. When tested on transgene-silenced transgenic squash, the ability of posttranscriptional gene silencing suppression of the mutated HC-Pro of GAC was not significantly affected. We concluded that the mutations of the HC-Pro of ZYMV reduce the degrees of pathogenicity on squash and also abolish the ability for eliciting the hypersensitive reaction on C. quinoa, and that the mutant GAC is a useful mild strain for cross protection.
The melanization of Dirofilaria immitis microfilariae in Armigeres subalbatus haemolymph in vitro is a two-step process. Firstly, the microfilariae are encased in a transparent capsule, then the capsule material is melanized later. Benzamadine HC1 and p-amidinophenylmethanesulfonyl fluoride, both serine protease inhibitors, inhibited the deposition of the transparent capsule material and melanization. Diethyldithiocarbamate, a phenoloxidase inhibitor, did not prevent the deposition of the transparent capsule material but it did inhibit melanization. m-Hydroxybenzylhydrazine, a dopa decarboxylase inhibitor, had no inhibitory action on the deposition of the transparent capsule material. However, the time for the transparent capsule to become melanized was delayed due to the presence of m-hydroxybenzylhydrazine in the test system. Immmunocytochemical localization showed that propheoloxidase and/or phenoloxidase was present in the transparent capsule material. These results suggest (1) that prophenoloxidase cascade is essential in the melanization of microfilariae in mosquitoes and its putative activation behaviour is similar to that of other insects and (2) that the deposition of transparent capsule material is the result of the activation of prophenoloxidase by serine proteases and the melanization of the transparent capsule material is due to the presence of active phenoloxidase in capsule.
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