Submitted to: Journal of Invertebrate Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/7/1997
Publication Date: N/A
Interpretive Summary: Microsporidia (Protozoa) are organisms that hold promise for biological control of insects. Microsporidian spores contains high concentrations of the sugar trehalose. This sugar is essential for germination and infection of a new host. Its presence is also a good indicator of the health of the spore. This study provides basic knowledge on the quantity of sugar within microsporidian spores and when it is acquired. Spores were fed to corn earworm larvae and harvested at various times during development. Stages of development were separated by density gradient centrifugation (according to their buoyancy) then counted, measured and assayed for sugars. Large amounts of sugar was found to be present only in the most dense and mature spores. These results prove that the sugar is produced at the very end of development and is responsible for the increased density. These findings are significant for two reasons: The death of the insect host might be explained by the sudden nutritional drain occurring during spore maturation, also, mature, infective spores can be separated reliably from immature spores of similar appearance. This knowledge is useful for producing spores, either for biological control or for research.
Technical Abstract: Helicoverpa zea larvae were infected with Vairimorpha necatrix. The fat body was triturated and sporulation stages were fractionated according to buoyant density by Ludox density gradient centrifugation. Spores and sporulation stages formed two minor bands with buoyant densities of 1.072 and 1.121 g/ml, and two major bands with buoyant densities of 1.150 and 1.198 g/ml. The higher bands of less dense sporoblastic stages first appeared 96 hours following infection and the band containing the heaviest (1.198- g/ml) and most refringent mature spores appeared last, ca. 24 hr after the appearance of the other bands. Bands remained in the same relative positions, regardless of the time after inoculation. The concentration of sugar in the spores from the 1.198 g/ml band was more than four times the concentration found in spores in the 1.150 g/ml band and accounted for more than 60% of the increase in spore weight between the two density classes. Similar tests with Nosema algerae yielded similar results, with sugars accounting for 88% of the increased spore weight. Sugar acquisition appears to occur concurrent with attainment of the final spore density and perhaps signals spore maturation.