Hemolymph melanization and alterations in hemocyte numbers in Lymantria dispar larvae following infections with different entomopathogenic microsporidia

• Published in: Entomologia experimentalis et applicata Vol. 113; no. 2; pp. 77 - 86
• Main Authors: Hoch, G, Solter, L.F, Schopf, A
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Science Ltd 01.11.2004; Blackwell
• Subjects: Biochemistry. Physiology. Immunology; Biological and medical sciences; Biological control; Control; entomopathogenic protozoa; enzyme activation; Fundamental and applied biological sciences. Psychology; hemocytes; hemocytic encapsulation; hemolymph; hemolymph melanization; immune response; infection; insect immunity; Insecta; Invertebrates; larvae; Lepidoptera; Lymantria dispar; Lymantriidae; Malacosoma americanum; melanization; Microsporidia; microsporidiosis; Microsporidium; Physiology. Development; Phytopathology. Animal pests. Plant and forest protection; prophenoloxidase; Protozoa. Invertebrates; semi-permissive hosts; total hemocyte count; Vairimorpha; Host parasite relation; Entomopathogen; Insecta; Biological control; Microsporidia; Pest; Hemocyte; Microbiological control; Beneficial animal; hemolymph melanization; Melanization; Protozoa; Lymantriidae; Immune response; Forest tree; Hemolymph; Parasite; hemocytes; Defense; Cnidosporidia; Infection; Arthropoda; Lepidoptera; Invertebrata; Lymantria dispar
• ISSN: 0013-8703; 1570-7458; 1570-8703
• DOI: 10.1111/j.0013-8703.2004.00203.x

Lymantria dispar (L.) (Lepidoptera: Lymantriidae) larvae can be infected in the laboratory with a variety of entomopathogenic microsporidia. In many cases, however, L. dispar is only a semi‐permissive host for such infections. In this study, we analyzed changes in the melanization of hemolymph and hemocyte numbers in L. dispar larvae after inoculation with various entomopathogenic microsporidia. We compared the infections produced by microsporidia isolated from L. dispar and infections produced by isolates from other Lepidoptera to which L. dispar is only a semi‐permissive host. Microsporidiosis induced a significant activation of the prophenoloxidase system leading to melanization; activation was highest when the pathogen caused heavy infections of the fat body, which was the case with two microsporidia originally isolated from L. dispar. Infection of only the silk glands or light infection of the fat body by two Vairimorpha spp. from other lepidopteran hosts elicited a lower response. Very light infections caused by a microsporidium isolated from Malacosoma americanum were not accompanied by elevated hemolymph melanization activity. Heavy infections by Endoreticulatus spec. that remained restricted to the gut tissue likewise did not elicit melanization. One Vairimorpha spec. from L. dispar induced a significant increase in total hemocyte numbers; the other infections led to temporarily decreased numbers. Microscopic examinations showed that parts of infected tissue were encapsulated by hemocytes. We conclude that measured alterations in hemolymph melanization and hemocyte numbers were likely to be induced by the damaging effects of heavy infections. Observed defense responses did not prevent the progression of infections.