Immune reactions of Chironomus larvae (Insecta: Diptera) against bacteria

• Published in: Journal of insect physiology Vol. 33; no. 12; pp. 993 - 1004
• Main Authors: Götz, Peter, Enderlein, Gisela, Roettgen, Inge
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Ltd 1987; Elsevier
• Subjects: bacterial pathogenicity; Biochemistry. Physiology. Immunology; Biological and medical sciences; Chironomidae; Chironomus; encapsulation; Fundamental and applied biological sciences. Psychology; immunization; insect immunity; Insecta; Invertebrates; nodule formation; phagocytosis; phenoloxidase activation; Physiology. Development; phenoloxidase activation; phagocytosis; encapsulation; nodule formation; immunization; Chironomus; bacterial pathogenicity; insect immunity; Chironomidae; Encapsulation; Entomopathogen; Animal microorganism relation; Immune response; Insecta; Galleria mellonella; Defense; Pathogenicity; Pyralidae; Larva; Arthropoda; Lepidoptera; Bacteria; Chironomus thummi; Invertebrata; Chironomus plumosus; Diptera; Phagocytosis
• ISSN: 0022-1910; 1879-1611
• DOI: 10.1016/0022-1910(87)90013-8

Humoral encapsulation (“melanization”) represents the predominant defence reaction of Chironomus larvae against injected bacteria. Only low levels of phagocytic activity were observed; cellular encapsulation and nodule formation were completely missing due to low numbers of haemocytes. No other humoral antibacterial activity was detected in normal Chironomus haemolymph and even haemolymph of preinjected (“immunized”) Chironomus larvae showed little inhibition of bacterial growth on agar test plates. Low cellular and lytic activity of Chironomus haemolymph against bacteria is well compensated for by its fast and efficient capacity of humoral encapsulation. Within 5–10 min, even high numbers of injected bacteria (up to 10 5 per larva) were surrounded by capsular material. Within this range of injection dose, the fates of pathogenic and non-pathogenic strains were identical, and bacteria which are highly pathogenic for many other insects, e.g. larvae of Galleria mellonella, proved to be harmless to Chironomus larvae. The rapidity of humoral encapsulation may prevent the release of toxins or enzymes by which pathogenic bacteria normally damage its host and weaken its immune system.