Loss of Hemolectin reduces the survival of Drosophila larvae after wounding

Coagulation involving both hemocytes and humoral factors is important for insect survival and immune defense. Hemolectin is a major larval clotting factor in Drosophila, and hemolymph from hml mutants does not clot ex vivo. Yet surprisingly third instar hml larvae survived injury as well as controls. The number of hemocytes in circulation changes during larval development. Reasoning that this could affect coagulation, we studied larval survival after injury at different stages. We found that hml larvae survived less than controls when injured during the feeding stage with fewer hemocytes. This important in vivo result reinforces the role of Hemolectin in larval hemostasis. A subtle effect of hml on immunity was found in adults. Similar experiments on hml mutant larvae gave different results, but feeding stage hml larvae were differentially sensitive to infections with different strains of Serratia marcescens.

► Hemolectin is an important clot protein in Drosophila larvae.
► We show the 1st hml mutant larval in vivo phenotype.
► Larval developmental stage is important in Drosophila clot studies.
► Assessing the role of the larval clot in immunity is complex.