Hemocyte Density Increases with Developmental Stage in an Immune-Challenged Forest Caterpillar

Abstract

The cellular arm of the insect immune response is mediated by the activity of hemocytes. While hemocytes have been well-characterized morphologically and functionally in model insects, few studies have characterized the hemocytes of non-model insects. Further, the role of ontogeny in mediating immune response is not well understood in non-model invertebrate systems. The goals of the current study were to (1) determine the effects of caterpillar size (and age) on hemocyte density in naïve caterpillars and caterpillars challenged with non-pathogenic bacteria, and (2) characterize the hemocyte activity and diversity of cell types present in two forest caterpillars: Euclea delphinii and Lithacodes fasciola (Limacodidae). We found that although early and late instar (small and large size, respectively) naïve caterpillars had similar constitutive hemocyte densities in both species, late instar Lithacodes caterpillars injected with non-pathogenic E. coli produced more than a twofold greater density of hemocytes than those in early instars. We also found that both caterpillar species contained plasmatocytes, granulocytes and oenocytoids, all of which are found in other lepidopteran species, but lacked spherulocytes. Granulocytes and plasmatocytes were found to be strongly phagocytic in both species, but granulocytes exhibited a higher phagocytic activity than plasmatocytes. Our results strongly suggest that for at least one measure of immunological response, the production of hemocytes in response to infection, response magnitudes can increase over ontogeny. While the underlying raison d’ être for this improvement remains unclear, these findings may be useful in explaining natural patterns of stage-dependent parasitism and pathogen infection.

Mosquito hemocyte-mediated immune responses

“…Studies that have recognized additional hemocytes types in mosquitoes also report that oenocytoids and prohemocytes comprise only a small proportion of the total hemocytes in circulation [23-25,36]. Collectively, these data agree with data from D. melanogaster, several species of Lepidoptera and other arthropods, where consistently only a small proportion of circulating hemocytes are identified as oenocytoids (called crystal cells in Drosophila ) and prohemocytes [15,43,48]. However, these patterns differ strongly from Rodrigues et al [40], which in addition to reporting that A. gambiae adults contain between 25,000 and 40,000 circulating hemocytes, also divide them into 2% granulocytes, 38% oenocytoids and 60% prohemocytes.…”

Characterization and pathogenicity assessment of gut-associated microbes of muga silkworm Antheraea assamensis Helfer (Lepidoptera: Saturniidae)

“…Stoepler et al (2013) reported that granulocytes and plasmatocytes are phagocytic in Euclea and Lithacodes. In contrast, the treated groups of both the experiments showed significantly higher phagocytic activity as compared to the control groups.…”

“…First method was the use of fluorescent latex beads (in vivo) and other one utilized fluorescently labeled E. coli bacteria (in vitro) (Stoepler et al, 2013). For in vivo experiment, silkworms were injected with 10 4 CFU/ml of pathogenic strains separately and kept for one day.…”

Compatibility between the endoparasitoid Hyposoter didymator and the entomopathogenic fungus Metarhizium brunneum: a laboratory simulation for the simultaneous use to control Spodoptera littoralis

“…Furthermore, THC in control larvae increased over the five‐day observation period, particularly between days 3 and 5; this may be because larvae molt from L2 to L3 between days 3 and 5. In general, THC increases with the larval age reaching a maximum in pre‐pupae although THC also tends to increase prior to each molt, decrease at molting, and then increase again . Other studies have reported the same effect of parasitism on THC .…”