Effects of Parasitization and Envenomation by the Endoparasitic Wasp Pimpla turionellae (Hymenoptera: Ichneumonidae) on Hemocyte Numbers, Morphology, and Viability of Its Host Galleria mellonella Lepidoptera: Pyralidae)

Abstract

Venom from the pupal endoparasitoid Pimpla turionellae L. (Hymenoptera: Ichneumonidae) contains a mixture of biologically active components, which display potent paralytic, cytotoxic, and cytolytic effects toward hosts. Here, we further investigate whether parasitism or envenomation by P. turionellae alters hemocyte numbers of its host Galleria mellonella L. (Lepidoptera: Pyralidae). Total hemocyte counts declined sharply in pupae and larvae of G. mellonella exposed to P. turionellae. These same cellular responses occurred when wasp venom was artificially injected into hosts, suggesting that venom alone induces cytotoxicity in hemocytes. Analysis of the differential hemocyte counts in untreated pupae and larvae revealed that more than half of the circulating hemocytes were granular cells followed by plasmatocytes. Parasitism reduced the number of granular cells while increasing the number of plasmatocytes. This trend was most evident at 4 h postparasitism, and a similar trend was observed with the artificial injection of high (but not low) doses of venom. When isolated larval hemocytes were exposed to a LC99 dose of venom, a differential response was observed for granular cells versus plasmatocytes. Both types of cells displayed some formation of vacuoles within the cytoplasm within 15 min posttreatment. However, the degree of vacuole formation was much more extensive in granular cells at later time points than for plasmatocytes, and granular cells seemed much more susceptible to venom as evidenced by cell death.

Cellular reactions of the white grub larvae, Polyphylla adspersa, against entomopathogenic nematodes

“…The adhering haemocyte monolayer was then fixed in methanol:acetic acid (3:1, v/v) for 5 min, stained with Giemsa for 10 min, washed with distilled water and observed under a light micro scope. Haemocyte types were classified by morphological characteristics (Er et al, 2010;Altunta § et al, 2012).…”

Venom-Induced Immunosuppression: An Overview of Hemocyte-Mediated Responses

“…In endoparasitic wasps not transmitting PDVs, venom has been shown to paralyze [22,25], castrate the host [68], have an antibacterial effect [69], or affect the host immune system [10,23,[70][71][72]. Inhibition of host immune responses is critical for endoparasitic species to ensure that eggs and larvae are not recognized and eliminated by the cellular arm of the immune defenses.…”

“…Inhibition of host immune responses is critical for endoparasitic species to ensure that eggs and larvae are not recognized and eliminated by the cellular arm of the immune defenses. Protection for wasp progeny generally is achieved through disabling host hemocytes [71]. Several authors have reported on the effects of parasitism on total and differential hemocyte counts in different insect hosts.…”

“…Several authors have reported on the effects of parasitism on total and differential hemocyte counts in different insect hosts. Recently, studies have been conducted to examine the effects of parasitism and venom from P. turionellae on total and differential hemocyte numbers in two developmental stages of the host, Galleria mellonella (Lepidoptera: Pyralidae) [71]. Total hemocyte count indicated a considerable decline in the number of circulating hemocytes in G. mellonella pupae and larvae exposed to P. turionellae or any dose of wasp venom below the LD 99 calculated for G. mellonella pupae and larvae [25] injected experimentally [71].…”

“…Recently, studies have been conducted to examine the effects of parasitism and venom from P. turionellae on total and differential hemocyte numbers in two developmental stages of the host, Galleria mellonella (Lepidoptera: Pyralidae) [71]. Total hemocyte count indicated a considerable decline in the number of circulating hemocytes in G. mellonella pupae and larvae exposed to P. turionellae or any dose of wasp venom below the LD 99 calculated for G. mellonella pupae and larvae [25] injected experimentally [71]. Also, significant variations in the number of differential hemocyte counts of G. mellonella occurred among parasitization and venom treatments in vivo [71].…”