Superparasitism and Population Regulation of the Mosquito-Parasitic Mermithid Nematodes Romanomermis iyengari and Strelkovimermis spiculatus

Manar Sanad,Jennifer S Sun,Randy Gaugler,Yi Wang,Muhammad S M Shamseldean

doi:10.21307/jofnem-2017-078

Manar Sanad, Jennifer S Sun + Show 3 more

Open Access

https://doi.org/10.21307/jofnem-2017-078

Copy DOI

Abstract

Superparasitism is a common phenomenon in mosquito-parasitic mermithid nematodes. Multiple nematodes are needed in a single host to produce males. Host selection behavior and intraspecific competition among Romanomermis iyengari and Strelkovimermis spiculatus were investigated against their host, Culex pipiens pipiens in laboratory experiments. In a choice assay between previously infected and uninfected host larvae, infectious preparasites of both nematode species could distinguish not only between infected and uninfected hosts, but even between different parasite loads in showing a strong preference for uninfected hosts or hosts with a low parasite load. Host heart rate declined briefly immediately after parasitism. Superparasitism resulted in increased parasite mortality. Scramble competition within mosquito larvae for limited host nutrients, coupled with a skewed sex ratio favoring males, is assumed to lead to parasite population decline and subsequently toward host-parasite population equilibrium. The ability of mermithid preparasites to accurately assess parasite load likely plays an important role in host population dynamics and regulation.

Highlights

Superparasitism is a common phenomenon in mosquito-parasitic mermithid nematodes
The time for successive nematodes to penetrate an already parasitized host showed a steady increase with increasing parasitic load for both species; S. spiculatus was faster than R. iyengari up to the fourth penetration
A strong positive relationship between parasite load and infection time was detected for R. iyengari (r = 0.91, P, 0.01) and for S. spiculatus (r = 0.93, P, 0.01), respectively

Summary

Introduction

Superparasitism is a common phenomenon in mosquito-parasitic mermithid nematodes. Multiple nematodes are needed in a single host to produce males. Suboptimal host–parasite densities, can lead to male-dominant populations in some species, as is most evident for mosquito-parasitic mermithid nematodes (Petersen, 1980; Tingley and Anderson, 1986; Sanad et al, 2013), which serves to dampen parasite populations and reestablish host–parasite equilibrium. Preparasites initiate infection using a needle-like stylet to inject a ‘‘venom’’ (Shamseldean and Platzer, 1989) This causes a reduction in host heart rate and a concurrent temporary paralysis which facilitates nematode entry via a cuticular wound. Superparasitism in mermithid nematodes is essential for male production because single infections invariably produce a female (Sanad et al, 2013)

Methods

Results

Conclusion