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

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.

Effect of maternal age on primary and secondary sex ratios in the ectoparasitoid wasp Pachycrepoideus vindemmiae

“…To decrease mortality during development, females tend to lay more male offspring in larger clutch sizes, which is a maternal strategy to ensure male offspring survival and avoid zero fitness in female offspring (Green et al, 1982; Hardy & Cook, 1995). Mortality during development may be caused by self‐superparasitism in some species (Narayanan & Rao, 1955; Jackson, 1961; Rotary & Gerling, 1973; Devescovi et al, 2017; Sanad et al, 2017; Duval et al, 2018). Male survival is better than females (Ueno & Tanaka, 1997) under low‐egg quality conditions at the end of oviposition.…”

Perspectives of vector management in the control and elimination of vector-borne zoonoses

“…These nematodes are highlighted as potential vector biocontrol candidates, due to their parasitic relationship with various arthropods and several arachnids ( Stabler, 1952 ; Chapman, 1974 ). The hatched pre-parasitic juveniles of mermithid nematodes aggressively infect mosquito larvae (usually the early instars) by paralyzing the targeted hosts, followed by penetration of cuticular wound to establish the infection ( Sanad et al, 2017 ). Once infected, the mermithid parasites take over the cellular function regulatory authority of their hosts.…”

“…The emerged post-parasite stage then molts into the free-living adult to reproduce and lay eggs. Multiple mermithids may repeatedly infect an already infected larva, giving rise to a phenomenon called superparasitism ( Sanad et al, 2017 ). Different research groups have demonstrated the mosquito larvicidal effect of several mermithids such as Romanonermis iyengari (against Ae.…”

“…gambiae , Anopheles culicifacies , Anopheles stephensi , Anopheles subpictus , Armigeres subalbatus , Culex pipiens, Culex quinquefasciatus, Culex sitiens, Culex tritaeniorhynchus, and Mansonia annulifera ), Diximermis peterseni (against Anopheles crucians , Anopheles quadrimaculatus , and Anopheles punctipennis ) and Strelkovimermis spiculatus (against Aedes albifasciatus and Cx. pipiens ; Petersen and Willis, 1974 ; Levy and Miller, 1977 ; Poinar and Camino, 1986 ; Santamarina Mijares and Perez Pacheco, 1997 ; Paily and Balaraman, 2000 ; Sanad et al, 2013 , 2017 ; Abagli and Alavo, 2019 ; Abagli et al, 2019 ). However, the lack of culturable mermithids hinders mass application of this nematode as a biocontrol agent ( Kendie, 2020 ).…”

Biological Control Strategies for Mosquito Vectors of Arboviruses

“…The larvicidal toxins produced by Bti and Lysinibacillus sphaericus ( Ls ) have been used in biological control since their discovery and have been extensively commercialized. Penetration of mermithid nematodes, especially Romanomermis species, in mosquito larvae has also been evaluated for the development of biological control strategies [48]. However, it has proven difficult to commercialize because the viability of the microorganisms is difficult to maintain in storage and transportation.…”