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A gravid female Mermis nigrescens Dujardin (Mermithidae: Nematoda) was recovered from the mouth of a 1-month-old infant in Mehama, Oregon. This nematode is a parasite of grasshoppers and deposits its eggs on vegetation. The parasite was probably carried on the hair of the household dog or cat to the vicinity of the patient and was attracted to the moisture in the region of the mouth.
A double infection of the larvae of Aedes flavescens and A. cantans with Thelohania opacita and larvae of Mermithidae was established. The double infection is not accompanied by the rise of pathogenic effect of the parasites on the hosts. Mermithids parasitizing mosquitoes infected with microsporidians inhibit the development of Protozoa. The inhibition degree depends on the duration of contacts of coparasites as well as on the developmental phase of microsporidians at the moment of penetration of nematodes.
Hydromermis contorta (Kohn) and Hydromermis pseudocontorta n. sp. are described from chironomids in Lake Itasca and Long Lake, Minnesota, respectively. The former was recovered from adult females of Glyptotendipes paripes (Edwards) and the latter from fourth-instar larvae of Chironomus sp. Hydromermis pseudocontorta n. sp. resembles H. contorta in cephalic structures, overall size, and the presence of a restricted trophosome in the female. The terminal mouth, long uterine and vulvar limbs of the vagina, and the strongly chitinized brownish spicule of H. contorta contrast with the subventral mouth, short vaginal limbs, and the light yellow spicule of H. pseudocontorta n. sp. Both nematode species emerge from the host as sexually mature adults and both species give evidence of mating while in the host. The H. contorta described by Welch is designated as a new species, Hydromermis albionis n. sp.
Mosquito larvae of the species Anopheles pseudopunctipennis Theobald 1901 were studied under laboratory and field conditions to evaluate the level of susceptibility to the parasitism of nematode Romanomermis iyengari Welch 1964. Doses of 5:1 and 10:1 and development stage II larvae collected in natural reservoirs were used for the laboratory assays. A dose of 1,000 preparasitic agents/m2 was applied to field trials. The results of the lab and field tests yielded high levels of infestation in larvae with values ranging from 90 to 100% and from 85 to 95%, respectively. A marked reduction of the larval densities was observed in the 5 treated reservoirs seven days later, which showed an elevated susceptibility of the anopheline species to mermithid parasitism.
Biological control is "direct or indirect use of natural enemies of the injurious species to increase its mortality" (W.H.O., 1963). The more and more frequent apparition of resistant insects populations, the fears as regards the environment, the increase cost of hydrocarbur products and also some technic and operational difficulties to stop transmission by the use of only insecticide pulvérisation, impose this process. Nevertheless, practic use of natural enemies of vectors is yet unusual in spite of important research. (Identification problems, dynamic of species, insufficiency of ethology knowledge particulary of the host specificity, difficulties of application on the vectors which are the most usually widely scattered). For control of insects of medical importance (mosquitoes, black flies, tse-tse flies) it has been used either pathogen agents such as virus bacteria, microsporida or parasit agents such as fungi, mermithid nematods or at last, predators, essentially larvivorus fish. Actually, no biological agent is able to take the place of chemical and physical "traditional" means. In case of mosquito control which is more advanced, the only biological mean which is operational is the use of larvivorus fish and specially Gambusia.
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The method of "flooding" with mermitids, which was successfully used against mosquitoes, is unreal for biological control of black flies because of difficulties and unprofitableness of their laboratory maintenance and reproduction. A more probable way of solving the problem is the untroduction of effective forms of parasites. In perspective the cultivation of the adipose tissue of the host and biochemical overcoming of its protective reactions are necessary.
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A laboratory-based study was performed in order to assess the infestation capacity of the mosquito parasite nematode Romanomermis iyengari Welch, on Anopheles nuneztovari Gabaldón and Aedes aegypti L. For each mosquito species, nine hundred (900) I to III instars larvae were taken. These larvae were infested with pre-parasitic larvae of R. iyengari in proportions of 5:1 and 10:1. The infestation averages obtained were 3.9 and 6.7 for Anopheles nuneztovari, and 1.9 and 4.7 for Aedes aegypti respectively. Mortality ranked between 95 and 100% for both mosquito species and Anopheles nuneztovari showed the highest susceptibility to the nematode parasitism.
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A new species of Mermithidae was found parasitizing the larvae of Culex tritaeniorhynchus and Culex fatigans in Henan, China and then named Romanomermis yunanensis. Thirty-one species of Mosquitoes involving six genera have been tested for susceptibility to R. yunanensis and Culicinae mosquito have consistently been highly susceptible. At a 1:5 ratio of mosquito larvae to nematode juveniles, the parasitisms of Aedes aegypti, Ae. albopictus, Culex fatigans, Culex tritaeniorhynchus, Anopheles sinensts, Psorophora columbiae and Culesta inornata were 98.2%, 98.5%, 98.6%, 97.1%, 0%, 98.8%, and 99.0% respectively. R. yunanensis presented a phenomenon of retarted development in Anopheles maculatus, which remained at the parasitic stage both in the larvae and pupa of An. maculatus. The parasitism of An. dirus was 89.7%, but most (88.8%) parasitizing mermithids underwent melanization and died. The comparative susceptibility of some North American mosquitoes to R. yunanesis and R. culicivorax at a 1:5 infective ratio showed that both percentage infection and intensity of infection statistically supported the generalization that, under laboratory conditions, R. yunanesis is a more vigorous and aggressive parasite of Culicinae.
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Mermithid nematodes parasitize invertebrates only. A general account is given of their parasitism and the consequent mortality of blackflies. The author begins with a review of records of mermithid and blackfly association from different parts of the world and comments on the global distribution of the parasite. He discusses the life-histories of the parasites, stressing their adaptations to the moving environment of the aquatic stages of the blackfly and to the aerial environment of the adult. It is noted that the parasite usually kills its host upon emergence and has a restricted host range. Mermithids must be considered as selective mortality factors against blackfly populations. A survey of European and North American literature leads to conclusions concerning the role of the parasite in the natural regulation of blackflies. The possibility of utilizing these nematodes as biological control agents is discussed.
The action of bacterial insecticides based on Bacillus thuringiensis H-14 and B. sphaericus in a dose of 0.005-2 mg/l on the mermithids Romanomermis iyengari, R. culicivorax and R. jingdeensis was studied. It was shown that though bacterial agents suppressed mermithid preparasite larvae density about 30-40%, the survivors might invade 100% of mosquito larvae. The viability and fertility of adult mermithids did not change under the influence of bactoculicide in doses 5-50 times higher than those used against mosquitoes in practice. In combined field trials of sphaerolarvicide (1.5 kg/ha) and R. iyengari mermithids the infectivity of Anopheles sacharovi larvae reached 96%. Mermithids in combination with bactoculicide and sphaerolarvicide might be useful in integrated control systems because these bacterial agents are harmless for mermithids of all stages in doses useful against mosquito larvae.
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