J. J. Petersen

Role of mermithid nematodes in biological control of mosquitoes

Mermithid nematodes have been reported from at least 63 species of mosquitoes from all over the world, but until recently they have received little attention. Such nematodes are prime candidates as biological control agents because they have adapted to the life cycle of the host; are host specific; produce high levels of parasitism; kill the hosts; are easily handled; have a high reproductive potential; are free swimming and can be disseminated easily in the infective stage; and can be used in an inundative or inoculative manner to control mosquitoes. Nevertheless, with the exception of one mermithid species, little is known about factors that influence parasitism in mosquitoes. Also, only one species of mermithid has been successfully mass cultured to date. The exception is the mermithid Reesimermis nielseni. With this mermithid, high levels of parasitism can be obtained in natural populations of mosquitoes at reasonable dosages; preparasitic nematodes can be applied easily by using many of the standard techniques used to apply insecticides; and R. nielseni can establish itself in many of the sites in which it is released. The same potentials exist for mermithids of other aquatic insects.

Nematodes as Biological Control Agents: Part I. Mermithidae

Publisher Summary This chapter discusses the role of nematodes as biological control agents. Nematodes are usually considered pests because of the diseases they cause in humans and animals and the economic impact they have on many agricultural products. There are, however, a small but significant number of beneficial entomogenous nematodes—that is, nematodes associated, often parasitically, with insects. Some of these nematodes are of considerable interest because of their potential as biological control agents of pest insects. There are nine families— Allantone matidae, Diplogasteridae, Heterorhabditidae, Mermithidae, Neotylenchidae, Rhabditidae, Sphaerulariidae, Steinernematidae, and Tetradonematidae— that include species that attack insects and kill, sterilize, or alter host development. The chapter focuses on mermithids, which are a large and important group of nematodes. They are obligate parasites of arthropods, principally insects, but have also been recorded from spiders, crustaceans, earthworms, leeches, and mollusks. They are usually specific to a single species or to one or two families of insects and are almost always lethal to their hosts. Mermithids are particularly attractive because they offer little or no environmental hazard, they offer no threat from competitive displacement of other desirable organisms because of their life cycle, and the potential exists for inundative release to give high initial host reduction or inoculative releases to establish the nematode and give partial control for an indefinite period. The morphology, taxonomy, and biology of Mermithids are presented in the chapter. The mass propagation, including in vivo and in vitro methods is discussed.

Seasonal Activity of Entomophthora muscae (Zygomycetes: Entomophthorales) in Musca domestica L (Diptera: Muscidae) with Reference to Temperature and Relative Humidity

Abstract The fungus, Entomophthora muscae (Cohn) Fresenius, commonly infects house flies, Musca domestica L., on feedlots and dairies in southeastern Nebraska. During two fly breeding seasons, disease prevalence increased from

Comparison of sentinel and naturally occurring fly pupae to measure field parasitism by pteromalid parasitoids (Hymenoptera)

Abstract In a series of studies over a 4-year period, the effectiveness of releases of pteromalid wasps for the control of house flies, Musca domestica L., and stable flies, Stomoxys calcitrans (L.), on beef cattle confinements was evaluated using sentinel house fly pupae (artificially reared and placed in the environment) and naturally occurring house fly and stable fly pupae. The two methods were compared using percentage parasitoid emergence and species composition. At confinements where no parasitoid releases occurred, parasitoid emergence was significantly higher from naturally occurring hosts. Muscidifurax zaraptor Kogan and Legner comprised 97 and 76% of the parasitoids recovered from sentinel and naturally occurring hosts, respectively. Spalangia spp. made up 16% of the parasitoids from naturally occurring hosts. Few Spalangia spp. were recovered from sentinel hosts. Similar results were obtained from locations where M. zaraptor was released except that M. zaraptor comprised a greater proportion of the parasitoids recovered by both methods. At locations where Spalangia cameroni Perkins was released, 76% of the parasitoids recovered from sentinel hosts were M. zaraptor, and 21% were S. cameroni, compared with 62% M. zaraptor and 34% S. cameroni from naturally occurring hosts. At locations where Pachycrepoideus vindemiae (Rondani) was released, this species was recovered significantly more often from sentinel hosts. Naturally occurring pupal method appears to be more reliable and sensitive to the entire parasitoid species complex. However, because of the difficulty in obtaining adequate samples, it is recommended that both methods be employed.

Current status of nematodes for the biological control of insects

This review highlights published research on the principal entomogenous nematodes that have potential as biological control agents of insects. The life-cycles and status of promising members of the families Allantonematidae, Diplogasteridae, Heterorhabditidae, Mermithidae, Neotylenchidae, Rhabditidae, Sphaerulariidae, Steinernematidae and Tetradonematidae are discussed. Emphasis is placed on attempts to control insect populations with these nematodes. Mass propagation of the Steinernematidae and Mermithidae are also discussed, including current in vivo and in vitro rearing systems. A number of these nematodes show promise as biological control agents but commercial development has been slow because of environmental limitations, host specificity and inherent problems associated with manipulation of living organisms. Although some of these nematodes have been considered for commercial preparation, it appears that they will remain ‘on the shelf’ until the need for such biological control provides small businesses with the incentive to make them available for general use.

Biology of Octomyomermis muspratti, a parasite of mosquitoes as it relates to mass production☆

Abstract The first- and second-instar larvae of Culex pipiens quinquefasciatus were equally susceptible to parasitism by the mermithid nematode Octomyomermis muspratti; the third-instar hosts were significantly less susceptible. The yield of postparasitic nematodes was higher from hosts exposed as second instars then from hosts exposed as first or third instars at comparable levels of parasitism. Mortality of the host prior to emergence of the nematode occurred most frequently among first- and third-instar hosts. About 4% of the infected hosts exposed as first and second instars and 37% of the infected hosts exposed as third instars pupated prior to emergence of the postparasitic nematodes. The exposure of mosquitoes as second instars was the most efficient for mass rearing and resulted in the highest yields of postparasitic O. muspratti.

Parasitoid-induced mortality of house fly pupae by pteromalid wasps in the laboratory

Abstract House fly, Musca domestica L., pupae were exposed to six species of pteromalid parasitoids, Muscidifurax zaraptor Kogan and Legner, M. raptor Girault and Sanders, M. raptorellus Kogan and Legner, Pachycrepoideus vindemiae (Rondani), Spalangia nigroaenea Curtis, and Urolepis rufipes Ashmead. Exposures were made for 48 h at six parasitoid-to-host ratios to measure the effect of parasitoid density on parasitoid-induced mortality (PIM) of hosts (excluding mortality as measured by parasitoid emergence). PIM was evident at all parasitoid-to-host ratios for all six species. Fly eclosion declined with a corresponding increase in the parasitoid-to-host ratio; the reverse was generally true for PIM. Parasitoid emergence increased initially with a corresponding increase in the parasitoid-to-host ratio to a point (depending on the parasitoid species), but then declined. The three Muscidifurax spp. and P. vindemiae exhibited similar behavior and generally avoided previously stung hosts until ovipositional restraints broke down at the higher parasitoid-to-host ratios. S. nigroaenea and U. rufipes exhibited little ovipositional restraint, resulting in a high proportion of PIM of hosts. Understanding factors that influence PIM will provide better evaluations of field releases of parasitoids to control flies and will aid in the development of the most economic procedures for large scale rearing of pteromalid parasitoids.

Evaluation of Muscidifurax zaraptor and Pachycrepoideus vindemiae (Hymenoptera: Pteromalidae) for controlling flies associated with confined beef cattle

Abstract Releases of Muscidifurax zaraptor Kogan and Legner and Pachycrepoideus vindemiae (Rondani) (Hymenoptera: Pteromalidae) were made at four beef cattle feedlots in eastern Nebraska. The ability of the parasites to parasitize house fly (Musca domestica L.) and stable fly [Stomoxys calcitrans (L.)] pupae under ambient environmental conditions was measured. The two species were released seven times at 2-week intervals from a central location within each of the four feedlots. Both species were recovered significantly more often from sentinel pupae placed around the perimeter of each feedlot than from sentinel pupae at untreated feedlots. Mean mortality of sentinel pupae for the four release feedlots ranged from 28 to 42% compared with 4.8% for two untreated feedlots. Parasites recovered from sentinel pupae comprised 87% M. zaraptor and 12% P. vindemiae. Correlations between the percentage mortality of sentinel pupae and the number of parasites released were poor. However, when the interaction of weekly mean air temperature was considered, a significant correlation between reduction of sentinel pupae and the number of parasites released was evident. Differences in parasitism between release and control sites were not as apparent when parasite emergence from naturally occurring house fly and stable fly puparia was determined. The indigenous M. zaraptor was clearly superior to the introduced P. vindemiae and readily parasitized house fly pupae placed around the perimeter of the release feedlots. The results also suggested that periods of mean weekly temperature exceeding 27°C appeared to adversely affect both parasite species.

Diximermis peterseni (Nematoda: Mermithidae): A potential biocontrol agent of Anopheles mosquito larvae☆

Abstract The mermithid nematode Diximermis peterseni was successfully transferred and established in an artificial pond and then in a natural pond. The exposure in the artificial pond initially produced 92% parasitism in introduced larvae of Anopheles quadrimaculatus; then parasite activity gradually decreased and disappeared. However, it reappeared 8 months after the introduction and has been observed in introduced hosts during each of the 40 months since. The release of 2300 Anopheles (85–90% infected) into a natural pond (January–March 1971) produced 12–100% parasitism during the 8-month period between September 1971, and March 1972. Furthermore, during the same months in 1972–1973, an average of 88% of the Anopheles in the pond were parasitized. These data indicate that D. peterseni can be easily established and will produce significant levels of parasitism despite long periods of dry weather and low host densities.

Observations on the biology of Octomyomermis muspratti, a nematode parasite of mosquitoes

Abstract The mosquito parasite Octomyomermis muspratti was able to infect mosquitoes in diluted sea water with conductivity readings of 4000 μmho/cm and in all dilutions of organically rich tree-hole water. In contrast, the infectivity of Romanomermis culicivorax, a more extensively studied species, was adversely affected in dilutions of sea water with conductivity of 1500 μmho/cm and no infections were observed at concentrations above 3000 μmho/cm. Also, R. culicivorax failed to infect hosts at any dilution of the tree-hole water. Diet was shown to have an effect on male-female sex ratios in developing O. muspratti, and this may be employed to enhance a better male-female ratio in laboratory cultures of this nematode. When cultures of O. muspratti were flooded every 3–4 months, they continued to produce infective-stage nematodes for up to 5 years. Also, cultures that were repeatedly flooded produced infective nematodes for more than 39 floodings.