Harold C. Chapman

Laboratory studies with the mosquito iridescent virus (MIV)

Abstract The regular mosquito iridescent virus and a blue MIV of Aedes taeniorhynchus were serially passed through 68 and 30 generations, respectively, of larvae of A. taeniorhynchus ; the average rate of infection for the regular MIV was 16%; that for the blue MIV was 21%. The maximum level of infection was usually reached when large numbers of early-instar larvae were exposed for 48 hr to substantial amounts of MIV material and the larvae were reared to the fourth stadium at 25°C. The rate of cross infection between known hosts of MIV was always less than 1%. Attempts to transmit MIV to larvae of nine species of mosquitoes not known to be hosts of MIV were successful only with Aedes sollicitans . About a 20% patent infection occurred in the larval progeny of adult A. taeniorhynchus derived from early fourth-instar larvae exposed to MIV. Such transovarian transmission was also observed in the MIV of Psorophora ferox .

Transovarian transmission of some Thelohania (Nosematidae: Microsporidia) in mosquitoes of California and Louisiana

Abstract Diagnostic studies on the progenies of mosquitoes reared from infected eggs collected in the field confirmed earlier evidence that transovarian transmission of Thelohania (Microsporidia) occurs commonly and may account for levels of infection observed in certain populations of mosquitoes. In some species of mosquitoes, however, peroral transmission is a prerequisite for transovarian transmission.

Coelomomyces dodgei: Establishment of an in vivo laboratory culture

Abstract An in vivo laboratory culture of the fungus Coelomomyces dodgei (Chytridiomycetes: Blastocladiales) was established, using the copepod Cyclops vernalis as an intermediate host and the larvae of the mosquito Anopheles quadrimaculatus as the definitive host. The culture was perpetuated by infecting copepods and mosquitoes using separate procedures. Copepods were infected by being combined with dehiscing sporangia. Patently infected copepods, which contained either light amber, bright orange, or both light amber and bright orange mycelia, were collected daily beginning 12 days later. Mosquitoes were infected by combining 100 first-instar larvae for 48 hr with a mixture of 12 infected copepods, four of each of the above types. The mean rate of infection for the first 100 trials was 41%. When groups of 100 first-, second-, third-, and fourth-instar larvae were exposed to a similar mixture of infected copepods for 48 hr, the mean rates of infection were 37.4, 27.0, 17.8, and 2.4%, respectively. Observations and experimental evidence suggest that the differentially pigmented mycelia found in infected copepods are gametophytes which develop into gametangia that subsequently release gametes of opposite mating types, the light amber gametangia producing female and the bright orange gametangia producing male gametes. Zygotes resulting from the fusion of these gametes lead to the infection of mosquito larvae. Thus, C. dodgei appears to have an Euallomyces type of life cycle with sporophyte and gametophyte generations alternating between mosquito and copepod hosts, respectively, with differentially pigmented sexual structures present in the gametophyte phase.

Incidence of the fungus Coelomomyces punctatus and C. dodgei in larval populations of the mosquito Anopheles crucians in two Louisiana ponds

Abstract The incidence of Coelomomyces punctatus and C. dodgei was studied in larval populations of Anopheles crucians in two ponds (Chloe 3 and Chloe TNT) in southwestern Louisiana for 4 1 4 and 2 1 4 years, respectively. The annual level of infection of C. punctatus in Chloe 3 decreased progressively each year from a high of 67% in 1966 to a low of 12% in 1970; about one-third of all larvae collected from this pond were infected. In Chloe TNT, the level of infection of C. dodgei was lowest in 1968 (24%) and increased each year to a high of 59% in 1970; almost half the larvae collected were infected. In Chloe TNT, the highest average monthly levels of infection occurred in January and September, and the highest occurred in Chloe 3 in January, March, and October. In Chloe TNT which dried only one time, no relationship was seen between levels of infection and temperature. Also in this pond, the incidence of parasitism generally increased as the larval populations increased although this difference was not significant. The persistence of C. punctatus was especially apparent since it appeared in larval populations after an absence of 29 wks caused principally by lack of water.

Plistophora caecorum sp. n., a microsporidian of Culiseta inornata (Diptera: Culicidae) from Louisiana

Abstract The morphology and development cycle of the microsporidian Plistophora caecorum sp. n. are described. The parasite invades the gastric caeca of the mosquito Culiseta inornata and is transmitted transovarially. Laboratory and field observations of host-parasite relationships are presented.

Scanning electron microscopy of the sporangia of species of Coelomomyces (Blastocladiales: Coelomomycetaceae)

Abstract A scanning electron microscope was used to study the sporangia of at least 6 species of Coelomomyces from 9 species of mosquitoes. The scanning micrographs obtained of (1) Coelomomyces punctatus from Anopheles quadrimaculatus , (2) C. dodgei from A. crucians , (3) C. quadrangulatus from A. crucians , (4) C. macleayae from Aedes triseriatus , (5) C. pentangulatus from Culex erraticus , (6) C. sp., probably pentangulatus , from Culex peccator , (7) C. psorophorae from Psorophora howardii , (8) C. near psorophorae from Culiseta inornata , (9) from Aedes sollicitans , and (10) from Aedes taeniorhynchus showed morphological differences in the surface microstructure of the sporangia of most species.

A mosquito parasite from a mosquito predator.

Abstract The fungus Coelomomyces macleayae has been reported from treehole mosquito larvae of three Aedes subgenera in Australia, Fiji, and the United States. This fungus is now recorded for the first time from a mosquito of the genus Toxorhynchites, the large predatory larvae of which are of some importance in the naturalistic control of associated mosquito pests and vectors. A single parasitized larva of T. rutilus septentrionalis was collected from a magnolia treehole (previously used for A. triseriatus infection experiments) near West Lake, Louisiana, in September, 1971. Larval A. triseriatus and Orthopodomyia signifera were also present but were uninfected.