Author Institution: Principal Entomologist, Sanitary Engineering Branch, Engineer Research and Development Laboratories, Fort Belvoir, Virgini

Edmunds, Lafe R.

The Ohio Journal of Science

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A NOTE ON THE BIOLOGY OF THE MOSQUITO,PSOROPHORA DISCOLOR (COQUILLETT), IN MISSISSIPPI(DIPTERA: CULICIDAE)LAFE R. EDMUNDSPrincipal Entomologist, Sanitary Engineering Branch,Engineer Research and Development Laboratories, Fort Belvoir, VirginiaPsorophora discolor (Coquillett) is found from Mexico northward to NewJersey and westward to Oklahoma. It reaches peak populations in the ricegrowing areas of Mississippi, Arkansas, and Louisiana, where it is an importantand serious pest of men and livestock. Mathis et al. (1955), in a previous studyin Bolivar County, Mississippi, found that Psorophora discolor made up from 14to 44 percent of the total specimens taken in light traps. Outside of the ricegrowing areas of these states and over most of its range it is considered an uncom-mon species.During the summer of 1955, observations on the biology of Psorophora discolorwere started near Cleveland, Mississippi, and continued during the summer of1956 near Greenwood, Mississippi. These studies were made to determine theimportant breeding sites of this species, and to learn something of its larvalassociations, seasonal distribution, and habits.In the Mississippi Delta area Psorophora discolor passes the winter in the eggstage. Eggs are deposited on moist soil in the fall and hatch when ground poolsare flooded from the dry state in the spring. The larvae appear first in groundpools formed by precipitation, and later in rice fields and other breeding sitesresulting from irrigation. Normally the mosquito populations would drop as thesurface pools formed by precipitation dried up. However, the irrigation of cropsstarts in Mississippi at just about the time the first brood of Psorophora discolorcompletes its development. This makes available large areas of water highlysuitable for additional mosquito breeding, and results in continued high populations.In the vicinity of Cleveland, Mississippi, the principal breeding sites ofPsorophora discolor were found to be shallow grassy ditches, irrigated rice fields,and surface pools in pastures. Small numbers of larvae wTere also found developingin irrigated cotton fields, sloughs, and roadside borrow pits. In 1956 in thevicinity of Greenwood, Mississippi, very similar conditions were noted. Thetypical breeding sites support dense stands of grass and are largely devoid ofcanopy shade.The larval populations of Psorophora discolor reached a seasonal peak in 1955,during the week ending June 18. The highest populations occurred followingconsiderable rainfall and at the beginning of the irrigation season. A second butless important peak occurred during the week ending July 9,- and resulted almostentirely from breeding in irrigated rice fields and pastures.Psorophora discolor was found most often in association with Psorophoraconfinnis, and Anopheles quadrimaculatus Say. It was collected occasionally withAedes vexans Meigen, Psorophora ciliata (Fabricus), Culex salinarius Coquillett,Culex erraticus (Dyar and Knab), Culex restuans Theobald, and Culex pipiensLinn. In ditches and pastures Psorophora discolor was second to Psorophoraconfinnis in numbers, and was more abundant than Anopheles quadrimaculatus.In rice fields it was third in abundance, ranking behind Psorophora confinnis andAnopheles quadrimaculatus.If disturbed, the larvae of Psorophora discolor immediately submerge to thebottoms of the pools or ditches and lie with their ventral sides up, each supportedTHE OHIO JOURNAL OF SCIENCE 57(5): 313, September, 1957.314 LAFE R. EDMUNDS Vol. 57on its air tube and stiff thoracic hairs. The length of time that a larva canremain submerged was timed with a stop watch. This time period ranged from3 to 88 minutes, with an average of 44 minutes. In routine mosquito samplingthis species is often missed because of its ability to remain submerged for longperiods. To get an accurate sample it is necessary to scrape the dipper throughthe bottom debris, and then carefully examine the contents.In practically every habitat studied a mixture of species was encountered.Psorophora larvae appeared shortly after flooding and no further hatching occurredunless there was another rise in water level. Psorophora confinnis was able tocomplete development to the pupal stage in approximately 6 days and the adultsemerged in 8 days. The larvae of Psorophora discolor developed more slowly,requiring 10 or more days to reach the pupal stage. The broods of Psorophorawere thus clearly defined, with most of the Psorophora confinnis adults havingemerged before the Psorophora discolor larvae reached the pupal stage.Irrigation is increasing yearly in the Mississippi Delta area, and with it themosquito problem is becoming more acute. Emphasis should be given to elimina-tion of habitats resulting from over-irrigation and poor drainage. Proper landpreparation and leveling is now being done by many of the farmers and this practiceshould be encouraged. Measures to prevent the flooding of ditches should beutilized where needed, and drains should be provided for the removal of surpluswater.LITERATURE CITEDMathis, W.» C. Elmore, and H. F. Schoof. 1955. Further studies on the chemical control ofrice field mosquitoes in Mississippi. Mosq. News 15(3): 148-153.

A Note on the Biology of the Mosquito, Psorophora Discolor (Coquillett), in Mississippi (Diptera: Culicidae)

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A Note on the Biology of the Mosquito, Psorophora Discolor (Coquillett), in Mississippi (Diptera: Culicidae)

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