Evaluation of Romanomermis Culicivorax as a Biocontrol Agent of Larval Mosquitoes in Louisiana Ricelands (Mermithidae, Nematode, Psorophora Columbiae, Parasitism).

Bionomic data were collected to evaluate Romanomermis culicivorax as a biocontrol agent of larval mosquitoes in Louisiana ricelands. In laboratory studies, the ability of R. culicivorax preparasites to infect Psorophora columbiae larvae substantially decreased after hosts were approximately 28 hr old. Parasitism at typical Louisiana rice field temperatures of 26, 29, and 32 (+OR-) 0.5(DEGREES)C showed a significant linear decrease (P \u3c 0.01) as the percentage of older larval instars increased at the times of exposure. These data emphasized the need for a synchronous field application of preparasites to challenge the rapidly developing early instars of Ps. columbiae. Based on those data, applications of postparasites to potential mosquito breeding habitats offer greater flexibility in larval mosquito control programs. A floating bioassay container, constructed of plastic pipe, 50 mesh screening, and 8 oz (0.24 liter) sample bottles, was developed to evaluate R. culicivorax postparasites in irrigated agricultural land. Applications of postparasites applied at dosage rates of 0.025 and 0.05 g/m(\u272) resulted in the establishment, recycling, and overwintering of R. culicivorax in a riceland habitat in southern Louisiana. Infection rates ranged from 0 to 54.1% during the 22 month study. There was no significant differences (P \u3e 0.05) between dosage rates among the plots and parasitism of Ps. columbiae larvae held in the bioassay containers. Depth of oviposition by R. culicivorax was determined by using soil cores previously inoculated with postparasites. Romanomermis culicivorax was found to primarily oviposit in the uppermost 2 cm of riceland soil. Effects of aerially applied riceland agrichemicals upon R. culicivorax postparasites were determined at 2 and 25 days posttreatment. At 2 day posttreatment, nematode mortalities ranged from 0 to 11.4% with fentin hydroxide responsible for the highest percentage. Fertilizers were significantly (P \u3c 0.01) more toxic to the nematode than insecticides at 2 and 25 days posttreatment. Approximately 80 to 84% of the surviving females, previously exposed to insecticides as postparasites, were gravid at 25 day posttreatment; there was only one agrichemical treatment lower, ammonium sulfate-P-K fertilizer at 79.0%. Subsequent F(,1) generation preparasites were able to cause \u3e67% parasitism in Culex quinquefasciatus; the only exception occurred with urea at 25.9%