Computer simulation of management strategies for Psorophora columbiae in the rice agroecosystem.

Various control strategies were evaluated using a previously-described and validated (Focks et al. 1988a, 1988b) simulation model (PcSim) of the population dynamics of Psorophora columbiae breeding in the rice agroecosystem. As expected from field experience, focally-applied ground or aerial ULV aerosols of insecticides were seen to provide local control of peak populations. Similar control was predicted for larvicides when also used in and around urban and suburban areas. Both of these measures were predicted by simulation to provide only short term control of adults as a result of immigration of adults from surrounding, untreated provide only short term control of adults as a result of immigration of adults from surrounding, untreated areas. Evaluations of the effectiveness of diapause egg control or the elimination of early spring broods to provide lasting, season-long suppression were not encouraging if only conventional methods such as insecticides or tillage were used. This was primarily because the ability of Ps. columbiae to recolonize treated areas during the course of a breeding season would require the treatment of prohibitively large, parish- (i.e., county-) sized areas. Evaluations of host management (either removal or residual insecticide treatment of cattle) in and around urban and suburban areas were more encouraging. This technique, by providing continuing pressure on populations, has the potential to offset the impact of immigration and thereby afford long-term suppression in local areas. Finally, evaluations of the impact of modifications to irrigation practices indicated that this approach warrants consideration as a supplemental control technique. These results suggest that field evaluations of model predictions would be useful. They emphasize the need to better understand the movement and spatial distribution of Ps. columbiae. These factors would bear directly on the cost and therefore, the practicality of several of the long-term suppression strategies evaluated as they determine the size of the treatment area surrounding population centers needed to offset the impact of immigration from surrounding, untreated areas.