JoURNALoF THE AMERIcANMosqurro ConrRor, AssocrerroN VoL.4,No.3 A DYNAMIC LIFE TABLE MODEL OF PSOROPHORACOLUMBIAE IN THE SOUTHERNLOUISIANA RICE AGROECOSYSTEMWITH SUPPORTINGHYDROLOGIC SUBMODEL. PART 1. ANALYSIS OF LITERATURE AND MODEL DEVELOPMENT1 D. A. FOCKS,' R. E. McLAUGHLIN2 A^ro B. M. SMITH3 InsectsAffecting Man and Animals ResearchLaboratory, Agrirultural ResearchSeruice, U. S. Department of Agriculture, Gainesuillc,FL 32604 ABSTRACT. During the past decade,the rice agroecosystemand its associatedmosquitoes have been the subject of an extensive research effort directed toward the development and implementation of integratedpest management(IPM) strategies.The objectiveof this work was to synthesizethe literature and unpublished data on the rice agroecosysteminto a comprehensivesimulation model of the key elementsof the systemknown to influence the population dynamics of Psorophora columbine.Subsequent companionpapers will presenta validation ofthese models,provide an in-depth analysisofthe population dynamics of Ps. colum.biae,and. evaluate current and proposed IPM strategies for this mosquito. This paper describesthe developmentof 2 models: WaterMod: Because spatial and temporal distributions of surface water and soil moisture play a decisiverole in the dynamics of Ps. colutnbioe,an essentially hydrological simulator was developed.Its purpose is to provide environmental inputs for a secondmodel (PcSim) which simulates the population dynamics of Ps. columbiac.WaterMod utilizes data on weather, agricultural practices, and soil charac- teristics for a particular region to generate a data set containing daily estimates of soil moisture and depth of water table for 12 representativeareas comprising the rice agroecosystem.This model could be usedto provide hydrologic inputs for additional simulation models of other riceland mosquito species. PcSim: This model simulates the population dynamics of Ps. columbioeby using the computer to maintain a daily accounting of the absolute number of mosquitoeswithin each daily age class for each life stage.The model createsestimates ofthe number ofeggs,Iarvae, pupae, and adults for a representative l-ha area of a rice agroecosystem. INTRODUCTION Researchersof the Riceland Mosquito Man- agementProject (RMMP) and the closely asso- According to the Food and Agriculture Orga- ciated ARS/CSRS Regional Project on Riceland nization, rice is the staple food of half of the Mosquitoes(5-122) have been directing multi- human race with the projected demand for this institutional and multi-disciplinary researchef- cereal expectedto increaseby almost 90% from forts toward the development and implementa- 1975 levels by the year 2000 (Tsutsui 1984). tion of better integrated pest management Most rice-producing land in developing coun- (IPM) schemesagainst mosquitoesarising from tries is flooded for relatively long periods of time the rice agroecosystemof the United States since 1977.These efforts are basedon the prem- and much of it subsequentlyproduces disease "mosquito vectors, including primarily snails and mosqui- ise that populations associatedwith toes (Myers 1984). In the United States, rice such systems are ... among the most likely acreagehas increased ca. 55% during the past targets for the immediate application of IPM decade (N. G. Gratz, 1981, unpublished data, strategies since they have adapted themselves World Health Organization). This expansion to habitats which are already largely under hu- was accompaniedin many areasby a significant man control and have becomerather dependent increase in the abundanceof several speciesof upon man and his land use practices for their (Olson ricelandmosquitoes (Paine 1983). continuedexistence" 1983). A major objectiveof the RMMP and 5-122 programs is to develop a better understanding l This researchwas conductedby the U.S. Depart- of the rice agroecosystemas it pertains to mos- ment of Agriculture, Agricultural ResearchService in quito production by means of systemsanalysis; cooperationwith the USDA, CSRS Southern Regional this work representsa contribution toward that Project 5-122 involving State Agricultural Experiment goal. This objective stems from the belief that Station personnel located in Arkansas, California, improved control of riceland mosquitoes will Louisiana, Mississippi, and Texas. 2 come from a more rigorous understanding of the InsectsAffecting Man and Animals ResearchLab- population dynamics of the mosquitoescoupled ResearchService, U.S. Depart- oratory, Agricultural of new and/or improved ment of Agriculture,P.O. Box 14565,Gainesville, FL with the development 32604. control and survey techniques.Systems analysis 3Department of Neurosurgery,College of Medicine, through computer simulation is a useful and University of Florida, Gainesville,FL 32610. necessarytool in the understanding of the com- SEPTEMBER1988 PsoRopHoRA qoLUMBTAESrvur,errou Moonl,-PeRr I 267 plex interactions between environmental and (WaterMod) was developedto utilize data on biological factors of the rice agroecosystem.The weather, agricultural practices, and soil charac- developmentof models allows an integration of teristics for a particular region to generate a the current base of knowledge; it highlights data set containing daily estimates of soil mois- areas where additional information is required ture and depth of water table for representative and can be used to develop estimates of popu- areas comprising the rice agroecosystem.This lation parameters that are difficult to obtain model was also designedto provide hydrologic from field studies. Additionally, becauselarge- inputs for additional simulation models of other scale field trials are expensive,simulation is an riceland mosquito species. important adjunct to the development, evalua- In the present work, WaterMod provides en- tion, and optimizationof IPM schemes.Finally, vironmental inputs to a second model which the simulation model of Psorophora columbia.e simulatesthe population dynamics of.Ps. colum- (Dyar and Knab) could be used in an expert biae (PcSim). The major attributes of PcSim systemdesigned to aid mosquito abatementper- include: 1) developmentaltimes of immatures as sonnel with control decisionson a day-to-day a function of daily water temperatures derived basis. from air temperatures,2) survival of immatures Major rice growing regions of the United as a function of larval density and habitat. States include California and the southern elapsed time since a particular habitat was statesof Texas,Louisiana, Mississippi, and Ar- flooded, and the presenceof surface water, 3) kansas.In southern rice areas,the dark rice field survival of adults as a function of soil moisture mosquito, Ps. columbiae,is the major periodic and host density, 4) the proportion ofdiapausing (or floodwater) mosquito pest of humans and and non-diapausingeggs deposited in the fall as animals. It was a primary vector of Venezuelan determined by day length and air temperature, equine encephalitis (VEE) when this virus was 5) survival of eggsas a function of the diapause introduced into the United Statesin 1971(Sudia status ofthe egg and by the duration and sever- and Newhouse1971, Sudia et al. 1971,Olson ity of freezing temperatures during the winter, and Newton 1973). In addition, it is known to and 6) the habitat and elevation where oviposi- adverselyaffect livestock production (Steelman tion occurs as a function of land use patterns, and Schilling 1977, Steelman et al. 1972, L973). irrigation and drainage events, weather as it Becauseof its importance in southern rice areas, influences the spatial and temporal distribution this floodwater specieswas selectedas a primary of surface water and soil moisture. and the target of the RMMP/S-122 investigators. searchingability of femalesto locate appropriate In the rice agroecosystemof the southern ovipositionsites. USA, Ps. columbiaebreeds in temporary pools This paper describesthe developmentofthese such as swale areasand grassyroadside ditches, models from a synthesis of the literature and soybeanand rice fields,and pastures(Schwardt unpublished data. Subsequent companion pa- 1939,Horsfall1942, 1955; Meek and Olson1976, pers will provide validation of the models pre- 1977;Curtis 1985,Welch et al. 1986).The winter sentedhere, present an in-depth analysisofthe months and dry periods are spent primarily in population dynamics of Ps.columbioe, and eval- the egg stage.Oviposition occurs directly on the uate IPM strategiesfor this mosquito. earth and at locations and elevations where soil moisture ranges between 75 and 100% of field T[aterMod capacity(FC) (Olsonand Meek 1977,1980). The Severalcomprehensive models are able to pre. number of generations of Ps. columbiae each dict surface and subsurface hydrology on the seasonis limited primarily by the frequency of basis of soil characteristics, topography, inundation of eggswith water of summer tem- weather, and agricultural practices (e.g.,Knisel peratures (Horsfall 1955). While many factors 1980,Skaggs 1980). These models were deemed influence larval and pupal survival, a requisite unsuitable for our purposes becausethey were to immature survival and subsequent adult difficult to use by non-specialists and, more emergenceis the continued presenceof surface importantly, required prohibitive amounts of de- water until near the time of eclosion(AI-Azawi tailed, on-site data. However, a common feature and Chew 1959). of the soil profile of rice growing regions, the The major objectiveofthe effort reported here shallownessof the impermeablehardpan