JUNE 1991 VERTICALDrstRIsuttoN Qr P. enrsnt'tlra 287 VERTICAL DISTRIBUTION OF PSYCHODAALTERNATA (DIPTERA: PSYCHODIDAE)IN SOIL RECEIVINGWASTEWATER UTILIZED FOR TURF CULTIVATION ARSHAD ALI, MOH LENG KOK-YOKOMI EUO J. BRUCE ALEXANDER [Jniuersity of Florida, IFAS, Central Florida Researchand Education Center,2700 East CelcryAuentr'e, Sanford, FL 32771-9608 ABSTRACT. Vertical distribution of immature Psychodaalternata in soil to a depth of 15 cm was studied in Jacksonville, FL. Samples were randomly taken from large circular land areas receiving a brewery wastewaterutilized for commercial turf cultivation and included turfed and bare habitats. Total organic matter was quantified at various soil depths. Overall, 88.5 and 95.8Volawae and 91.3 and 94.0% pupae were recoveredfrom the top 2.5 cm of soil at turfed and bare habitats, respectively.The highest concentration of total organic matter at both habitat t5,peswas in the top 2.5 cm. There were strong positive relationships beiween the number of Iarvae and pupae and total organic matter, indicating highest concentrationsof immatures in nutrient-rich topsoil with an abundant supply of larval food. We suggestthat insecticidal treatment directed against immature P. alternatabreedingin such habitats need not penetrate to a depth of more than a few centimeters to affect almost all of the population of this pestiferousinsect. INTRODUCTION vertically in the soil were determined and cor- related with the populations of P. alternata. An Psychodaalternata Say,which breedsin semi- understandingof this aspectof the ecologyof P. aquatic habitats, occurs in a variety of sources alternata is essential for the development of suchas hay infusion (Haseman1907), decaying control measuresagainst the pest. vegetables,cow and horse dung (Turner 1925) and seaweedpiles (Saunders1928). It is one of only 3 speciesin its subfamily able to live under MATERIALS AND METHODS heavily polluted conditions, and capitalizes on The turf farm is located at approximately the rich enerry resourcesavailable in biological 80'46' W longitudeand 30'31'N latitude,Duval filter beds of sewagetreatment plants; popula- County, FL. At the farm, several areas ranging tions reach such levels that it is commonly "trickling from 6 to 40 ha are under turf cultivation. Each known as the filter fly" (Quate 1955). cultivated area receives approximately 123,000 The tolerance of P. alternata for strong sewage liters/ha of the wastewater 2-3 times a week allows it to thrive free from interspecific com- dischargedthrough a long largeboom containing petition in many habitats heavily polluted with several nozzles and moving at a set speed in a organic material (Rutz et al. 1980).In biological circular manner. filter beds,the larvae may perform an important pivot, "zoog- Under each there is an elaborate net- function by grazingon the algal scum ot work of underground drains approximately 60 Iea" that coversthe stonesofthe filter bedsand cm abovethe water table. which is ca. 1-1.5 m thus prevent clogging.However, the adults from below the surface.The subterraneandrains col- such sourcesemerge in Iarge numbers and can lect and carry any leached wastewater into becomea nuisancein the vicinity of their breed- ditches situated at the periphery of each pivot. ing sites (Tomlinson and Stride 1945,Woods et The ditchesempty into small man-madeponds. al. 1978).This type of a problem exists in one Some ditches and ponds are equipped with re- situation in Jacksonville, FL, where 6-8 million leasegates used when necessary.The soil under Iiters ofwastewater derived daily as a by-product the pivots was considered to be the primary of a beerbrewing processare dischargedthrough breeding sourceof P. alternata, with turfed and pivot irrigation systemsonto large circular land bare sites which were apparently the 2 distinctly areas to cultivate turf. The nutrient-rich was- different types ofP. alternata habitats. tewater, discharged over several hundred ha, Soil samplesfrom the turfed and bare habitats createsfavorable conditions for the development under various pivots were randomly obtained by of very large populations of P. alternata. Large driving a 3.8-cm (inner diam) plexiglasscore numbers of adults disperseto neighboring resi- tube (Ali 1984) into the ground to a depth of dences,posing considerabledistress to local in- 20-25 cm with a rubber mallet. The collected habitants. column of soil was extracted from the tube with This study reports the vertical distribution of a plunger and its upper 15 cm length was sepa- immature P. alternata in the irrigated soil. Con- rated and fractioned into 2.5-cm-longsections centrations of total organic matter distributed and transferred into 6 separate, labeled poly- 288 JounNer, or rnr AnrsRrcln Mosqutro CoNrRor,Assocrnrlotv VoL.7,No.2 Table 1' Vertical distribution of Psychod.aalternata larvae and pupae and percent total organic matter in soil (turfandbare habitats)in largecircular land areascultivatedto turfiniacksonville, Fi (October19g9- February1990). + Mean no. SD of immat:ul.ePsychoda alternata per 10 cores"or mean % concentration of total organicmatter per 5 cores . Soil depth Total Vo organtc (cm) L1b L3 L4 larvae' Pupae" matter ,TURF 0.0-2.5 1.0+ 0.8 5.0+ 3.3 28.0+ 11.3 88.7{- 31.4 1.22.7a 38.7a -f 2.60+7.07 2.5-5.0 1.0 1.4 3.0+ 2.9 3.8-f 5.2 13.0b 2.0b 1.59+0.14 5.0-7.5 0.0 + 0.0 0.7+ 0.9 0.3 + 0.5 1.0+ 1.4 2.0b 0.7b t.26+0.17 7.5-10.0 0.0+ 0.0 0.0 + 0.0 0.3+ 0.5 0.0 t 0.0 0.3b 1.0b 0.95+0.12 10.0-12.5 0.0+ 0.0 0.0+ 0.0 0.0 r 0.0 0.3+ 0.5 0.3b 0.0b 1..25r- 0.12 12.5-15.0 0.0+ 0.0 0.3+ 0.5 0.0+ 0.0 0.0+ 0.0 0.3b 0.0b r.22+0.12 BARE -{- 0.0-2.5 33.3+ 38.7 163.3 187.4 70.7+ 18.5 74.3+ 95.2 347.7a 30.0a 3.36+ 0.32 2.5-5.0 0.3+ 0.5 4.7+ 3.3 4.7+ 3.7 2.0-f 0.0 11.7b 1.3b 2.22+ 0.02 5.0-7.5 0.0+ 0.0 0.0+ 0.0 0.0+ 0.0 1.0-f 0.8 1.0c 0.0b 1.99+ 0.30 7.5*10.0 0.0+ 0.0 0.0+ 0.0 0.0+ 0.0 1.0-f 1.4 1.0c 0.3b 1.83+ 0.18 -f 10.0-12.5 0.0+ 0.0 0.0 0.0 0.3+ 0.5 1.0-f 1.4 1.3c 0.3b 2.02+ 0.28 -r 12.5-15.0 0.0{- 0.0 0.0 0.0 0.0+ 0.0 0.0 -f 0.0 0.0 c 0.0b 1.52-f 0.16 'Each core 3.8 cm in diam and 2.5 cm deeo. r'Ll-L4: larval instars I to 4. " Means in a column followed by the same latter are not significantlydifferent (P > 0.01)as analyzedby ANOVA and Duncan's multiple range test. thene bags. At each habitat, 10 such cores ofsoil to elucidate relationship betweenpopulations of were collected and the fractioned subcores ofthe immature P. alternata and the total organic same depth were pooled. Larval and pupal sam- matter at various depths. ples were collected on 3 occasions between Oc- tober 1989 and February 1990. An additional 5 cores of soil from equivalent depths were col- RESULTS AND DISCUSSION lected each time for the determination of total Among immaturesof psychodids,only P. ol- matter organic at different depths. ternata larvae and pupae were recognizedin the In the laboratory, each soil sample collected collectedsamples. The mean numbersof P. al- for assessment of immature P. alternato popu- ternata per 10 soil corestaken at various depths Iation was washedthrough a series of U.S. stand- arepresented in Table 1; a total of 30 coresfrom ard sieves. Large pieces of vegetation were eachhabitat were collected.Generally, the bare washed clean of soil and discarded. The residue habitat supported higher populations of larvae on the finest screen (250-pm pore size, U.S. than the turfed habitat. As expected,the first Standard sieve No. 60) was collected, preserved instars in both habitat categoriesoccurred only in 707o alcohol and examined under a binocular in the top 5 cm of soil since the eggsare laid at microscope (10X magnification) to identify and or near the soil surface. Overall, 88.5% latvae count psychodid larvae and pupae. Each sample and,91.3%pupae recoveredfrom soil samples was examined in parts by placing small portions collected from turfed habitats were in the top in a 8.5-cm diam Petri dish with a l-cm grid 2.5 cm. At bare locations,the percentagesfor marked on the bottom. The taxonomic keys in this upper most level werc 95.8Volarvae and Quate (1955) were used. 94.0% ptqae. These proportions of larvae and To determine total organic matter, soil sam- pupaein the top 2.5cm of soil weresignificantly ples were dried at 40"C and ground to pass different (P < 0.01) from those encounteredin through a 4O-mesh sieve. The wet oxidation the variousdepths below 2.5 cm. The numberof method of Nelson and Sommers (1982) was used larvae or pupae collected5 cm below the surface to determine percent total organic matter in was 13Vo of the total larvae or pupae collected each sample. from either habitat. Negligible numbers oc- Populations of total larvae and pupae of P.