Open Ditch Research Articles

Application of DRAINMOD-Ks-STMAX to Predict Deep Chiseling Effects on a Drained Southern Alluvial Soil

Deep chiseling in heavy drained soils can help increase infiltration and hence reduce erosion, potentially enhancing growth by reducing excess water in the root zone and reducing nutrient losses through the reduction of runoff to surface waters. The goals of this study were to apply DRAINMOD-Ks-STMAX, a modified form of the water management model, DRAINMOD 1) to predict the effects of deep chiseling on hydrology for a subsurface drained plot and 2) to determine the frequency and timing of deep chiseling. Data from a subsurface drained plot at Ben Hur Research site near Baton Rouge, Louisiana, were used. Simulation results indicated that deep chiseling a Commerce silt loam, a southern alluvial soil, increased cumulative infiltration (CI) by 16% and reduced cumulative sub-surface drainage (CSD) and cumulative surface runoff (CRO) by 26% and 37%, respectively, between 28 September 1995 and 21 November 1996. Between 22 November 1996 and 22 November 1997, it increased CI and CSD by 9% and 17%, respectively, and reduced CRO by 22%. Vertical saturated hydraulic conductivity (Ks) had decreased by 99%, from a maximum initial value immediately after deep chiseling, by the time 150 cm of rain had fallen (approximately 12 months) since deep chiseling. For high rainfall states like Louisiana, with average annual rainfall often exceeding 150 cm, this translates to deep chiseling once every year whereas in drier states deep chiseling can be done once every two to three years depending on the amount of rainfall. Depending on the cumulative amount of rainfall at planting, producers can lose 85% or more of the maximum deep chiseling benefits due to reduced Ks. Because of great rainfall variability in Louisiana and other southern states, it is advisable for farmers to deep chisel their fields just prior to the planting season. Results of this model simulation study indicate that DRAINMOD-Ks-STMAX can be used as a cost-effective (saving time and money) tool to predict the effects of deep chiseling in poorly drained soils with subsurface drainage and potentially open ditch drainage, and to advise farmers on the frequency and timing of deep chiseling based on science. However, the model needs to be tested for longer time periods and under different climatic conditions and soil types before it can be recommended for general application for the purposes listed above.

Effect of open ditch draining on sediment and soil properties in cultivated areas in southeast Mexico

In the last 10 years in many parts of the coastal plain of Tabasco, SE-Mexico open ditch draining systems were installed. From April to October 2003 we investigated the effect of draining on sediment deposition on floodplain soils with agricultural and pasture use. Open ditch draining reduced the amount of sediment deposited on inundated soils. This was due to the fact that the number of inundations that occurred in the drained area was smaller than in natural areas. However, neither the amount of sediment deposited on the floodplain soils after a single inundation nor the nutrients or heavy metals (Zn, Pb) transported with the sediment deposited by a single inundation were influenced by the draining. The total amount of deposition in the drained areas varied from 94.2 to 123.5 t ha − 1 (April to October) and did not show any significant differences between different land uses. In the natural area the deposition was significantly higher (242.6 t ha − 1 ). Organic matter, Ntot, Ptot and Zntot content of the new sediment did not differ between natural and drained sites. In none of the sediments Pb was detected. However, in the natural area organic matter, Ntot and Ptot content in topsoil increased significantly between April and October 2003 whereas in the drained areas only the Ptot content in topsoil increased. Eighty-five percent of the amount of organic matter and Ntot deposited on the topsoil of the natural area was lost probably by mineralization and lateral transport. The input of Zntot deposited with the sediment in all sites exceeded the trigger value of 1200 g ha year − 1 for critical load inputs in soils [Bundes-Bodenschutz- und Altlastenverordnung, 1999. http://www.fh-kehl.de/projekt_bodenschutz/bundesrecht/BodSchV.htm] due to extremely high quantity of sediment deposition.

Grass Swale-Perforated Pipe Systems for Stormwater Management

The performance and potential of perforated pipes for stormwater quantity and quality control is evaluated. The studied design consists of a grass swale underlain by a section of perforated pipe enclosed in an infiltration trench. The grass swale-perforated pipe system results in a pleasant curbless design, which may replace open ditch systems, in low density residential areas. Current design practices and construction methods were assessed by a survey completed by 53 towns and municipalities in Ontario, Western Canada and the United States. The survey of municipal experience showed that while 50% of the municipalities have experience with perforated pipes used as storm sewers, only few municipalities used a combined system of grass swales and perforated pipes for the purpose of urban runoff infiltration. Seventy six percent of the respondents however are willing to use the system as an alternative to other stormwater management methods. Through a series of laboratory tests, it was found that exfiltration rate out of pipe perforation is not directly proportional to the orifice area. The analysis of the results indicated that the orifice discharge coefficient varied with orifice size and the head above the orifice. Field tests were conducted to measure the infiltration rates of typical grass swales and existing pipe trenches. The infiltration rates obtained were found to be consistent with literature values. Finally, according to a 3 month field monitoring program, the total seasonal discharge for a properly designed perforated pipe system was found to be 13 times smaller than for a conventional stormwater system, which shows the favorable effect of the perforated pipe system on the hydrologic budget and pollutant loading.

HYDRAULICS, WATER QUALITY AND VEGETATION CHARACTERISTICS OF GROUNDWATER-FED OPEN DITCHES

A novel peatland management strategy to utilise the high nutrient-retention potential of degenerated peatlands has been implemented in Northern Germany. The effect of raised water levels and extensive land-use management on hydraulic properties, water quality and vegetation characteristics of heavily vegetated and groundwater-fed open ditches, was investigated at the River Elder Valley - a nationally important wetland case study. A better understanding of the effect of vegetation on the temporal flow patterns and the hydraulic retention times is of high scientific interest, especially for improving nutrient standards in lowland rivers. Within-ditch vegetation and other hydraulic obstructions, including accumulated silt and organic debris, increase the hydraulic retention time and lead to an improvement of the water quality along the open ditch. Lower parts of the open ditches were flooded by the River Elder, due to the absence of a mowing scheme during late summer.

Evidence for the use of reflected self-generated seismic waves for spatial orientation in a blind subterranean mammal

Subterranean mammals like the blind mole-rat (Rodentia: Spalax ehrenbergi) are functionally blind and possess poor auditory sensitivity, limited to low-frequency sounds. Nevertheless, the mole-rat demonstrates extremely efficient ability to orient spatially. A previous field study has revealed that the mole-rat can assess the location, size and density of an underground obstacle, and accordingly excavates the most efficient bypass tunnel to detour around the obstacles. In the present study we used a multidisciplinary approach to examine the possibility that the mole-rat estimates the location and physical properties of underground obstacles using reflected self-generated seismic waves (seismic 'echolocation'). Our field observations revealed that all the monitored mole-rats produced low-frequency seismic waves (250-300 Hz) at intervals of 8+/-5 s (range: 1-13 s) between head drums while digging a bypass to detour an obstacle. Using a computerized simulation model we demonstrated that it is possible for the mole-rat to determine its distance from an obstacle boundary (open ditch or stone) by evaluating the amplitude (intensity) of the seismic wave reflected back to it from the obstacle interface. By evaluating the polarity of the reflected wave the mole-rat could distinguish between air space and solid obstacles. Further, the model showed that the diffracted waves from the obstacle's corners could give the mole-rat precise information on the obstacle size and its relative spatial position. In a behavioural experiment using a special T-maze setup, we tested whether the mole-rat can perceive seismic waves through the somatosensory system and localize the source. The results revealed that the mole-rat is able to detect low frequency seismic waves using only its paws, and in most cases the mole-rats determined accurately the direction of the vibratory source. In a histological examination of the glabrous skin of the mole-rat's paws we identified lamellate corpuscle mechanoreceptors that might be used to detect low frequency seismic waves. The combined findings from these different approaches lead us to suggest that a specialized seismic 'echolocation' system could be used by subterranean mammals to determine the most energy-conserving strategy with which to bypass an obstacle, as well as to estimate their distance from the surface, keeping their tunnels at the optimal depth.

Hydraulic characteristics of groundwater-fed open ditches in a peatland

The Environmental Ministry of Schleswig-Holstein has implemented a novel peatland management strategy in order to utilize the high nutrient retention potential of degenerated peatlands, and to improve the habitat at the same time. The effect of raised water levels and passive land use management on hydraulic properties of heavily vegetated and groundwater-fed open ditches was investigated at the ‘Eider River Valley’. The flow properties of selected representative open ditches were regularly assessed at different discharge levels during different vegetation cover periods. The hydraulic residence time is predominantly a function of the open ditch geometry and the overall obstruction cover including the presence of macrophytes. Typical mean discharges measured ranged between 0.2 and 2.5 l/s. Within-ditch vegetation and other hydraulic obstructions, like accumulated silt and organic debris, slow down the hydraulic residence time. The experimental results were evaluated to acquire more realistic values for total bed-roughness under different hydraulic flow regimes. Further findings show that the lower parts of the open ditches were flooded by the Eider River due to the absence of a mowing scheme. Typical water level increases were 0.5 m. This led to a reduction of the velocity and an increase of the dispersion within the ditch.

Detours by the blind mole-rat follow assessment of location and physical properties of underground obstacles

Orientation by an animal inhabiting an underground environment must be extremely efficient if it is to contend effectively with the high energetic costs of excavating soil for a tunnel system. We examined, in the field, the ability of a fossorial rodent, the blind mole-rat, Spalax ehrenbergi, to detour different types of obstacles blocking its tunnel and rejoin the disconnected tunnel section. To create obstacles, we dug ditches, which we either left open or filled with stone or wood. Most (77%) mole-rats reconnected the two parts of their tunnel and accurately returned to their orginal path by digging a parallel bypass tunnel around the obstacle at a distance of 10–20cm from the open ditch boundaries or 3–8cm from the filled ditch boundaries. When the ditch was placed asymmetrically across the tunnel, the mole-rats detoured around the shorter side. These findings demonstrate that mole-rats seem to be able to assess the nature of an obstacle ahead and their own distance from the obstacle boundaries, as well as the relative location of the far section of disconnected tunnel. We suggest that mole-rats mainly use reverberating self-produced seismic vibrations as a mechanism to determine the size, nature and location of the obstacle, as well as internal self-generated references to determine their location relative to the disconnected tunnel section. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

Hydrologic Modeling of a Drained Pine Plantation on Poorly Drained Soils

Abstract Three experimental watersheds in eastern North Carolina have been continuously monitored since 1988 to study long-term hydrology of loblolly pine (Pinus taeda L.) forests on poorly drained soils. This study was conducted to test the forestry version of an agricultural hydrology model DRAINMOD with 10 yr (1988–1997) of data collected at one of these watersheds under conventional (open ditch) drainage. The model, which is based on hourly water balance for the land between parallel drainage ditches, simulates interception, evapotranspiration (ET) as the sum of canopy transpiration and soil evaporation, drainage, and surface runoff. Results showed that model predictions of daily water table elevations and flow rates on an average annual basis were within 0.15 m and 0.61 mm, respectively, compared to the measured data. Relative errors on drainage outflow varied from -18% to 23%, with an average of 0.4%. Errors in measured flow rates during weir submergence, missing rainfall and weather data, and uncertainty in estimates of stomatal conductance contributed to the differences between model predictions and field observations. It was concluded that the model is a reliable tool for assessing hydrologic impacts of silvicultural and water management treatments, as well as climate changes, on these pine stands. FOR. Sci. 47(1):103–114.

Environmental road and lot drainage designs: alternatives to the curb-gutter-sewer system

Traditionally, road and lot drainage systems have been designed to convey storm runoff away as quickly as possible to reduce localized ponding. This drainage concept, using curb-gutter-sewer systems, has led to downstream flooding, erosion, water-quality degradation, reduced groundwater recharge and stream baseflow, and aquatic habitat destruction. This paper examines the pros and cons of curb-gutter-sewer systems and qualitatively compares various forms of open ditch - swale drainage alternatives with the conventional curb-gutter-sewer drainage system. These open ditch - swale drainage alternatives not only provide drainage functions but also promote infiltration, trap sediments, and reduce flow velocity along the drainage path. Thus, they can reduce erosion, enhance runoff quality, and increase groundwater recharge. However, they usually require a wider right-of-way than the conventional curb-gutter-sewer systems and may not be suitable for sites with steep topography or erosive soils. For sites that are suitable for the application of these alternative drainage systems, their environment functions make them more attractive than the conventional curb-gutter-sewer system.Key words: drainage systems, storm water, curbs, gutters, sewers, ditches, swales.

Environmental road and lot drainage designs: alternatives to the curb-gutter-sewer system

Traditionally, road and lot drainage systems have been designed to convey storm runoff away as quickly as possible to reduce localized ponding. This drainage concept, using curb-gutter-sewer systems, has led to downstream flooding, erosion, water-quality degradation, reduced groundwater recharge and stream baseflow, and aquatic habitat destruction. This paper examines the pros and cons of curb-gutter-sewer systems and qualitatively compares various forms of open ditch - swale drainage alternatives with the conventional curb-gutter-sewer drainage system. These open ditch - swale drainage alternatives not only provide drainage functions but also promote infiltration, trap sediments, and reduce flow velocity along the drainage path. Thus, they can reduce erosion, enhance runoff quality, and increase groundwater recharge. However, they usually require a wider right-of-way than the conventional curb-gutter-sewer systems and may not be suitable for sites with steep topography or erosive soils. For sites that are suitable for the application of these alternative drainage systems, their environment functions make them more attractive than the conventional curb-gutter-sewer system.Key words: drainage systems, storm water, curbs, gutters, sewers, ditches, swales.

Diamondback Moth (Lepidoptera: Plutellidae) in Cabbage: Influence of Initial Immigration Sites on Population Distribution, Density and Larval Parasitism

Examinations of cabbage plants in five fields near Bunnell, Flagler Co., FL, in spring 1995 showed that larvae of the diamondback moth, Plutella xylostella (L.), were more abundant on the field ends (perpendicular to cabbage rows) adjacent to weed-filled drainage ditches than the fields ends abutting wooded swamp areas. There were no significant differences in the numbers of diamondback moth larvae on cabbage plants on the ends next to other cabbage fields or at sites located within the interior of the fields. Cabbage heads rated for damage due to diamondback moth larvae at harvest showed a distributional pattern similar to that observed for diamondback moth larvae. Parasitism of diamondback moth larvae was not significantly different between field ends and interior fields. Cabbage damage ratings on field sides (parallel to cabbage rows) showed that no edge effect was detected on the sides abutting other cabbage fields, that edge effect only occurred on the first one or few rows on the sides adjacent to other cabbage fields but separated by irrigation ditches, and that edge effect occurred continuously and decreased from the first to the 12th row on sides adjacent to earlier planted cabbage or an open weed-filled ditch area. These results suggest that diamondback moth first invaded cabbage fields from outside areas, and that more diamondback moth spread to the interior of the fields from adjacent open, weed-filled ditches than from bordering wooded and bushy areas.

Modelling the hydrological impacts of open ditch drainage

Open ditch drainage has been observed to have a significant effect on catchment runoff regimes, yet the processes generating the changes are not well understood. An approach of physically based modelling is used, with a fine grid resolution, on a very simple hill-slope model to analyse how ditches affect runoff. Results from the simulations show that the most important process is the change in behaviour of the sub-surface, under near-saturated conditions, when there is a much higher and more variable sub-surface exchange flow into the stream network. The speed of the surface runoff response is also affected. From the results of the analysis a method using effective parameterisation has been developed to recreate the effects of the drainage in a coarser resolution catchment model. The method involves calculating effective saturated hydraulic conductivities for the sub-surface flows and effective Strickler coefficients for the surface flows. The application of the method is demonstrated for a sub-catchment of the River South Tyne at Alston. Results from these simulations show that predictions of flow for the catchment can be improved by using the effective parameterisation to create a pseudo drainage representation of the sub-grid-scale channels within the model. Simulations of more intensive drainage scenarios show that the effects of open ditch drainage on hydrology are significant and that the direction of change is not intuitive.

Log-jam effects on bed-load mobility from experiments conducted in a small gravel-bed forest ditch

Bed-load transport experiments have been conducted in a steep gravel-bed open ditch. This initially straight ditch has been neglected for many years and looks at present like a second-order natural stream channel. The channel flows through a spruce forest and several log-jams have produced chutes and pools, creating supplementary roughness. The total shear stress has been evaluated using the slope-hydraulic radius product, and the ratio between grain and bed-form shear stresses has been calculated using different methods. The shear stress has also been evaluated from the shear velocities, and this gives a good evaluation of the grain shear stress. Additional experiments have been conducted with marked pebbles to estimate particle mobility and to improve the motion equations. Equations such as θ c = a(D i/D 50) b)b , defined by Andrews, apply in these cases but the values of a and b are lower than those produced by this author. In a second stage of experimentation, we have destroyed the log jams resulting in a diminution of the roughness and critical shear stress (when the total shear stress is used), an increase of the grain shear stress, and thus greater bed particle mobility for the same discharge. It emerges from these experiments that the log-jams contribute to the reduction of bed-load evacuation and explain the very weak bed-load discharge measured by a bed-load trap (0.3 t · km −2 yr −1).

Water movement and salt leaching in drained and irrigated marsh soils of southwest Spain

The Guadalquivir river marshes in southwest Spain, are situated in a former estuary that has now been drained. They cover some 140 000 ha. Soils formed in this zone are alluvial, very clayey, salinesodic, and of vertic character with a shallow, very-saline water table. An area within these marshes, reclaimed in 1979, is the object of this detailed study which looks at some physical and chemical properties of soil, and also the influences of sprinkler and furrow irrigation on drainage and salt leaching. These studies were conducted between 1988 and 1990. A 1 ha experimental plot was used for this purpose. The plot is situated within an area of the marshes being used for standard agricultural practices, equipped with a drainage system of ceramic pipes buried 1 m deep and spaced 10 m apart, ending at an open ditch collector which is perpendicular to them. The following measurements have been carried out: soil bulk density changes with water content, hydraulic conductivity and sorptivity, soil water content and water tension profiles changes, water table level, drainage outflow and salt content of soil, soil solution and drainage water. Cotton was used as the crop. The results obtained show that after ca. 10 years in reclamation the electrical conductivity and exchangeable sodium percentage decreased in the 0–90 cm layer of this soil, particularly in the top 50 cm, that reduces the adverse effects of salinity on crop development. During both sprinkling and furrow irrigation a rapid response of the drain pipes was observed because of the soil fissures and crack network that resulted from the shrinking and swelling processes. Maximum drainage outflow was reached when the irrigation stopped. Water movement in this soil is characterized by an initial rapid phase, due to the soil fissures and cracks, followed by a second slow one controlled by the soil matrix. The efficiency of irrigation in salt leaching was higher in the case of furrow irrigation (16 g of salt leached per litre of applied water) than in the case of sprinkling irrigation (10 g l −1), owing to the use of more water in the latter. The salinity of soil and soil solution decreases after irrigation starts, the time taken to reach a minimum value for the different soil layers and the irrigation method used were different. In 1989 due to water restrictions at some time of the crop period, the irrigation schedule was different to that normally used, and the crop was affected by water stress and capillary rise of saline water.

Drainage-Subirrigation Design For Pelham Loamy Sand

ABSTRACT This project was conducted on the Bell farm located in Pierce County, GA on Pelham loamy sand soil. The study area included 40 ha of land under controlled drainage-subirrigation (CD-SI) system of which 38 ha were in blueberries. The system installation included two drain spacings of 15.3 and 20 m, and two types of control structures for the drainage system outlet water level, which were an open ditch and a closed conduit system network. The blueberry section of the field was in a closed conduit system network with lateral drains spaced at 15.3 m. Seventeen punch-tape recorders were used to measure the water table elevations in the soil profile within the field over the drain tiles, and midway between drainlines, at the open ditch and closed system control structures (one for each), and in an undrained-nonirrigated section of the farm. A punch-tape rainfall recorder was also used to measure rainfall at the site. Surface runoff, drainage effluent, or subirrigation volume was not measured. Experimental results showed that the water table and soil-water conditions could be adequately managed in the blueberry field, thus excellent crop growth and yield resulted. DRAJNMOD, a water management model for shallow water table conditions, was used to simulate the system performance for the study site. Simulation results indicated that a subsurface drain spacing of 20 m is satisfactory for controlled drainage-subirrigation (CD-SI) systems for Pelham loamy sand soils in Pierce County, GA. Simulations were done using 20 years of climatological data from Augusta, GA. Additional research is needed to develop specific design guides for other soil types in the Georgia Flatwoods region.

Drainage‐Subirrigation Effect on Water Quality in Georgia Flatwoods

The effects of controlled‐drainage‐subirrigation (CD‐SI) systems on subsurface and outflow water quality must be evaluated before these systems can be promoted for use in the Georgia flatwoods region of the eastern Coastal Plain. In this paper, Nitrate‐nitrogen (N), ammonium‐N, and orthophosphorous (P) concentrations are measured from shallow subsurface wells and outlets of a CD‐SI system in the Georgia flatwoods for comparison to adjacent forested and grassland areas (the most common current land uses). Nitrate‐N concentrations did not exceed 10 mg/L from any of the outflow samples although almost 6% of the well samples taken from the CD‐SI area had concentrations exceeding 10 mg/L, Nitrate‐N concentrations in most of the wells in the CD‐SI area were significantly higher than in the forested and cleared areas. Ammonium‐N and ortho‐P concentrations were relatively low and do not appear to be a problem based on this limited data. No significant differences in ammonium‐N and ortho‐P concentrations were shown between any of the sites. Ammonium‐N concentrations did exceed 2 mg/L from at least one sample of the scrub forest, one of the CD‐SI blueberry sites, an open ditch (1.8 m depth), and one of the cleared unirrigated sites. Ortho‐P concentrations ranged from 0 to 1.94 mg/L, with average concentrations from all sites near 0.1 mg/L.

Adopting water-conserving irrigation technology: The case of surge irrigation in Arizona

Surge-flow irrigation technology is a potential means for increasing irrigation efficiencies in desert agriculture. An economic analysis of the adoption decision for Arizona farmers reveals that an investment in surge irrigation is only economically viable when developing new agricultural lands or where gated pipe is already in use. Since the majority of the agricultural land in Arizona is furrow irrigated using ditches and syphon tubes, the potential for high adoption rates on existing farmland is rather limited. The analysis indicates that water costs, under conservative but realistic assumptions, would have to rise to US$ 0.08/m 3 (US$ 100 per acre foot) before surge irrigation would be economically viable as a substitute for open ditch furrow irrigation. Further research is needed on potential labor savings and management efficiencies related to surge irrigation in order to measure potential profitability more accurately.

Microbial measurements in relation to sewage pollution of the Firth of Forth, Scotland

SynopsisThe history of Edinburgh's sewage disposal to the sea from the open ditch system of the 17th century to the present day, together with the changes in legislation affecting sewage discharges to the firth, are reviewed. During the last thirty years sewage discharges have been monitored monthly for levels of faecal coliform bacteria at approximately thirty-four shore sites and twenty offshore sites. These coliform counts are used as bacteriological indicators of sewage pollution, in order to assess the risk to humans of infections that might result from the consumption of contaminated shellfish or from bathing in sewage-polluted waters. Most of the areas sampled from the inner firth were shown to be grossly polluted, particularly in late summer, and regularly to exceed guideline levels throughout the year. Since the commissioning of the new Seafield sewage works in 1979, a general improvement in bacterial and viral counts has been recorded on the south shore of the inner firth. In the last decade two European Community directives relating to the quality of seawater for bathing and shellfish growing have been promulgated, which set guideline and mandatory levels for the number of faecal coli in seawater. The Scottish Development Department has recently designated five beaches as bathing beaches and two areas on the north and south shores of the firth as shellfish growing areas. These areas have been regularly monitored by the Forth River Purification Board and the published results of both surveys are analysed. The virological studies carried out by the Forth Pollution Group of Napier College before and after the major change in the sewage discharge pattern into the Firth of Forth are reviewed.

An Open Ditch Surge Flow Furrow Irrigation System

AN automated rotating gate enabled an existing open channel furrow irrigation system to be adapted to surge flow. Equipment performance was quite reliable. System hydraulics were analyzed with respect to unequal outlet elevations, spatially varied flow within an irrigation bay, and unsteady flow due to the opening or closing of the automated gate. System design considerations are presented.

PATHOGENICITY OF METARHIZIUM ANISOPLIAE VAR. ANISOPLIAE1 TO MOSQUITO LARVAE

Water samples from various mosquito breeding habitats did not have an effect on the efficacy of Metarhizium anisopliae var. anisopliae isolate E9 when treated in the laboratory against 3rd instar of Culex quinquefasciatus. At the highest dosage rate (5.0 mg), the percent mortality varied from 89.1 ± 4.8 in rice field water to 94.4 ± 4.1 in sewer drainage and open ditch water. In another laboratory test, all field collected instars (89.25% Culex, 8.50% Aedes and 2.25% Psorophora) were found to be highly sensitive to isolate E9. At the 5.0 mg rate the percent mortality ranged from 91.2 ± 2.9 in the 2nd instars to 100.0 in the 3rd instars. There was no significant difference (P = 0.05) in mortality between instars except at the lowest dosage (1.25 mg) where the 4th instar mortality (28.6 ±8.5%) was significantly lower than those of other instars. The LT50 values for the 1st through the 4th instar increased with age and ranged from 1.1 to 1.8, 1.7 to 2.7, and 2.0 to 4.3 days at the 5.0, 2.5 and 1.25 mg dosages, respectively. In a preliminary field test to determine the susceptibility of field collected 3rd instar, up to 97.9 ± 1.8% mortality was recorded at the 800 mg rate.