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Midge Flies and Wastewater Plants
Lauren Lochstampfor
Regional Biologist
703-297-2437
Why are midges important to control in WWTP’s?
• Economic estimates of midge impact vary
– Damage to pumps and moving parts
– Clogged filters
• Health and Safety Hazard for WWTP Employees
• Many municipal WWTP’s are located in or near residential areas.
1. Marshall, Stephen. Insects Their Natural History and Diversity. Firefly Books, 2006. Pg 391.
Chironomid Midge Flies
• Look like mosquitoes
• Red Worms
• Numbers can be in tens of thousands per square meter
• Larvae present in most aquatic habitats.
Chironomid Biology
• Adult males swarm. Females rest on surrounding structures and fly up to males and select one to mate with.
• Egg masses are laid on the surface of the water and sink down into the sludge.
• Larvae hatch in the sludge and create case like tubes around themselves.
• After 2-7 weeks pupae emerge and it starts again. • Adult midges only live a few days but can lay up
to 3000 eggs!
Psychodid Midge Flies
Trickle Filter Files (P. alternata)
• Also called moth flies or sometimes sand flies
• Larvae are found on wet nutrient rich films
• In San Diego, CA – one municipal Sewage Plant estimates that they discharge up to 20 million Psychodids each day. 1
1. Marshall, Stephen. Insects Their Natural History and Diversity. Firefly Books, 2006. Pg 391.
Psychodid biology
• Females lay 10-200 eggs directly onto moist organic debris
• Eggs hatch in less than 2 days and larvae feed on organic matter
• After 9-15 days larvae pupate and spend 1-2 days in the “slime” as pupae
• Adults live for only a few days.
Simplified Sewage Treatment Process
Source: http://en.wikipedia.org/wiki/Sewage_treatment
Many Shapes and Sizes
Pretreatment
Primary Treatments
PrimaryTreatments
Secondary Treatment
Trickle Filters and Medium
Sewage Tertiary Treatment
• Any treatment above primary or secondary that helps to make the water more suitable for discharge
• Can include disinfection, microfiltration, and lagooning
• May also include nutrient and/or odor removal
Control Methods – Talk to the Operator!
• Understand where in the plant the midge flies are emerging from.
• Know what type of WWTP structures you will be treating and where you will be treating.
– Psychodid’s like trickle filters
– Chironomid’s like clarifiers
• Larval control is more effective than adult control
Control Methods
• Larval Control– Use liquid larvicide products
• Vectobac 12AS has a technical bulletin for filter fly control in WWTP’s. Methreprene and mono-molecular films also work.
• Make sure you get the plant flow rate from the operator to calculate the correct application rate.
• Start with a high dosage, and decrease your dose rate after that.
• Treatment timing can vary depending on time of year and type of midge.
Larval Control Methods
• Trickle filters– Treat at point before water enters
filters.– Have WWTP operator recirculate the
treated water through each filter for at least 30 minutes.
• Clarifiers– Treat either directly into clarifier or
at flow divider/stabilizer before clarifiers.
– Any treatments to flowing water should be timed to occur over 30 minutes
Adult Control Methods
• Barrier treatments indoors and outdoors are effective at adult control
• Can be performed in conjunction with larval control to knockdown large populations.
• Can have WWTP Operators hose down walls
Other Control Methods
• Gambusia fish where possible
– Lagoons, storage tanks, etc
• Regular cleaning and maintenance
– Hosing down surfaces
– Removing slime/sludge
• Plant re-design
Additional Resources
• http://www.tpomag.com/editorial/2012/06/where_have_all_the_solids_gone
• http://www.ces.ncsu.edu/depts/ent/notes/Urban/drainfly.htm
• Biever, K.D. and Mulla, M.S. “Effects of Temperature on the Developmental Stages of Psychoda alternata(Diptera – Psychodidae).” Mosquito News 26(3): 416-419.
• Ali, Arshad. “A Concise Review of Chironomid Midges (Diptera: Chironomidae) as Pests and Their Management.” Journal of Vector Ecology 21(2): 105-121
