midge flies and wastewater plants - est....

Midge Flies and Wastewater Plants

Lauren Lochstampfor

Regional Biologist

lwright@clarke.com

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