Moisture, temperature key in fly control

Dr. Simon Zebelo, discusses fly control on poultry farms during a recent Grower Lunch Break meeting. (Photo by Sean Clougherty)

SALISBURY, Md. — Raising chickens in confined houses at controlled temperatures has proven extremely efficient, but it also fosters insects like house flies, the No. 1 pest in livestock production.
Dr. Simon Zebelo, University of Maryland Eastern Shore assistant professor in entomology, discussed Integrated Pest Management approaches to control flies during a Feb. 1 Grower Lunch Break meeting hosted by the Extension services in Maryland and Delaware and the Delmarva Chicken Association. Winter isn’t prime season for fly issues on poultry farms but conditions inside houses can keep the pests producing year-round, an entomologist reminded poultry growers, Zebelo said. Not just a nuisance, the flies can transmit over 100 human and animal disease-causing organisms.
In poultry houses, flies breed in manure, spilled feed or any decaying organic matter, Zebelo said and can lay between 1,000 and 1,400 eggs in their four-week lifespan, cranking out batches every 3-4 days in optimal conditions.
Temperature is a key factor on determining how long eggs will take to hatch, Zebelo said. At 85 degrees F, eggs can hatch 10 days after they are laid; at 60 degrees F, it can take 45 days and below 60 degrees survival nosedives, he said.
The goal of an IPM approach is to keep fly populations below economic thresholds, Zebelo said. The threshold can vary as well with disease transmission, time of year, age of the birds and other factors. If they pass the threshold into economic injurious levels, “the damage is already done,” he added, and effort to control the pest increases, often with added cost.
Zebelo recommended monitoring fly population in houses and on poultry farms to signal when an economic threshold is approaching. Baited jug traps, sticky cards and spot cards are a few monitoring tools.
Zebelo offered threshold levels at 250 flies per week for baited traps, 100 flies per sticky card and 100 fly specks per spot card.
Cultural controls include managing manure in the house, especially the moisture level.
“If you want to control flies just manage the manure, it’s as simple as that,” he said.
Zebelo said manure below 50% moisture is inhospitable to larval growth and preferred by beneficial insects like the hister beetle and macrohelid mite, which act as a biological control, feeding on flies.
Parasitic wasps are another biological control. They lay their eggs in fly pupae, which then becomes a food source for the new tiny wasps. Zebelo added the wasps exists naturally but their population can be boosted by commercial sources, sending new wasps periodically.
Pesticides should be the option of last resort, Zebelo said, but they are also cost effective and have different modes of action that should be rotated to ward off resistance issues.
Pesticides also kill beneficial insects and without their protection, a resurgence of flies can be a consequence.