Yuma Ag and You: “Fly in the Ointment!”

Bobbi Stevenson-McDermott      May 10, 2015 publication

You never know what you will find when you read the paper! Last Sunday was a small article in Ag Glance announcing a citrus, date seminar for the following Tuesday. As I like to keep up with what is happening in the Ag industry, I attended and learned about a serious problem in Yuma County that I was really unaware of.

The topic of the presentation was ‘Pesky Little Flies in my Grove’ by Paula Rivadeneria, PhD of the U of A Cooperative Extension Service. I expected the talk to concern the perennial eye gnats we fight each year, but this was about Flies! There has been a dramatic increase in fly populations in Yuma, so much so that on the South Mesa particularly, they have created conditions at schools, towns and residences where it is impossible to eat out of doors, due to flies.

Dr. Rivadeneria was asked to do a study on the flies by the Yuma County Pest Abatement District whose gnat traps are being overwhelmed by flies as well as complaints from county residents.

The study discovered that the South Yuma County Landfill is permitted to accept human waste from the state of California. The biosolids received at the landfill are leftovers after sewage sludge (raw human waste) is treated in a wastewater treatment facility. Why does the Yuma landfill take California waste? Primarily revenue but now the landfill is also using this waste as cover for the trash instead of soil.

The types of biosolids are Class A that contain no detectable levels of pathogens and Class B that can have up to 2 million coliform bacteria per gram of waste. The amounts of biosolids delivered each month are staggering. 2,648 tons per month come in containing nearly 2 trillion coliform bacteria. Why is this important? Excessive bacteria growing in biosolids can be picked up by flies and birds feeding on the landfill contents. Fly populations reproduce exponentially using human waste as media to incubate eggs and feed larvae.

Flies live up to one month, lay up to 600 eggs in their life time and can travel up to 2 miles. Flies are dirty! They are known to carry up to 100 pathogens including parasites, bacteria and viruses. Flies transmit pathogens via fecal material, vomit and hairs on the exoskeleton.

The human health issue involved for people who live and work near the landfill, primarily agricultural workers, suffer from the nuisance of ever increasing fly populations. Flies can carry pathogens that could make these people sick.. The research conducted looked at the flies presumed to be reproducing in biosolids at the landfill and whether they carried intestinal pathogens. A second question is, are the flies able to transmit these pathogens to people in the area.

Fly traps were set at the boundary of the landfill and at varying distances as well as at a distant lettuce disposal site with flies. The lettuce disposal site was considered a control site known to have as many or more flies as the landfill. It was theorized that these flies would be ‘cleaner’ than the landfill flies. Lab tests on the flies looked for 3 pathogens, E. coli O157 (the bad one); non-O157 Shiga-toxin producing E. coli (STEC) and Salmonella. The good news is that none of the fly samples tested positive for E. coli O157. The further the samples sites were from the landfill, the less infected flies were found for the Non-O157 STEC and Salmonella, but the sampling and testing showed that 80 percent of the samples within a kilometer of the landfill were positive for Non-O157 STEC and 20 to 40 percent were positive for Salmonella.

This was a small sampling of the flies at a single time of the year and a short trapping time at a single time of day. It must be emphasized that strains and subtypes of pathogens were NOT identified.

The most obvious solution would be source reduction by dramatically reducing or eliminating biosolids entering the South Yuma County Landfill. Biosolids could also be managed in a manner to prevent fly reproduction.

This is a problem that needs input from citizens, city councils and county supervisors. Communication with local leaders is the primary way to bring attention to the seriousness of the fly problem. You can help by supporting research by Dr. Rivadeneria by allowing her to put test stations near homes, schools and fields. Contact Chris Sumner at the Yuma County Pest Abatement District; Charles Salter, member of the Pest Abatement board at 928-580-6877 or Dr. Rivadeneria at 928-919-2611. This is one of those issues that the public needs to become involved with, the proverbial ‘fly in the ointment’!