black onion fly

(Tritoxa flexa)

Conservation Status
black onion fly
Photo by Dan W. Andree
  IUCN Red List

not listed

     
  NatureServe

not listed

     
  Minnesota

not listed

     
           
           
           
           
           
           
           
 
Description
 
 

Black onion fly is a medium-sized picture-winged fly. It occurs in the United States from New Hampshire to Minnesota and south to Missouri and North Carolina. It is uncommon in Minnesota, where it is at the western extent of its range. It is a serious pest of cultivated onion and garlic crops in the Northeast and North Central states.

The female is slender, ¼ to (6 to 10 mm) long. The head, body, and legs are entirely black or brownish-black. The body is shiny and is covered with short hairs. The wings are dark and have three clear cross bands. The outer two bands are slightly arced. The inner band (nearest to the body) is straight and is tapered to a point near the inner margin. The knob-like flight-balancing organs (halteres) are mostly white, black just at the base.

The male is similar but smaller, 3 16 to 5 16 (5 to 8 mm) long.

 
     
 

Size

 
 

Female: ¼ to (6 to 10 mm)

Male: 3 16 to 5 16 (5 to 8 mm)

 
     
 

Similar Species

 
     
     
 
Habitat
 
 

Fields, meadows

 
     
 
Biology
 
 

Season

 
 

Three generations: Early May through late summer

 
     
 

Behavior

 
 

 

 
     
 

Life Cycle

 
 

The female lays eggs singly or in groups usually under the lowest leaf sheath, sometimes higher on the plant, sometimes in the soil near the plant. Larvae feed on the bulb. Third instar larvae overwinter within the onion bulb. The following spring they pupate in the soil within twelve inches of the base of the host plant. Adults emerge 5 to 17 days later. There are two complete and one overwintering generation each year. The generations overlap so there are adults present all summer.

 
     
 

Larva Food

 
 

Bulbs of onion and garlic

 
     
 

Adult Food

 
 

Probably flower nectar

 
     
 
Distribution
 
 

Distribution Map

 

Sources

24, 27, 29, 30.

 
  9/8/2019      
         
 

Occurrence

 
 

Uncommon in Minnesota

 
         
 
Taxonomy
 
 

Order

Diptera (gnats, mosquitoes, true flies)  
 

Suborder

Brachycera (circular-seamed flies, muscoid flies, short-horned flies)  
 

Infraorder

Muscomorpha  
  No Rank Eremoneura  
  No Rank Cyclorrhapha (circular-seamed flies)  
  Zoosection Schizophora (muscoids)  
  Zoosubsection Acalyptratae (acalyptrate muscoids)  
 

Superfamily

Tephritoidea (fruit, signal, and picture-winged flies)  
 

Family

Ulidiidae (picture-winged flies)  
 

Subfamily

Otitinae  
 

Tribe

Cephaliini  
 

Genus

Tritoxa  
       
 

Synonyms

 
 

Trypeta arcuata

Trypeta flexa

 
       
 

Common Names

 
 

black onion fly

 
       

 

 

 

 

 

 

 

 

Glossary

Halteres

In flies: a pair of knob-like structures on the thorax representing hind wings that are used for balance.

 

 

 

 

 

 
 
Visitor Photos
 
           
 

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Dan W. Andree

 
 

Black Onion Flies

They were obviously mating. It was windy out so it wasn’t easy trying to get them focused in as they would bobble back and forth in the wind. Seen a pair a few minutes after arriving onto the prairie and then another pair when leaving 3-4 hours later.

There are a lot of goldenrod soldier beetles mating to now. They are very, very abundant. These photos were taken on the 13th of Aug. 2019 Frenchman’s Bluff SNA. I kind of like that area because of the big hill and views from up top and also often have the place to myself so can concentrate on subjects better without interruptions. But all prairies have life and interesting things sometimes one just has to look a little closer and even on a smaller scale for some subjects. I thought at first these were some kind of wasp, hornet or even flying ant so couldn’t find out what they were until I remembered reading something about flies have two wings and these seemed to just have 2. So I checked flies and that is where I found out what they were. Interesting and cool wing colors for a fly.

  black onion fly  
       
    black onion fly  
           
 
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  Dan W. Andree
8/13/2019

Location: Frenchman’s Bluff SNA

They were obviously mating. It was windy out so it wasn’t easy trying to get them focused in as they would bobble back and forth in the wind. Seen a pair a few minutes after arriving onto the prairie and then another pair when leaving 3-4 hours later.

There are a lot of goldenrod soldier beetles mating to now. They are very, very abundant. These photos were taken on the 13th of Aug. 2019 Frenchman’s Bluff SNA. I kind of like that area because of the big hill and views from up top and also often have the place to myself so can concentrate on subjects better without interruptions. But all prairies have life and interesting things sometimes one just has to look a little closer and even on a smaller scale for some subjects. I thought at first these were some kind of wasp, hornet or even flying ant so couldn’t find out what they were until I remembered reading something about flies have two wings and these seemed to just have 2. So I checked flies and that is where I found out what they were. Interesting and cool wing colors for a fly.

black onion fly  
           
 
MinnesotaSeasons.com Sightings
 
 

 

 

 

 

Binoculars


Created: 9/8/2019

Last Updated:

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