Delia Identification

Submitted by BMcGowan on

Hi there, 

I am new to Dipterists and would appreciate some help with identification. I am a PhD researcher focussing on the Bean Seed Fly complex (Delia platura Delia florilega). I have been using a key by Savage et al. 2016 to identify Bean Seed Fly. The key starts off by differentiating Delia species from Botanophila fugax. It states in B. fugax the prealar bristle is "well-developed but always shorter than posterior notopleural bristle." In Delia species it states that the prealar bristle is "either longer than posterior notopleural bristle (pale blue arrow) (Fig. B) or absent/hair-like." 

It also states in B fugax there is a short-developed hair at the anepst below the anterior notopleural bristle. This is not normally present in Delia species. 

I have posted some pictures of a few specimens (name displayed on the photos) and a description of how I have identified them as either Delia or not Delia.  

1.     Specimen1: The prealar bristle is shorter than the posterior notopleural bristle and there is no hair at the anepst below anterior notopleural bristle. As the prealar bristle is short and there is no hair below the anterior notopleural bristle I have classed this as a Delia species

2.     Specimen2: The prealar bristle is short. There is no distinct hair at the anepst below the anterior notopleural bristle. However, there are a few faint hairs. I have classed this as a Delia species.

3.     Specimen6: The prealar bristle is short. There is a clear hair below the anterior notopleural cristle at the anepst. I have classed this as not being a Delia species.

4.     Specimen7: The prealar bristle is short. There is no hair at the anepst below the anterior notopleural bristle. However there might be a few faint hairs. I have classed this as being a Delia species.

5.     Specimen 8: There are 2 short hairs where the prealar bristle should be. There are quite a few hairs below the anepst. I have not classed this as a Delia species.

Would someone be able to advise me if they agree or disagree with my classifications. I am finding it difficult to differentiate the prealar bristle from being "well-developed but always shorter than posterior notopleural bristle" and “absent/hair-like.”

Thank you very much in advance!

Comments

Hi Tony, 

Thanks for your message. Apologies I had issues putting the photos into the correct format. With help from Martin they should be in the correct format and uploaded now! 

Kind regards, 

Becca 

Hi Becca,

Can't really help with your images. However, I wondered why you are relying on this feature? There are a number of differences between the two Delia species you mention and B. fugax. The most obvious difference is the more or less complete, evenly spaced row of c.20 erect PV setae on the hind tibiae in both Delia species (though not present in many other Delia species). The male genitalia are also very different between the genera and can be easily examined without dissection on fresh specimens by leavering out the surstyli using a micropin. Of course you may well already be aware of these feature and have a reason to use the prealar bristle character. Obviously neither of the characters I've mentioned is of any help if you're working on females.

Sam