Dear Dr Robinson:

Thank you very much for submitting your manuscript "Responses of the putative trachoma vector, Musca sorbens, to volatile semiochemicals from human faeces" (PNTD-D-19-01361) for review by PLOS Neglected Tropical Diseases. Your manuscript was fully evaluated at the editorial level and by independent peer reviewers. The reviewers appreciated the attention to an important topic but identified some aspects of the manuscript that should be improved.

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Sincerely,

Jeremiah M. Ngondi, MB.ChB, MPhil, MFPH, Ph.D

Associate Editor

PLOS Neglected Tropical Diseases

Mathieu Picardeau

Deputy Editor

PLOS Neglected Tropical Diseases

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Reviewer's Responses to Questions

Key Review Criteria Required for Acceptance?

As you describe the new analyses required for acceptance, please consider the following:

Methods

-Are the objectives of the study clearly articulated with a clear testable hypothesis stated?

-Is the study design appropriate to address the stated objectives?

-Is the population clearly described and appropriate for the hypothesis being tested?

-Is the sample size sufficient to ensure adequate power to address the hypothesis being tested?

-Were correct statistical analysis used to support conclusions?

-Are there concerns about ethical or regulatory requirements being met?

Reviewer #1: Objectives could have been more strongly stated. A trapping system was developed to capture adult flies and flies were reared to produce adults for the GC-EAG studies. Description of traps is confusing. One complete trap design should be described, then the modifications made to arrive at the next design and so on. Line 165 - sounds like the yellow sticky trap is really a yellow disc coated with adhesive, but do not know. Lines 166-167 - Nylon and polyester mesh used to prevent entry of flies into the traps, correct? Is there a mesh size to be used? Line 170 - which company manufacturers Rat Stop? Lines 172-173 - Wire frames. Made from individual wires, pieces of wire fence or what? Coated in black electrical tape? Size of frames given in cubic cm. This can be many shapes. Need length, width and height. Discussion of feces collections do not strongly state how fresh the feces must be to qualify for the studies. Line 196 - soil from uncontaminated areas. Contaminated with what? Collected near trap sites. How near or far? Moisture content of feces would be interesting to know. Line 201 - traps were separated by 50 cm. This seems a bit close. Line 227 - was the portable air entrainment kit made by the authors, or a commercial model? Fly rearing paragraph could be more clearly stated. Line 252 - need dimensions of BugDorms, not cubic cm. How many BugDorms and how many flies in each? Line 253 - what is blue roll? Lines 253-254 - on a small pot of damp soil? Lines 264-266 - run on sentence. Actual photos of the traps would be better than the casual drawings. Was GC-EAG done on only 4 flies?

Reviewer #2: (No Response)

Reviewer #3: Well done authors!

This is an important piece of work which is well over-due. The objectives and methods are clearly stated and described and the interpretation appropriate. This represents a HUGE amount of work!!

I have a couple of minor comments and noticed a few typos

Major comments:

None

Minor comments:

1) In the title and throughout the ms the authors use the term "putative trachoma vector". I suggest removing the word 'putative' as there is no longer any reasonable question as to whether M. sorbens is a trachoma vector. M. sorbens is a mechanical vector of trachoma, it does not however, have an obligatory role in the transmission of trachoma as Aedes mosquitoes do in the transmission of human Yellow Fever and Dengue. It would be worth mentioning this in the introduction. The relative importance of eye-seeking flies in trachoma transmission will likely vary in time and space. Controlling eye-seeking flies will not block trachoma transmission. Stopping fly-eye contact will not block trachoma transmission.

2) The findings of the work do not identify the role of the electrophysiologically active semio-chemicals identified. It is reasonable to assume that they are attractants for oviposition, since their presence was associated with a convincingly high proportion of gravid female sorbens. However, the presence of an electrophysiological response does not in itself predict behaviour. The compounds may act individually as attractants or repellents, or in combination elicit a different response. This should be the focus of future work

Typos and other nit-picking:

Lines 127-130: Starting 'It is unknown however, ..." the sentence is presented as an 'either/or' construction, when both are reasonable suggestions. I would suggest constructing the sentence to be 'The more prolific emergence could be a result of better larval survival, more eggs being laid as a result of its greater relative attractiveness to ovipositing flies or other factors'. For me I'd continue to consider it as the preferred and 'better' medium for larval development due to the size of the flies emerging after pupation.

Line 145: Repetition of The Gambia

Line 217: Suggest defining gravidity for the lay-audience and the specific context. It is typically used to mean 'mated with developed eggs', was the stage of gravidity estimated?

Line 300: Any idea what the 'unidentified Musca spp' were in Oromia? That's intriguing. Any idea if these unidentified species are caught from human eyes too?

Line 306: Do you mean 'per night' or per 24hr period?

Line 379: "...a preference for non-herbivore faeces." made me chuckle. Surely the preference is for "the faeces of non-herbivores"?

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Results

-Does the analysis presented match the analysis plan?

-Are the results clearly and completely presented?

-Are the figures (Tables, Images) of sufficient quality for clarity?

Reviewer #1: Results are weakly stated with relation to the stats. Lines 302-303 - For feces baits other than horse and sheep, > 50% of flies collected were gravid. Lines 303-305 - run on sentence. Too long. Figure 2 might be more effective in tabular form with means and standard deviation show along with letters indicating statistical separation of means. Tables need more complete titles.

Reviewer #2: (No Response)

Reviewer #3: (No Response)

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Conclusions

-Are the conclusions supported by the data presented?

-Are the limitations of analysis clearly described?

-Do the authors discuss how these data can be helpful to advance our understanding of the topic under study?

-Is public health relevance addressed?

Reviewer #1: Data basically support conclusions. Limitations of analysis not mentioned. Authors discuss how data might be helpful. Authors do not mention the possibility of feces management. This might be difficult to impossible, but people need to know that these are sources of the flies that are transmitting disease to them and their children. Lines 384-387 and lines 405-408 - run on sentences. Too long.

Reviewer #2: (No Response)

Reviewer #3: (No Response)

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Editorial and Data Presentation Modifications?

Use this section for editorial suggestions as well as relatively minor modifications of existing data that would enhance clarity. If the only modifications needed are minor and/or editorial, you may wish to recommend “Minor Revision” or “Accept”.

Reviewer #1: The paper could use a thorough revision for clarity and organization. I think the science is basically ok, but the paper can be difficult to read in some places. I have tried to attach a scan of the paper so more of my comments can be seen. I would call this revision minor.

Reviewer #2: (No Response)

Reviewer #3: (No Response)

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Summary and General Comments

Use this section to provide overall comments, discuss strengths/weaknesses of the study, novelty, significance, general execution and scholarship. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. If requesting major revision, please articulate the new experiments that are needed.

Reviewer #1: The study is a very simple one, but very important for determining the breeding materials used by this fly. Also the evaluation of chemical compounds found in the feces might be developed into efficacious baits. The sentence structure needs to be tightened up and things more clearly stated.

Reviewer #2: This is an excellent paper overall. The writing is impeccable. With the exception of a single typographical error on line 202 (bais for bias) I did not find any errors throughout the manuscript.

The work is important, and the degree of replication in different study sites sufficient to make the results quite convincing.

A few minor comments for the authors consideration:

1) A photograph of the assembled trap would be helpful, either instead of or supplemental to the schematic drawing.

2) Most of the flies collected from Boiram were M. domestica. Although the focus of the paper was on M. sorbens, it would be interesting to see the collection results for domestica as well. How were the house fly collections distributed? Was the pattern substantially different from that of M. sorbens?

3) The climate information is mentioned in the Methods but never mentioned again except for some entries in Table that I was unable to decode. Suggest removing the climate data or discussing it in the context of the collection data.

4) The number of flies examined by EAG seems rather small. Although I have no expertise with this type of work I wonder whether an EAG response by two flies is sufficient to make conclusions about the attractiveness of the chemical constituents.

Reviewer #3: (No Response)

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Reviewer #1: No

Reviewer #2: No

Reviewer #3: No

Attachments

Attachment

Submitted filename: Reviewed paper.pdf

Dear Dr Robinson,

We are pleased to inform you that your manuscript, "Responses of the putative trachoma vector, Musca sorbens, to volatile semiochemicals from human faeces", has been editorially accepted for publication at PLOS Neglected Tropical Diseases.

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Thank you again for supporting open-access publishing; we are looking forward to publishing your work in PLOS Neglected Tropical Diseases.

Best regards,

Jeremiah M. Ngondi, MB.ChB, MPhil, MFPH, Ph.D

Associate Editor

PLOS Neglected Tropical Diseases

Mathieu Picardeau

Deputy Editor

PLOS Neglected Tropical Diseases

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