Evaluation of the Contact Toxicity and Physiological Mechanisms of Ginger (Zingiber officinale) Shoot Extract and Selected Major Constituent Compounds against Melanaphis sorghi Theobald

Round 1

Reviewer 1 Report

This manuscript provides an account of interest in the selection of botanical biopesticides which are needed to replace the highly hazardous insecticides. The chemistry and laboratory assessments provide an important assessment of the potential of ginger (Zingiber officinale) shoot extract to be effective against Melanaphis sacchari.  My concern is that it is not clear how effective it would be when applied on plants exposed to sunlight.  Other insecticides extracted from plants, such as pyrethrins are rapidly deactivated in sunlight so do not persist sufficiently to control pests and are only useful inside buildings/storage areas etc.  I mention this as the tests reported in this ms are on individual leaves inside a laboratory.

The Discussion should be expanded to expand on the last part of the abstract , namely "The above results indicated that the GSE may become a botanical pesticide for aphid control and provide new resources for the development of aphid biological agents", if it is resistant to break-down in sunlight or could be formulated to persist sufficiently to be effective against the pests.

Author Response

Please see the attachment.

Dear Reviewer,

Many thanks for giving us an opportunity to improve our manuscript. We also would like to thank you for the suggestions. All the suggestions are very valuable and helpful. We have read the comments carefully and revised the manuscript accordingly.

Thank you very much for your work on our manuscript. We look forward to hearing from you.

With best regards,

Qie Jia Email：jiaqie020@163.com

Manuscript ID: horticulturae-1938604

Responses to reviewer 1

Q1: This manuscript provides an account of interest in the selection of botanical biopesticides which are needed to replace the highly hazardous insecticides. The chemistry and laboratory assessments provide an important assessment of the potential of ginger (Zingiber officinale) shoot extract to be effective against Melanaphis sacchari. My concern is that it is not clear how effective it would be when applied on plants exposed to sunlight. Other insecticides extracted from plants, such as pyrethrins are rapidly deactivated in sunlight so do not persist sufficiently to control pests and are only useful inside buildings/storage areas etc. I mention this as the tests reported in this MS are on individual leaves inside a laboratory.

Response: Thank you for your suggestion.

As for Ref. [Keosaeng, K.; Songoen, W.; Yooboon, T.; Bullangpoti, V.; Pluempanupat, W. Insecticidal activity of isolated gingerols and shogaols from Zingiber officinale Roscoe rhizomes against Spodoptera spp. (Lepidoptera: Noctuidae). Nat. Prod. Res. 2022, 36, 1-6]. Studies have shown that gingerol and gingerol are contact toxicity to Spodoptera litura, Spodoptera exigua, and Spodoptera frugiperda in sunlight. The LD₅₀ of 8-gingerol against S. frugiperda was 7.68 and 3.96 µg/larva after 24 h and 48 h of treatment, which showed stable efficacy. Compared with the above study, the gingerols measured may have similar stability in this study. The insecticidal effect of ginger shoot extract has just been found in laboratory tests. The stability of its compounds needs to be further investigated in sunlight. At present, we can only show that it has potential to develop botanical insecticide.

Q2: The Discussion should be expanded to expand on the last part of the abstract, namely "The above results indicated that the GSE may become a botanical pesticide for aphid control and provide new resources for the development of aphid biological agents", if it is resistant to break-down in sunlight or could be formulated to persist sufficiently to be effective against the pests.

Response: Thanks for your suggestion. We added relevant summaries to the discussion and rewrote the conclusion.

• Our results indicated that the main compounds of GSE had aphidicidal activities against sorghum aphids. However, since field experiments or greenhouse experiments were not carried out in this study, the efficacy stability of the main compounds need to be further studied. This has been added in the manuscript, as can been seen in Page 11 Lin 387-390.
• In summary, the main active compounds of GSE demonstrated contact toxicity against sorghum aphids. According to growth experiments and enzyme activity experiments, GSE may also inhibit the growth and development of sorghum aphids by inhibiting digestive enzymes and affecting protective enzymes and detoxification enzymes, thus leading to the death of the aphids. Field test research on the insecticidal active compounds of ginger now needs to be carried out urgently. Combined with this research, it could provide a theoretical basis for the development of new botanical aphidicides. This has been revised in the manuscript, as can been seen in Page 12 Lin 438-444.

Author Response File: Author Response.docx

Reviewer 2 Report

The Authors aimed at determining the main components of ginger shoot extract (GSE), assessing impact (mortality, development, reproduction as measurement endpoints) of the GSE and its selected components on sorghum aphid (M. sacchari) and highlight the physiological mechanims in the treated target pest under controlled (laboratory) conditions. 

The topic is relevant, the potential use of ginger extract as botanical insecticide is important.

The Authors should first clarify the target pest status. They wrote sorghum aphid (M. sacchari) while the literature clearly distinguish sugarcane aphid, the Melanaphis sacchari (Zehntner, 1897) and sorghum aphid, Melanaphis sorghi (Theobald, 1904) (see DOI: 10.1371/journal.pone.0241881 and others).

The entire manuscript needs strong English language revision since many sentences, wordings do not allow readers to clearly understand what the authors wanted to say.

The Discussion sometimes is a repetition of the introduction, references to support the new scientific results in the manuscript are weak or missing.

Conclusion are too general and again partly repetition of the aims of the study.

The Reviwer strongly encourages the authors to proceed, revise, adjust the manuscript so that their valuable work and results will reach a level for publication.

Author Response

Please see the attachment.

Dear Reviewer,

Many thanks for giving us an opportunity to improve our manuscript. We also would like to thank you for the suggestions. All the suggestions are very valuable and helpful. We have read the comments carefully and revised the manuscript accordingly.

Thank you very much for your work on our manuscript. We look forward to hearing from you.

With best regards,

Qie Jia Email：jiaqie020@163.com

Manuscript ID: horticulturae-1938604

Responses to reviewer 2

Q1: The Authors should first clarify the target pest status. They wrote sorghum aphid (M. sacchari) while the literature clearly distinguish sugarcane aphid, the Melanaphis sacchari (Zehntner, 1897) and sorghum aphid, Melanaphis sorghi (Theobald, 1904) (see DOI: 10.1371/journal.pone.0241881 and others).

Response: Thanks for your suggestion. We have read this article "Morphometric and Molecular Discrimination of the sugarcane aphid, Melanaphis sacchari, (Zehntner, 1897) and the sorghum aphid Melanaphis sorghi (Theobald, 1904)", and have modified the Latin name of the sorghum aphid from "Melanaphis sacchari" to "Melanaphis sorghi" in the manuscript. This has been revised in the manuscript.

Q2: The entire manuscript needs strong English language revision since many sentences, wordings do not allow readers to clearly understand what the authors wanted to say.

Response: Thanks for your suggestion. We have submitted to the English editing services listed at https://www.mdpi.com/authors/english. The revisions are marked with "Track Changes" in the manuscript.

Q3: The Discussion sometimes is a repetition of the introduction, references to support the new scientific results in the manuscript are weak or missing.

Response: Thanks for your suggestion. We added the latest references and replaced the weaker references in the discussion.

• As for Ref. [30] (30. Keosaeng, K.; Songoen, W.; Yooboon, T.; Bullangpoti, V.; Pluempanupat, W. Insecticidal activity of isolated gingerols and shogaols from Zingiber officinale Roscoe rhizomes against Spodoptera spp. (Lepidoptera: Noctuidae). Prod. Res. 2022, 36, 1-6.), the description has been revised as “Similarly, previous studies have shown that 6-gingerol has significant contact toxicity to both Nilaparvata lugens and Spodoptera spp. [29,30]”. This has been revised in the manuscript, as can been seen in Page 10 Lin 384-385.
• As for Ref. [35] (Chen, Y.Z.; Zhang, B.W.; Yang, J.; Zou, C.S.; Li, T.; Zhang, G.C.; Chen, G.S. Detoxification, antioxidant, and digestive enzyme activities and gene expression analysis of Lymantria dispar larvae under carvacrol. Asia-Pac. Entomol. 2020, 24, 208-216.), the description has been revised as “Similarly, Chen et al. [35] found that carvacrol can inhibit digestive enzyme activities in Lymantria dispar”. This has been revised in the manuscript, as can been seen in Page 11 Lin 406-407.

Q4: Conclusion are too general and again partly repetition of the aims of the study.

Response: Thank you for your valuable comment. The conclusions have been revised.

In summary, the main active compounds of GSE demonstrated contact toxicity against sorghum aphids. According to growth experiments and enzyme activity experiments, GSE may also inhibit the growth and development of sorghum aphids by inhibiting digestive enzymes and affecting protective enzymes and detoxification enzymes, thus leading to the death of the aphids. Field test research on the insecticidal active compounds of ginger now needs to be carried out urgently. Combined with this research, it could provide a theoretical basis for the development of new botanical aphidicides. This has been revised in the manuscript, as can been seen in Page 12 Lin 438-444.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

The Manucript went through significant improvement. This improvement allows readers to understand the scientific message by the authors.

Two-three minor remarks by the Reviewer:

L40, the first sentence is a bit confusing. Suggest to simplify it, maybe "Aphids are worldwide known and spread pests of crops." or similar.

L82-83 Sentence not clear what the Authors want to say. "Insect resistance of plant extracts...........drug resistance of pests...etc."?

Insect resistance development to plant extract?

Resistance of plants to insect pests through plant metabolites? or?

L223 Table 1 is referred under chapter Results but the Table itself is in Chapter Materials and Methods?

Author Response

Dear Reviewer,

Many thanks for giving us an opportunity to improve our manuscript. We also would like to thank you for the suggestions. All the suggestions are very valuable and helpful. We have read the comments carefully and revised the manuscript accordingly.

Thank you very much for your work on our manuscript. We look forward to hearing from you.

With best regards,

Qie Jia Email：jiaqie020@163.com

Manuscript ID: horticulturae-1938604

Responses to reviewer 2

Q1: L40, the first sentence is a bit confusing. Suggest to simplify it, maybe "Aphids are worldwide known and spread pests of crops." or similar.

Response: Thanks for your suggestion. The first sentence has been modified to "Aphids are worldwide known and spread pests of crops." The revisions are marked with "Track Changes" in the manuscript, as can been seen in Page 1 Lin 40.

Q2: L82-83 Sentence not clear what the Authors want to say. "Insect resistance of plant extracts...........drug resistance of pests...etc."? Insect resistance development to plant extract? Resistance of plants to insect pests through plant metabolites? or?

Response: Thank you for your valuable comment.

• L82-83 We wanted to analyze insecticide resistance of pests to botanical insecticides through physiological mechanism, but the expression may not be clear enough, so we improved the language. The description has been revised as "Botanical insecticides not only consider their control effect, but also needs to consider the insecticide resistance of pests. The insecticidal mechanism is the key to studying insecticide resistance of pests, among which the relevant enzymes in pests are the important targets". The revisions are marked with "Track Changes" in the manuscript, as can been seen in Page 2 Lin 83-86.
• The main purpose of this study was to explore the insecticidal action and insecticidal mechanism of GSE. We may have confused the concepts, so now all the concepts of "insect resistance" in the paper have been modified to "insecticidal". The revisions are marked with "Track Changes" in the manuscript, as can been seen in Page 2 Lin 81-82 and Page 10 Lin 375-376.

Q3: L223 Table 1 is referred under chapter Results but the Table itself is in Chapter Materials and Methods?

Response: Thanks for the reminder. We had adjusted the position of Table 1. The revisions are marked with "Track Changes" in the manuscript, as can been seen in Page 6 Lin 232-235.

Author Response File: Author Response.docx