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. 2022 Dec;29(12):103433.
doi: 10.1016/j.sjbs.2022.103433. Epub 2022 Sep 7.

Seagrasses extracts as potential mosquito larvicides in Saudi Arabia

Hayat S Al-Rashidi  1 , Jazem A Mahyoub  1 , Khalid M Alghamdi  1 , Wafa Mohammed Al-Otaibi  2
Affiliations

Seagrasses extracts as potential mosquito larvicides in Saudi Arabia

Hayat S Al-Rashidi et al. Saudi J Biol Sci. 2022 Dec.

Abstract

The present study aimed to evaluate the toxic and biological effects of some extracts of seagrasses (Cymodocea rotundata; Halophila ovata& Thalassia hemprichii) against Aedes aegypti, which transmits dengue fever, and Culex pipiens, which is the dominant species of mosquitoes in the Kingdom of Saudi Arabia, as a safe method for its control. The cumulative death rate during larval development into pupae and adults was used as a criterion for evaluating tested seaweed extracts against Ae. aegypti, Cx. Pipiens. According to the obtained IC50 values ​​(the concentration that inhibits the exit of 50 % of adult mosquitoes), the results showed that C. rotundata extract (70.78 & 77.47 ppm) was more effective against A. aegypti and Cx. pipiens in comparison with H. ovata (86,98 & 95,87 ppm) and T. hemprichii (83,94 & 88,82) extracts by (1.186, 1.229, 1.146 & 1.237) fold, respectively. The results showed that the treatment with marine plant extracts against mosquito larvae of Cx. Pipiens and Ae. Aegypti gave different biological effects similar to those of other insect growth regulators (IGRs). The results also revealed the presence of morphological abnormalities in larvae that were treated with all seaweed extracts and these effects extended to all stages of growth, which caused damage to the insect without completing its life cycle. Generally, the results indicate the importance of carrying out bio-assessment tests for the pesticides that are used against mosquitoes and establishing a database to be referenced when planning control programs and making the right decision about the pesticide used.

Keywords: Aedes aegypti; Control; Culex pipiens; Cymodocea rotundata; Halophila ovata; Thalassia hemprichii.

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Conflict of interest statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Figures

Fig. 1
Fig. 1
The eggs (A) Cx. pipiens (B) Ae. Aegypti.
Fig. 2
Fig. 2
The larva (A) Cx. pipiens (B) Ae. Aegypti.
Fig. 3
Fig. 3
The pupa (A) Cx. pipiens (B) Ae. Aegypti.
Fig. 4
Fig. 4
The adult (A) Cx. pipiens (B) Ae. Aegypti.
Fig. 5
Fig. 5
Seagrasses tested.
Fig. 6
Fig. 6
The relationship between the tested concentrations of C. rotundata extract and the percentage of adult emergence inhibition resulting from the treatment of the fourth instar larvae of Ae. aegypti & Cx. Pipiens.
Fig. 7
Fig. 7
The relationship between the tested concentrations of T. hemprichii extract and the percentage of adult emergence inhibition resulting from the treatment of the fourth instar larvae of Ae. aegypti & Cx. pipiens.
Fig. 8
Fig. 8
The relationship between the tested concentrations of H. ovata extract and the percentage of adult emergence inhibition resulting from the treatment of the fourth instar larvae of Ae. aegypti & Cx. pipiens.
Fig. 9
Fig. 9
IC-p lines that show the relationship between the concentrations of the tested extracts (C. rotundata, T. hemprichii & H. ovata) and the percentage of mortality of the fourth instar larvae of Ae. aegypti after continuous exposure to the extract for several days.
Fig. 10
Fig. 10
IC-p lines that show the relationship between the concentrations of the tested extracts (C. rotundata, T. hemprichii & H. ovata) and the percentage of mortality of the fourth instar larvae of Cx. pipiens after continuous exposure to the extract for several days.
Fig. 11
Fig. 11
Morphological effects of the tested extracts against different stages of Cx.pipiens. A: (1) untreated larva; (2) Elongation in the neck; (3) Shrinking of the abdominal rings; (4) pigmentation B): (5) Untreated pupa; (6) An intermediate stage between adults and pupa; (7) An intermediate stage; (8) Failed to develop in to an adult insect C): (9) Untreated adult mosquitoes; (10–12) Failed to get the adult insect out of moulting skin.
Fig. 12
Fig. 12
Morphological effects of the tested extracts against different stages of Ae. aegypti A: (1) untreated larva; (2) Elongation in the neck; (3) Shrinking of the abdominal rings; (4) pigmentation B): (5) Untreated pupa; (6) An intermediate stage between adults and pupa; (7) Albino pupa; (8) Failed to develop into an adult insect C): (9) Untreated adult mosquitoes; (10–12) Failed to get the adult insect out of moulting skin.
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