PHWR Public Health Weekly Report

Mosquitoes pose a significant health risk as vectors of various diseases such as malaria, dengue, chikungunya fever, and Zika virus infection [1]. In the Republic of Korea, mosquito-borne diseases include malaria, transmitted by Anopheles spp., and Japanese encephalitis, transmitted by Culex tritaeniorhynchus [2]. In addition, Aedes albopictus and Culex pipiens complex that transmit dengue fever, Zika virus infection and West Nile fever, which are diseases that do not occur domestically but are highly likely to be introduced, are distributed nationwide [3,4].

Public health centers and health center and county hospital (hereinafter referred to as public health institutions) conduct basic medical and public health services to improve and promote public health within their respective regions. Public health institutions are established by local governments under [Article 10 of the Regional Public Health Act] and are engaged in activities such as sanitation, pest control, and surveillance of patients with vector-borne diseases.

Mosquito control methods are categorized into physical, chemical, and eco-friendly approaches [5]. Physical control involves using attractants or light to capture vectors, reducing their density, and eliminating larval habitats and adult nesting places. Chemical control focuses on killing adult mosquitoes and larvae using insecticidal agents. Eco-friendly control employs microorganisms (Bacillus thuringiensis israelensis [Bti]), natural substances (such as essential oils), and aquatic animals (natural enemies) to reduce mosquito larva density.

Health institutions are controlling mosquitoes, but it is very difficult to grasp the overall status of control because each institution uses different vector control insecticides. Therefore, this study aims to indirectly assess the status of mosquito control by analyzing insecticides purchased by health institutions nationwide.

Health institutions in the Republic of Korea were identified based on information provided in the second half of the 2021 National Regional Health Care Institutions report published by the Ministry of Health and Welfare [6]. To investigate pest control drugs purchased by public health institutions, the purchase of insecticides (item number: 10191509) from January to December 2022 was investigated using data procured from the Procurement Information Open Portal of the Public Procurement Service [7]. We selected and analyzed insecticides for mosquitoes from among various sanitary pests (ticks, flies, cockroaches, etc.).

1. 2022 Purchase Status of Vector Control Insecticides

In 2022, a total of 361 health institutions purchased vector control insecticides, amounting to a total cost of KRW 29,654 million, marking an increase of KRW 1,500 million (5.3%) compared with the cost in 2021 (Table 1). The average cost of pest control per 100,000 people was KRW 57.7 million, with Jeonnam being the region with the highest control cost relative to the population (KRW 275.2 million). Among the purchased vector control insecticides, 77.6% (KRW 23,008 million) were chemical insecticides, 22.4% (KRW 6,647 million) were repellents, and 5.5% (KRW 1,628 million) were eco-friendly insecticides.

Table 1 Increase or decrease in the cost of purchased insecticides in 17 provinces in 2022

Provinces	Cost of purchasing insecticides in 2022 (%)	Cost of purchasing insecticides in 2021 (%)	Difference in insecticide cost (%)	Average mosquito control cost per 100,000 populations
SE	1,641 (5.5)	1,173 (4.2)	468 (39.9)	17.5
IC	1,456 (4.9)	1,347 (4.8)	109 (8.1)	48.5
DJ	311 (1.0)	304 (1.1)	7 (2.3)	22.2
GJ	471 (1.6)	366 (1.3)	105 (28.7)	33.6
DG	798 (2.7)	729 (2.6)	69 (9.5)	33.3
US	554 (1.9)	503 (1.8)	51 (10.1)	50.4
BS	1,720 (5.8)	1,574 (5.6)	146 (9.3)	52.1
SJ	132 (0.4)	125 (0.4)	7 (5.6)	33.0
GG	4,703 (15.9)	4,305 (15.3)	398 (9.2)	34.6
GW	1,539 (5.2)	1,638 (5.8)	△99 (△6.0)	102.6
CB	1,491 (5.0)	1,502 (5.3)	△11 (△0.7)	93.2
CN	2,585 (8.7)	2,626 (9.3)	△41 (△1.6)	123.1
GB	2,268 (7.6)	2,112 (7.5)	156 (7.4)	87.2
GN	2,818 (9.5)	2,964 (10.5)	△146 (△4.9)	85.4
JB	1,841 (6.2)	1,824 (6.5)	17 (0.9)	102.3
JN	4,953 (16.7)	4,804 (17.1)	149 (3.1)	275.2
JJ	373 (1.3)	258 (0.9)	115 (44.6)	53.3
Total	29,654	28,154	1,500 (5.3)	57.7

Unit: million won. SE=Seoul; IC=Incheon; Dj=Daejeon; GJ=Gwangju; DG=Deagu; US=Ulsan; BS=Busan; SJ=Sejong; GG=Gyeonggi-do; GW=Gwangwon-do; CB=Chungcheongbuk-do; CN=Chungcheongnam-do; GB=Gyeongsangbuk-do; GN=Gyeongsangnam-do; JB=Jeollabuk-do; JN=Jeollanam-do; JJ=Jeju-do. △: Decreased purchase amount of mosquito control chemicals compared to 2021..

2. Comparison of Vector Control Insecticides by Mechanism of Action

The vector control insecticides were classified into 12 classes based on the mechanism of action of pesticides [8] (Table 2). pyrethroid were confirmed to have the highest purchase rate at 51.4%, followed by benzoylurea (11.3%) and organophosphote (4.7%).

Table 2 Comparison of classes of insecticides purchased in 17 provinces in 2022

Group	Target	Classes		Chemical name	Cost (%)
C	Adult, larva	PY		D-phenothrin	6,506 (21.9)
				Etofenprox	4,573 (15.4)
				λ-cyhalothrin	1,659 (5.6)
				Bifenthrin	964 (3.3)
				Deltamethrin	940 (3.2)
				Cypermethrin	307 (1.0)
				α-Cypermethrin	146 (0.5)
				Permethrin	105 (0.4)
				d-cis/trans prallethrin	24 (0.1)
				Sub total	15,224 (51.4)
	Larva	IGR	Benzoylureas	Diflubenzuron	3,173 (10.7)
				Teflubenzuron	75 (0.3)
				Bistrifluron	45 (0.2)
				Novaluron	6 (0.0)
			Pyriproxyfen	Pyriproxyfen	139 (0.5)
			Hormone	S-methopren	128 (0.4)
				Sub total	3,566 (12.0)
	Adult, larva	OP		Temepose	1,253 (4.2)
				Dichlorvos	102 (0.3)
				Pirimiphos	43 (0.1)
				Sub total	1,398 (4.7)
	Adult	Mixture	Pyrethroid+LP gas	D-fenothrin+Phthalthrin	673 (2.3)
			Pyrethroid+pyrethroid	Cypermethrin+Tetramethrin	108 (0.4)
			Pyrethroid+organophosphate	Cypermethrin+Clorpyrifos	43 (0.1)
			Pyrethroid+pyrethroid	Imiprothrin+d-T80-Cyphenothrin	25 (0.1)
			Pyrethroid+benzoylureas	Permethrin+Novaluron	21 (0.1)
			Pyrethroid+oxadiazines	Etofenprox+S-indoxacarb	16 (0.1)
				Sub total	886 (3.0)
	Adult	Neonicotinoid		Dinotefuran	206 (0.7)
				Imidacloprid	100 (0.3)
				Sub total	306 (1.0)
Total of chemical					21,380 (72.1)
E	Larva	Biotic insectcide		Bti	1,069 (3.6)
		Spinosyne		Spinosad	276 (0.9)
		Natural pyrethrin		Pyrethrin X	192 (0.6)
		Silicone		Dimethicon	91 (0.3)
Total of eco-friendly pest control chemicals					1,628 (5.5)
R	-	Unknown		Icaridin	4,679 (15.8)
				IR3535	1,406 (4.7)
				DEET	562 (1.9)
Total of repellent chemicals					6,647 (22.4)
Total					29,654 (100.0)

Unit: million won. C=chemical; E=eco-friendly pest control insecticides; R=repellent chemicals; PY=pyrethroid; IGR=Insect Growth Regulator; OP=organophosphate; LP=liquefied petroleum; Bti=Bacillus thuringiensis israelensis; DEET=N,N-diethyl-m-tolumide..

3. Proportion of Pest Control Drugs by Growth Stage

Analysis of the proportion of adulticides and larvicides purchased by public health institutions revealed that the purchase rate of adulticides was 72.5% and that of larvicides was 27.5% (Table 3). Seoul had the highest purchase rate of larvicides (51.9%), whereas Sejong had the highest purchase rate of adulticides (90.9%).

Table 3 Purchase rate of adult and larval control chemicals purchased in 17 provinces in 2022

Provinces	Purchase rate of insecticides (%)		Total
	Adult	Larva
SE	708 (48.1)	765 (51.9)	1,473
IC	793 (67.7)	378 (32.3)	1,170
DJ	192 (67.8)	91 (32.2)	283
GJ	323 (73.1)	119 (26.9)	442
DG	468 (64.8)	254 (35.2)	730
US	267 (75.9)	85 (24.1)	352
BS	977 (65.4)	516 (34.6)	1,493
SJ	100 (90.9)	10 (9.1)	110
Metropolitan city (mean)	479 (63.3)	277 (36.7)	756
GG	2,846 (70.1)	1,215 (29.9)	4,061
GW	900 (84.9)	160 (15.1)	1,059
CB	917 (80.8)	218 (19.2)	1,135
CN	1,262 (68.4)	582 (31.6)	1,858
GB	1,220 (81.9)	269 (18.1)	1,497
GN	1,575 (74.6)	536 (25.4)	2,111
JB	991 (81.0)	233 (19.0)	1,224
JN	2,892 (77.2)	855 (22.8)	3,747
JJ	230 (87.8)	32 (12.2)	262
Provincial(mean)	1,426 (75.8)	456 (24.2)	1,881
Total	16,661 (72.5)	6,318 (27.5)	22,979

Unit: million won. SE=Seoul; IC=Incheon; DJ=Daejeon; GJ=Gwangju; DG=Deagu; US=Ulsan; BS=Busan; SJ=Sejong; GG=Gyeonggi-do; GW=Gwangwon-do; CB=Chungcheongbuk-do; CN=Chungcheongnam-do; GB=Gyeongsangbuk-do; GN=Gyeongsangnam-do; JB=Jeollabuk-do; JN=Jeollanam-do; JJ=Jeju-do..

From 2013 to 2022, a total of 5,204 cases of malaria were reported in the Republic of Korea, averaging more than 500 cases annually [9]. Vector management is very important to reduce the spread of mosquito borne diseases, including malaria. This study examines the status of mosquito control by analyzing vector control insecticides purchased by public health institutions.

In 2022, health institutions nationwide spent KRW 29,654 million on vector control insecticides, marking an increase of approximately KRW 1,500 million (5.3%) from the cost in 2021. The average cost per 100,000 people was KRW 57.7 million. The purchases of chemical insecticides accounted for 72.1%, which was higher than the purchases of insect repellent (22.4%) and eco-friendly insecticides (5.5%). Classification of vector control insecticides based on mechanism of action revealed 12 classes. Pyrethroid (51.4%) is an insecticide used for mosquito control worldwide, including in the Republic of Korea. Their mechanism involves continuous nerve stimulation, paralysis by interfering with opening and closing of the voltage of sodium channels in the nerve membrane, and interrupting the electrical signal transmission in the nervous system [10]. Insect Growth Regulator (IGR), a larval agent, which can be classified into inhibition of chitin synthesis (benzoylureas), growth hormone inhibition (such as pyriproxyfen), and inhibition of Adenosine triphosphate (ATP) synthesis from mitochondria (such as diafenthiuron) by the mechanism of action [11]. In the Republic of Kroea, insecticides that inhibit chitin synthesis or growth hormones were used. In addition, insecticides such as organophosphate, which kills insects by inducing hypersecretion of acetylcholine, and neonicotinoid, which acts on the nicotine acetylcholine receptor in insects, were purchased [12,13].

While chemical control is widely used in the Republic of Korea and around the world, the long-term use of chemicals leads to insecticides resistance and reducing their effectiveness. According to the World Health Organization (WHO), 78 countries identified insecticides resistance to one class from 2010 to 2020, with 29 of these 78 countries identifying resistance to at least four class (organophosphate, pyrethroid, organochlorine, and carbamate) [14]. Also, insecticide resistance to pyrethroid and organophosphate has also been reported in the Republic of Korea [15,16]. In order to reduce insecticide resistance, insecticide with different mechanisms must be cross-used. However, pyrethroids are the most registered on insecticides with the Public Procurement Service, with limited representation of IGR and eco-friendly insecticides. Therefore, it is believed that chemical control and physical control should be used in parallel, or IGR or eco-friendly insecticide should be alternately used.

Eco-friendly insecticides include substances derived from natural products (hereinafter referred to as natural substances), biological control agents such as natural enemies, insect viruses, parasites, and fungi [17]. The purchase of eco-friendly insecticides accounted for 5.5% of health institutions in the Republic of Korea. The global market of eco-friendly insecticides is growing yearly, and approximately 175 eco-friendly insecticides have been registered worldwide [18]. The most used eco-friendly insecticides in the Republic of Korea is the microbial insecticide Bti (3.6%), which is widely effective for larval control worldwide [19]. Bti operates by entering the bodies of mosquito larvae and releasing protein toxins, including Cry 4A, Cry 4B, Cry 11A, and Cyt 1A to kill them [20]. In addition, Natural substances and silicones are used in the Republic of Korea. However, the limited adoption of eco-friendly insecticides in the Republic of Korea is attributed to their perceived lower insecticidal efficacy compared to chemical insecticides, along with delayed confirmation of effectiveness [21].

Comparing the purchasing rate of insecticides by growth stage among health institutions, the larvicides was covered 27.5%, which is still below the level of developed countries, though it has been steadily increasing since 2020 (22.7%) (Table 4). Given that the larvae live in a limited place, they have an excellent control effect compared to adult control, particularly in restrictive environments such as urban areas compared to that in agricultural areas with many unspecified habitats [22,23]. Therefore, integrated mosquito management (IMM), which minimizes the use of adulticides and increases the proportion of larval control, is recommended [24]. Additionally, monitoring of larval habitats and mosquito densities, as well as mosquito control promotion and education, must be carried out [25]. In Florida, USA, the combined application of ultra-low volume (ULV) control and larval control of Ae.aegypti showed a lower average adult density than that shown in the control group [26]. Therefore, the simultaneous control of larvae and adults through IMM is an efficient strategy for effective mosquito control.

Table 4 Comparison of larvicide exterminators purchased at public health centers from 2018 to 2022

Year	Purchase rate of insecticides (%)
	Adult	Larva
2018	73.9	26.1
2019	73.8	26.2
2020	77.3	22.7
2021	74.1	25.9
2022	72.5	27.5
Mean	74.3	25.7

An analysis of the current state of mosquito control showed that health institution mainly used chemicals to control adult insects. Considering the potential side effects of long-term chemical control such as insecticide resistance, adopting eco-friendly or physical control measures is advisable. For efficient control, it is necessary to establish a vector control strategy for balancing with larval and adult control.

Ethics Statement: Not applicable.

Funding Source: None.

Acknowledgments: None.

Conflict of Interest: The authors have no conflicts of interest to declare.

Author Contributions: Conceptualization: HIL. Data curation: GHK, SRC. Formal analysis: GHK, SRC. Investigation: GHK, CWJ, SRC. Project administration: HIL. Resources: GHK, CWJ, SRC. Supervision: HIL. Visualization: GHK, SRC. Writing – original draft: GHK. Writing – review & editing: HIL.