[ieee 2010 2nd international conference on chemical, biological and environmental engineering...

2010 2nd International Conference on Chemical, Biological and Environmental Engineering (ICBEE 2010)

Residual bioefficacy of diflubenzuron (Dimilin®) against larvae of dengue vector, Aedes aegypti (Linnaeus) in Kuala Lumpur, Malaysia

Koon Weng Lau

Institute of Biological Sciences, Faculty of Science, University of Malaya

Kuala Lumpur, Malaysia e-mail: [email protected]

Han Lim Lee

Medical Entomology Unit, Institute for Medical Research,


Abstract- The residual bioefficacy of diflubenzuron, a chitin synthesis inhibitor, was evaluated against the larvae of a dengue vector, Aedes aegypti. Dimilin® WP (wettable powder), 25 % w/w was used in this study. Diflubenzuron (0.1112 mg a.i.lL) was used to treat a set of plastic containers placed both indoor and outdoor. Thirty laboratory-bred early 3rd ins tar larvae were introduced into each container and observed daily. The number of emerged adults was calculated and recorded. The indicators of effectiveness of the IGR for these studies were: (i) duration of residual activity, and (ii) percentage of emergence inhibition (EI). Generally, the treated indoor containers showed complete emergence inhibition up to 6 weeks, while treated outdoor containers indicated that the emergence was completely inhibited up to 4 weeks. The duration of effectiveness which caused 50% emergence inhibition under indoor and outdoor conditions was up to 12 weeks and 6 weeks, respectively. On the whole, diflubenzuron appeared to perform better under indoor than outdoor condition. Application of diflubenzuron is simple and straightforward, as well as an effective method of long term control of mosquito larvae.

Keywords-Dij1ubenzuron; insect growth regulator; Aedes aegypti; emergence inhibition; residual efficacy

I. INTRODUCTION

Aedes aegypti (Linnaeus) is a cosmo-tropical mosquito as well as the most important domestic vector for dengue and urban yellow fever [1, 2]. Several approaches can be used to control the mosquito populations: biological control, physical control, chemical control, source reduction and integrated vector management [3]. Although there are many options, the application of chemicals is still the primary strategy to control the mosquitoes.

Insecticides have played an important role in the control of insect vectors of disease since early 20th century. Insect growth regulators (lGRs) are now increasingly used to control Aedes and other mosquito larvae. Insect growth regulator is a substance that interferes with the normal

978-1-4244-8749-3/10/ $ 26.00 © 2010 IEEE 311

Chee Dhang Chen

Zoological & Ecological Research Network, Faculty of Science, University of Malaya,


Mohd Sofian-Azirun

Institute of Biological Sciences, Faculty of Science, University of Malaya


development or growth of insects and these compounds are often selective and do not persist in the environment [4].

Dimilin® (diflubenzuron), 1-( 4-chlorophenyl)-3-(2,6-difluorobenzoyl) urea, is an insect growth regulator that inhibits the synthesis of chitin and hence interferes with molting. Mosquito larvae treated with diflubenzuron fail to completely shed the old cuticles or molt, or have soft weak cuticles that cannot protect them, and die soon after ecdysis in the pupal stage or during eclosion of adults [4, 5].

Diflubenzuron WP has been used to control mosquito larvae since the mid-1970's at the WHOPES (WHO Pesticide Evaluation Scheme) recommended dosages of 25-100 glha. Unfortunately, the remarkable ability of insect population to evolve resistance to every class of insecticide that has been developed often leaves control programs with few insecticides option [6]. Because of the wide-spread use of diflubenzuron this region, there is a need to study and ensure the bioefficacy of diflubenzuron as an effective control agent against Aedes larvae. Thus, this study was conducted to evaluate the residual efficacy of diflubenzuron against a container-breeder, Aedes aegypti in plastic container.

A. Test Site

II. MATERIALS AND METHODS

The study was conducted in the laboratory (indoor) and on the rooftop (outdoor) of Institute of Biological Sciences, Faculty of Science, University Malaya, Kuala Lumpur.

B. Test Containers

Plastic containers with an opening of 22.0cm in diameter, base diameter of 19.5cm and 21.7cm in height were used in this study. Five containers were placed in outdoor and indoor, respectively. Before initiating the study, all containers were washed with tap water and tested for the presence of any larvicidal contaminant by introducing 30 lab-bred early 3rd

instar Ae. aegypti larvae. The larvae were observed daily until complete emergence.


C. Test Insect

Larvae of lab-bred Ae. aegypti were used in the test. The colony was maintained in the laboratory for more than 30 years and not exposed to any control agents.

D. Chemical (Dijlubenzuron - Dimilin®)

Dimilin® WP (wettable powder), 25% w/w was used in this study. The applied concentration was 10 times of 90% lethal concentration (LC90). The LC90 was obtained by using standard larval bioassay procedures recommended by WHO [7]. The concentration used in this study was 0.1112 mg a.i.!L.

E. Trial Procedures

Five containers holding 5 liter of water were set up in indoor and outdoor under the eave. Plastic containers without the chemicals served as untreated controls were also set up in indoor and outdoor. In each test, 30 laboratory-bred 3rd instar larvae were introduced into each plastic container and monitored daily. Beef liver powder was provided as larvae food. Mortality of larvae, pupae and adults was assessed daily and emergence of adults was counted. The live larvae and pupae were collected into paper cups after a week for observation until all individual died or emerged as adults. A 50% of the volume of water in the containers was removed and replenished weekly. The procedure was repeated by adding new batch of larvae into the containers weekly.

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F. Date Analysis

The indicators of effectiveness of diflubenzuron for these studies were: • duration of effectiveness of tested chemical, and • percentage of emergence inhibition (EI) = (Number of

larvae introduced - Number of adult emerged) / Number of larvae introduced X 100%

A cut-off point at 50% emergence inhibition (EI) or mortality was considered effective. Statistical software (SPSS vi 1.5) was used to analysis the data.

III. RESULTS AND DISCUSSION

Figure 1 showed the weekly percentage of emergence inhibition (EI) of Ae. aegypti in plastic containers treated with diflubenzuron under indoor and outdoor conditions. The outdoor containers treated with diflubenzuron showed complete inhibition for 4 weeks, similar to that reported by Chen et al. [8]. The residual activity lasted for another 2 weeks, before decreasing to a point lower than 50% EI in week 7. On the other hand, indoor containers treated with diflubenzuron showed complete emergence inhibition for 6 weeks; while diflubenzuron still exhibited >50% EI for another 6 weeks. After week 12, the effectiveness of diflubenzuron in indoor containers was less than 50% EI.

9 10 11 12 13 14 15 16 17 18 19

[ _ Treated (Outdoor) """*""" Treated (Indoor) � Control (Outdoor) ----A- Control (Indoori.]

Figure I. Residual effectiveness of diflubenzuron against larvae of Aedes aegypti in indoor and outdoor plastic containers.

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By using the 50% emergence inhibition as indicator, the residual activity of indoor containers treated with difubenzuron was longer (12 weeks), in comparison to outdoor (6 weeks), probably diflubenzuron in outdoor containers was degraded by sunlight and heat. It s known that the stability of insecticides and duration of their effectiveness are affected by direct sunlight and temperature. Robertson & Pope [9] and Ogg et al. [10] reported that freezing and excess heat can shorten the shelf life of insecticides and direct sunlight also will degrade the insecticides. However, the degradation rate of the insecticide by sunlight and heat in this trial was not studied and remained unknown.

Lam [11] reported that the duration of effectiveness of application of Dimilin® WP-25 in septic tanks to control Ae. albopictus breedings was up to 8 weeks. Seccacini et al. [12] reported that in the simulated field study, the granular formulation of diflubenzuron was able to control Ae. aegypti up to 4 months (:::::16 weeks).

Cetin et at. [13] conducted a study on diflubenzuron (25% wettable powder and 4% granular formulation) against Culex pipens. Their results indicated that both formulations tested at 0.01, 0.02 and 0.03 mg a.i.1L were able to achieve 100% adult inhibition up to 4 weeks post treatment. Besides, many researchers have also reported that diflubenzuron was able to control Anopheles mosquitoes [14], houseflies [15] and stored product mites [16].

The Dimilin® WP formulation mixed well with the water and did not give rise to any turbidity in the water. However, due to the mode of action of IGR, the treated larvae will still be present and alive and this may discourage use of IGR in the control of the Aedes larvae. This is because in certain countries, the presence of Aedes larvae is ground for the enforcement officers to take legal action against the houseowners in spite of the application of IGR in the containers, since the larvae are still active until affected by the chemical later on. Thus, the user and the enforcer should be educated on the use of IGR.

The current study showed that the duration of efficacy of diflubenzuron (Dimilin® WP) is longer in indoor compared to outdoor condition. The method of application is simple and can be easily applied in areas such as drains and ponds and in places where a long-term control is desired. Further study can be done on the degradation rate of the chemical under both outdoor and indoor conditions.

ACKNOWLEDGMENT

The authors wish to thank University Malaya Research Grant, UMRG (RG034/09SUS) and Postgraduate Research Grant University of Malaya (PSI94/2009A) for funding this research.

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REFERENCES

[1] DJ. Gubler, "Dengue," in The Arboviruses, vol. II, Epidemiology and ecology, T. Monarth, Eds. Florida: CRC Press, 1988, pp. 223-260.

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[5] WHO, "Report of ninth WHOPES working group meeting," WHOICDSINTDIWHOPES: Feb. 2006, pp. 4--36.

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[7] WHO, "Instructions for determining the susceptibility or resistance of mosquito larvae to insect development inhibitiors," WHONBC/8 1. 8 12: 1981,pp. 1 - 6.

[8] e.D. Chen, B. Seleena, YF. Chiang and H.L. Lee, "Field evaluation of the bioefficacy of diflubenzuron (Dimilin®) against containerbreeding Aedes sp. mosquitoe," Tropical Biomedicine, vol. 25, March 2008, pp. 80--86.

[9] A. Robertson and R. Pope. Storing fungicides safety. USA: Iowa State integrated Crop Management, 2005.

[10] e.L. Ogg, L.D. Schultz and S.T. Kamble, "Safe transport, storage and diposal of pesticides," Extension Bulletin EC 2507. Lincoln: University of Nebraska.

[11] WK Lam, "A field trial to evaluate Dimilin WP-25, an insect growth regulator, as a larvicide for controlling Aedes albopictus (Skuse) breeding in septic tanks in Kuala Kangsar, Perak," Tropical Biomedice, vol. 7, 1990, pp. 83-89.

[12] E. Seccacini, A Lucia, L. Harburguer, E. Zerba, S. Licastro and H. Masuh, "Effectiveness of pyriproxyfen and diflubenzuron formulations as larvicides against Aedes aegypti," Journal of the American Mosquito Control Association, vol 24, Sep. 2008, pp. 398-403.

[13] H. Cetin, A. Yaniloglu and J.E. Cilek, "Efficacy of diflubenzuron, a chitin synthesis inhibitor, against Culex pipens larvae in septic tank water," Journal of American Mosquito Control Association, vol. 22, 2006,pp. 343-345.

[14] J.Z. Zhang and KY Zhu, "Characterization of chitin synthase cDNA and its increased mRNA level associated with decreased chitin synthesis in Anopheles quadirmaculatus esposed to diflubenzuron," Insect Biochemistry and molecular biolody, vol. 36, Sep. 2006, pp. 712-725.

[15] R. Tilak, AK Verma and u.B. Wankhade, "Effectiveness of Diflubenzuron in the control of houseflies," Journal of Vector Borne Diesease, vol. 47, Jun. 2010, pp. 97-102.

[16] J. Stara, T. Erban and J. Hubert, "The effect of chitin metabolic effectors on the population increase of stored product mites," Experimental and Applied Acarology, Mar. 2010, doi: 10.1007 Is 10493-0 I 0-9352-1.

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