Larvicidal Potential of Five Selected Dragonfly Nymphs in Sri Lanka Over Aedes Aegypti (Linnaeus) Larvae Under Laboratory Settings
Total Page：16
File Type：pdf, Size：1020Kb
Hindawi BioMed Research International Volume 2018, Article ID 8759459, 10 pages https://doi.org/10.1155/2018/8759459 Research Article Larvicidal Potential of Five Selected Dragonfly Nymphs in Sri Lanka over Aedes aegypti (Linnaeus) Larvae under Laboratory Settings Chathurika Samanmali,1 Lahiru Udayanga ,2,3 Tharaka Ranathunge ,2 Sandun J. Perera,1 Menaka Hapugoda,2 and Chathura Weliwitiya4 1 Department of Natural Resources, Faculty of Applied Sciences, Sabaragamuwa University of Sri Lanka, Sri Lanka 2Department of Biosystems Engineering, Faculty of Agriculture & Plantation Management, Wayamba University of Sri Lanka, Sri Lanka 3Department of Biosystems, Faculty of Agriculture & Plantation Management, Wayamba University of Sri Lanka, Sri Lanka 4HELPO Eco Green Ltd., Talbot Town, Galle, Sri Lanka Correspondence should be addressed to Taraka Ranathunge; [email protected] Received 3 August 2018; Revised 4 November 2018; Accepted 19 November 2018; Published 3 December 2018 Academic Editor: Ceferino M. L´opez S´andez Copyright © 2018 Chathurika Samanmali et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Introduction. Limitations in breeding source reduction practices, development of insecticide resistance in mosquitoes, and ill efects of chemical controlling methods on human and ecosystem health have motivated Sri Lankan authorities working for dengue control to seek for alternative, ecofriendly, and sustainable approaches for controlling of Aedes vectors, to manage dengue epidemics. Te present study attempted to investigate the predation efciency of locally available dragonfy nymphs over Aedes aegypti under laboratory conditions, aiming to evaluate the potential of using dragonfies as biocontrol agents against dengue. Methods. Nymphal stages of fve locally abundant dragonfy species were collected from diferent stagnated water bodies in Belihuloya area. Afer morphological identifcation, a well grown individual of each species was starved for 12 hours and introduced into a glass tank containing 1L of pond water with 200 larvae (4th instar) of Aedes aegypti. Number of larvae survived in the tank was enumerated hourly up to 48 hours. In case where >75% of larvae are consumed by dragonfy nymphs, additional Ae. aegypti larvae were introduced into such tanks. Experiment was repeated for fve times. Same procedure was followed with diferent stages of growth of the dragonfy nymphs characterized by the highest predation rate. General Linear Model followed by Tukey’s pairwise comparison was used for statistical analysis. Results. Te predation rates of diferent dragonfy species varied signifcantly (p<0.05), whereby Anax indicus (110±7.14 per day) indicated the highest, followed by Pantala favescens (54.07±5.15) and Gynacantha dravida (49.00±11.89), while Tolymis tillarga (23.47±2.48) had the lowest. Further, signifcant variations in the larval predation were found among diferent maturity stages (10–20; 25-35; and 35–45 mm in body length) of Ana. indicus (p<0.05). Regardless of statistical signifcance, a relatively higher larvicidal activity was observed at dusk than in dawn. Conclusion. Ana. indicus,whichis characterized by the highest predation rate, and P. f av es c e n s that has the widest geographical distribution within Sri Lanka along with a notable predation efcacy could be recommended as potential candidates for feld trials in biological control of dengue outbreaks via suppression of Ae. aegypti larvae. 1. Background About 50 million dengue viral infections occur every year and virtually 2.5 billion people live in dengue endemic countries Mosquitoes pose one of the main hazards to human health as [2]. Approximately, 1.8 billion people (more than 70%) are at they perform a major role in the transmission of vector borne risk for dengue viral infection within the member states of diseases [1]. Among them, dengue is a fast growing mosquito- the World Health Organization’s Western Pacifc and South- borne viral disease, which is widely spreading over the world. East Asia Regions, which contribute to approximately 75% 2 BioMed Research International of the recent global disease burden due to Dengue Fever controlling agent [9]. Among diferent food preferences of [3]. dragonfy nymphs, small larval forms such as Aedes larvae Sri Lanka has been afected by epidemics of Dengue Fever remain preferred by them even in their natural habitats, while (DF) and Dengue Haemorrhagic Fever (DHF) for over two adult dragonfies also predate on adult mosquitoes [15, 16]. decades. In Sri Lanka, Aedes aegypti remain as the primary Further, Odonates bear no harmful impacts on the humans vector supported by Ae. albopictus as the secondary vector. [17, 18]. Many countries in the world, especially in the South- Dengue viral infections have been reported from Sri Lanka Asian region, have evaluated the practical efcacy of using since the mid-1960s. DF was serologically corroborated in nymphal Odonates as mosquito control agents. Myanmar 1962 and the existence of DF in all of the major towns situated [19] and India [12, 20] have successfully used a variety of below 1200 m elevation was confrmed within the period of dragonfies as a potential biological resource in regulating the 1976–1978 [4]. With its change in serotype(s), an alarming larval populations of vector and pest mosquitoes [18]. increase in the incidence of dengue is at play in Sri Lanka, Since, 1960s the authorities working for dengue control in causing the highest ever number of dengue cases as 186, 101 Sri Lanka have focused more on the chemical based vector with over 440 deaths in 2017 [5]. management, while the efort on biological controlling of Absence of efective drugs and vaccines for the four Aedes is only limited to larvicidal feasibility assessments of serotypes of dengue virus has restricted the efcacy of few copepod and fsh species [21]. Regardless of the remark- patient management approaches, making vector control and able diversity and wide distribution of dragonfies within the management as the most practical option to control dengue country, Sri Lanka has not paid any attention to the dragon- within Sri Lanka. For this, a variety of approaches such fies as a potential biocontrol agent of Aedes mosquitoes. With as environmental management, chemical control and bio- realization of the restrictions in current vector controlling logical control, etc. are being considered recently. Difer- activities, the country should move towards simple, efcient, ent, chemical insecticides are being widely used to control and ecofriendly methods of vector management. Terefore, adult and larval mosquitoes for many decades, within many the current study was devised to evaluate the potential of countries including Sri Lanka. However, the unintended using dragonfies as a biocontrol agent to suppress the vector side efects on human and ecosystem health, development population of Ae. aegypti aiming towards management of of resistance within mosquitoes, and prominent fnancial dengue epidemics within the country. costs have resulted in notable failures in use of chemical based controlling approaches such as larvicides, long-lasting 2. Methods insecticidal nets, Indoor Residual Spraying (IRS), etc. [6–8]. Terefore, authorities working for dengue control seek for 2.1. Establishment of Aedes aegypti Colony. An adult mos- alternative, innovative, and ecofriendly methods to reduce quito collection was conducted in the Narangodapaluwa both larval and adult vector densities [9]. Among numerous Medical Ofcer of Health (MOH) area, Ragama, and cap- novel strategies, such as Sterile Insect Technique (SIT) and tured mosquitoes were transported to the laboratory for mass Incompatible Insect Technique (IIT), controlling aquatic rearing at the Molecular Medicine Unit, Faculty of Medicine, larval stages of vector mosquitoes by using their indigenous University of Kelaniya, Sri Lanka. Within the laboratory, natural enemies (pathogens, parasites, and predators), also only the Ae. aegypti mosquitoes were separated through known as biological control, remain as one of the low cost morphological identifcation by well-trained entomologists. and ecofriendly approach of integrated vector control [9]. Eggs laid by a single Ae. aegypti blood-engorged female were Biological control methods attempt to utilize the natural used to establish a mosquito colony of Ae. aegypti. Each enemies of mosquitoes at diferent stages of life cycle, both colony was maintained in 24 x 24 x 24 cm cages with mesh as predators and parasites. A great diversity of living organ- screening on top, under a 12:12 (light:dark) cycle at standard ∘ isms including microbes, fungi, protozoa, nematodes, other conditions (at 27 ± 2 Cand75± 5% humidity), adhering to invertebrates, and vertebrate predators have been recognized the standard protocols suggested by Gunathilaka et al. [22, as potential mosquito control agents [10, 11]. Among diferent 23]. Cattle blood was used to feed the mosquitoes through biological controlling agents, predatory insects like damselfy the metal plate feeding technique [23]. and dragonfy nymphs have gained a high consideration as Te eggs laid by them were allowed to be hatched within signifcant predators of many microinvertebrates including 2-3 days afer oviposition. Te frst instar larvae (L1)were the larvae of Aedes mosquitoes [11–13]. Both damselfies transferred daily