|Year : 2020 | Volume
| Issue : 1 | Page : 58-62
Impact of antagonistic crustaceans on the population of Aedes aegypti L. larvae under laboratory conditions
A Thakur, DK Kocher
Department of Zoology, Punjab Agricultural University, Ludhiana, India
|Date of Submission||07-Jun-2018|
|Date of Acceptance||13-Dec-2018|
|Date of Web Publication||05-Feb-2021|
Dr A Thakur
Department of Zoology, Punjab Agricultural University, Ludhiana, Punjab
Source of Support: None, Conflict of Interest: None
Background & objectives: Dengue and chikungunya are two mosquito-borne viral diseases transmitted by Aedes mosquito species and are a great public health concern in India. The present study was aimed to check the influence of antagonistic crustaceans, especially Mesocyclops aspericornis and Daphnia magna on Ae. aegypti L. mosquito population.
Method: Variable ratios of these crustaceans (Aedes: Mesocyclops: Daphnia) against Ae. aegypti larvae were tested by putting them in plastic beakers having dechlorinated water along with yeast stock solution provided as food, and kept in BOD incubator at a temperature of 26 ±1°C.
Results: Out of all tested concentrations, 1:1:3 where the number of D. magna was thrice the number of Mesocyclops and Aedes; larvae showed a significant delay of 5–6 days in the developmental period. Maximum reduction in the emergence of females was recorded in the ratio 1:1:3, i.e. only 6.5 ± 0.47 females emerged when Daphnia used thrice the number of Aedes larvae. Body size of both males and females emerged from treated sets was found to be significantly reduced. The longevity of adults was also reduced from 8–17 days to 5–8 days in the case of males and from 14–26 days to 5–9 days in females.
Interpretation & conclusion: Among variable ratios tested under laboratory conditions, 1:1:2 and 1:1:3 ratios were found to be the effective ratios that greatly reduced the development duration, survivorship of larvae, and the number of larvae emerging into adulthood. Thus, antagonistic crustaceans specifically Mesocyclops and Daphnia can be used as biocontrol agents for the sustainable control of container breeding mosquitoes.
Keywords: Aedes aegypti; antagonistic; crustaceans; Daphnia magna; Mesocyclops aspericornis; peridomestic
|How to cite this article:|
Thakur A, Kocher D K. Impact of antagonistic crustaceans on the population of Aedes aegypti L. larvae under laboratory conditions. J Vector Borne Dis 2020;57:58-62
|How to cite this URL:|
Thakur A, Kocher D K. Impact of antagonistic crustaceans on the population of Aedes aegypti L. larvae under laboratory conditions. J Vector Borne Dis [serial online] 2020 [cited 2021 Nov 28];57:58-62. Available from: https://www.jvbd.org/text.asp?2020/57/1/58/308802
| Introduction|| |
Mosquitoes are accountable for the transmission of numerous therapeutically vital parasites and pathogens like bacteria, viruses, protozoans, and nematodes, causing serious illnesses like dengue, malaria, yellow fever, chikungunya, and filariasis. Nowadays, dengue, one of the mosquito-borne sicknesses, has created havoc all over the world. Globally, 950 species of Aedes are reported and to which India contributes 115 species and out of these, two species, namely Aedes aegypti and Ae. albopictus (Diptera: Culicidae) are major vectors for the transmission of dengue infection from the infected to healthy persons. Dengue is endemic in all the states and union territories of India and a total of 99,913 dengue cases and 220 deaths were reported in 35 states and union territories of India during 2016. In 2018, dengue cases were also reported from Bangladesh, Cambodia, India, Myanmar, Malaysia, Pakistan, Philippines, Thailand, and Yemen. An estimated 500,000 cases of severe dengue require hospitalization each year worldwide (with ~2.5% case fatality). The incidences of vector-borne diseases are increasing alarmingly due to many factors including uncontrolled urban developments that support the breeding of vector mosquitoes. Biocontrol of mosquito larvae with predators and competitors becomes more convenient and mitigates the requirement for frequent chemical use. Recent studies have demonstrated the deterrent effects of predators (like cyclopoid copepods) and competitors (like cladocerans) on mosquito populations, either by direct feeding on larvae or by altering their oviposition process and thereby affecting their overall fitness. Thus, predators and competitors are highly effective in controlling the population growth of mosquito larvae and can be used as biocontrol agents,,. Therefore, the present study was aimed to check the influence of antagonistic crustaceans, particularly Mesocyclops aspericornis and Daphnia magna on Ae. aegypti L. mosquito population.
| Material & Methods|| |
Adult M. aspericornis and D. magna especially females taken out from the pure cultures maintained under laboratory conditions, were starved for 24 h and transferred into beakers containing 1L of dechlorinated water. The I instar Ae. aegypti larvae were separated from water samples collected from peridomestic water containers from Punjab Agricultural University, Ludhiana plus its neighbouring sites, and were introduced along with M. aspericornis and D. magna in variable ratios, i.e. 1:1:1 (20:20:20), 1:2:1(20:40:20), 1:3:1 (20:60:20) and 1:1:2 (20: 20:40), 1:1:3 (20:20:60) in triplicate (Aedes: Mesocyclops: Daphnia, respectively), where the number of larvae was kept constant. Food (10 ml of yeast slurry solution) was provided on the starting day of the experiment, i.e Day 0, and on Day 4. Three replicates were performed for each test and the control set (without Mesocylops and Daphnia having Aedes larvae only) was also run simultaneously. All the beakers were placed in an unilluminated BOD incubator maintained at a temperature of 26 ± 1°C. Beakers were checked every 24 h till the emergence of the adult and time taken for the development (from larva to pupa and from pupa to adult) by the survived Aedes larvae (both in treated and control) were recorded. Percent larval mortality and other parameters like emerged adult body size, male-female ratio, and adult longevity were also recorded.
Total mortality per container was scored as per the formula given below:
Data were statistically analyzed with the help of SPSS statistical software version 16 by comparing antagonistic crustaceans treated trials with that of control sets using ANOVA (Duncan multiple range test) at 5% level of significance.
| Results & Discussion|| |
The effects of antagonistic crustaceans on the population of Ae. aegypti are presented under the following heads:
On the developmental period
In the control set, having Aedes larvae only, the duration of larval stages, i.e. I, II, III and IV instars, pupa till adult form was 1.33 ± 0.23, 1.66 ± 0.23, 3.16 ± 1.04, 4 ± 0.4, and 2 ± 0.5 days (total 8.5–17 days), respectively. However, the time taken for the conversion of I instar stage to II instar and II instar to III instar was similar, i.e. 2–3 days and 3–5 days, respectively in all the treatment sets — 1:1:1, 1:2: 1, 1:3:1, 1:1:2 and 1:1:3 [Table 1]. A significant delay was recorded in the case of III instar to IV instar, i.e. it took 2–4 days and 3–5 days in treatment sets 1:1:1 and 1:2:1, respectively. This duration was higher (from 3–6 days) in the treated sets 1:3:1, 1:1:2, and 1:1:3. Conversion of IV instar larva to the pupal stage took similar time in the control set as well as treatment sets 1:1:1 and 1:2:1 (3–6 days). Statistically, a significant delay was observed in the conversion of pupal to the adult stage, i.e. 4–6 days, and a delay of only one day was observed in the treatment sets 1:3:1, 1:1:2, and 1:1:3, respectively. Overall development was found to delay significantly, i.e. 13.5–23 days in treatment sets 1:1:2 and 1:1:3 when compared with the control set (8.5–17 days) [Table 1]. Thus, D. magna was found to be an effective competitor than M. aspericornis being larger and resulted in delaying the overall developmental period of Aedes larvae efficiently. It has been reported that density-dependent competition for food during the early larval stages is considered the most important factor affecting the mosquito population dynamics. The importance of effect imposed by a predator and controphic species on mosquito population has also been assessed; which showed that both of these components are vital in influencing mosquito populations.
|Table 1: Effect of antagonistic crustaceans on developmental period of Ae. aegypti|
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Experiments conducted on Culex spp. have shown that controphic species especially D. magna cause the Culex larvae to develop more slowly and to pupate at a smaller size. Reduced size at metamorphosis may have large negative consequences for mosquito fitness. Slower development rates also decrease seasonal mosquito population growth.
On the mortality of developmental stages
Average percent mortality was found to be statistically significant in the case of I instar larvae, i.e. 46.10 ± 0.56, 50 ± 0.33, 56.05 ± 0.5, 46.10 ± 0.57, and 40.25 ± 0.02, respectively in 1:1:1, 1:3:1, 1:1:2 and 1:1:3 ratios. It might be due to the predatory behaviour of M. aspericornis against Aedes I instar stage. However, II and III instar larvae are almost equally prone to mortality when exposed to 1:2:1 and 1:3:1 ratios of antagonistic crustaceans as shown in [Table 2]. Significant and similar pupal percent mortality, i.e. 29 ± 0.54 was observed in the treatment sets 1:2:1, 1:1:2, and 1:1:3, respectively. Cyclopoid copepods are important predators of early instars of Aedes larvae and can feed up to seven larvae or wounding per day. It was also observed that the predatory cyclopoid, M. aspericornis consumed I and II instar Aedes larvae in greater numbers. Though there was little consumption of later instars of larvae of mosquitoes being larger in size, but the cyclopoids punctured or injured the larvae which lead to constrained development, thus resulting in the death of the larva.
|Table 2: Effect of variable number of antagonistic crustaceans on mortality of developmental stages of Ae. aegypti|
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On the emergence of Ae. aegypti mosquitoes
The emergence recorded in control sets was 100%, out of which male emergence was 55 ± 0.81, and female emergence was 45 ± 0.81. Further, it was observed that both male and female emergence ratio was significantly reduced in all the treatment sets when compared with the control set. However, there was a significant reduction in the emergence of both males and females, i.e. 15 ± 0 and 8.3 ± 0.57 in the treatment set 1:3:1, where the number of cyclopoids was thrice than the Aedes larvae [Table 3]. Under conditions of food shortage, a significant decrease in the percentage of emerging adults was recorded. It has been demonstrated that intraspecific competition for food among larvae of Ae. albopictus had a significant reduction in the number of adults that emerged.
|Table 3: Effect of variable number of antagonistic crustaceans on emergence of Ae. aegypti|
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On the body size of emerged males
In control sets, the average total body length of emerged males was 4.37 ± 0.03 mm (proboscis 0.86 ± 0.03 mm, abdomen 1.70 ± 0.01 mm, and wing 1.81 ± 0.02 mm). It was observed that the body length of emerged males was significantly reduced in all the treatment sets in comparison to control sets. Overall body size of emerged males was 3.74 ± 0.04, 3.85 ± 0.04, 3.80 ± 0.01, 3.71 ± 0.07, and 3.64 ± 0.07 mm in all the treatment sets i.e. 1:1:1, 1:2:1, 1:3:1, 1:1:2, and 1:1:3, respectively [Figure 1].
|Figure 1: Effect of antagonistic crustaceans on the body size of adult Aedes mosquitoes.|
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On the body size of emerged females
Average body length of emerged females was 5.56 ± 0.05 mm (proboscis 1.37 ± 0.01 mm, abdomen 1.91±0.01 mm and wing 2.28 ± 0.03 mm) in control set. It was observed that the overall body size of emerged females reduced significantly in all the treatment sets when compared with that of the control sets. Total body size of emerged females was nearly similar, i.e. 4.26 ± 0.06 mm, 4.30 ± 0.06 mm and 4.27 ± 0.04 mm in the treatment sets 1:1:1, 1:2:1, and 1:3:1, respectively [Figure 1]. Further, when the ratio of D. magna was increased twice and thrice the time of Mesocyclops, the body length of emerged females reduced more, i.e. 4.11 ± 0.03 and 4.09 ± 0.01 mm in the treatment sets 1:1:2 and 1:1:3, respectively. In accordance with the fact that the body length of males is generally shorter than that of females, there are highly significant differences in the size between the two genders. Comparing adults of the same gender in conditions of food shortage, the difference in size was highly significant. Thus, intraspecific competition for food affects the size of adult mosquitoes. Similar results were reported on the American population of Ae. albopictus,. The size of adult females is correlated to fertility; bigger females are able to lay more eggs whereas smaller females lay lesser number of eggs. For this reason, the measurement of the body size of females is useful to assess reproductive fitness.
On the longevity of adult Ae. aegypti
The average longevity of Aedes mosquitoes in the case of males and females was 13.33 ± 3.85 and 20.66 ± 4.98 days, respectively in the control set. It was observed that the longevity of both the males and females was reduced significantly in all the treatment sets when compared with that of the control sets. Maximum reduction in longevity of males was 6.66 ± 1.24 (5–8 days) and in the case of females, it was 7.33 ± 1.69 (5–9 days) when the ratio of D. magna than M. aspericornis was twice and thrice, i.e. 1:1:2 and 1:1:3, respectively [Table 4]. The degree of intraspecific competition had a significant effect on the adult longevity under low humidity conditions. Competition is known to play an important role in mosquito larval development. Crustaceans (D. magna) occur in high number and have the capability to colonize new biotypes within a short duration of time. They are filter feeders, using similar food resources as mosquito larvae. The D. magna increased the time of larval metamorphosis and size. Similar experiments conducted on Anopheles quadrimaculatus showed that both predators and competitors greatly increased the time for larvae to grow into adulthood, causing longer generation time, which slow the rate at which mosquito populations can increase.
|Table 4: Effect of variable number of antagonistic crustaceans on the longevity of adult Ae. aegypti|
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| Conclusion|| |
The study provides evidence that interspecific competition and predation provided by antagonistic crustaceans (M. aspericornis and D. magna) result in longer duration of developmental stages, i.e. 6–7 days, higher mortality of I instar Aedes larvae when Mesocyclops ratio was thrice the number of Aedes larvae. Among the tested crustaceans, M. aspericornis acts as a predator against Aedes I instar larvae and competitor against later stages (II and III) of Aedes larvae. The D. magna also plays an important role as a competitor against Aedes larvae. Therefore, biological control using these mixed antagonistic crustaceans appears to be an alternative approach to the systematic failure of insecticidal usage.
| Acknowledgements|| |
The authors are thankful to the Head of the Department of Zoology, Punjab Agricultural University for providing valuable facilities. This study was a part of the Ph.D. research project “Effect of antagonistic crustaceans on population and development of Aedes larvae”.
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