|Year : 2019 | Volume
| Issue : 4 | Page : 303-307
Interspecific competition between larval stages of Aedes aegypti and Anopheles stephensi
S Haq, Gaurav Kumar, Ramesh C Dhiman
ICMR–National Institute of Malaria Research, New Delhi, India
|Date of Submission||06-Jul-2015|
|Date of Acceptance||12-Jun-2019|
|Date of Web Publication||30-Nov-2020|
Dr. Ramesh C Dhiman
ICMR–National Institute of Malaria Research, Sector 8, Dwarka, New Delhi–110 077
Source of Support: None, Conflict of Interest: None
Background & objectives: Interspecific competition occurs between members of two or more different species and can often have an influence on mosquito populations. Both Aedes aegypti and Anopheles stepehensi are container breeding mosquitoes and co-exist which may result in larval competition. In this study, interspecific competition between the above two species has been monitored under the laboratory conditions.
Methods: Three sets of experiments were conducted with different stages of Ae. aegypti and An. stephensi larvae. First two experiments were set up with I/II instar and III/IV instar larvae of Ae. aegypti and An. stephensi respectively in the ratios of 20:20, 20:40 and 40:20 in plastic bowls. For third set of experiment 20 IV instar larvae of Ae. aegypti were put with equal number of I instar larvae of An. stephensi.
Results: In the presence of food, 12.5–15 % mortality was recorded in I/II stage larvae of Ae. aegypti while in An. stephensi mortality ranged from 21–55%. Pupation commenced from Day 6 onwards in Ae. aegypti while in An. stephensi it commenced from Day 11 onwards. In the absence of food, there was no pupation in both the species but Ae. aegypti survived up to longer duration (7.5–18.5 days with 50% mortality) in comparison to An. stephensi (2–7 days with 50% mortality). When younger stages of An. stephensi (I/II) were put together with older stages of Ae. aegypti (III/IV) in the presence of food, pupation was completed in 85% Ae. aegypti population while there was 100% mortality in An. stephensi population.
Interpretation & conclusion: The better survival and development of Ae. aegypti than An. stephensi under the same conditions exhibits interspecies competition showing competitive advantage of Ae. aegypti over An. stephensi. Further research is required to have a thorough understanding of the interaction between these two container inhabiting mosquito species in the nature.
Keywords: Aedes aegypti; Anopheles stephensi; interspecific competition; larvae; predation
|How to cite this article:|
Haq S, Kumar G, Dhiman RC. Interspecific competition between larval stages of Aedes aegypti and Anopheles stephensi. J Vector Borne Dis 2019;56:303-7
|How to cite this URL:|
Haq S, Kumar G, Dhiman RC. Interspecific competition between larval stages of Aedes aegypti and Anopheles stephensi. J Vector Borne Dis [serial online] 2019 [cited 2021 Apr 21];56:303-7. Available from: https://www.jvbd.org/text.asp?2019/56/4/303/302032
| Introduction|| |
Malaria and dengue are two major vector borne diseases causing about 3,34,693 cases and 50 deaths due to malaria while 1,36,422 cases and 132 deaths due to dengue annually. Aedes aegypti (Diptera: Culicidae) is the primary vector of dengue with Ae. albopictus playing a secondary role in disease transmission. Aedes mosquitoes predominantly breed in man-made containers, viz. cement tanks, overhead tanks, desert coolers, underground tanks, tyres, pitchers, discarded containers, flower pots and discarded junk yards. In urban areas, main vector of malaria is Anopheles stephensi (Diptera: Culicidae) which also breeds in association with Ae. aegypti in most of the artificial containers cited above,.
When two species breed together, competition for space, food and ultimate survival is bound to take place. Biotic interactions such as interspecific competition and predation can often have a strong influence on both container and wetland breeding mosquito populations. Earlier, several studies on interspecific competition and effects of competition on adults, intra-specific competition, predation between different mosquitoes and among sibling species has been carried out in respect of Aedes,, Anopheles, and Culex mosquito species.
Cannibalism has also been described in malaria vectors from several parts of the world, the first one in case of Anopheles gambiae (Diptera: Culicidae) becoming cannibalistic when deprived of food. In case of malaria vectors from the Indian subcontinent, it has been observed that nearly all I instar larvae of An. stephensi Liston were consumed by IV repotred to instars of the same species. Similarly An. culicifacies Giles (Diptera: Culicidae) is also reported to exhibit cannibalistic behaviour.
The review of literature on the interspecific competition between vector mosquito species reveals that studies in respect of competition between An. stephensi and Ae. aegypti have not been taken up. Our hypothesis is that Ae. aegypti being larger in size may dominate the smaller An. stephensi especially in early larval stages and may restrict the building up of the adult An. stephensi vector population and subsequently the disease transmission. Therefore, the present study was conducted to find out interspecific competition between An. stephensi and Ae. aegypti under the laboratory conditions.
| Material & Methods|| |
Aedes aegypti and An. stephensi mosquitoes were collected from field in Delhi and after morphological identification using standard key maintained as cyclic colony in the insectary following the method of Patil et al. The larval food comprising of a mixture of dog biscuits and fish food (60:40) was used for larval feeding. All the experiments were conducted at 27±1 °C temperature and 70±5% RH in the insectary.
Three sets of experiments were conducted with different stages of Ae. aegypti and An. stephensi larvae in the laboratory. The I/II and III/IV instar larvae were used in the first and second experiment respectively. The experiments were conducted with Ae. aegypti and An. stephensi larvae in following three ratios, i.e. 20:20, 20:40 and 40:20 in plastic bowls having 300 ml water. For third set of experiment 20 IV instar larvae of Ae. aegypti were put in the plastic bowl having 300 ml water with equal number of I instar larvae of An. stephensi. The same experiment was repeated using 20 I instar Ae. aegypti larvae and 20 IV instar An. stephensi larvae. All the three sets of experiments were run with and without larval food. Control experiments were also conducted using 20, 40 and 60 An. stephensi and Ae. aegypti larvae. Two replicates for each of the experiment were conducted. Water and food was changed every other day to prevent scum formation. Containers were examined on a daily basis, observations were recorded for live larvae and pupae formed. Dead larvae, if any, were removed from the bowl. Mean value and standard deviations of different parameters were calculated using MS Excel.
Ethical statement: Not applicable
| Results|| |
[Table 1] shows the results of the experiments conducted with I/II instar larvae in the presence of food which revealed 12.5–15% mortality in Ae. aegypti while it was 21–55% in An. stephensi. Pupation began much earlier in Ae. aegypti (from Day 6 onwards) than in An. stephensi (from Day 11 onwards). In Ae. aegypti 50% pupation was completed within 7–12.5 days as compared to An. stephensi (11.5–20.5 days). In control experiment with An. stephensi, pupation began 8–9 day onwards and ended within 11–14 days while in case of Ae. aegypti, pupation commenced 6–7.5 days onwards and completed within 10–11.5 days.
|Table 1: Interspecific competition between I/II stage larvae of Ae. aegypti and An. stephensi|
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When experiment was conducted with III/IV stage of both the mosquito species in the presence of food, mortality was higher in An. stephensi (20–70%) as compared to Ae. aegypti (2.5–5%). Pupation began Day 2 onwards and completed within 10–12 days in both the species [Figure 1]. In the absence of food, there was no pupation in both the species (I/II instars) but Ae. aegypti survived for a longer duration (7.5–11.5 days with 50% mortality) as compared to 2–3 days with 50% mortality in An. stephensi. [Figure 2]
|Figure 1: Interspecific competition between III/IV stage larvae of Ae. aegypti and An. stephensi in the presence of food.|
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|Figure 2: Interspecific competition between I/II stage larvae of Ae. aegypti and An. stephensi in the absence of food.|
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When younger stages of An. stephensi (I/II) were placed together with older stages of Ae. aegypti (III/IV) in the presence of food, pupation was more pronounced in Ae. aegypti (85%). But in case of An. stephensi, there was no pupation rather there was 100% larval mortality indicating adverse impact on its survival in association with larger Ae. aegypti [Table 2]. Similarly, in the absence of food, more than 80% An. stephensi larvae died on Day 2 while the Ae. aegypti larvae survived up to Day 9 of the experiment [Figure 3]. When III instar larvae of An. stephensi and I instar larvae of Ae. aegypti were placed together, there was only 17.5% mortality in Ae. aegypti but 45% mortality in An. stephensi.
|Table 2: Interspecific competition between III/IV vs. I/II larvae of Ae. aegypti and An. stephensi|
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|Figure 3: Interspecific competition between III/IV stage larvae of Ae. aegypti and I/II stage larvae of An. stephensi in the absence of food.|
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| Discussion|| |
In this study, interspecific competition has been monitored mainly in relation to availability and absence of food under the laboratory conditions. Both Ae. aegypti and An. stepehensi are container breeding mosquitoes and co-exist which may result in larval competition. There was consistent difference in the behaviours of both the experimental species. Segregation was observed in respect of territorial occupation, An. stephensi occupying the surface area of the container and Ae. aegypti larvae occupying the column and bottom area most of the time. Spatial segregation on similar resources is a common explanation for how species may decrease or avoid competition. Under the natural conditions, this phenomenon of territorial segregation might be more conspicuous, thus providing chances for survival of both the species. Though the phenomenon of predation was not conspicuous between An. stephensi and Ae. aegypti but the results of this study indicate the occurrence of interspecific competition and also adverse impact on the development of An. stephensi. In the presence of food, the growth rate of Ae. aegypti was far better than that of An. stephensi as in Ae. aegypti 50% pupation was completed much earlier (7–12.5 days) than An. stephensi (11–20.5 days). Mortality was also higher in An. stephensi (21–55%) as compared to Ae. aegypti (12.5–%). Larvae of latter species survived longer (up to 18.5 days) than An. stephensi larvae (up to 7 days) in the absence of food. In control experiment, An. stephensi pupation began 7.5 days onwards and ended within 13.5 days which is also in affirmation of experiment on the interspecific competition. When younger stages of An. stephensi (I/II) were placed together with older stages of Ae. aegypti (III/IV) in the presence of food, An. stephensi exhibited delayed development and did not transformed into pupal stage even after all larvae of Aedes moulted into pupae. It indicates the possibility of competition for food in confinement. Being larger in size Ae. aegypti might have consumed larger share of the food depriving An. stephensi for food inhibiting its proper development. The higher survival rate of Ae. aegypti in the absence of food indicates that the species is strong as compared to An. stephensi. The higher mortality in case of An. stephensi may be due to some physical damaged caused by the Ae. aegypti.
Species which have a competitive advantage over other species can maintain positive population growth. The better survival and development of Ae. aegypti under the same conditions exhibits its competitive advantage over An. stephensi. One of the possible explanations for this competitive advantage may be better food intake. Similar observations are also made in case of Ae. aegypti and Ae. albopictus where Ae. albopictus maintained positive population growth than Ae. aegypti under field conditions. In one of the studies, Pocock found that Ae. polynesiensis competes better than Ae. aegypti as the emergence rate of Ae. polynesiensis was higher as compared to Ae. aegypti in the presence of food thus exhibiting competitive advantage.
Interspecific competition between container inhabiting mosquitoes has been found as major determinant of species distribution and ultimately of community structure,. Delhi was endemic for malaria till nineties. Since 1996, it has experienced several outbreaks of dengue. As the number of dengue cases started to rise in Delhi, reverse situation with malaria has happened where cases declined from several thousands to hundreds in numbers (Municipal Corporation of Delhi data). One of the probable reasons for this may be the interspecific competition between Ae. aegypti and An. stephensi which might have caused the An. stephensi population to go down as revealed from this study. Similar observations have been also made in southeastern United States where interspecific competition between Ae. aegypti and Ae. albopictus resulted decline in Ae. aegypti abundance ,
This study provides evidence of the competition between the two species under laboratory conditions. However, in field conditions other factors like variations in temperature, rainfall, sun exposure, container type, season, apparent competition mediated by shared enemies may influence larval competition,,,. Further research is required to have a thorough understanding of the interaction between these two container inhabiting mosquito species in the nature and the possible succession of An. stephensi by Ae. aegypti in urban ecosystems.
Conflict of interest
There is no conflict of interest among the authors.
| Acknowledgements|| |
The authors thank Dr Menno Bouma, London School of Hygiene & Tropical Medicine, London (UK) for his valuable inputs and suggestions in carrying out the study. Authors are also thankful to the Director, ICMR–NIMR Delhi for providing the necessary facilities to carry out the work.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2]