Reduced hatchability of Anopheles gambiae s.s eggs in presence of third instar larvae
© Gotifrid et al.; licensee BioMed Central Ltd. 2014
Received: 25 January 2013
Accepted: 4 April 2014
Published: 11 April 2014
We investigated the hatchability rates of freshly laid Anopheles gambiae s.s. eggs in presence of third instars larvae. These experiments were conducted using 30 eggs in larval densities of 20, 60 and 100 larvae in microcosms. These experiments were designed to evaluate the eggs hatchability in habitats with late larvae instars of the same species (experimental) or no larvae at all (control). Freshly laid eggs of An.gambiae s.s. were washed in microcosms containing larvae of third instars in different three densities (20, 60 and 100) and likewise in control microcosms (without larvae). Eggs hatchability was monitored twice daily until no more first instar larvae emerged. The numbers of first instars larvae were recorded daily and lost eggs were considered preyed upon by third instars.
The findings of this study showed that egg hatchability was significantly influenced by larval density.
The findings of this study suggest that presence of larvae in habitats may significantly reduce hatchability of eggs.
KeywordsAnopheles gambiae s.s Microcosms Hatchability Larvae
Hatchability comparison of eggs between controls bowls and bowls with different larvae densities
Number of eggs
Percentage egg hatchability
% hatchability reduction
Study was conducted at Tropical Pesticides Research Institute Insectary, based in Arusha Tanzania for two months.
Adult mosquitoes rearing and eggs laying
Three days old females of An. gambiae s.s post emergence mosquitoes were fed on rabbit for 30 minutes. Blood fed females were then kept in insectary at a temperature of 27 ± 2°C, Relative humidity 78 ± 2% and light 12 L: 12D. The gravid females after 72 hrs post feeding were given a wet filter paper in a cage to act as oviposition substrate. The eggs laid were used immediately for these experiments.
Hatchability experimental set up
Experiments were set up in white microcosms having a diameter of 16.7 cm and depth of 1.7 cm. The sides of the microcosms just at the level of the water were lined with white paper to prevent the eggs from adhering to the surface of the microcosm and drying up. Freshly laid eggs on filter papers were washed in microcosms with dechlorinated water with third instar larvae in three densities of 20, 60 and 100. In the control arm, eggs were washed in microcosms without larvae and in both experiments; hatchability was monitored for three days. Hatched first instar larvae were collected and taken out of the microcosms every two hours’ time. Insectary temperature was maintained at 27 ± 2°C and relative humidity was 78 ± 2%. Thirty freshly laid eggs of An. gambiae s.s. were introduced in each microcosm in all three densities of An.gambiae s.s larvae. Each experiment had six replicates for each density and control.
Data were analyzed using SPSS 17.0 (SPSS Inc., Chicago, IL). Comparison of the mean number of hatched eggs was compared by ANOVA between the larvae densities in treatments and control. The significance level for the means of the three densities of 20, 60 and 100 were separated by Tukey HSD test.
The study was approved by Tropical Pesticides Research Institute (TPRI), Proposal review and ethical committee. The use of rabbit for feeding mosquitoes was approved as a daily routine permission in mosquito colony maintenance at TPRI.
This study has shown that the existence of the third instar larvae in breeding sites affect egg hatchability but also survivorship of the newly hatched first instars. More studies have to be done in semi field environment to determine egg hatchability in more complex environments and investigation of larva produced chemical factors (cuticle exudates) that play the role of emergence inhibitors of conspecific eggs is on progress.
Authors wish to thank Mr. Adrian Massawe and Ms. Ester Lyatuu for mosquitoes rearing, experimental set up and eggs hatchability monitoring.
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