INTERSPECIFIC LARVAL COMPETITION:
One further point to explain the expansion of
Aedes albopictus
Introduction
Invasive species are frequently good colonizers of unsaturated sites (r-selected traits) but invaders often have to colonize areas already occupied Îthey should have higher competitive abilities than resident or previously introduced species.
Materials et methods
Discussion
¾ In the range20-30°C, temperature does not affect the outcome of competitive interactions between both species ¾ Ae. aegypti is more affected by intraspecific interaction than is Ae. albopictus
Results
Leïla BAGNY, Hélène DELATTE, Didier FONTENILLE,
Serge QUILICI; leila.bagny@cirad.fr
0. 2 0 .4 S u rv ie m o y enne L1 -51 0 T e m p s de p upai s o n a a a a a a a b c a bc a
Survie en condition optimale d'alimentation P50 en condition optimale d'alimentation
Température 20 25 30 Température 20 25 30 0.4 0.2 10 5 20° 25° 30° 20° 25° 30° 0. 2 0 .4 S u rv ie m o y enne L1 -51 0 T e m p s de p upai s o n a a a a a a a b c a bc a
Survie en condition optimale d'alimentation P50 en condition optimale d'alimentation
Température 20 25 30 Température 20 25 30 0.4 0.2 10 5 20° 25° 30° 20° 25° 30° Survivorship Ae. albopictus Ae. aegypti P50 (days)
Fig.1a Mean survivorship (±SE) at different temperatures Fig.1b
P50 (in days) (±SE) at different temperatures
No significant differences in survivorship of both species between 20°C and 30°C
Different letters indicate significant differences (P<0.05) using Wilcoxon pairwise test with “Benjamini & Hochberg (BH)” correction
Ae. aegypti develops faster than Ae. albopictus Minimun developement time is observed at 25°C
Fig.2 Mean survivorship (±SE) of both species at25°C
Fig.3 Mean wings length (±SE) (mm) for both species at25°C Different letters indicate significant differences (P<0.05) using Wilcoxon pairwise test with “Benjamini & Hochberg (BH)” correction
a a a d e bce bce c bc bc bc b Intraspecific interaction Ae. albopictus Interspecific interaction a ab ab ab ab ab ab ab ab b b b Aeg Albo 0 20 0 40 0 60 10 10 20 20 30 30 20 0 40 0 60 0 Aeg Albo 0 20 0 40 0 60 10 10 20 20 30 30 20 0 40 0 60 0 0.8 1 0.6 0.4 0.2 0 Intraspecific interaction Ae. aegypti
Optimal diet Limited diet
0.8 1 0.6 0.4 0.2 0 S u rv iv o rs h ip Ae. albopictus Ae. aegypti ab ab ab ab b ab b cd cd c c d ab ab a abcabc bc abc ab ab abc c abc Aeg Albo 0 20 0 40 0 60 10 10 20 20 30 30 20 0 40 0 60 0 Aeg Albo 0 20 0 40 0 60 10 10 20 20 30 30 20 0 40 0 60 0 2.4 2.6 2.2 2.0 1.8 2.4 2.6 2.2 2.0 1.8 W in g le n g th (m m )
Optimal diet Limited diet
Minimum length for eggs laying (Aeg)
Minimum length for eggs laying (Albo)
Different letters indicate significant differences (P<0.05) using Wilcoxon pairwise test with “Benjamini & Hochberg (BH)” correction
REGION REUNION
Bagny, L., Delatte, H., Fontenille, D., Quilici, S. Progressive decrease in Ae. aegypti distribution in Reunion Island since the 1900’s. J. Med. Entomol. (In press) Bagny, L., Delatte, H., David, P., Fontenille, D., Quilici, S. Could life history traits explain the displacement and reduction of Ae. aegypti populations in La Réunion? (In prep)
Intecol 10, Brisbane, 16-21 August 2009
Aedes albopictus (Diptera:Culicidae) is among the 100 of the World's Worst Invasive Alien Species and has replaced Ae.
aegypti in many countries.
In Reunion Island Ae. albopictus is the most common mosquito and Ae. aegypti is rarer and coexists at larval stages with this invasive species (Bagny et al, 2009). A comparative study on life history traits realised there on both species revealed several differences but was not sufficient to explain the pattern of distribution observed. (Bagny et al, in prep)
Could competitive interactions contribute to the expansion of Ae. albopictus in areas already occupied by Ae. aegypti?
Several factors were studied with four replicates for each treatment:
- Effect of abiotic factor: ambient temperature (20°, 25°, 30°C) on mean survivorship and median pupation time (P50) of both species (density: 20Ae. albopictus / 20Ae. aegypti)
- Effect of biotic factors: larval densities of conspecifics and heterospecifics (20, 40, 60 individuals for 200 mL of water) / food availability (limited and optimal diet: leaf litter+additional food) on individual performance (mean survivorship and mean fecundity) of both species
On optimal diet: - Decrease of survivorship of Ae. albopictus only
due to presence of Ae. aegypti (no density effects)
- Decrease of survivorship of Ae. aegypti linked with increase of conspecifics density (intraspecific interaction) and linked with presence of Ae. albopictus (whatever the density)
On limited diet: significantly lower survivorship than under optimal diet at all density for both species
Significant decrease of wing length of Ae. albopictus only under limited diet but the species is still able to lay eggs
Significant decrease of wing length of Ae. aegypti when species density increases under optimal treatment. (Limited diet Î No eggs laying)
