Invertebrate carcasses as a resource for competing Aedes albopictus and Aedes aegypti (Diptera: Culicidae)

Abstract

Terrestrial invertebrate carcasses are an important resource for insects developing in pitcher plants. However, little is known of the role of these carcasses in other containers, which also receive leaf fall and stemflow inputs. This experiment investigated effects of accumulated invertebrate carcasses as a resource for two competing mosquitoes, Aedes albopictus (Skuse) and Aedes aegypti (L.), whether either species differentially benefited from accumulated carcasses, and if such a benefit affected interspecific competition. First, we measured accumulation of invertebrate carcasses in standard containers at a field site. We then used a replacement series with five different species ratios at the same total density, and varied the input of invertebrate carcasses [dead Drosophila melanogaster (Meigen) ] in three levels: none, the average input from our field site, or the maximum input recorded at our field site. Survivorship, development time, and mass were measured for each mosquito species as correlates of population growth, and were used to calculate a population performance index, lambda'. There were strong positive effects of invertebrate carcass additions on all growth correlates and lambda'. Differences in performance between species were pronounced in small or no carcass additions and absent in large inputs of invertebrate carcasses, but there was little evidence that inputs of invertebrate carcasses altered the competitive advantage in this system. These results suggest that terrestrial invertebrate carcasses may be an important resource for many types of container communities, and large accumulations of dead invertebrates may reduce resource competition between these mosquitoes, thus favoring coexistence. We propose that the total amount of resource, including accumulated invertebrate carcasses, may explain observed patterns of replacement involving these mosquitoes.

Fig. 1

Least square mean estimates of population performance (λ′, the composite index of population performance for the cohort) for A. albopictus and A. aegypti at three levels of added invertebrate carcasses. Carcass addition treatments were as follows: no added carcasses (control), an average natural level of invertebrate carcass accumulation (small), or the largest natural accumulation (large). The dotted line at λ′ =1 represents conditions where the population is being replaced, with no growth or decline. Letters denote interspecific differences that are significantly different across treatments. Error bars denote ±1 SE.

Fig. 2

Least square mean percent survivorship (percentage of the original number of larvae of each species surviving to adulthood) of A. albopictus and A. aegypti at three levels of added invertebrate carcasses. Asterisks denote cases where there are significant interspecific differences (ΔSurv = Surv_alb − Surv_aeg ≠0). Letters denote interspecific differences (ΔSurv) that are significantly different across treatments. Error bars denote ±1 SE.

Fig. 3

Least square mean mass of A. aegpyti females at eclosion, expressed on a natural scale. Missing data points in the control treatment result from no A. aegpyti females eclosing in the 10:30 and 20:20 ratios (A. albopictus: A. aegypti). Error bars denote ±1 SE.

Fig. 4

Least square mean interspecific differences in adult female mass, at small and large additions of invertebrate carcasses. The control treatment is not represented because none of the ratios in the control treatment produced females of both species that could be weighed. Asterisks denote significant interspecific differences. Letters denote interspecific differences that are significantly different across treatments. The dotted line at zero represents conditions where there is no difference in female mass between the two species. Error bars denote ±1 SE.

Fig. 5

Least square mean interspecific differences in adult female development time as a function of invertebrate carcass additions and species ratio. Asterisks denote significant interspecific differences. The control treatment is not represented because only one replicate produced females of both species, with only a single A. aegypti female eclosing in that replicate. The dotted line at zero represents conditions where there is no difference in female development time between the two species. Error bars denote ±1 SE.