Le régime alimentaire des stades larvaires deChaoborus flavicans(Diptera : Chaoboridae) dans une lagune d'épuration des eaux usées du Sud-Ouest de la France

Abstract

Keywords : purification lagoon, lake typology, macrobenthos, diet, Index of Relative Importance.The food of larvae of Chaoborus flavicans was studied in the third basin (depth = 0,8 m) of a purification lagoon for waste water from a village. On a annual basis, the water was always satured with oxygen at the surface, but saturation varied between 62,8 and 141,4 on the bottom. The mean annual concentration of chlorophyll a was 99,3ug/l and the mean annual biomass of zoóplankton was 4,4g dry weight/m 2 ; the most important species being Brachionus calyciflorus and Polyarthra remata.(roú-fers), and Daphnia pulex (cladoceran). The population of C. flavicans attained five generations per year and its density varied from 1931 to 21586 larvae/m 2 . The percentage of empty stomachs was not significantly different for the four larval instars. The food of the larvae was characterized by the following indices : Frequency, Numerical Contribution, Contribution by Weight, and especially Relative Importance, an index already used for fish (Pinkas et al. 1971). The first three larval instars fed exclusively on B. calyciflorus. In contrast, for the fourth instar the larvae fed on a wide range of food that was not significantly different on the bottom or in open water. The Index of Relative Importance and the Index of Selectivity (Vanderploeg & Scavia 1979) indicated that the latter larvae exploited the food resources of the lagoon along a gradient of decreasing vulnerability for the prey. Les larves de Chaoborus sont de puissants préda-teurs qui présentent un éventail alimentaire très large.

Day-Night Vertical Distribution and Feeding Patterns of Fourth Instar ofChaoborus Larvae in a Neotropical Reservoir (Socuy Reservoir, Venezuela)

“…This is consistent with results from other natural populations of larvae (GOLDSPINK and SCOTT, 1971;KAJAK and RYBAK, 1979;DURIEU and THOMAS, 1995;CROTEAU et al, 2003). Although, there has been some speculation that larvae might feed during benthic phase (GOLDSPINK and SCOTT, 1971;PAS-TOROK, 1980).…”

“…The percentage of crops with food found in fourth instar larvae of Chaoborus population from Socuy Reservoir is in the middle of the range reported for other studied populations of fourth instar larvae (SWIFT, 1976;LEWIS, 1977;CHIMNEY et al, 1981;Hare and CARTER, 1987;MOORE, 1988;DURIEU and THOMAS, 1995;IRVINE, 1997;SUTOR et al, 2001;CROTEAU et al, 2003). Differences in the proportion of crops with food between larvae populations, can be explained by differences in availability of prey (CHIMNEY et al, 1981), differences in migratory behavior and predation behavior of larvae (GOLDSPINK and SCOTT, 1971;SWIFT, 1976;HARE and CARTER, 1987;FUKUHARA et al, 1993), and variations in time of digestion of different kinds of prey at different temperatures (GIGUÈRE, 1981;MOORE, 1988).…”

“…As larvae are developing, they pass through four larval instars before they pupate. During this larval development, mouth diameter and predatory capacities of larvae increase (FEDORENKO, 1975;MOORE, 1988;SWIFT, 1992;DURIEU and THOMAS, 1995). Due to these ontogenetic changes, and the highest time of development in fourth instar (CRESSA and LEWIS, 1986;LÓPEZ and CRESSA, 1996), the major effect of Chaoborus predation on zooplankton usually have been found during last larval stage (e.g.…”

“…Although the differently sized species of the phantom midge show slight differences in their gape diameter and diet (SWIFT, 1992), usually, the older instars are carnivorous and prefer crustacean zooplankton over other prey (LEWIS, 1977;DURIEU and THOMAS, 1995;IRVINE, 1997;LÜNING-KRIZAN, 1997;SUTOR et al, 2001;CROTEAU et al, 2003;PAGANO et al, 2003). However, some studies in both temperate and tropical populations have shown that larvae in all instars can also actively consume phytoflagellates (HARE and CARTER, 1987;MOORE, 1988;MOORE et al, 1994;ARCIFA, 2000).…”

Influence des facteurs abiotiques sur la sortie des sédiments deCyclops vicinuset Chaoborus flavicans dans les zones sub-littorale et profonde d'un lac tempéré eutrophe

“…Les variations saisonnières de densité et de biomasse de cette faune ont été surtout étudiées durant la phase pélagique. De plus, ces travaux concernent le plus souvent soit le macrobenthos (Durieu & Thomas 1995) soit le méiobenthos (Strayer 1985, Santer & Lampert 1995. Cependant, bien que ces deux composants apparaissent simultanément et à des densités non négligeables dans les écosystèmes d'eau douce, la nature de leurs interactions n'est pas encore très claire (Lodge et al 1988 (Lair & El Ghachtoul 1989).…”