7 Systematics, Biology and Ecology of Genera and Species
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Chironomidae Larvae 7 SYSTEMATICS, BIOLOGY AND ECOLOGY OF GENERA AND SPECIES (A) DESCRIPTIONS In this chapter the systematics and distribution of species will be treated briefly, and their biol- ogy and ecology more extensively. As a rule, we refer to the literature where necessary. For the ecology of the species in particular, we have drawn extensively from other sources, mainly data from investigations by many workers in the Netherlands who sent material and reports. The databases held by water authorities have not been investigated thoroughly. This section contains written descriptions. For a numerical evaluation see the tables in section B and Moller Pillot and Buskens (1990). Ablabesmyia Johannsen, 1905 IDENTIFICATION OF SPECIES In this book we follow the differences between the three European species published earli- er (Moller Pillot, 1984). These differences are based on Laville (1971) and our own reared material of A. monilis and A. phatta (A. monilis has also been reared and described by Goddeeris, 1983: 135). Fittkau and Roback (1983) and Sergeeva (1998; 2004) give the reverse characteristics for the palpus of A. monilis and A. longistyla. Sergeeva (personal correspon- dence) wrote that she had mistakenly swapped the species; Fittkau could not check his material and wrote that making such a swap was possible. Moreover we found sometimes the basal part of the palpus of A. monilis divided into three segments, in one case only at one side. We found some overlap between the exuviae of A. monilis and A. longistyla, as described by Langton (1991). Further, in Belorussian material some larvae and exuviae have sizes inter- mediate between A. phatta and A. monilis. However, adult males that could not be identi- fied have never been found. Our conclusion is that the original descriptions are most probably correct, but the possibil- ity that the two species interbreed cannot be excluded.Therefore the palpus is not always reliable. A few specimens cannot be identified as a larva because of intermediate sizes. As proposed earlier in an unpublished key, we use the name A. monilis agg. for specimens belonging to A. monilis or A. longistyla, in contrast to A. phatta. Some workers will identify only to aggregate level because identification up to species level can be very time consum- ing, and because there are hardly any ecological differences between these species. In many cases two or even three species of Ablabesmyia are found living together. FEEDING The larvae of Ablabesmyia are predators, actively attacking Chironomidae, Oligochaeta and to a lesser extent also smaller swimming animals such as Cladocera (Konstantinov, 1961; Roback, 1969a; Loden, 1974; Mackey, 1979). However, dead prey, diatoms, filamentous algae and detritus are also eaten, especially when animal prey is scarce (Armitage, 1968). Mackey (1977) found that development was slow and possibly incomplete if the larvae received only detritus. 74 Tanypodinae-Systematics, biology and ecology MICROHABITAT The larvae live mainly among plants and on sediments containing organic material; they are nearly absent from fully mineral water bottoms, but found sometimes on wood or stones (Shilova, 1976; Bijlmakers, 1983; Klink, 1991; Verberk et al., 2005; Buskens: sand pits, unpublished). Bijlmakers (1983) found a slightly higher proportion on water bottoms with less organic material. In some places small differences were found between the microhabi- tat of different species of the genus, but such differences were not observed in other places. An exception could be A. phatta, which seems to live more among submerged vegetation (Steenbergen, 1993). Ablabesmyia monilis (Linnaeus, 1758) DISTRIBUTION IN EUROPE AND THE NETHERLANDS A. monilis has been recorded in all regions of Europe (Fittkau and Reiss, 1978). In the Netherlands the species seems to be less common than both other species of the genus, especially in the Holocene parts of the country (Nijboer and Verdonschot, 2001). LIFE CYCLE In late spring there is often a period without older Ablabesmyia larvae after the first emer- gence period because of the strong synchronisation. According to Goddeeris (1983) A. monilis has three generations a year in the fish ponds in Mirwart in the Belgian Ardennes. The larvae have a winter diapause in the second and third instar. In the Netherlands the first larvae in the fourth instar can be found in the second half of March. In most countries in Western Europe emergence first takes place from the end of April to the end of May; the second and third generations emerge mainly from July into September, and rarely to the middle of October (Mundie, 1957; unpublished Dutch data). In northern and mountain regions only one or two generations occur (Brundin, 1949; Laville and Giani, 1974 (A. longistyla)). The aberrant life cycle given by Mackey (1976) is probably based on incorrect identification (see Goddeeris, 1983: 25). As a result of local circumstances, the winter or summer generation can be very small or absent (Mundie, 1957; own unpublished data; compare Shilova, 1976: A. phatta). FEEDING AND MICROHABITAT See under the genus. DENSITIES The densities of larvae are usually low. In two pools near Oisterwijk, Bijlmakers (1983) rarely found more than 100 larvae/m2. Brundin (1949) mentions much higher densities of D Pentaneurini (often mainly Ablabesmyia) in Swedish lakes: as high as over 500 larvae/m2 in June and more than 900 in October. EGG DEPOSITION The cylindrical egg masses contain 100 up to 400 eggs arranged in a spiral, which makes them more easily identifiable than those of most other Tanypodinae (Koreneva, 1959; Nolte, 1993). Koreneva found the egg masses attached to Potamogeton in the littoral zone. pH Leuven et al. (1987) found A. monilis at a pH from 3.8 to 7. In the Dutch province of North Holland the species was also not rare at a pH higher than 8 (Steenbergen, 1993). The larvae therefore seem to be indifferent to this factor. 75.