Full-text - Norsk entomologisk forening

· soo8 12 16 20 24Fig. 2. Day-degrees needed for eggs at differenttemperatures. The stippled line is the mean for alltemperatures. The mean value for each temperatureis also indicated.egg batch from each female, since severalfemales could have laid eggs in the same dishat the same time.Newly laid eggs did not show any visiblesign of an embryo.DISCUSSIONThe egg incubation time of C. schilleri isclearly temperature dependent. Other factorsinfluencing the incubation time are individualvariation within the egg batch and variationbetween egg batches from different females,as well as differences between the differentegg batches from a single female. Thesame pattern is revealed in the study of Brittain(1977) on Taeniopteryx nebulosa (L)(Taeniopterygidae) and the studies of Saltveit(1977), Brittain (1978) and Rekstad(1979) on different species of Nemouridae,though with different inclination of the regressionline for the different species. Lillehammer(l975b) found different incubationtime for different egg batches at the sametemperature for several species of Capniidae,Nemouridae and Leuctridae. Late in thisstudy I started wondering wether the size ofthe egg batch had any influence on the incubationtime and especially on the hatchingsuccess, since some of the smallest batchesdiffered a little from the others. This might bebecause these batches were the last ofseveralbatches from the same female, but with smallerresources. It would be interesting to followthis line of investigation further.Probably there are also differences betweendifferent populations regarding the relationshipbetween incubation time and temperature.Brittain (1978) and Rekstad (1979),who investigated populations of Nemurellapictetii Klapalek from a high mountain siteand a lowland site respectively, found somedifferences. But Brittain et al. (1984) foundthat population differences made no significantcontribution to variation in egg incuba­:ion time in Capnia atra. Probably the results)fthis study are generally applicable to otherJopulations of C. schilleri, but some variationis to be expected. The only study that hasbeen made of another population is the studyof Berthelemy (1973) from Tunisia, but heused fluctuating temperatures, so it is difficultto make a direct comparison.The high hatching success at very diversetemperatures would indicate that C. schillericould thrive under very different environmentalconditions, no one temperature beingclearly optimal for the egg stage. Since therewas no sign of diapause or delayed hatchingor ovovivipary, the regulation of the lifecycle to suit the different conditions the specieswill meet must be in other stages of thelife cycle, namely the nymphal stage. Berthelemy(1973) says that C. schilleri in Tunisiahas a diapause in the larval stage during thehot summer.The egg development of C. schilleri inNorway is quick; 6 eggs hatched after only 7days in one egg batch at 20°C. Since the eggswere inspected only once every day there is apossibility that these eggs were laid nearlyone day before the batch was registered andhatched just before the first nymphs werediscovered. This could mean that the realjevelopment time is 8 days and not 7. Thislpplies to all the eggs on all temperatures of;ourse, but is a relatively greater source of~rror at the highest temperatures. To have~xact development time one would have toinspect the eggs much more often, but this isnot always possible.ACKNOWLEDGEMENTSMany thanks are due to Curator Or. PhiI. A.Lillehammer for supervising the study andgiving good advice, to Cand. real. Jan Brekkefor help with the statistics and to Cand. phil.Knut Pettersen for correcting the English.REFERENCESBerthelemy, C. 1973. Donnees preliminaires surles Plecopteres de Tunisie. Verh. Internal. Ver.Theor. Angew. Limnol. 18, 1544-1548.43