Studies on oviposition and egg development of Gilpinia hercyniae Htg. (Hymenoptera, Diprionidae) on needles of diseased and apparently healthy Norway spruce (Picea abies (L.) Karst.)
1990
Sabsch, R. (Goettingen Univ. (Germany, F.R.). Inst. fuer Forstzoologie) | Schopf, R.
Choice experiments were performed in the laboratory to investigate the oviposition and embryonic developemnt of the European spruce sawfly Gilpinia hercyniae Htg. (Hym., Diprionidae) on twigs of visibly healthy or diseased Norway spruce. The most striking symptom of diseased trees was the discolouration of needles caused by air pollution and a K-Mg-Ca-deficiency of the soil. The discolouration varied between pale green and brown according to the individual degree of damage, but in the experiments only twigs with yellowish needles were compared with healthy ones. The females of G. hercyniae cut a significant lower number of egg slits into diseased needles (16.7/female compared to 22.8) and inserted a lower number of eggs into the slits (15.6/female compared to 22.0). Differences in egg mortality were not significant. A smaller number of larvae hatched from the diseased needles (12.4/female compared to 16.7, p below 0.01). Successful embryonic development could be attributed to egg slits, which were almost the same length in healthy (1.96 mm) and in symptomless (2.02 mm) needles. Compared with this result eggs remained undeveloped or died in slits which were longer (2.17 mm) in the case diseased needles or shorter (1.76 mm) in the case of healthy ones
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