ISHS Acta Horticulturae 800: X International Pear Symposium
TEMPERATURE AND NATURAL PARASITISM IN THE POPULATION DYNAMICS OF THE PEAR PEST PHYLLONORYCTER CORYLIFOLIELLA HB. |
| Authors: | L.B. Frăsin, A.C. Cosac, G. Teodorescu |
| Keywords: | thermal constants, parasitoids, degree day |
| DOI: | 10.17660/ActaHortic.2008.800.131 |
| Abstract:
Phyllonorycter corylifoliella Hb. is one of the pests which has produced significant damage in Romanian pear orchards during the last few years. For this reason, knowledge of the thermal developmental constants, the determination of the degree day accumulation (DD) necessary for each stage of development and each generation and the role of the biotic factors in the dynamics of populations of this pest are of special importance. The development of P. corylifoliella Hb. occurs according to the formula of Săvescu (1965). Thus, the threshold value is T0=6°C, the thermal constant K=630°C, the prolificacy threshold value O=11°C, the optimum thermal O1=28,3°C and the upper threshold T=31.1°C. Of practical interest for the control of this pest are the degree day (DD) accumulated to the start of adult flights, the maximum of the flight curve and egg laying period. The medium values of these were: 21.5°C and 157.3°C for the overwintered generation (the 3rd generation), 423.7°C , 807.9°C and 37.7°C for the 1st generation, 979.2°C, 1790.6°C and 46.9°C for the 2nd generation. The average degree day (DD) accumulation, corresponding to each point of the insect phenology are: for the 1st generation - egg - 37.70°C, larva - 88.35°C, pupa - 286.73°C, adult - 423.70°C; for the 2nd generation - egg - 469.00°C, larva - 628.98°C, pupa - 850.13°C, adult - 979.20°C; for the 3rd generation - pupa - 9.53°C, adult - 21.48°C. The main parasitoids identified were the Hymenoptera Apanteles circumscriptus, Holcothorax ssp. and Sympiesis ssp. The parasitism rate varied between 11 and 60%. A. circumscriptus gave the highest rate of parasitism. | |
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