ISHS Acta Horticulturae 288: VI International Symposium on Pollination
CHALKBROOD RESISTANCE IN A UNIVOLTINE STRAIN OF THE ALFALFA LEAFCUTTING BEE |
| Authors: | G.H. Rank, F.P. Rank |
| Abstract:
In southerly latitudes the main limiting factors in the field management of the alfalfa leafcutting bee are second generation and chalkbrood (Ascosphaera aggregata) sensitivity. Undesirable features of the field emergent second generation include (i) reduction of female sex ratio, (ii) reduced population increase, and (iii) mechanical spread of chalkbrood spores. Over an eight-year period, we have bred a univoltine chalkbrood resistant strain of leaf-cutting bee. Field tests at Ontario, Oregon (44°N) showed the percentage of univoltine prepupae infected with sporulating chalkbrood to be 1% compared to 12% for a commercial bivoltine strain. The univoltine's 12-fold increased resistance was due to a hereditary tolerance to the fungal pathogen and a reduction in spore dispersion by summer emergent progeny. The magnitude of univoltine strain resistance to chalkbrood is sufficiently high to be useful in field management. | |
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