Free access
Volume 21, Number 3, 1990
Page(s) 209 - 219
Apidologie 21 (1990) 209-219
DOI: 10.1051/apido:19900306

Chalkbrood (Ascosphaera aggregata) resistance in the leafcutting bee (Megachile rotundata). I. Challenge of selected lines

W.P. Stephen and B.L. Fichter

Oregon State University, Department of Entomology,Corvallis, OR 97331-2907, USA

Abstract - Twenty-nine cell series of the leafcutting bee, Megachile rotundata (Fabr), each containing 5 or more healthy larvae, no chalkbrood (Ascosphaera aggregata Skou) and no pollen masses were isolated from a population with over 36% chalkbrood. This selected subpopulation was split and isolated for 4 and 6 generations before being challenged by forcing the females to nest in heavily contaminated media, or by weekly dustings with approximately 175 x 108 A aggregata spores. The incidence of chalkbrood in both challenged lines was markedly lower than that of the wildtype, and comparable to that of the selected lines, suggesting a genetic component for resistance in both lines. The very low incidence of pollen masses (dead eggs or early instar larvae) in the selected lines throughout the 4 yrs of the study indicates that this trait may also be genetically mediated, either linked to, or independent of disease resistance.

Key words: chalkbrood / Ascosphaera / leafcutting bee / resistance / Megachile