Spore Load of Ascosphaera Species on Emerging Adults of the Alfalfa Leafcutting Bee, Megachile rotundata

Abstract

The spore load of Ascosphaera species spores on larval chalkbrood cadavers and newly emergent adults of the alfalfa leafcutting bee, Megachile rotundata, was determined. The spore content of chalkbrood cadavers ranged from 3 x 106 to 5 x 108. Adults emerging through zero to nine cadavers carried spores on all body parts examined by scanning electron microscopy. Estimates of the total number of spores obtained from a series of adult washes ranged from 9 x 104 to 8 x 107. Some adult males which emerged through no cadavers carried 104 to 105 spores, indicating that nesting materials might also have been contaminated. However, the control of chalkbrood in commercial bee populations may not be accomplished simply by providing clean nesting materials as adults may still emerge through diseased larvae.

Drifting in populations of the alfalfa leafcutting bee, Megachile rotundata (Fab.) (Hym., Megachilidae)

“…In many areas of western Canada where the bee is utilized for alfalfa seed production, alfalfa seed fields managed by several producers may be found within a relatively small area. Individual females may carry millions of chalkbrood spores (VANDENBERG et al, 1980) and drifting of bees between shelters within fields and between adjacent alfalfa seed fields could thus result in the spread of disease.…”

Cell production by the alfalfa leafcutting bee (Megachile rotundata F.) in new and used wood and polystyrene nesting materials

“…Also some results to the contrary were obtained in the latter study where nesting was reduced in new paper nesting tunnels impregnated with the test mixtures. The authors concluded that the practice employed by producers of placing previously filled bee boards among used ones or a few loose cells beneath new boards could be a more practical and inex ensive method to increase nesting in view of the large chalkbrood spore loads that are found in nesting material and bee-cell leaf material ( VANDENBERG et al 1980;STEPHEN et al 1981;STEPHEN 1982). Until effective methods to control chalkbrood are established to facilitate the use of used nesting material and/or bee cells to help offset losses in cell production in new material, other alternative avenues to increase the nesting success in new material must be pursued.…”

Chalkbrood (Ascosphaera aggregata Skou.) resistance of a univoltine strain of the alfalfa leafcutting bee, Megachile rotundata F.

“…The chalkbrood fungal pathogen, Ascosphuera uggregutu, is such a serious larval pathogen that USA producers are unable to sustain their bee populations. Greater than 50% of chalkbrood diseased larvae have been reported in some populations sampled (VANDENBERG and STEPHEN 1982). Current management practices rely on the importation of chalkbrood-free prepupae from Canada.…”

“…have been documented ( STEPHEN et al 1981;STEPHEN 1982, 1983a, 198313;KISH 1982;BISSETT 1988). Fungal spores are spread by contaminated hives and shelters, and by adults that become contaminated by chewing through chalkbrood cadavers during spring incubation of prepupae ( VANDENBERG et al 1980). An important field vector in the spread of this disease results from prepupae that break diapause under field conditions and become a field-emerged second generation.…”

“…By chewing through sibling larval cadavers, emerging adults become contaminated with up to 10' spores (VANDENBERG et al 1980). Thus offspring from the summer-emergent (second) generation have an increased exposure due to chalkbrood spores ( VANDENBERG et al 1980;VANDENBERG and STEPHEN 1982;STEPHEN et al 1981 The increased diapause intensity of the European univoltine strain of M. rotundata (RANK and RANK 1989) may help control chalkbrood by reducing second generation progeny as a disease vector. In addition, ASENSIO (1982) reported that Ascosphaera killed 65 % of larvae of Coelioxys parasites, whereas only 3.4 % of Spanish M .…”