Effects of temperature and host developmental stage on Ascosphaera torchioi Youssef and McManus prevalence in Osmia lignaria propinqua Cresson (Hymenoptera: Megachilidae)

Abstract

Summary — Eggs and fifth instar larvae of Osmia lignaria propinqua were inoculated with known concentrations of Ascosphaera torchioi spores and reared at 3 different temperatures. Chalk-brood prevalence was highest following inoculation of bees in the egg stage and when reared at lower temperatures (21 °C).

Temperature and chalkbrood development in the alfalfa leafcutting bee, Megachile rotundata

“…apis is similar to A. aggregata in that greater infection rates occur at lower temperatures (25-30°C), or if the larvae are chilled (Bailey, 1967;Flores et al, 1996). Likewise, Rust and Torchio (1992) found a greater prevalence of chalkbrood at lower temperatures for A. torchioi infections in the blue orchard bee (Osmia lignaria propinqua Cresson). Unfortunately, humidity was neither controlled nor reported in any of these reports.…”

“…However, he does not offer any supporting evidence that this actually occurs. Rust and Torchio (1992) suggest that lower temperatures promote infection because insect development is delayed, and the period of time that the larval gut remains blind is extended, increasing chances for infection. However, I found that fungal development is also retarded at the cooler temperatures.…”

“…Previous experimenters have added spores to the pollen provision in an aqueous suspension to increase infection levels (e.g. Vandenberg and Stephens, 1982;McManus and Youssef, 1984;Rust and Torchio, 1992;Torchio, 1992;Vandenberg, 1992Vandenberg, , 1994Goettel et al, 1995); however, I wanted to avoid having to modify the pollen provision because wetting the provision can sometimes affect larval health in solitary bees (Torchio, 1992;Vandenberg, 1994).…”

“…3). Une réduction similaire du taux de maladie parallè-lement à une augmentation de la température a déjà été notée par d'autres auteurs pour cette abeille (Vandenberg et Goettel, 1995), pour Osmia lignaria propinqua avec A. torchioi (Rust et Torchio, 1992) et pour Apis mellifera avec A. apis (Bailey, 1967 ;Flores et al, 1996). La raison pour laquelle la plus grande probabilité de survenue de cette mycose n'a pas lieu aux températures optimales pour la croissance et la germination d'Ascopharea spp.…”

Presence of Ascosphaera apis, the causative agent of chalkbrood disease, in honeybees Apis mellifera (Hymenoptera: Apidae) in Japan

“…Similarly, it is reported that higher infection rates with Ascosphaera torchioi occur at low temperatures in the blue orchard bee (Rust and Torchio 1992). Continuous monitoring of A. apis to observe the seasonal variations of the fungal infection is of great interest in Japan, because Japan has a rainy season from early June through July.…”