Behavioral Responses of Apis mellifera Adult Workers to Odors from Healthy Brood and Diseased Brood

Abstract

Studies of adult workers' responses to infected brood were undertaken to isolate discrete volatile compounds that elicited honeybee hygienic behavior. Using a freeze-killed brood assay, we determined that in healthy colonies adult workers recognized and emptied infected cells with a 95% clearance rate. SPME-GC-MS results emptied >95% infected cells indicated differences in the composition and relative content of volatile compounds released by healthy and diseased brood. Additionally, we determined that the main volatile compound released from the pathogen Ascosphaera apis was phenethyl alcohol. The Y-tube olfactometer indicated that 10-to 20-day-old workers of healthy colonies, but only 15-day-old workers of diseased colonies, were significantly sensitive to differences in characteristic volatile compounds. This information could facilitate honey bee selection based on mechanisms that contribute to chalkbrood disease tolerance.

Identification and Discrimination of Volatiles Associated With Chalkbrood Infection in European Honey Bees (Apis Mellifera), Eastern Australia

“…As such, the major VOCs identi ed as derived from A. apis were not novel or unexpected.The VOC pro les of the four groups measured: healthy larvae, freeze killed brood, infected larvae, and cultured fungi had distinctive volatile pro les with limited overlap. Healthy larvae and FKB had the fewest amount of VOC, consistent with other reports(Swanson et al 2009;Zhao et al 2015). Curiously, the volatile pro le of infected larvae was predominately comprised of lactones with small amounts of phenethyl alcohol while the pro le of cultured A. apis consisted of mainly phenethyl alcohol derivatives, including phenethyl acetate, but not phenethyl alcohol itself.…”

“…Curiously, the volatile pro le of infected larvae was predominately comprised of lactones with small amounts of phenethyl alcohol while the pro le of cultured A. apis consisted of mainly phenethyl alcohol derivatives, including phenethyl acetate, but not phenethyl alcohol itself. Although γ-decalactone production from infected larvae has previously been reported(Zhao et al 2015), we are the rst to report the presence of several other lactones produced as a result of chalkbrood infection.Continued efforts should examine the potential effects of honey bee genetics, A. apis strain variation, epigenetics and gene by environmental interactions. It is unclear if honey bee genetics in Australia are similar to that of the United States but Australia does not appear to harbor any particularly unique A. apis strains(Gerdts et al 2021), however, variation in volatile pro les in response to environmental conditions is widely corroborated.…”

“…Bees from hygienic lines were able to discriminate between VOCs produced by healthy and chalkbroodinfected brood at lower concentrations than bees from a non-hygienic line (Masterman et al 2001). One particular volatile produced by chalkbrood-infected larvae, phenethyl acetate (Swanson et al 2009;Zhao et al 2015), was also experimentally shown to induce hygienic behaviour (Swanson et al 2009) and identi ed as a possible trigger for hygienic removal of infected larvae.…”

Volatile Organic Compounds from Offspring of Stingless Bee Sacrificed in Hygienic Behavior Test

“…This type of fiber has already been successfully used in studies with volatile compounds from bees. [56] Using the SPME manual holder, the fiber was exposed to the sample, allowing the extraction of volatiles in headspace mode for 30 min. Subsequently, the fiber was inserted into the gas chromatograph to desorb volatile organic compounds for 4 min at 250 °C, to conduct the analysis by gas chromatography coupled to mass spectrometry (GC-MS).…”

“…The GC-MS method was adapted from previous work. [56] The chromatographic analysis of the compound profile was conducted using GC-MS (model GCMS-QP2010 Plus, Shimadzu®, Japan), with electron impact ionization (EI) of 70 eV. The gas chromatograph contains a capillary column with a stationary phase of the HP-5 MS type (30 m×0.25 mm id ×0.25 μm) (Agilent®, Palo Alto, California, USA), and used the Helium gas as the mobile phase (flow 0.59 mL min À 1 ).…”