Feeding essential oils and 2-heptanone in sugar syrup and liquid protein diets to honey bees (Apis mellifera L.) as potential Varroa mite (Varroa destructor) controls

Summary

Essential oils were fed to honey bees to determine whether the components were absorbed into bee larvae. The oils were added in either sucrose syrup (origanum and 2-heptanone) or in a liquid protein diet (origanum oil, cinnamon oil, thymol, and 2-heptanone), because sugar and protein sources are differentially utilized in food fed to larvae of different ages. The volatiles emitted by isolated larvae from oil-supplemented colonies were sampled at three different ages (Day 4, Day 6 and Day 9) by Solid Phase Micro-Extraction (SPME) and analyzed by Gas Chromatography-Mass Spectrometry (GC-MS). The only oil volatiles recovered in larvae were the origanum oil components carvacrol and thymol; neither 2-heptanone nor the cinnamon oil components were detected in any larvae. For larvae from colonies fed oil- supplemented sugar syrup, carvacrol volatiles were emitted at higher amounts in younger larvae (Day 4) than in older larvae (Day 9). In contrast, carvacrol and thymol volatiles were detected only in older larvae (Day 6 and Day 9) in colonies reared on oil-supplemented liquid protein diet. Carvacrol was also detected in the cocoons of Day 9 larvae from colonies fed oil-supplemented liquid protein diet, but not oil-supplemented sugar syrup diet. We believe that the age-related differences in oil incorporation by bee larvae reflect the relative importance of supplemental sugars and protein as food sources for bee larvae of these ages. Supplementation in a liquid protein diet represents a more efficacious route for the incorporation of origanum oils in fifth instar bee larvae targeted for invasion by Varroa destructor mites.

Resumen

Se añadieron aceites esenciales para alimentar a abejas para determinar si los componentes son absorbidos por las larvas. Los aceites se añadieron al sirope de azúcar (orégano y 2-heptonona) o a una dieta líquida con proteínas (aceite de orégano, aceite de canela, timol y 2-heptanona) porque las fuentes de azúcar y proteínas se usan de forma diferente en la alimentación de las larvas de diferente edad. Los volátiles emitidos por larvas aisladas de colonias suplementadas con aceite se muestrearon en tres momentos diferentes (día 4, día 6 y día 9) mediante cromatografía de gases y espectometría de masas (CG-EM). Los únicos aceites volátiles recuperados en las larvas fueron los componentes carvacrol y timol del aceite de orégano, no se detectaron componentes de la 2-heptanona ni del aceite de canela en ninguna larva. En larvas de colonias alimentadas con sirope de azúcar suplementado con aceite, se emitieron cantidades mayores de volátiles de carvacrol en larvas jóvenes (día 4) que en las mayores (día 9). Por otro lado, volátiles de carvacrol y timol se detectaron sólo en larvas mayores (días 6 y 9) en colonias criadas con dietas de proteína líquida suplementada con aceite, pero no con la dieta de sirope de azúcar suplementada con aceite. Creemos que las diferencias relacionadas con la edad en la incorporación de los aceites a las larvas reflejan la importancia relativa de suplementar azúcar y proteína como fuente de alimento para larvas de esas edades. El suplemento en una dieta de proteína líquida representa una ruta más eficaz para la incorporación de aceites de orégano en larvas de quinto instar objeto de la invasión de ácaros Varroa destructor.

Keywords:

• essential oils
• honey bee larvae
• liquid protein diet
• SPME
• Varroa destructor