RNAi-mediated silencing of vitellogenin gene function turns honeybee (Apis mellifera) workers into extremely precocious foragers

Abstract

The switch from within-hive activities to foraging behavior is a major transition in the life cycle of a honeybee (Apis mellifera) worker. A prominent regulatory role in this switch has long been attributed to juvenile hormone (JH), but recent evidence also points to the yolk precursor protein vitellogenin as a major player in behavioral development. In the present study, we injected vitellogenin double-stranded RNA (dsVg) into newly emerged worker bees of Africanized genetic origin and introduced them together with controls into observation hives to record flight behavior. RNA interference-mediated silencing of vitellogenin gene function shifted the onset of long-duration flights (>10 min) to earlier in life (by 3-4 days) when compared with sham and untreated control bees. In fact, dsVg bees were observed conducting such flights extremely precociously, when only 3 days old. Short-duration flights (<10 min), which bees usually perform for orientation and cleaning, were not affected. Additionally, we found that the JH titer in dsVg bees collected after 7 days was not significantly different from the controls. The finding that depletion of the vitellogenin titer can drive young bees to become extremely precocious foragers could imply that vitellogenin is the primary switch signal. At this young age, downregulation of vitellogenin gene activity apparently had little effect on the JH titer. As this unexpected finding stands in contrast with previous results on the vitellogenin/JH interaction at a later age, when bees normally become foragers, we propose a three-step sequence in the constellation of physiological parameters underlying behavioral development.

Vitellogenin in inflammation and immunity in social insects

“…Social insect queens have very high vitellogenin levels in the hemolymph (insect blood), whereas, worker vitellogenin levels are connected to task-specialization [17] . For example, in workers, the behavioral change from brood care (high vitellogenin) to foraging outside the hive or nest is preceded by a drastic drop in vitellogenin levels in the hemolymph of bee/ant workers [19,21,22] . These differences in vitellogenin levels are linked to the variation observed in the immunocompetence and life span of the distinct castes and worker types in social insects, mostly studied in the honey bee [23] .…”

Developing an in vivo toxicity assay for RNAi risk assessment in honey bees, Apis mellifera L

“…qRT-PCR was performed using SYBR green (Applied Biosystems Inc., Foster City, CA) and the 7500 Fast System real-time PCR detection system following the supplier's protocol (Applied Biosystems Inc., Foster City, CA). Relative quantification of the transcripts were calculated using the comparative 2-ddCT method (Livak and Schmittgen, 2001) and were normalized to A. mellifera β-actin (Antonio et al, 2008).…”

Protein levels and colony development of Africanized and European honey bees fed natural and artificial diets

“…Foragers preferentially consume nectar (Crailsheim et al, 1992) and a low protein diet (Slansky and Scriber, 1985). Studies made with Africanized and European honey bees have shown that workers that had the gene encoding vitellogenin silenced by RNAi made foraging flights earlier (Nelson et al, 2007;Marco Antonio et al, 2008).…”